unsteady vortex behavior in the asian monsoon anticyclone the asian monsoon anticyclone ama which is primarily driven by the latent heat released by monsoon precipitation is one of the dominant features of the northern hemisphere summer circulation in the upper troposphere and lower stratosphere due to variations in the diabatic heating interactions with rossby waves propagating along the subtropical jet and internal dynamics within the anticyclone the circulation of the ama is unsteady here we use the era interim dataset and trajectories computed with era interim winds to show that the ama contains two or three distinct synoptic scale subvortices 69 of the time while a single circulation center is present only 23 of the time more than three simultaneous subvortices are uncommon observed behaviors of the subvortices include 1 splitting of a single vortex into two vortices 2 merger of two vortices into a single vortex 3 vortex shedding in the eastward direction 4 vortex shedding in the westward direction and 5 formation movement and dissipation of a vortex the evolution of the subvortices is closely tied to stirring and transport

patterns of recent sea level rise in the east japan sea from satellite altimetry and in situ data 1 patterns of recent sea level rise in the east japan sea ejs are investigated through the analyses of topex poseidon t p sea level anomalies thermosteric sea level tsl and long term tide gauge data the 9 year long t p analyses reveal average trends of 5 4 0 3 mm yr 1 for all of ejs and 6 6 0 4 mm yr 1 for the southern ejs these are much larger than the global rates of 3 1 0 4 mm yr 1 reported by cabanes et al 2001 and 2 8 0 4 mm yr 1 by cazenave and nerem 2004 this t p rate compares relatively well with those from tsl data and tidal sea level gauges indicating that sea level rise in the ejs is mainly due to thermal expansion the southern ejs shows a nonuniform sea level trend pattern with the western part of the ulleung and yamato basins having values of 10 mm yr 1 and larger this nonuniform pattern is discussed in terms of variable thermal expansions arising from a recent decadal trend in the temperature anomaly in the upper layer of the two basins the 40 year long tsl time series also reveals a decadal oscillation in the ulleung and yamato basins that can be explained by interannual to decadal variations in temperature in the upper ocean layers with weaker anomalies at most of the other ejs locations it is hypothesized that the long term oscillation in the southern ejs may be related to the decadal variability of heat content anomaly in the upper 300 m of the pacific ocean as reported by levitus et al 2000 and to the north south migration of the warm tsushima current and eddies in the southern ejs

characteristics and mechanisms of the subseasonal eastward extension of the south asian high abstractthis study investigates the features of eastward extension of the south asian high sah and its connection with diabatic heating and rainfall over eastern asia on subseasonal time scales the causes of sah s eastward extension are examined by potential vorticity pv diagnosis with emphasis on the joint role of diabatic heating feedback and midlatitude wave train the sah s eastward extension features eastward propagation of a wave train across eurasia among the wave train the migration of weak high from the western flank of the tibetan plateau tp to the east of tp contributes to the sah s eastward extension at the early stage when the sah approaches its easternmost position a strong negative pv positive geopotential height center prevails to the east of the tp at 200 hpa the associated anomalies in diabatic heating and rainfall include the anomalous heating and above normal rainfall over the south china sea scs and subtropical western pacific occurring 12 days before the sah s eastern

sediment resuspension and implications for turbidity maximum in the changjiang estuary abstract a comparative study on the properties and transport of the cohesive sediments in the mouths of the changjiang estuary proves that the suspended sediment concentration ssc is principally enhanced by the resuspension of bottom sediment in the mouth bar reach coupled with the deformed tidal wave and strong tidal current salinity intrusion and vertical gravitational circulation lead to the trapping of the suspended sediment inflowed from the river and the sea the turbidity maximum tm is therefore delivered by the local resuspension of the accumulated materials and bed erosion the tm in the changjiang estuary is marked not only by its high ssc relative to the adjacent reaches but also by the high wash load content transport of sediment is very important settling velocity of suspended sediment is increased by flocculation the massive settling during weak current periods often gives rise to the formation of fluid mud the tm coincides locally with the mouth bars the transport of suspended sediment in the tm is analysed by using a splitting method it is concluded that the contributing factors consist of advective terms and tidal pumping advective transport is dominant in the north channel and tidal pumping predominate in the north branch and south passage and the north passage is in an intermediate situation

shoal morphodynamics of the changjiang yangtze estuary influences from river damming estuarine hydraulic engineering and reclamation projects abstract concerns regarding estuarine shoal morphodynamics have increased worldwide because of intensive anthropogenic activities to explore response of estuarine shoals to possible couplings of multiple artificial interferences in river basins and within estuaries the link between the morphodynamic processes of the nanhui shoal nhs which is located along the southern margin of the changjiang estuary the largest estuary in asia and river damming estuarine hydraulic engineering and reclamation projects is discerned in this study the results reveal that the nhs exhibited secular polarization during 1998 2013 with a significant accretion of 1 8 10 8 m 3 landward from the tidal ridge and an erosion of 0 3 10 8 m 3 on the seaward edge respectively forming a steep slope with an elevation between 2 and 3 m meanwhile the nhs morphodynamics could be divided into 3 stages mild accretion with an undisturbed tidal channel during 1998 2002 strong sedimentation with a disrupted tidal channel during 2003 2008 and large scale landward accretion with an infilled tidal channel after 2009 moreover the nhs s volume variations exhibited an 18 month cycle even though an increased area of 35 km 2 above 2 m and a decreased area of 45 km 2 between 2 and 5 m were observed the primary causes of theses periodic changes in the nhs s volume are determined as the fluctuating changjiang water discharge and cyclically altered hydrodynamics of the south passage the deep waterway project dwp and reclamation projects were responsible for the polarization of seaward erosion and landward accretion respectively moreover these reclamation projects dominated the staggered changes in nhs morphodynamics by inducing continuous accretion within the tidal channel compared to estuarine engineering river damming induced dramatic declines in distal sediment may have played a minor role in flat changes of nhs

the influence of wave trains in mid high latitudes on persistent heavy rain during the first rainy season over south china based on daily precipitation data from the chinese meteorological administration and reanalysis data from the national centers for environmental prediction department of energy the character of low frequency precipitation variability during the first rainy season april june over south china and its corresponding atmospheric circulations in the mid high latitudes are investigated the results show that the precipitation anomalies during this period exhibit obvious quasi biweekly oscillation qbwo features with a period of 8 24 days the influence of wave trains in the mid high latitudes to low frequency persistent heavy rain event phr lf event the 8 24 day filtered precipitation larger than one standard deviation of filtered time series and persisting at least three days over south china is further discussed during the first rainy season over south china there are two low frequency wave trains in the mid high latitudes associated with the phr lf event the wave train crossing the eurasian continent and the wave train along the subtropical westerly jet analysis of wave activity flux indicates that the wave energy disperses toward eastern china along these two low frequency wave trains from north to south and from west to east and then propagates downward over south china accordingly the disturbance of the relative vorticity of the cyclonic anomalies over eastern china is strengthened which enhances the meridional gradient of relative vorticity owing to the transport of low frequency relative vorticity and geostrophic vorticity by meridional wind the ascending motion over south china intensifies and lasts for a long time triggering a phr lf event in addition the tropical system is also a key factor to phr lf event the qbwo of the convection over the south china sea provide moisture for phr lf events maintaining persistent rainfall and vertical ascending motion over south china

spatio temporal stability analysis applied to monsoon anticyclone flow flow on a beta plane driven by a steady localised anticyclonic forcing of potential vorticity or equivalently a mass source is considered as a simple model of the asian monsoon flow in the upper troposphere previous authors have noted that the response may be steady or unsteady according to the magnitude of the forcing with the unsteadiness manifested as westward eddy shedding a detailed study of the transition between steady and eddy shedding regimes reveals a third regime break up for intermediate forcing magnitude where the flow is steady in the neighbourhood of the forcing but the westward extending plume of low potential vorticity breaks up into isolated anticyclonic vortices some distance away from the forcing region a related spatio temporal instability problem for flow on a beta plane is specified and analysed the flow can be stable convectively unstable or absolutely unstable it is argued that these three stability regimes correspond to the steady break up and eddy shedding regimes for the forced flow and good quantitative correspondence between the regimes is demonstrated by explicit solution of the spatio temporal stability problem

role of subtropical precipitation anomalies in maintaining the summertime meridional teleconnection over the western north pacific and east asia abstract the meridional teleconnection patterns over the western north pacific and east asia wnp ea during summer have a predominant role in affecting east asian climate on the interannual time scale a well known seesaw pattern of tropical subtropical precipitation is associated with the meridional teleconnection and the subtropical precipitation anomaly has been previously viewed as a result of anomalous circulations associated with the teleconnection in this study however the authors suggest that subtropical precipitation anomalies in turn can significantly affect large scale circulations and may be crucial for maintenance of the meridional teleconnection diagnosis by using observational and reanalysis data indicates that the meridional teleconnection patterns are clearer in summers when the subtropical rainfall anomalies are greater the simulated results by a linear baroclinic model indicate that a subtropical heat source which is equivalent to the diagnosed positive subtropical precipitati

south flank of the yangtze delta past present and future abstract chenier plain and mudflat development in the south flank of the yangtze delta are examined by multi disciplinary methods over different spatiotemporal scales and changing human earth interactions the study site contains a narrow belt of elongated ridge complexes that formed along the sediment deficient open coast from 6500 to 4000 yr bp since then and until the past two decades shoreline progradation has accelerated due to increasing sediment supply fueling rapid deltaic expansion superimposed on this trend are a series of discrete sand dominated ridges deposited during several stormy intervals tidal flat development is regulated by complex estuarine processes short term morphodynamic variations at the site are caused by the alternations of tides and waves while intermediate morphodynamic variations are controlled by the multi decadal shifting of river stem channel and stormy climates the ongoing rapid accretion on the tidal flats is predicted to continue into the near future because the estuarine buffer effect is expected to balance the adverse impacts of decreasing riverine sediment discharge and rising sea level technological developments during the last 2000 years are exemplified by seawall construction against sea flooding marking a transition from passive to active dike construction has been used more frequently and intensively to reclaim land since the 1970s in support of the booming socioeconomic development in the region lessons from complex morphodynamic change and human earth interactions in the southern yangtze delta admonish us to not reclaim coastal wetland by lower flat enclosures constructing new dikes near the low waterline while an optimal alternative would be to implement upper flat enclosures constructing new dikes around the high waterline on the continuously accretionary tidal flats with auxiliary biological restoration engineering to satisfy both socioeconomic development and sustainable wetland conservancy

origin of the summertime synoptic scale wave train in the western north pacific abstract the origin of the summertime synoptic wave train in the western north pacific is investigated with a multilevel nonlinear baroclinic model a realistic three dimensional summer mean state is specified and eigenvectors are calculated by introducing small perturbation initially to the model numerical experiments indicate that the origin of the synoptic wave train may arise from instability of the summer mean flow in the presence of a convection frictional convergence cfc feedback in the lack of the cfc feedback the summer mean flow supports only a least damped mode characterized by a northwest southeast oriented wave train pattern with a zonal wavelength of 2500 km in the presence of both the realistic summer mean flow and the cfc feedback the model reproduces a fast growing mode whose structure and propagation characters are similar to the observed sensitivity experiments with different initial perturbation patterns indicate that the model solution is not sensitive to initial conditions

sea level fingerprinting as a direct test for the source of global meltwater pulse ia the ice reservoir that served as the source for the meltwater pulse ia remains enigmatic and controversial we show that each of the melting scenarios that have been proposed for the event produces a distinct variation or fingerprint in the global distribution of meltwater we compare sea level fingerprints associated with various melting scenarios to existing sea level records from barbados and the sunda shelf and conclude that the southern laurentide ice sheet could not have been the sole source of the meltwater pulse whereas a substantial contribution from the antarctic ice sheet is consistent with these records

new estimates of secular sea level rise from tide gauge data and gia modelling summary during the last three decades at least 30 independent estimates of the secular global mean sea level rise gmslr have been published based on sufficiently long tide gauge tg records despite its apparent simplicity the problem of gmslr is fraught with a number of difficulties which make it one of the most challenging questions of climate change science not surprisingly published estimates show considerable scatter with rates ranging between 1 and 2 mm yr 1 for observations on the century timescale in previous work the importance of glacial isostatic adjustment gia upon the assessment of the gmslr has been clearly demonstrated in particular starting from the 1980s gia models have been routinely employed to decontaminate tg observations from the effects of melting of the late pleistocene ice sheets to fully highlight the sea level variations driven by climate change however uncertainties associated with the earth s rheological profile and the time history of the past continental ice sheets can propagate into the gia corrections after revisiting previous work and estimates we suggest a significant modification of the criteria for the selection of the tgs which are most suitable for the robust assessment of the secular gmslr in particular we seek a set of tgs for which gia corrections are essentially independent of the parametrization of the rheological profile of the earth s mantle and of the detailed time chronology of surface loading this insensitivity is established by considering predictions based upon three gia models widely employed in the recent literature namely ice 3g ice 5g and the one developed at the research school of earth sciences of the national australian university applying this approach and selection criteria previously proposed in the literature we identify a set of 22 sufficiently evenly distributed tgs by simple statistical methods these records yield a preferred gia independent gmslr estimate since 1880 namely 1 5 0 1 mm yr 1 rms 0 4 mm yr 1 wrms 0 3 mm yr 1 this value is consistent with various previous estimates based on secular tg observations and with that proposed for the 20th century by the intergovernmental panel on climate change ipcc fourth assessment report 1 7 0 5 mm yr 1

recent rates of sedimentation on irregularly flooded boreal baltic coastal wetlands responses to recent changes in sea level abstract boreal baltic coastal wetlands differ markedly from temperate salt marshes by their generally low maximum elevation between 0 and 1 m above m s l low seaward gradients and the irregular nature of flooding that is characteristic of the ne baltic sea coastal region as a result of these factors these wetlands have been considered to be threatened by future sea level rise this study presents results for two boreal baltic coastal wetland sites in estonia using the 210 pb and 137 cs radiometric dating methods to investigate the sedimentary development of these coastal systems recent coastal evolution has been largely driven by continuing glacio isostatic adjustment gia with maximum rates of 2 8 mm yr 1 around the nw estonian coast and the inherited geomorphological setting of generally flat lying coastal topography resulting in coastal emergence broad agreement exists between calculated rates of sedimentation identified within the core sequences average rates of sedimentation using the 210 pb excess cf cs or simple model range between 0 2 and 1 3 mm yr 1 these rates are corroborated using 137 cs which also suggests an increase in sedimentation rates during recent decades approaching maximum values for current land uplift additionally the 210 pb excess crs model reveals periods of sedimentation greatly in excess of these values in response to coastal flooding from known storm activity this study indicates that changes in sea level caused by variations in atmospheric pressure and storm surges can contribute a significant sedimentary component which coupled with gia processes has driven coastal wetland development emergence and the historical progradation of these wetland systems the recent acceleration in the rate of global sea level rise may subtly alter this relationship however current rates of gia and sedimentation will continue to maintain the progradation of boreal baltic coastal wetlands in the coming decades

the influence of human activities on morphodynamics and alteration of sediment source and sink in the changjiang estuary abstract several works have discussed the morphological evolution in the changjiang estuary cje in recent years the erosion of its subaqueous delta in recent decades has been ascribed to a decline in fluvial sediment input however the interaction between the reduction of riverine sediment load and human activities in the estuary that could have caused morphological change has not been considered in this work we provide evidence on the morphological evolution around the delta front zone since 1986 and use a numerical model to explore the correlation between the change in hydrodynamics and the evolution pattern bathymetric data analysis suggests a decrease of net accretion rate from 16 7 mm year 1986 1997 to 9 1 mm year 1997 2010 in the study area spatially the tidal flats accreted whereas the subaqueous delta switched from deposition between 1986 and 1997 to erosion between 1997 and 2010 we used two indicators tidal energy dissipation and erosion rate to quantify the change in hydrodynamics and found that the erosion of the subaqueous delta in recent decades can readily be explained by the alteration of the hydrodynamics the newly built navigation training works in the north passage had a significant effect on the estuarine hydrodynamics resulting in a local morphological adjustment this erosion generated a new source of sediments to maintain the high suspended sediment concentration and tidal flat progradation the erosion of the subaqueous delta may continue and gradually slow down until the altered hydrodynamics and morphology reach an equilibrium state in the future

spatial and temporal shoreline changes of the southern yellow river huanghe delta in 1976 2016 abstract in this study 364 landsat satellite images were utilized to study the spatial and temporal shoreline changes of the southern yellow river delta in 1976 2016 and a new method revised and improved after zhang et al 2016 was proposed by employing that method the calculated sea levels calculated from simulated tidal heights and instantaneous shoreline positions rather than simulated tidal heights were used to correct fluctuations in instantaneous shoreline positions caused by tidal height and seasonal sea level changes and other random sea level fluctuations when calculating the shoreline erosion rates and beach slopes a statistical analysis of a large number of corrected shoreline positions was used to reduce the influence of random errors that were mainly caused by waves and other casual factors the shoreline erosion rates and beach slopes presented in this paper are therefore more precise and reliable than those derived in previous studies which only used two satellite images the results of this study show that the shoreline of the southern yellow river delta primarily experienced gradual erosion during 1976 2016 with an average erosion rate of 26 9 m year the average shoreline erosion rate increased from 24 9 m year in 1976 1996 to 34 9 m year in 1996 2016 an increase of 40 probably due to the reduction in sediment discharge and shifting northward course of the yellow river after 1996 the shoreline erosion rate of the central coast decreased from 50 2 m year in 1976 1996 to 27 1 m year in 1996 2016 a decrease of 46 probably due to the protection offered by coastal hard structures the average shoreline erosion rate caused by relative sea level rise was 8 5 m year or 32 of the total average shoreline erosion rate relative sea level rise plays an important role in the erosion of the southern yellow river delta due to its flat beach the beach slope of the southern yellow river delta was flat and stable in 1976 2016 and the average slope over most of the beach was 0 043

on the rate and causes of twentieth century sea level rise both the rate and causes of twentieth century global sea level rise gslr have been controversial estimates from tide gauges range from less than one to more than two millimetre yr 1 in contrast values based on the processes mostly responsible for gslr mass increase from mountain glaciers and the great high latitude ice masses and volume increase expansion due to ocean warming fall below this range either the gauge estimates are too high or one or both of the component estimates is too low gauge estimates of gslr have been in dispute for several decades because of vertical land movements especially due to glacial isostatic adjustment gia more recently the possibility has been raised that coastal tide gauges measure exaggerated rates of sea level rise because of localized ocean warming presented here are two approaches to a resolution of these problems the first is morphological based on the limiting values of observed trends of twentieth century relative sea level rise as a function of distance from the centres of the ice loads at last glacial maximum this observational approach which does not depend on a geophysical model of gia supports values of gslr near 2 mm yr 1 the second approach involves an analysis of long records of tide gauge and hydrographic in situ temperature and salinity observations in the pacific and atlantic oceans it was found that sea level trends from tide gauges which reflect both mass and volume change are 2 3 times higher than rates based on hydrographic data which reveal only volume change these results support those studies that put the twentieth century rate near 2 mm yr 1 thereby indicating that mass increase plays a much larger role than ocean warming in twentieth century gslr

twentieth century sea level an enigma changes in sea level relative to the moving crust are associated with changes in ocean volume mostly thermal expansion and in ocean mass melting and continental storage t steric t eustatic t recent compilations of global ocean temperatures by levitus and coworkers are in accord with coupled ocean atmosphere modeling of greenhouse warming they yield an increase in 20th century ocean heat content by 2 1023 j compared to 0 1 1023 j of atmospheric storage which corresponds to greenhouse 2000 3 cm the greenhouse related rate is accelerating with a present value greenhouse 2000 6 cm century tide records going back to the 19th century show no measurable acceleration throughout the late 19th and first half of the 20th century we take historic 18 cm century the intergovernmental panel on climate change attributes about 6 cm century to melting and other eustatic processes leaving a residual of 12 cm of 20th century rise to be accounted for the levitus compilation has virtually foreclosed the attribution of the residual rise to ocean warming notwithstanding our ignorance of the abyssal and southern oceans the historic rise started too early has too linear a trend and is too large melting of polar ice sheets at the upper limit of the intergovernmental panel on climate change estimates could close the gap but severe limits are imposed by the observed perturbations in earth rotation among possible resolutions of the enigma are a substantial reduction from traditional estimates including ours of 1 5 2 mm y global sea level rise a substantial increase in the estimates of 20th century ocean heat storage and a substantial change in the interpretation of the astronomic record

3d numerical simulation of turbulence and sediment transport within a tidal inlet abstract turbulence and sediment transport models are incorporated into a three dimensional hydrodynamics model to investigate the mechanisms of morphologic evolution of scour holes within the indian river inlet delaware usa the inlet bed had eroded slightly since stabilizing the channel walls in late 1930s through 1976 the mean rate of bed erosion roughly doubled as a response to anthropogenic activities within the inlet such as the removal of 80 piles remaining from an old bridge severe erosion near the in water bridge supports and cofferdams for the replacement bridge necessitated channel bed stabilization that along with the remained debris from the removal of old bridge piles enhanced the growth of two deep scour holes on the bayside and oceanside of the bridge cofferdams scour hole and channel bed evolution has decreased drastically since 1994 the present investigation suggests that initially flow concentration through the cofferdams of the replacement bridge was the main reason for scour hole development bed shear stress over the forward facing slope of the scour hole entrains sediment from the bed and extends the scour hole along the inlet and in the vertical direction flow separation within the developed scour holes after channel bed stabilization enhances turbulence and appears to be the dominant mechanism for further scour hole development

ocean response to meridional ekman transport in the atlantic and implication for gravity missions 1 wind friction at the ocean surface introduces energetic variations in the net mass transport across the oceanic basins to conserve mass the whole water column adjusts rapidly introducing a depth independent perturbation in the pressure field this signal is analyzed in a high resolution numerical model of the atlantic ocean while the pressure perturbation cannot be extracted from the energetic sea surface height signals it represents up to 90 of the bottom pressure signal when integrated across the atlantic ocean in the daily and monthly frequencies this signal will be an important part of the signal measured by the grace gravity recovery and climate experiment mission

transport in the low latitude tropopause zone diagnosed using particle trajectories abstract recent literature has described a transition zone between the average top of deep convection in the tropics and the stratosphere here transport across this zone is investigated using an offline trajectory model particles were advected by the resolved winds from the european centre for medium range weather forecasts reanalyses for each boreal winter clusters of particles were released in the upper troposphere over the four main regions of tropical deep convection indonesia central pacific south america and africa most particles remain in the troposphere descending on average for every cluster the horizontal components of 5 day trajectories are strongly influenced by the el nino southern oscillation enso but the lagrangian average descent does not have a clear enso signature tropopause crossing locations are first identified by recording events when trajectories from the same release regions cross the world meteorological organization lapse rate tropopause most crossing events occ

monsoon extratropical circulation interactions in himalayan extreme rainfall extreme precipitation and flood episodes in the himalayas are oftentimes traced to synoptic situations involving connections between equatorward advancing upper level extratropical circulations and moisture laden tropical monsoon circulation while previous studies have documented precipitation characteristics in the himalayan region during severe storm cases a comprehensive understanding of circulation dynamics of extreme precipitation mechanisms is still warranted in this study a detailed analysis is performed using rainfall observations and reanalysis circulation products to understand the evolution of monsoon extratropical circulation features and their interactions based on 34 extreme precipitation events which occurred in the western himalayas weh during the period 1979 2013 our results provide evidence for a common large scale circulation pattern connecting the extratropics and the south asian monsoon region which is favorable for extreme precipitation occurrences in the weh region this background upper level large scale circulation pattern consists of a deep southward penetrating midlatitude westerly trough a blocking high over western eurasia and an intensifying tibetan anticyclone it is further seen from our analysis that the key elements of monsoon midlatitude interactions responsible for extreme precipitation events over the weh region are 1 midlatitude rossby wave breaking 2 west northwest propagation of monsoon low pressure system from the bay of bengal across the indian subcontinent 3 eddy shedding of the tibetan anticyclone 4 ageostrophic motions and transverse circulation across the himalayas and 5 strong moist convection over the himalayan foothills furthermore high resolution numerical simulations indicate that diabatic heating and mesoscale ageostrophic effects can additionally amplify the convective motions and precipitation in the weh region

decadal variability in the large scale sea surface height field of the south pacific ocean observations and causes large scale sea surface height ssh changes in the extraequatorial south pacific ocean are investigated using satellite altimetry data of the past 12 yr the decadal ssh signals in the 1990s were dominated by an increasing trend in the 30 50 s band and a decreasing trend in the central south pacific ocean poleward of 50 s in recent years since 2002 there has been a reversal in both of these trends spatially varying low frequency ssh signals are also found in the tropical region of 10 25 s where the decadal ssh trend is negative in the eastern basin but positive in the western basin to clarify the causes for these observed spatially varying ssh signals a 11u2 layer reduced gravity model that includes the wind driven baroclinic rossby wave dynamics and the responses forced by ssh changes along the south american coast was adopted the model hindcasts the spatially varying decadal trends in the midlatitude and the eastern tropical regions well accumulation of the wind forced ssh anomalies along rossby wave characteristics is found to be important for both previously reported long term trends and their reversals in recent years the boundary forcing associated with the time varying ssh signals along the south american coast is crucial for understanding the observed ssh signals of all time scales in the eastern tropical south pacific basin but it has little impact upon the midlatitude interior ssh signals

steric sea level change in the northern seas abstract ocean temperature and salinity data over the period 1950 2000 in the northern seas defined here as the north atlantic ocean north of 50 n north pacific ocean north of 40 n and arctic oceans are combined to diagnose the steric i e density contribution to sea level variation the individual contributions to steric height from temperature thermosteric height and salinity halosteric height are also analyzed it is found that during 1950 2000 steric height rose over the study s domain mostly as a result of halosteric increases i e freshening over a shorter time period late 1960s to early 1990s during which climate indices changed dramatically steric height gradients near the nordic seas minimum were reduced by 18 32 it is speculated that this may be associated with a local slowing of both the meridional overturning circulation and the southward flow through fram strait however steric height increases in the north pacific ocean during this time imply a possible accelerati

modeling the growth limit of the changjiang delta river deltas grow in response to sediment discharge from the land it is not clear however whether or not there is a limit for such growth conceptual geometric models are used in this paper in association with the principle of mass conservation in an attempt to answer this question preliminary analyses of the changjiang delta indicate that delta growth is constrained by a number of factors the original topography bathymetry sediment supply sediment retention in the estuary sea level rise ground subsidence the quantity of sediment supply per unit area and the sediment retention index for the subaqueous delta decrease as the delta progrades towards deeper water resulting in a decreasing rate of growth the limit of growth is reached when the index approaches zero i e the shoreline reaches the shelf edge if the combined effect of sea level rise and ground subsidence is considered together with decrease in the sediment discharge from land the limit is reached at an earlier stage for the changjiang delta the model output using hypothesized sediment retention index estimates implies that the delta growth will reach its limit in the near future this will occur sooner if the sediment output of the river is reduced to 60 of its original level in response to the upstream basin changes further knowledge however is required of the retention index together with the information on future changes in river input and the character of the sediments in order to improve the accuracy of the simulations

new velocity map and mass balance estimate of mertz glacier east antarctica derived from landsat sequential imagery automatic feature tracking on two landsat images acquired in january 2000 and december 2001 generates a complete velocity field of mertz glacier east antarctica this velocity field shows two main tributaries to the ice stream between the tributaries a likely obstruction feature in the bedrock results in a slow down of the flow a third landsat image acquired in 1989 and combined with the 2000 image permits the determination of the glacier mean velocity during the 1990s although some parts of the mertz glacier system show evidence of slight speed increase we conclude that the mertz flow speed is constant within our uncertainty 35 m a 1 using this complete velocity field new estimates of the ice discharge flux 17 8 km 3 a 16 4 gt a and of the basal melting of the tongue 11m a of ice are given our results lead to an apparent imbalance of the drainage basin ice discharge 3 5 km 3 a lower than the accumulation considering previous studies in the mertz glacier area we discuss the uncertainty of this imbalance and the problems with accumulation mapping for this region

evidence of meridional motion in the summer lower stratosphere adjacent to monsoon regions twenty one years of rawinsonde data were used together with 8 years of uninitialized european centre for medium range weather forecasts ecmwf analyses to describe the climatological structure of large scale circulations adjacent to monsoon regions in northern and southern hemisphere summers in the upper troposphere and lower stratosphere equatorward and poleward motions occur on the eastern and western sides of monsoon regions respectively it is shown that significant meridional velocities 1 ms 1 penetrate the lower stratosphere up to a maximum height of 50 30 mbar largest meridional velocities are observed in connection with the asian monsoon in northern summer although evanescent in height these motions are relatively important for horizontal transport of constituents in the summer lower stratosphere when planetary waves are otherwise small asian and mexican monsoons in this season are displaced sufficiently far from the equator in close proximity to the tropopause break to have a significant role in stratosphere troposphere s t exchange the companion paper by chen 1995 provides evidence of irreversible s t exchange in the upper middle world during northern summer

routes of transport across the antarctic polar vortex in the southern spring abstracttransport in the lower stratosphere over antarctica has been studied in the past by means of several approaches such as contour dynamics or lyapunov exponents this paper examines the problem by means of a new lagrangian descriptor which is referred to as the function m the focus is on the southern spring of 2005 which allows for a comparison with previous analyses based on lyapunov exponents with the methodology based on the function m a much sharper depiction of key lagrangian features is achieved and routes of large scale horizontal transport across the vortex edge are captured these results highlight the importance of lobe dynamics as a transport mechanism across the antarctic polar vortex

frontal movements and property fluxes contributions to heat and freshwater trends in the southern ocean we examine the synoptic variability of temperature and salinity in the southern ocean using a static gravest empirical mode gem mapping based on historical hydrography and a time evolving projection of the gem created using satellite altimetry satgem the gem and satgem projections allow the separation of observed trends into a component due to a shift of the circumpolar fronts adiabatic using the satgem and a component due to changes in water masses diabatic expressed as a temporal trend in residual between historical hydrography and the static gem the mean southward movement of the antarctic circumpolar current acc fronts drives an adiabatic warming of 1 196 0 090 w m 2 distributed over most of the acc and at all depths this is strongest where the meridional temperature gradient is largest such as in the upper 1000 dbar of the subantarctic front saf there is a weak adiabatic freshening of 6 57 0 18 mm yr 1 m 2 concentrated mainly below the antarctic intermediate water and south of the saf residuals between historical hydrography and the static gem field driven by diabatic changes in the water mass structure have temporal trends in temperature and salinity when these trends are integrated over the whole acc there is a net cooling of 0 628 0 129 w m 2 and strong freshening of 30 27 0 70 mm yr 1 m 2 by combining the diabatic and adiabatic components and integrating over the acc the net increase in heat and freshwater in the region is 0 570 0 099 w m 2 and 36 91 0 72 mm yr 1 m 2 respectively the sum of the adiabatic and diabatic changes are consistent with previous trends inferred from observations

global interannual trends and amplitude modulations of the sea surface height anomaly from the topex jason 1 altimeters abstract this study uses the global ocean topography experiment topex jason 1 altimeters time series to estimate the 13 yr trend in sea surface height anomaly these trends are estimated at each grid point by two methods one fits a straight line to the time series and the other is based on the difference between the average height between the two halves of the time series in both cases the trend shows large regional variability mostly where the intense western boundary currents turn the authors hypothesize that the regional variability of the sea surface height trends leads to changes in the local geostrophic transport this in turn affects the instability related processes that generate mesoscale eddies and enhances the rossby wave signals this hypothesis is verified by estimates of the trend of the amplitude of the filtered sea surface height anomaly that contains the spectral bands associated with rossby waves and mesoscale eddies the authors found predominantly positive tendency in the amplit

heat budget in the north atlantic subpolar gyre impacts of atmospheric weather regimes on the 1995 warming event abstract in the mid 1990s the north atlantic subpolar gyre has shown a dramatic warming event that has been thoroughly investigated from observations and numerical simulations some studies suggest that it was due to an interannual wind driven weakening and shrinking of the gyre that facilitated the penetration of warm atlantic water the weakening of the gyre being attributed to changes in the north atlantic oscillation nao and in the east atlantic pattern which are the two dominant modes of atmospheric variability in the north atlantic however other studies suggest that the warming event was due to a decadal buoyancy driven strengthening of the meridional overturning circulation and subsequent intensification of the poleward heat transport in response to the positive nao conditions of 1988 1995 to reconcile this discrepancy the heat budget in the north atlantic subpolar gyre is reconstructed from four ocean hindcast simulations sharing the same modelling platform but using different settings the novelty of this work is the decomposition of the subpolar gyre into a western and an eastern subregion which is motivated by water mass distribution around reykjanes ridge and by the fact that deep convection only occurs in the western subpolar gyre in the western subpolar gyre the 1995 warming event is the decadal baroclinic ocean response to positive nao conditions from 1988 to 1995 the latter induced increased surface heat loss in the labrador sea that intensified deep convection hence strengthened the meridional overturning circulation and the associated poleward heat transport in the eastern subregion a concomittant warming is induced by an interannual barotropic adjustment of the gyre circulation to an abrupt switch from positive nao conditions in winter 1995 to negative nao conditions in winter 1996 indeed the gyre response to negative nao conditions is a cyclonic intergyre gyre that increases northward volume and heat transports at the southeastern limit of the subpolar gyre therefore the discrepancies found in the literature about the 1995 warming event of the north atlantic subpolar gyre are reconciled in the present work which suggests that the atmospheric drivers the mechanisms at stake and the associated timescales are different to the east and to the west of reykjanes ridge

rates and causes of recent global sea level rise inferred from long tide gauge data records abstract tide gauge data at seven sites of the permanent service for mean sea level psmsl with information for relative sea level during the past 140 200 yr were analyzed to examine the rates and causes of the global sea level rise gslr during the twentieth century by subtracting linear trends for relative sea level rise during the past 100 yr from the observed data we get the apparent gslrs of 1 mm yr 1 for five sites around the baltic sea and brest the rate for san francisco is significantly larger than this with an optimum value 2 mm yr 1 the spatial difference of 1 mm yr 1 between these sites is reasonably explained by the recent melting of the greenland ice sheet with an equivalent sea level rise of 1 mm yr 1 the predicted relative sea level change for this melting scenario is 0 5 mm yr 1 at sites around the baltic sea and brest and 1 5 mm yr 1 for san francisco the residuals between observations and predictions 0 5 mm yr 1 at all sites may be contributed by thermal expansion of seawater and or other melting sources these results suggest the rate of twentieth century gslr to be 1 5 mm yr 1

quasi biweekly oscillations of the south asian monsoon and its co evolution in the upper and lower troposphere the upper tropospheric quasi biweekly oscillation uqbw of the south asian monsoon is studied using the potential vorticity field on the 370 k isentrope the uqbw is shown to be a common occurrence in the upper troposphere during the monsoon and its typical evolution is described we suggest that the uqbw is a phenomenon of both the middle and tropical latitudes owing its existence to the presence of the planetary scale upper tropospheric monsoon anticyclone the uqbw is first identified as rossby waves originating in the northern flank of the monsoon anticyclone these rossby waves break when reaching the pacific ocean and their associated cyclonic pv anomalies move southward to the east of asia and then westward across the indian ocean and africa advected by the monsoon anticyclone a strong correlation or co evolution between the uqbw and quasi biweekly oscillations in the lower troposphere qbw is also found in particular analysis of vertically integrated horizontal moisture transport 850 hpa geopotential and outgoing long wave radiation show that the uqbw is usually observed at the same time as and co evolves with the lower tropospheric qbw over south asia we discuss the nature of the uqbw and its possible physical link with the qbw

shoreline change of chongming dongtan and response to river sediment load a remote sensing assessment summary chongming dongtan located in the center of the yangtze estuary is a ramsar wetland of international importance and national nature reserve the dramatic decrease in river sediment load has attracted considerable scientific interest to this area but few studies have paid attention to the shoreline dynamics this study uses landsat images spanning from 1987 to 2010 and an orthogonal transect method which was previously developed by the authors to model the spatial and temporal characteristics of shoreline change and explore its relationship to reduced river sediment load by use of regression analysis on three different spatial scales results show a general decrease in the average rates of shoreline change throughout the entire study period the maximum average shoreline change rate of 115 5 m year occurred in the 1987 1990 interval and the minimum rate of 20 4 m year occurred from 2006 to 2008 based on average rates of shoreline change the coast of dongtan was divided into three segments the erosion segment eastern accretion segment and northern accretion segment the temporal pattern of the northern accretion segment is almost completely opposite to that of the eastern accretion segment the strongest correlation transects are located on the northern side of the eastern tip of dongtan and the next strongest transects are located on the south side other transects have a very low correlation transect 19 near the easternmost tip of dongtan has a near zero correlation r2 0 0045 but has the fastest accretion rate and in general an increase in the shoreline change rate the average rate of shoreline change and the net accretion area in dongtan as a whole are significantly associated with sediment discharge at datong station r2 0 69 and 0 75 respectively this implies that shoreline accretion in dongtan will probably slow down gradually if the river sediment load continues to decrease in the future the shoreline change rates achieved using our approach are consistent with previous studies but the relationship with the river sediment load is different from results in a previous study on intertidal wetland based on bathymetric maps the results and methods may be helpful in coastal management and understanding the evolution of the entire delta from the perspective of shoreline change

the low frequency variability of the southern ocean circulation abstractlong time series of sea surface height ssh sea surface temperature and wind stress curl are used to determine the main modes of low frequency variability of the southern ocean so circulation the dominant mode is a trend of increasing ssh at an average rate of 3 3 mm yr 1 similar trends have been reported in previous studies and the analysis indicates that the tendency of sea level increase over the so has become more spatially homogeneous during the last decade with changes in the increasing rate in 2000 and 2006 the other modes consist of stationary basin type modes and an eastward propagating wave the stationary modes are particularly dominant in the indian and atlantic ocean basins where their spatial structure appears to be shaped by the basin geometry and the bottom topography the wavelike patterns travel eastward with a period of approximately 10 years two waves were identified in the analysis a complete cycle between 1997 and 2007 and a second cycle starting in 2000 such w

intercomparison of deep convection over the tibetan plateau asian monsoon region and subtropical north america in boreal summer using cloudsat calipso data abstractdeep convection in the tibetan plateau southern asian monsoon region tp samr is analyzed using cloudsat and cloud aerosol lidar and infrared pathfinder satellite observations calipso data for the boreal summer season june august from 2006 to 2009 three subregions are defined the tp the southern slope of the plateau pss and the samr and deep convection properties such as occurrence frequency internal vertical structure system size and local environment are compared among these subregions to cast them in a broader context four additional regions that bear some similarity to the tp samr are also discussed east asia ea tropical northwestern pacific nwp and western and eastern north america wna and ena respectively the principal findings are as follows 1 compared to the other two subregions of the tp samr deep convection over the tp is shallower less frequent and embedded in smaller size convection systems but the cloud tops are more densely packed these characteristi

adjusting internal model errors through ocean state estimation abstract oceanic state estimation is a powerful tool to estimate internal model parameters simultaneously with the model s initial conditions and surface forcing field that jointly would bring a model into consistency with time varying large scale ocean observations here an attempt to estimate geographically varying fields of horizontal and vertical viscosity and diffusivity within a 9 yr long estimation procedure is presented the estimated coefficients are highly efficient in preserving watermass characteristics and frontal structures by reducing the model temperature and salinity drift especially around the southern ocean the estimated mean circulation results in stronger transports of western boundary currents and of the antarctic circumpolar current moreover an increase of about 10 in the strength of the meridional overturning circulation and in the poleward heat transport can be found estimated changes in the horizontal mixing coefficients seem to agree with the notion that diapycnal mixing i

cross equatorial response to middle latitude forcing in a zonally varying basic state abstract a nonlinear model based on the shallow water equations is used to study cross equatorial propagation of forced waves in the presence of a longitudinally varying time mean basic state zonal wind field it is found that global scale planetary waves are unable to propagate past a critical latitude where the mean zonal wind speed vanishes however if the longitudinally asymmetric basic state includes a duet in which the zonal winds are westerly waves of zonal scale less than the zonal scale of the westerly duct may propagate from one hemisphere to the other even though the zonally symmetric mean zonal wind remains easterly in the equatorial region the amplitude of the response in one hemisphere to forcing in the opposite hemisphere increases strongly with the magnitude of the westerlies in the equatorial duct the existence and annual variations of a westerly duct region in the upper troposphere in the eastern pacific appear to account for some features of the low frequency variability in the no

two interannual dominant modes of the south asian high in may and their linkage to the tropical sst anomalies the variations of the intensity and position of the south asian high sah in may are critical for the interannual change in the asian summer monsoon onset process the present work has defined two dominant modes of the sah in may via the principal component analysis of sah s strength zonal extension and ridgeline position indices during 1979 2015 the first mode sah intensity mode features a coherent enhancement of the sah strength and zonal extension while the second mode sah position mode exhibits a meridional swing of the sah ridgeline both diagnosis analysis and numerical experiments validate that the distinct evolution of enso in boreal spring determines its different influences on the two modes when an el nino decays quickly during march may its resultant warm anomalies of sea surface temperature sst in the tropical indian ocean can affect the sah intensity mode by modifying the tropical convection over the southwestern bay of bengal acting as a local sst forcing to the circulation however the sah position mode depends on the persistence of the enso event during boreal spring the remote el nino related sst forcing can enhance the large scale descent over the indo pacific ocean which suppresses the tropical convection to modify the mid upper level thermal structure over south asia inducing the interannual variation of the sah ridgeline in may

condensation heating of the asian summer monsoon and the subtropical anticyclone in the eastern hemisphere the effects of condensation heating on the formation of the subtropical anticyclone in the eastern hemisphere eh are studied by means of theoretical analysis and numerical simulation the complete vorticity equation is employed for the analysis it is found that due to the vertical gradient of strong condensation heating the distribution of cyclone and anticyclone in the upper troposphere is out of phase with that in the middle and lower troposphere this is confirmed by a series of numerical experiments the horizontal gradient of the condensation heating also affects the configuration of the subtropical anticyclone it is concluded that condensation heating is a key factor for the formation and location of the summer subtropical anticyclone in the eh the latent heating released by the asian monsoon rainfall contributes to the formation of the 200 hpa south asian anticyclone on the western side of the heating center and the 500 hpa western pacific subtropical anticyclone on the eastern side of the center such configurations are modified to some extent by surface sensible heating and orography the circulation in mid latitudes is also affected by the latent heating in the subtropical area through the propagation of rossby waves

identifying robust transport features of the upper tropical troposphere multimodel ensembles of back trajectories calculated from four different analysis data sets and two different trajectory formulations diabatic and kinematic are analyzed to investigate seasonal mean boundary layer to tropopause 100 hpa transport in the tropics transport paths are separated into two legs convective uplift boundary layer to detrainment and radiative ascent detrainment to tropopause the following three diagnostic measures are used source location source to tropopause transport time and the source influence i e the fraction of air with short transport times at 100 hpa ensemble means and standard deviations identify robust features i e common to all ensemble members while experimental hybrid calculations explain model to model discrepancies convective uplift is a major contributor to uncertainties in boundary layer to tropopause transport times and source locations spatial patterns of boundary layer influence at 100 hpa are nevertheless robust detrainment to tropopause transport times are robust despite substantial model to model variations of convective detrainment height because ascent rates are faster at low altitudes than at high altitudes detrainment to tropopause transport also has robust horizontal spatial patterns for both convective sources and convective influence particularly during boreal winter most model to model discrepancies occur at small spatial scales and are associated with differing distributions of convection the location of maximum convective influence associated with the asian summer monsoon is a notable exception this exceptionally large discrepancy is associated primarily with radiative ascent the fact that the observed maxima of important tropospheric constituents are collocated with the maximum convective influence for the diabatic calculations but not for the kinematic calculations suggests that diabatic trajectories could be more reliable in this region

the formation mechanism of the bonin high in august the bonin high is a subtropical anticyclone that is predominant near japan in the summer this anticyclone is associated with an equivalent barotropic structure often extending throughout the entire troposphere although the equivalent barotropic structure of the bonin high has been known for years among synopticians because of its importance to the summer climate in east asia there are few dynamical explanations for such a structure the present paper attempts to provide a formation mechanism for the deep ridge near japan we propose a new hypothesis that this equivalent barotropic ridge near japan is formed as a result of the propagation of stationary rossby waves along the asian jet in the upper troposphere the silk road pattern first the monthly mean climatology is examined in order to demonstrate this hypothesis it is shown that the enhanced asian jet in august is favourable for the propagation of stationary rossby waves and that the regions of descent over the eastern mediterranean sea and the aral sea act as two major wave sources second a primitive equation model is used to simulate the climatology of august the model successfully simulates the bonin high with an equivalent barotropic structure the upper tropospheric ridge is found to be enhanced by a height anomaly of more than 80 m at 200 hpa when a wave packet arrives sensitivity experiments are conducted to show that the removal of the diabatic cooling over the asian jet suppresses the silk road pattern and formation of an equivalent barotropic ridge near japan while the removal of the diabatic heating in the western pacific does not copyright 2003 royal meteorological society

connection between anomalous zonal activities of the south asian high and eurasian summer climate anomalies abstractusing the daily mean anomalies of atmospheric variables from the ncep reanalysis 1 ncep r1 this study reveals the connection between anomalous zonal activities of the south asian high sah and eurasian climate anomalies in boreal summer an analysis of variance identifies two major domains with larger geopotential height variability located in the eastern and western flanks of the sah at around 100 and 150 hpa respectively for both eastern and western domains extreme events are selected during 1981 2014 when normalized height anomalies are greater than 1 0 less than 1 0 standard deviation for at least 10 consecutive days based on these events four sah modes that include strong and weak tibetan modes stm and wtm respectively and strong and weak iranian modes sim and wim respectively are defined to depict the zonal sah features the positive composite in the eastern western domain indicates the stm sim manifests a robust wavelike pattern with an anomalous low at 150 hpa and su

recent human impacts on the morphological evolution of the yangtze river delta foreland a review and new perspectives abstract this paper reviews the morphological change in the yangtze river delta due to increasing human impacts from three major aspects the first is the reduction of sediment supply to the ocean due to dam construction soil conservation and sand mining within the yangtze river basin the reduced sediment supply has decreased the progradation rate of the delta and triggered erosion in the front of the delta the second impact relates to the reclamation of intertidal wetlands by human activities since the 1950s approximately 1100 km 2 of intertidal land has been embanked resulting in the disappearance of salt marshes and even the entire intertidal zone along some sections of the coastline the third change in the delta due to human interference is the construction of deep waterway structures at the mouth bar which has greatly modified the local hydrodynamics and morphology sediment accretion has increased significantly in these areas as a result of sheltering by these deep waterway structures this review shows that human activities have severely altered the natural balance among the hydrodynamics and sediment supply affecting the morphological features of the yangtze river watershed and delta human impacts on the morphological evolution of deltaic coasts in general are becoming an increasingly concern and more attention should be paid to the management and mitigation of these effects

rapid response of the changjiang yangtze river and east china sea source to sink conveying system to human induced catchment perturbations abstract in order to investigate human impact in the changjiang east china sea source to sink conveying system we analyze the siltation and erosion state of the estuary shelf deposition systems and discuss the response intensity and timing of the depositional system of the changjiang subaqueous delta and the related changjiang distal mud results show that after the three gorges dam was put into operation in 2003 the abrupt reduction of the sediment discharge to the estuary disturbed the equilibrium between the estuary coast shelf deposition systems modifying the siltation erosion balance and seabed sediment types from the changjiang subaqueous delta to its distal mud areas the degree of response to catchment changes diminishes with a larger response lag from north to south of the distal muds influenced by dam emplacements the change of the changjiang east china sea source to sink conveying system can be divided into three stages i e pre 1950 1950 2002 and post 2003 before 1950 the source to sink system remained relatively stable between 1950 and 2002 man made fluvial impoundments created an important sink for terrigenous sediment of the upstream regions but without profound system changes in contrast after 2003 the morphodynamic patterns for the entire mid lower reaches of the changjiang river the subaqueous delta and the distal muds shifted rapidly from siltation to erosion within a short period of time furthermore the upper reaches of the river became disconnected from the source to sink conveying system and the mid lower reaches of the river together with its subaqueous delta and northern distal mud area were converted into net sediment sources as such the sink area has shrunk while the source area expanded for the changjiang east china sea source to sink conveying system

observations of change in the southern ocean the southern ocean has been in a state of disequilibrium with its atmosphere and cryosphere during recent decades ocean station and drifting float observations have revealed rising temperatures in

structure and dynamics of the summertime pacific japan teleconnection pattern convective activity over the tropical western pacific is known to influence the extratropical circulation over east asia in the boreal summer in the form of teleconnection called the pacific japan pj pattern but its structure and dynamics have not yet been studied in depth in this study a composite analysis is performed for 32 monthly events of enhanced convection observed to the east of the philippines the composited monthly mean vorticity anomalies associated with the pj pattern are elongated zonally with a distinct poleward tilt with height this structure differs fundamentally from a combination of the first baroclinic mode in the tropics and the barotropic structure in midlatitudes as has widely been accepted as a conceptual model of the pj pattern a wave activity flux points polewards only in the lower troposphere indicating that rossby wave teleconnection occurs primarily through a low level south westerly jet those tilted anomalies over the western pacific can effectively gain kinetic energy in the exits of the mean jet streams in the upper and lower troposphere and available potential energy ape in the presence of the vertically sheared jets the enhanced convection can generate ape effectively and the associated low level anomalous circulation acts to increase moisture supply into the convective region while enhancing evaporation from the pre warmed ocean surface it is thus hypothesized that the pj pattern may be regarded as a dynamical mode that can be effectively excited in the zonally asymmetric baroclinic mean flow associated with the asian summer monsoon with an efficient self sustaining mechanism through moist processes copyright 2006 royal meteorological society

circumglobal teleconnection in the northern hemisphere summer analysis of the 56 yr ncep ncar reanalysis data reveals a recurrent circumglobal teleconnection cgt pattern in the summertime midlatitude circulation of the northern hemisphere this pattern represents the second leading empirical orthogonal function of interannual variability of the uppertropospheric circulation the cgt having a zonal wavenumber 5 structure is primarily positioned within a waveguide that is associated with the westerly jet stream the spatial phases of cgt tend to lock to preferred longitudes the geographically phase locked patterns bear close similarity during june august and september but the pattern in july shows shorter wavelengths in the north pacific north america sector the cgt is accompanied by significant rainfall and surface air temperature anomalies in the continental regions of western europe european russia india east asia and north america this implies that the cgt may be a source of climate variability and predictability in the above mentioned midlatitude regions the cgt has significant correlations with the indian summer monsoon ism and el nino southern oscillation enso however in normal ism years the cgt enso correlation disappears on the other hand in the absence of el nino or la nina the cgt ism correlation remains significant it is suggested that the ism acts as a conductor connecting the cgt and enso when the interaction between the ism and enso is active enso may influence northern china via the ism and the cgt additionally the variability of the cgt has no significant association with the arctic oscillation and the variability of the western north pacific summer monsoon the circulation of the wave train shows a barotropic structure everywhere except the cell located to the northwest of india where a baroclinic circulation structure dominates two possible scenarios are proposed the abnormal ism may excite an anomalous west central asian high and downstream rossby wave train extending to the north pacific and north america on the other hand a wave train that is excited in the jet exit region of the north atlantic may affect the westcentral asian high and thus the intensity of the ism it is hypothesized that the interaction between the global wave train and the ism heat source may be instrumental in maintaining the boreal summer cgt

an estimate of global mean sea level rise inferred from tide gauge measurements using glacial isostatic models consistent with the relative sea level record this study is concerned with the influence of the glacial isostatic adjustment caused by the last pleistocene deglaciation on the present day sea level the viscoelastic deformation caused by the time variable ice and ocean loads is simulated by computing the resulting perturbations for a spherical self gravitating incompressible maxwell viscoelastic earth model the associated variation of the earth rotation is described in terms of the liouville equation which is solved by means of the maccullagh formulae this allows the determination of the vertical displacement and geoid height and thus the solution of the sea level equation we test several viscosity and ice models and evaluate them by comparison of the computed response with the holocene relative sea level record using the optimum combination of viscosity and ice models we then estimate the influence of the last pleistocene deglaciation on the tide gauge measurements a comparison between the observational and residual linear trends for the tide gauge measurements shows a significant reduction of the variance and geographical variability for the latter in particular for the formerly ice covered regions of north america and scandinavia the favoured value determined for the global mean sea level rise is 1 46 0 2 mm a 1

detection of a large scale mass redistribution in the terrestrial system since 1998 earth9s dynamic oblateness j2 had been undergoing a decrease according to space geodetic observations over the past 25 years until around 1998 when it switched quite suddenly to an increasing trend that has continued to the present the secular decrease in j2 resulted primarily from the postglacial rebound in the mantle the present increase whose geophysical cause s are uncertain thus signifies a large change in global mass distribution with a j2 effect that considerably overshadows that of mantle rebound

eddy shedding from the upper tropospheric asian monsoon anticyclone abstract the authors investigate the transient behavior of the asian monsoon anticyclone in the summertime upper troposphere for the four northern summers 1987 90 the evolution of potential vorticity near the tropopause shows the development of westward migrating anticyclones breaking off from the main anticyclone a few times each summer these disturbances are relatively shallow being confined to the upper troposphere

sea level rise during past 40 years determined from satellite and in situ observations the 3 2 0 2 millimeter per year global mean sea level rise observed by the topex poseidon satellite over 1993 98 is fully explained by thermal expansion of the oceans for the period 1955 96 sea level rise derived from tide gauge data agrees well with thermal expansion computed at the same locations however we find that subsampling the thermosteric sea level at usual tide gauge positions leads to a thermosteric sea level rise twice as large as the true global mean as a possible consequence the 20th century sea level rise estimated from tide gauge records may have been overestimated

sea level changes since the last glacial maximum an appraisal of the ipcc fourth assessment report the ipcc fourth assessment report ar4 stated that global sea level rose by about 120 m between the last glacial maximum lgm and 3 2 ka and did not rise again until the late 19th century a review of relevant literature demonstrates that the rise may have been larger by 10 15 m that the timing of stabilisation is poorly constrained within the last 7 ka bp and that the onset of modern rates of sea level rise is not synchronous and uniform across the globe the lgm lowstand as defined in the ar4 is based on the classic barbados sea level history but the sea level curve from this island may not be an accurate eustatic approximation if glacial isostatic adjustment gia processes were significant as suggested by various authors the barbados sea level curve revealed the existence of meltwater pulse mwp 1a at around 14 000 cal a bp questions about the source and causal mechanism of mwp 1a are still being explored by field scientists and gia modellers these problems have direct relevance for contemporary measurements of ice mass changes because space geodetic measurements rely on information provided by gia models to separate land motion from ice mass changes global patterns of holocene sea level change are controlled by regional sea level variability not only through isostatic and tectonic processes but also through steric effects longer wavelength gravitational changes produced by changing ice ocean mass flux and hemispheric scale perturbations in the earth s rotation eustasy is therefore merely a concept not a measurable quantity constraining the late holocene ice melt contribution to global sea level rise and determining regional sea level rise patterns in the 18th and 19th centuries are important future tasks for sea level scientists these will establish the baseline contributions to 20th and 21st century sea level rise and will help to determine the causes of modern rates of sea level rise constraining historical sea level accelerations and short term ice mass flux will aid models of ice sheet dynamics and help to reduce current uncertainties in future sea level predictions the ar4 shows that regional sea level variability is clearly present in sea level change patterns for the past 50 a and an important challenge for the next ipcc assessment is to incorporate this variability into regional future sea level rise scenarios copyright 2009 john wiley sons ltd

the mean meridional transport circulation of the troposphere in an idealized gcm abstract large numbers of particle trajectories are used to characterize the mean meridional transport circulation of an idealized general circulation model gcm the gcm has a uniform land surface no topography or land sea contrasts and no seasonal cycle the trajectories are analyzed using both lagrangian mean statistics and an approach based on the green s function of the tracer transport equation it is shown that the distribution of particle trajectories provides an estimate of the ensemble mean green s function for the inviscid transport equation lagrangian means have a number of problems that render their interpretation difficult including boundary effects and selection of the appropriate averaging period the green s function on the other hand provides a quantitative description of the transport circulation that is easy to visualize and interpret the results demonstrate that within the idealized model the atmosphere can be divided into three parts the southern hemisphere extratropics the

climate related change of sea level in the extratropical north atlantic and north pacific in 1993 2003 1 climate related change of sea level is one of the most challenging concerns for the humankind here we present a comparative analysis of the interannual variability of sea level in the extratropical north atlantic and north pacific oceans based on the high accuracy topex poseidon jason 1 and ers 1 2 measurements from november 1992 to june 2003 we found indications of the interdecadal variability of the sea level in the north pacific possibly related to the pacific decadal oscillation and suggested that the observed decadal rise of sea level in the subpolar and eastern north atlantic may have been related to the interdecadal change while the north atlantic subtropical and subpolar gyres decelerated the opposite occurred in the north pacific the year to year variations of sea level showed coherence between the north atlantic oscillation el nino la nina and pacific decadal oscillation events and respective gyre scale changes

sea level on the u s east coast decadal variability caused by open ocean wind curl forcing one of the puzzling features of sea level on the east coast of the united states is the decedal scale variability the fluctuations are 10 15 cm peak to peak at periods longer than a few years the authors find that this variability in the frequency band treated with the model is largely caused by a deep sea signal generated by the wind stress curl over the north atlantic a simple forced long rossby wave model of the response of the thermocline to wind forcing is used computing long wave speeds from observed hydrographic data the authors model the response of the ocean at periods longer than 3 years for the full width of the atlantic and for the north south extent of the main anticyclonic gyre 188 388n the model output in deep water shows remarkably good agreement with tide gauges both at bermuda 328n and puerto rico 188n as well as with dynamic height fluctuations of 20 cm peak to peak once these fluctuations reach the western side of the ocean the authors estimate coastal sea level by constructing a complementary coastal model the coastal model is geostrophic and conserves mass within a nearshore region that encompasses the gulf stream by extending this nearshore region as far south as 148 188n and using only the oceanic fluctuations to force the variability in the stream between 80 and 90 of the variance of sea level at coastal tide gauges can be explained sea level along the coast is used to test the model assumptions the basic results however seem important because they are constrained only by open ocean wind forcing and not by input boundary conditions

global sea level contribution from the patagonian icefields since the little ice age maximum the melting of mountain glaciers and ice caps is expected to contribute significantly to sea level rise in the twenty first century 1 3 although the magnitude of this contribution is not fully constrained glaciers in the patagonian icefields of south america are thought to have contributed about 10 of the total sea level rise attributable to mountain glaciers in the past 50 years 3 however it is unclear whether recent rates of glacier recession in patagonia are unusual relative to the past few centuries here we reconstruct the recession of these glaciers using remote sensing and field determinations of trimline and terminal moraine location we estimate that the north patagonian icefield has lost 103 20 7 km 3 of ice since its late holocene peak extent in ad 1870 and that the south patagonian icefield has lost 503 101 1 km 3 since its peak in ad 1650 this equates to a sea level contribution of 0 0018 0 0004 mm yr 1 since 1870 from the north and 0 0034 0 0007 mm yr 1 since 1650 from the south the centennial rates of sea level contribution we derive are one order of magnitude lower than estimates of melting over the past 50 years 3 even when we account for possible thinning above the trimline we conclude that the melt rate and sea level contribution of the patagonian icefields increased markedly in the twentieth century

changes in progradation rate of the tidal flats at the mouth of the changjiang yangtze river china progradation rates of tidal flats at the chiangjiang river mouth china over different periods were examined based on surveys and historical records rapid progradation after the holocene sea level rise began about 2000 years ago because of an increase in riverine sediment the tidal flats at the river mouth have grown at a rate of about 5 km2 year and the southern mainland shoreline in front of the river mouth has advanced at a rate of 17 m year in recent decades the lateral progradation rate at the frontal area has been from tens to hundreds of meters per year the evolutionary process of the tidal flat is highly episodic under this general tendency of progradation spring neap cyclicity shows clearly in calm seasons while the bare flat surface is sensitive to windy conditions different seasonal patterns occur between the marsh and the bare flat because of the influence of vegetation spatial changes in sedimentation rate are also striking which could be attributed to differences in sediment distribution and hydrodynamics the changeability of sediment surface shows a shoreward reduction from the subtidal area to the high marsh likely due to the shoreward decrease in water energy and submergence time as well as the protective effect of marsh vegetation it is predicted that the general progradation could be greatly slowed when the sharp reduction in riverine sediment caused by the three gorges project and the south to north water diversion will coincide with the rapid relative sea level rise

rossby wave breaking and transport between the tropics and extratropics above the subtropical jet abstractrossby wave breaking is an important mechanism for the two way exchange of air between the tropical upper troposphere and lower stratosphere and the extratropical lower stratosphere the authors present a 30 yr climatology 1981 2010 of anticyclonically and cyclonically sheared wave breaking events along the boundary of the tropics in the 350 500 k potential temperature range from ecmwf interim re analysis era interim lagrangian transport analyses show net equatorward transport from wave breaking near 380 k and poleward transport at altitudes below and above the 370 390 k layer the finding of poleward transport at lower levels is in disagreement with previous studies and is shown to largely depend on the choice of tropical boundary in addition three distinct modes of transport for anticyclonic wave breaking events are found near the tropical tropopause 380 k poleward equatorward and symmetric transport associated with cyclonic wave breaking events however is predominantly poleward

redistributing earth s mass since the end of the last glaciation postglacial rebound of earth9s crust has resulted in a net transfer of mass from the equatorial regions to high latitudes this small mass transfer has been monitored for 25 years but a report by cox and chao suggests that since 1998 the mass transfer has changed direction in their perspective cazenave and nerem discuss possible mechanisms that may have caused this change

impact of tropical cyclone development on the instability of south asian high and the summer monsoon onset over bay of bengal this paper analyzes the evolution of the south asian high sah during and after the development of tropical cyclone neoguri over the south china sea scs in mid april 2008 the formation of tropical storm nargis over the bay of bengal bob in late april and the asian summer monsoon onset as well as their interrelationships numerical sensitivity experiments are conducted to explore the underlying mechanism responsible for these seasonal transitions in 2008 it is demonstrated that strong latent heating related with tropical cyclone activities over the scs can enhance the development of the sah aloft and generate zonal asymmetric potential vorticity pv forcing with positive vorticity advection to its east and negative advection to its west following the decay of the tropical cyclone this asymmetric forcing leads to instability development of the sah presenting as a slowly westward propagating rossby wave accompanied by a westward shift of the high pv advection a strong upper tropospheric divergence on the southwest of the sah also shifts westward while positive pv eddies are shed from the high pv advection and eventually arrives in the southern bob such synoptic patterns provide favorable pumping conditions for local cyclonic vorticity to develop the latent heating release from the cyclogenesis further intensifies the upper layer divergence and the lower and upper circulations become phase locked leading to the explosive development of the tropical cyclone over the southern bob consequently a tropical storm is generated and the bob summer monsoon commences

spatial temporal evolution of the eastern nanhui mudflat in the changjiang yangtze river estuary under intensified human activities abstract the eastern nanhui mudflat enm located in the southern flank of the changjiang yangtze river estuary plays a key role in storm protection defense against sea level rise and land resource provision for shanghai china s largest city recently there has been a great deal of concern for its evolutionary fate since a drastic reduction in the changjiang sediment discharge rate and an increased number of estuarine enclosures might negatively impact the environmental protection functions that this mudflat provides in this paper a novel method which employed the envelope lines of instantaneous shoreline positions identified in 436 landsat satellite images from 1975 to 2016 was used to demonstrate the evolution of the mudflat high and low tide lines in a detailed quantitative way our study reveals the southeast progradation rate of the mudflat doubled from 24 m yr in 713 1974 ce to 49 m yr in 1975 1995 ce probably due to the influence of the estuarine turbidity maximum zone shifting to the enm under the ample sediment input directly from the turbidity maximum zone the spatial evolution of the enm was governed predominantly by the changing morphology of the south passage due to the quick progradation of the enm which narrowed the south passage by pushing the south passage trumpet southeastward therefore the enm experienced rapid accretion during 1975 2016 the accretion rate of the high tide line increased 2 13 times due to vegetation and intertidal enclosures resulting in the rapid reduction of the intertidal area the area decreased from 97 km2 in 1976 to 66 km2 in 1995 mainly due to vegetation and continued decreasing to 12 km2 in 2006 due to the intertidal enclosures in contrast the accretion rate of the low tide line increased by 25 times due to subtidal enclosures and caused the intertidal area increased to 78 km2 in 2015 the almost disappeared intertidal zones in 2006 reappeared however this reappearance might be a temporary transitional state and once the subtidal enclosures are completed most of the intertidal zones will be replaced by enclosure land our study reveals that the drastic reduction in the changjiang sediment flow to the sea has not caused a decline in the enm in contrast the enm has experienced rapid accretion in the past 40 years resulting in the strengthening of its functional abilities to protect shanghai an unexpected outcome

transport above the asian summer monsoon anticyclone inferred from aura microwave limb sounder tracers 1 tracer variability above the asian summer monsoon anticyclone is investigated using aura microwave limb sounder mls measurements of carbon monoxide ozone water vapor and temperature during northern hemisphere summer june to august of 2005 observations show persistent maxima in carbon monoxide and minima in ozone within the anticyclone in the upper troposphere lower stratosphere utls throughout summer and variations in these tracers are closely related to the intensity of underlying deep convection temperatures in the utls are also closely coupled to deep convection cold anomalies are linked with enhanced convection and the three dimensional temperature patterns are consistent with a dynamical response to near equatorial convection upper tropospheric water vapor in the monsoon region is strongly coherent with deep convection both spatially and temporally however at the altitude of the tropopause maximum water vapor is centered within the anticyclone distant from the deepest convection and is also less temporally correlated with convective intensity because the main outflow of deep convection occurs near 12 km well below the tropopause level 16 km we investigate the large scale vertical transport within the anticyclone the mean vertical circulation obtained from the era40 reanalysis data set and a free running general circulation model is upward across the tropopause on the eastern end of the anticyclone as part of the balanced threedimensional monsoon circulation in addition to deep transport from the most intense convection this large scale circulation may help explain the transport of constituents to tropopause level

implications of flow control by the three gorges dam on sediment and channel dynamics of the middle yangtze changjiang river china the impacts of a dam on the river downstream in terms of hydrology and morphology are determined by a complex mix of variables that includes the patterns of release of water through the dam and the characteristics of the downstream channel scour of the downstream channel is a common response because large dams cause a significant interruption to sediment continuity here we show that in the case of china9s three gorges dam on the yangtze river the outcome is complicated as is commonly the case in large rivers the downstream channel and floodplain system compose an area of long term sediment accumulation and unstable channels with seasonally contrasting erosion and deposition patterns related to the migrating seasonal monsoon rainfall zones in achieving one of the main purposes of this dam that of flood control in the middle and lower basins the pattern of flows released from the dam will closely resemble those seasonal flows that are responsible for channel instability in the middle catchment thus effectively making erosive conditions the most common during a year there is obviously concern about the ultimate impact of sediment storage in the dam on the dynamics of the delta and adjacent coast and we show that this depends on the trajectory and duration of the erosive responses in the middle yangtze basin in this particular case the outcome is of great significance to the well being of the densely populated riparian areas of the river

local diagnostics to estimate density induced sea level variations over topography and along coastlines 1 in the open ocean sea level variability is primarily steric in origin steric sea level is given by the depth integral of the density field raising the question of how tide gauges which are situated in very shallow water feel deep ocean variability here this question is examined in a high resolution global ocean model by considering a series of assumptions we show that if we wish to reconstruct coastal sea level using only local density information then the best assumption we can make is one of no horizontal pressure gradient and therefore no geostrophic flow at the seafloor coastal sea level can then be determined using density at the ocean s floor when attempting to discriminate between mass and volume components of sea level measured by tide gauges the conventional approach is to take steric height at deep ocean sites close to the tide gauges as an estimate of the steric component we find that with steric height computed at 3000 m this approach only works well in the equatorial band of the atlantic and pacific eastern boundaries in most cases the steric correction can be improved by calculating steric height closer to shore with the best results obtained in the depth range 500 1000 m yet for western boundaries large discrepancies remain our results therefore suggest that on time scales up to about 5 years and perhaps longer the presence of boundary currents means that the conventional steric correction to tide gauges may not be valid in many places

statistical analysis of recent mediterranean sea level data abstract the global rate of sea level rise during the 20th century is generally agreed to be 1 2 5 mm year an examination of the four sea level data series available for the mediterranean shows a sea level rise of a similar rate a statistical analysis based on linear regression reveals this trend to be inconsistent over the century the four time series were divided into two different sets the first consists of records prior to 1960 when sea level was rising consistently and the second from 1961 and onward when there was no significant sea level trend dividing these two data sets into shorter time periods by using additional data from 41 tide gauging stations in the mediterranean showed a consistent trend prior to 1960 between 1961 and 1989 the records show no significant trend this can be due to a rise in mean surface atmospheric pressure of 1 74 3 31 hpa during that period rather than an eustatic decrease in the rate of sea level rise from 1990 onward the sea level recorded in most mediterranean tide gauges indicates a rise in sea level at a rate 5 10 times higher than the 20th century mean rate while this trend should be regarded with some caution because of the relatively short data series the trend observed coincides with the increase in global land and marine surface temperatures during the 1990s and it is important to note that no other short sub period in the data sets shows such an extreme trend

recent estuarine sedimentation rates from shallow inter tidal environments in western scotland implications for future sea level trends and coastal wetland development during the mid late holocene large sections of the scottish coastline have been characterized by falling relative sea levels resulting from differential glacio isostatic uplift of this region of northern britain the complex interplay between crustal and sea level movements continues to influence the morphological development of the scottish coast a number of geophysical models predict ongoing uplift of the scottish landmass however a number of recent studies based upon the analysis of satellite altimetry data indicate a late 20th century acceleration in the rate of eustatic sea level rise detailed geochemistry radiometric dating and diatom analysis on selected sediment cores from four mature coastal marsh environments in argyll western scotland provides an opportunity to investigate the linkages between twentieth century crustal movements eustatic sea level rise and recent rates of sedimentation recorded within marsh sediments across the proposed scottish glacio isostatic uplift dome solid phase major and trace element geochemistry has been used to examine the extent to which post depositional physical disturbance and or chemical reactions may have influenced the reliability of the radiometric dating methods geochemical data indicate that the evolution of these marsh environments has not been significantly influenced by physical disturbance and overall the supply of minerogenic material to the marshes has been quite uniform vertical distributions of 210pbexcess and 137cs activity have been measured and used to develop models of recent marsh vertical accretion dating of the cores reveals subtle variations in the rates of sediment accumulation over the last c 70 years between sites for much of the last hundred years or so sedimentation rates have been in good overall agreement with various estimations for sea level rise although at the more easterly sites these estimates are generally exceeded however quasi equilibrium between marsh sedimentation and sea level rise for much of the twentieth century is indicated from the diatom analysis over the most recent period of marsh development 10 years a significant increase in the rate of surface sedimentation is recorded at all sites across the study area diatom analysis of these surface layers reveals an increase in the relative abundance of marine polyhalobous taxa in the near surface sediments this signifies a very recent increase in the rate of regional relative sea level rise indicating that a regional threshold in coastal forcing has now been exceeded these findings provide clear evidence that recent relative sea level rise is now outpacing estimated rates of glacio isostatic adjustment gia across the proposed scottish uplift dome

human influence and the changing geomorphology of mediterranean deltas and coasts over the last 6000 years from progradation to destruction phase the present geomorphology of the mediterranean s coasts is largely a product of an intricate long term relationship between nature and human societies a cradle of ancient civilisations the mediterranean has seen its shores occupied by humans since prehistory and is therefore a particularly pertinent unit of analysis the morphotectonic context and other forcing agents e g climate shaped out a highly diversified coastal morphology and generated a sediment supply regime potentially favourable to the formation of numerous open coast deltas and bay head deltas in infilled rias as sea level stabilised during the mid holocene this supply of riverine sediment has also been the key agent in mediating human occupation of the mediterranean s clastic coasts expressions of this relationship have been extensively archived in clastic coastal deposits including base level deltaic and estuarine sedimentary sinks which comprise records to explore the interactions between geosystems and the human environment the stratigraphic sequences in these coastal sedimentary archives comprise in many places a clearly identified anthropogenic signature notably in ancient harbours some of which underwent extremely rapid silting up due to massive sediment sourcing generated by new agricultural practices from the neolithic onwards increasing human influence especially over the last 3000 years has been in turn an important driver of changes in sediment supply strongly modulating deltaic development pulses of sediment supply from catchments rendered vulnerable by human perturbations during the roman period resulted in a new cycle of inception of many other deltas and in rapid delta growth e g the ebro the po the arno and the ombrone another progradation dynamic during the little ice age at a time of strong rural population growth river discharge increases technological developments and urbanisation further consolidated delta growth understanding the life cycle of these deltas since their initial formation is in turn key to unravelling the relative role of natural and anthropogenic forcing agents rapid climate changes are deemed to have contributed through both the stripping of landscapes rendered fragile by human activities and active fluvial sediment transport to the coast but disentangling climate change effects from human impacts in the mediterranean remains a challenge the patterns of subsequent deltaic growth and delta morphodynamics reflect adaptations to pulsed sediment supply river discharge variations the microtidal fetch limited context of the mediterranean and direct engineering interventions the progradation dynamic of the roman period and little ice age contrasts markedly with the situation of common coastal destabilisation over the last two centuries particularly well documented for the last 50 years this period has been characterised by reduced sediment flux to base level geosystems due to catchment reforestation retenion within reservoirs fluvial regulation and dredging resulting in the erosion of deltas and barrier lagoon and beach dune systems large stretches of shoreline and narrow coastal plains have been massively engineered for coastal defence and protection against erosion but also for the construction of marinas leisure harbours and artificial beaches resulting in the emergence of veritable artificial seafronts these interventions have collectively and progressively raised societies to a pervasive and overarching position in the geomorphic stability instability of the mediterranean s coasts a situation that will be exacerbated by pressures from sea level rise paving the way for rampant coastal erosion and delta destruction

the role of subglacial water in ice sheet mass balance subglacial water can significantly affect the velocity of ice streams and outlet glaciers of ice sheets depending on the geometry and capacity of the subglacial hydrologic system increased surface melting in greenland over the coming decades may influence the ice sheet s mass balance furthermore subglacial lakes in antarctica can modulate ice velocities and act as nucleation points for new fast flowing ice streams in the coming decades significant changes in the polar regions will increase the contribution of ice sheets to global sea level rise under the ice streams and outlet glaciers that deliver ice to the oceans water and deformable wet sediments lubricate the base facilitating fast ice flow the influence of subglacial water on fast ice flow depends on the geometry and capacity of the subglacial hydrologic system water moving rapidly through a well connected system of conduits or channels will have little impact on ice sheet velocities but water injected into a spatially dispersed subglacial system may reduce the effective pressure at the base of the ice sheet and thereby trigger increased ice sheet velocities in greenland the form of the subglacial hydrologic system encountered by increasing surface melt water will determine the influence of changing atmospheric conditions on ice sheet mass balance in antarctica subglacial lakes have the capacity to both modulate velocities in ice streams and outlet glaciers and provide nucleation points for new fast ice flow tributaries climate models of ice sheet responses to global change remain incomplete without a parameterization of subglacial hydrodynamics and ice dynamics

extratropical influences on the inter annual variability of south asian monsoon the effects of extratropical dynamics on the interannual variations in south asian monsoon sam are examined based on ncep ncar reanalysis and cru precipitation data a conditional maximum covariance analysis is performed on sea level pressure 200 hpa geopotential heights and the sam rainfall by removing the linear effects of el nino southern oscillation from the fields it is found that two modes provide a strong connection between the upper level circulation in the atlantic european region and sam rainfall the circumglobal teleconnection cgt and the summer north atlantic oscillation snao the structures in the 200 hpa heights of both modes in the atlantic region are similar in the atlantic region and their southeastward extension to south asia sa also corresponds to upper level ridges in their positive phases in slightly different positions nevertheless the influence of both modes on sam rainfall is distinct whereas a positive cgt is related to a widespread increase of rainfall in sam a positive snao is related to a precipitation dipole with its positive phase over pakistan and the negative phase over northern india the physical mechanisms for the influence of cgt and snao on sam are related to the upper level geopotential anomaly which affects the amplitude and position of the low level convergence the small displacements of the centers of these responses and the low level cold advection from the north east of sa in case of snao explain the differences in the corresponding sam rainfall distributions these findings are confirmed with the relatively high resolution coupled climate model ec earth which gives confidence in the physical basis and robustness of these extratropical variability modes and their influence on the south asian monsoon rainfall

decline in suspended sediment concentration delivered by the changjiang yangtze river into the east china sea between 1956 and 2013 abstract the temporal evolution of suspended sediment concentration ssc in a river debouching into the ocean provides vital insights into erosion processes in the watershed and dictates the evolution of the inner continental shelf while the delivery of sediment from rivers to the ocean has received special attention in the recent past few studies focused on the variability and dynamics of river ssc especially in the changjiang yangtze river china the longest river in asia here variations in ssc delivered by the changjiang river to the east china sea and possible causes of its variability were detected based on a long term time series of daily ssc and monthly water discharge measured at the datong gauging station the ssc data are further compared to a hydrological analysis of yearly precipitation covering the entire catchment the results indicate the presence of a decline in ssc in the period 1956 2013 which can be divided into three phases i high ssc 0 69 kg m3 in the wet season and low ssc 0 2 kg m3 in the dry season from 1956 to 1970 ii relative high ssc 0 58 kg m3 in the wet season and low ssc 0 15 kg m3 in the dry season from 1971 to 2002 and iii low ssc 0 19 kg m3 in the wet season and very low ssc 0 09 kg m3 in the dry season after 2002 these three periods have a mean yearly ssc values of 0 62 0 42 and 0 18 kg m3 respectively compared with 1956 1970 the slope of the rating curve between ssc and water discharge decreased respectively by 2 and 30 during the period 1971 2002 and 2002 2013 soil erosion dam construction and banks reinforcement along the changjiang river are the main causes of ssc variations fluctuations in water discharge are also controlling the ssc long term variations specifically from 1956 to 1970 the effect of soil erosion overrules that of dam impoundment which is likely responsible for the high ssc during the period 1970 2002 the influence of dam impoundment increases while that of soil erosion decreases which together produce a small reduction in ssc since 2002 the impact of soil erosion further decreases and large scale sediment trapping behind the three gorges dam is responsible for the occurrence of extremely low ssc the results presented herein for the changjiang river can inform a better management strategy of sediment resources and water quality for both the river and the coast our conclusions can be well applied to other rivers discharging in the ocean subject to similar human activities

development of a foraminifera based transfer function in the basque marshes n spain implications for sea level studies in the bay of biscay abstract in order to reconstruct former sea level we have developed a foraminifera based transfer function using three models based on a modern dataset of 59 samples and 23 species obtained from four basque marshes in northern spain the relationship between observed and foraminifera predicted elevation illustrated the strong performance of the transfer function r 2 jack ranges from 0 74 to 0 81 these results indicated that precise reconstructions of former sea levels are possible error ranges from 0 11 to 0 19 m the transfer function was used to calibrate the foraminiferal assemblages collected from a 50 cm salt marsh core we placed the foraminifera based reconstructions into a temporal framework using 137 cs pb concentrations and 210 pb derived sediment accumulation rates the resulting relative sea level curve is in good agreement with regional tide gauge data both instrumental data and microfossil records suggest a rate of relative sea level rise of approximately 2 mm yr 1 for the 20th century

field experiments on bioturbation in salt marshes bombay hook national wildlife refuge smyrna de usa implications for sea level studies the suitability of marsh sites for sea level studies was examined based on field experiments along a transect from low to high marsh bead distributions were determined both seasonally and after 7 years seasonal sediment mixing was greatest in the low marsh and in the late spring and early summer when biological activity is greatest however after an initial interval of relatively intense reworking the bead concentrations reached an approximate equilibrium profile characteristic of each marsh environment as reflected by the profiles obtained after 7 years mixed layer thickness is greatest 10 cm in the intermediate and low marsh and burial rates are rapid 3 7 11 1 mm yr 1 moreover burial rates are comparable to or even surpass longer term 30 to 150 yr radiotracer derived sediment accumulation rates and rates of local and regional sea level rise 4 mm yr 1 therefore sediment accumulation rates appear to reflect primarily sediment resuspension redeposition within the system due to bioturbation thus bioturbation may be critical to the ability of marshes to keep pace with sea level while seemingly precluding the use of low marsh for high resolution sea level studies copyright 2008 john wiley sons ltd

boundary layer sources for the asian anticyclone regional contributions to a vertical conduit 1 the transport of air from the planetary boundary layer pbl into the asian summer monsoon anticyclone is investigated using backward trajectories initiated within the anti cyclone at 100 mb and 200 mb during august 2011 transport occurs through a well defined conduit centered over the southern tibetan plateau where convection lofts air parcels into the anticyclone the conduit as a dynamical feature is distinct from the anticyclone thus while the anticyclone influences transport through the upper troposphere and lower stratosphere it does not by itself define a transport pipeline through that region to quantify model sensitivities parcel trajectories are calculated using wind fields from multiple analysis data sets european centre for medium range weather forecasts national center for environmental prediction s global forecasting system and nasa s modern era retrospective analysis for research and applications merra and from synthetically modified data sets that explore the roles of vertical motion and horizontal resolution for discrepancies among these calculations all calculations agree on the relative contributions to pbl sources for the anticyclone from large scale regions with tibetan plateau and india se asia being the most important however they disagree on the total fraction of air within the anticyclone that was recently in the pbl at 200 mbar calculations using merra are clear outliers due to problematic vertical motion in those data large differences among the different data sets at 100 mbar are more closely related to horizontal resolution it is speculated that this reflects the importance of deep small scale convective updrafts for transport to 100 mbar

impact of indian summer monsoon on the south asian high and its influence on summer rainfall over china by using the monthly era 40 reanalysis data and observed rainfall data we investigated the effect of the indian summer monsoon ism on the south asian high sah at 200 hpa and the role played by the sah in summer rainfall variation over china it is found that in the interannual timescale the east west shift is a prominent feature of the sah with its center either over the iranian plateau or over the tibetan plateau when the ism is stronger weaker than normal the sah shifts westward eastward to the iranian plateau tibetan plateau the east west position of sah has close relation to the summer rainfall over china a westward eastward location of sah corresponds to less more rainfall in the yangtze huai river valley and more less rainfall in north china and south china a possible physical process that the ism affects the summer rainfall over china via the sah is proposed a stronger weaker ism associated with more less rainfall over india corresponds to more less condensation heat release and anomalous heating cooling in the upper troposphere over the northern indian peninsula the anomalous heating cooling stimulates positive negative height anomalies to its northwest and negative positive height anomalies to its northeast in the upper troposphere causing a westward eastward shift of the sah with its center over the iranian plateau tibetan plateau as a result an anomalous cyclone anticyclone is formed over the eastern tibetan plateau and eastern china in the upper troposphere the anomalous vertical motions in association with the circulation anomalies are responsible for the rainfall anomalies over china our present study reveals that the sah may play an important role in the effect of ism on the east asian summer monsoon

centennial scale cycles in middle holocene sea level along the southeastern swedish baltic coast submerged sea grasses and stoneworts growing in the immediate nearshore of the baltic sea are sensitive indicators of sea level the alternating changes in concentrations of sea grass and stonewort macrofossils obtained from an ancient lagoon of the baltic sea are ascribed to middle holocene sea level fluctuations along the southeastern swedish coast abundances of stonewort and sea grass macrofossils between 7500 and 6000 cal calibrated yr b p were lower and less variable indicating high and relatively stable sea level low frequency fluctuations of sea level with a 1470 yr period during this time may have been forced by tidal action in the millennial band after 6000 cal yr b p sea level was lower and exhibited strong fluctuations at centennial time scales as evident in the stonewort and sea grass macrofossil records such a high frequency oscillatory mode of sea level may have been regulated by centennial scale solar activities or tidal actions or both the modest variation in solar irradiance is unlikely to have resulted in large scale oscillations of sea level by directly changing the steric component instead it governed sea level fluctuations by changing the regional storminess through a north atlantic oscillation nao like system storms embedded in the nao induced southwesterly winds played a major role in the centennial scale fluctuations of the baltic sea level by pushing saltwater from the north sea into the baltic basin less

current and future mudflat losses in the southern huanghe delta due to coastal hard structures and shoreline retreat abstract coastal wetlands especially broad mudflats are facing an unprecedented crisis due to combined influence of intensified coastal development activities drastic river sediment reduction and rapid relative sea level rise however it is still a huge challenge to accurately assess the evolution of mudflats for the lack of reliable shoreline indicators on satellite images especially the indicators for shoreline at low tide this study based on instantaneous shoreline positions derived from 430 landsat satellite images during 1983 2019 uses sea level correction and statistical analysis methods to study the evolution of laizhou mudflat and the intertidal mudflat loss in laizhou mudflat was accurately assessed and the effects of multiple factors especially the effects of various coastal hard structures on the evolution of laizhou mudflat were quantitatively estimated for the first time the results show that the intertidal mudflat loss caused by the construction of cofferdams was 98 km2 93 of the total intertidal mudflat loss although the previous intertidal mudflat loss caused by shore parallel structures was less the shore parallel structures will cause great mudflat loss in the future and the broad laizhou mudflat will disappear in 110 years owing to the barrier effect of the widespread shore parallel structures if the current rapid shoreline retreat is not improved the construction of shore normal structures can slow the shoreline retreat of adjacent mudflat but accelerate downstream shoreline retreat as far as coastal protection is concerned the construction of shore normal structures in laizhou mudflat is inadvisable diverting 13 m ton year of huanghe sediment can totally offset the mudflat loss on the upstream of dongying pier however the mudflat located on the downstream of dongying pier is hard to restore owing to the block effect of the shore normal structures to the alongshore transported sediment another option is demolishing the shore parallel structures to recover the landward movement of shoreline avoiding the mudflat loss at the expense of land loss

estimates of the regional distribution of sea level rise over the 1950 2000 period abstract topex poseidon satellite altimeter data are used to estimate global empirical orthogonal functions that are then combined with historical tide gauge data to estimate monthly distributions of large scale sea level variability and change over the period 1950 2000 the reconstruction is an attempt to narrow the current broad range of sea level rise estimates to identify any pattern of regional sea level rise and to determine any variation in the rate of sea level rise over the 51 yr period the computed rate of global averaged sea level rise from the reconstructed monthly time series is 1 8 0 3 mm yr 1 with the decadal variability in the computed global mean sea level it is not possible to detect a significant increase in the rate of sea level rise over the period 1950 2000 a regional pattern of sea level rise is identified the maximum sea level rise is in the eastern off equatorial pacific and there is a minimum along the equator in the western pacific and in the eastern indian ocean a g

vertical diffusivity in the lower stratosphere from lagrangian back trajectory reconstructions of ozone profiles 1 we present a simple stochastic dynamical approach to estimate the turbulent vertical diffusivity d in the lower stratosphere from routinely observed ozone profiles first an observed ozone profile is reconstructed using three dimensional back trajectories obtained from analyzed winds and initializing the trajectories with ozone values from the output of a chemistry transport model assuming that diffusion in the vertical follows a simple random walk leading to a gaussian probability distribution for the particle displacements we perform monte carlo simulations with ensembles of particles originating along each point in the vertical profile by choosing different values of d as input in the calculations we generate different profiles that are smoothed through diffusion comparing with the observed profile we can identify that value of d which is in best agreement at an intermediate range of vertical length scales as an upper bound of the actual d for northern midlatitude lower stratospheric conditions during winter over a period of 12 days the best estimate is d 0 1 m2 s 1 or slightly larger the present results are discussed in the context of comparable estimations of vertical diffusivity in the literature