geophysical imaging and thermal modeling of subsurface morphology and thaw evolution of discontinuous permafrost 1 despite our current understanding of permafrost thaw in subarctic regions in response to rising air temperatures little is known about the subsurface geometry and distribution of discontinuous permafrost bodies in peat covered wetland dominated terrains and their responses to rising temperature using electrical resistivity tomography ground penetrating radar profiling and thermal conduction modeling we show how the land cover distributions influence thawing of discontinuous permafrost at a study site in the northwest territories canada permafrost bodies in this region occur under forested peat plateaus and have thicknesses of 5 13 m our geophysical data reveal different stages of thaw resulting from disturbances within the active layer from widening and deepening of differential thaw features under small frost table depressions to complete thaw of permafrost under an isolated bog by using two dimensional geometric constraints derived from our geophysics profiles and meteorological data we model seasonal and interannual changes to permafrost distribution in response to contemporary climatic conditions and changes in land cover modeling results show that in this environment 1 differences in land cover have a strong influence on subsurface thermal gradients such that lateral thaw dominates over vertical thaw and 2 in accordance with field observations thaw induced subsidence and flooding at the lateral margins of peat plateaus represents a positive feedback that leads to enhanced warming along the margins of peat plateaus and subsequent lateral heat conduction based on our analysis we suggest that subsurface energy transfer processes and feedbacks at scales of 1 100 m have a strong influence on overall permafrost degradation rates at much larger scales

fitting data but poor predictions reverberation prediction uncertainty when seabed parameters are derived from reverberation measurements for many decades researchers have been developing inverse techniques for estimating seabed parameters from reverberation data notably scattering strength generally the angular dependence of the scattering kernel is unknown and is either solved for or assumed fixed in either case agreement is typically quite good between the measured reverberation and that modeled by fitting scattering parameters however what are the resulting uncertainties in a reverberation prediction if the ocean or geometry changes the main results of the paper are that 1 these prediction uncertainties are surprisingly large of order 10 db at 10 km and thus 2 traditional current methods for reverberation inversion should be augmented mitigating the large prediction uncertainties by an additional measurement several options for additional measurements are discussed

ocean and atmosphere storm tracks the role of eddy vorticity forcing abstract signatures of eddy variability and vorticity forcing are diagnosed in the atmosphere and ocean from weather center reanalysis and altimetric data broadly covering the same period 1992 2002 in the atmosphere there are localized regions of eddy variability referred to as storm tracks at the entrance of the storm track the eddies grow providing a downgradient heat flux and accelerating the mean flow eastward at the exit and downstream of the storm track the eddies decay and instead provide a westward acceleration in the ocean there are similar regions of enhanced eddy variability along the extension of midlatitude boundary currents and the antarctic circumpolar current within these regions of high eddy kinetic energy there are more localized signals of high eady growth rate and downgradient eddy heat fluxes as in the atmosphere there are localized regions in the southern ocean where ocean eddies provide statistically significant vorticity forcing which acts to accelerate the mean flow

gap leaping kuroshio and blocking westward propagating rossby wave and eddy in the luzon strait 1 based on analysis of both observational data and data assimilation model product it is shown that there exists a gap leaping path of the kuroshio in the luzon strait numerical results of two sets of hybrid coordinate ocean model twin experiments indicate that bottom topography and islands in luzon strait exert control of kuroshio s gap leaping behavior especially existence of sharp northeast cape of philippine island is one of the most important factors for the gap leaping kuroshio path in model simulation corresponding to the gap leaping kuroshio there is steep westward shoaling of thermocline in luzon strait the enhanced upper layer stratification in south china sea due to westward shoaling thermocline results in strong zonal potential vorticity pv gradient one order higher than s induced planetary pv gradient and pv isolines are always parallel to the gap leaping path of the kuroshio this pv front acts as a dynamic barrier in the luzon strait blocking the westward propagating rossby waves and eddies from pacific this blocking effect is verified through sea surface height anomaly spectrum analysis radon transform based feature tracking method and eddy identification and tracking method numerical twin experiments demonstrate from another point of view that the gap leaping kuroshio can efficiently block the westward propagating rossby wave and eddy energy while the fluctuating kuroshio is less efficient for blocking

numerical study of the ocean circulation on the east china sea shelf and a kuroshio bottom branch northeast of taiwan in summer using the regional ocean model system the ocean circulation on the east china sea ecs shelf was examined by a fine resolution model which was nested in a coarse resolution pacific ocean model the high resolution simulation shows an accurate volume transport of 2 70 sv sv 10 6 m 3 s 1 through the tsushima strait which is more consistent with the previous 5 5 year observation value 2 64 sv than former model results for the taiwan strait it also shows a close volume transport 1 03 sv to a recent estimate 1 20 sv at the same time the model results reproduced almost all of the known circulation structure on the ecs shelf in addition the hindcast of 2009 shows a kuroshio bottom branch current to the northeast of taiwan kbbcnt the kbbcnt is confirmed by the observational bottom high salinity water from 15 august to 2 september 2009 whose distribution is also reproduced by the model results tracer and particle experiments were carried out to elucidate the formation of the high salinity water and the pathway of the kbbcnt in light of the field observation and numerical experiments a new pathway of the kbbcnt is proposed bifurcated from the subsurface water of kuroshio northeast of taiwan it upwells northwestward gradually from 300 to 60 m then turns to northeast in the region around 27 5 degrees n 122 degrees e and finally reaches 31 degrees n off the mouth of the changjiang river along similar to 60 m isobaths forming the bottom saline water off the coast of zhejiang province china

modeling reverberation time series for shallow water clutter environments the phenomenon of clutter in shallow water environments can be modeled from a variety of viewpoints one approach we have taken is to model reverberation time series for heterogeneous environments with a variety of scattering mechanisms to see if some of the characteristics of resulting estimates model the characteristics of experimentally observed clutter here we show reverberation time series estimates for the straits of sicily that seem to capture some of the clutter behavior observed during the boundary 04 experiment conducted in conjunction with the nato undersea research centre of particular interest is the appearance of coherent time frequency striation patterns in both the modeled and observed reverberation with compact time supported but broadband clutter features superimposed by the presence of environmental discontinuities work supported by onr phase ii sttr n00014 04 c 0399

oceanic eddy formation and propagation southwest of taiwan 1 oceanic eddies are active and energetic southwest of taiwan the formation and propagation of eddies in this area were investigated using 17 year satellite altimeter data cyclonic eddies ces and anticyclonic eddies aces often coexisted but there were more ces than aces generated during the period from october 1992 to october 2009 aces were stronger and in general lived longer than ces aces occurred more often in winter than in other seasons while ces were more frequent in summer compared with the direct local wind forcing the kuroshio path variability appears to be a dominant factor for eddy formation in this area a conceptual model of an eddy kuroshio interaction is proposed in summer there exists an outflow northwest of luzon island and the kuroshio likely leaps across the luzon strait to the north of the outflow and left of the kuroshio axis ces are often formed which in turn induce aces to the west of ces in winter under the influence of northeasterly monsoon the kuroshio current loop kcl appears southwest of taiwan more frequently than in other seasons and aces are frequently shed from the kcl most of the aces propagate westward and as a result ces are often spun up to the east of the aces the surface south china sea outflow in summer and the kcl in winter are however likely related to the monsoons therefore the indirect effects of monsoon winds are also evident in the seasonal variations of eddy occurrence

blocking and westward passage of eddies in the luzon strait satellite observations have shown the abundance of generally westward propagating eddies in the subtropical regions in the north pacific ocean especially north of 10 n eddies transport mass and can significantly impact the circulation as well as the heat salt and nutrient balances of the western pacific marginal seas this paper uses a numerical model to examine the conditions when eddies can or cannot freely propagate westward through the luzon strait into the south china sea scs composite analyses on the 10 year model data show that the fates of eddies depend on the strength and path of the kuroshio in one path that exists mostly during fall and winter the kuroshio loops westward into the scs the potential vorticity pv across the current is weak and eddies are likely to propagate freely through the luzon strait in another path which exists mostly during spring and summer the kuroshio tends to leap directly northward bypassing the scs the pv across it strengthens and eddies are then blocked and are constrained to also follow the northward path nonlinear eddy current interaction and the existence of a cyclone north of the luzon island during the looping phase explain why eddies of both signs can pass through the strait it is shown also that the upstream state of the kuroshio in the western tropical pacific plays an important role in dictating the different paths of the kuroshio the looping leaping path is caused by a weakened stronger kuroshio transport related to the northward southward shift of the north equatorial current in wintertime summertime

upper layer circulation in the south china sea abstract upper layer circulation is investigated by using all available historical temperature profiles combined with climatological temperature salinity relationships in the south china sea two cyclonic eddies are revealed one is located east of vietnam called the east vietnam eddy and the other is off northwest luzon called the west luzon eddy both local ekman pumping and remotely forced basin scale circulation are important mechanisms controlling these two eddies the luzon strait transport relative to 400 db is estimated to be of the order 3 0 sv 1 sv 1 106 m3 s 1 in the mean and has a seasonal cycle dominated by the annual signal with a maximum 5 3 sv in january february and a minimum 0 2 sv in june july pressure gradients are also examined to explore the dynamics of the intrusion of waters from the pacific into the south china sea through the luzon strait

acoustic scattering from mud volcanoes and carbonate mounds submarine mud volcanoes occur in many parts of the world s oceans and form an aperture for gas and fluidized mud emission from within the earth s crust their characteristics are of considerable interest to the geology geophysics geochemistry and underwater acoustics communities for the latter mud volcanoes are of interest in part because they pose a potential source of clutter for active sonar close range single interaction scattering measurements from a mud volcano in the straits of sicily show scattering 10 15db above the background three hypotheses were examined concerning the scattering mechanism 1 gas entrained in sediment at near mud volcano 2 gas bubbles and or particulates emitted in the water column 3 the carbonate bio construction covering the mud volcano edifice the experimental evidence including visual acoustic and nonacoustic sensors rules out the second hypothesis at least during the observation time and suggests that for this particular mud volcano the dominant

multiscale processes and nonlinear dynamics of the circulation and upwelling events off monterey bay the nonlinear multiscale dynamics of the monterey bay circulation during the second autonomous ocean sampling network aosn ii experiment august 2003 is investigated in an attempt to understand the complex processes underlying the highly variable ocean environment of the california coastal region using a recently developed methodology the localized multiscale energy and vorticity analysis ms eva and the ms eva based finite amplitude hydrodynamic instability theory the processes are reconstructed on three mutually exclusive time subspaces a large scale window a mesoscale window and a submesoscale window the ocean is found tobe most energetic in the upper layers and the temporal mesoscale structures are mainly trappedabove 200 m through exploringthenonlinear window window interactions itisfound that the dynamics underlying the complex surface circulation is characterized by a well organized self sustained bimodal instability structure a bay mode and a point sur mode which are located near monterey bay and west of point sur respectively both modes are of mixed types but they are distinctly different in dynamics the former is established when the wind relaxes while the latter is directly driven by the wind either way the wind instills energy into the ocean which is stored within the large scale window and then released to fuel temporal mesoscale processes upon wind relaxation the generated mesoscale structurespropagate northward along the coastline in a form with dispersion properties similar to that of a free thermocline trapped coastal trapped wave between these two modes a secondary instability is identified in the surface layer during 15 21 august transferring energy to the temporal submesoscale window also studied is the deep layer flow which is unstable all the time throughout the experiment within the bay and north of the deep canyon it is observed that the deep temporal mesoscale flow within the bay may derive its energy from the submesoscale window as well as from the large scale window this study provides a real ocean example of how secondary upwelling can be driven by winds through nonlinear instability and how winds may excite the ocean via an avenue distinctly different from the classical paradigms

kuroshio intrusion and the circulation in the south china sea 1 the princeton ocean model is used to study the circulation in the south china sea scs and its seasonal transition kuroshio enters leaves the scs through the southern northern portion of the luzon strait the annually averaged net volume flux through the luzon strait is 2 sv into the scs with seasonal reversals the inflow season is from may to january with the maximum intrusion of kuroshio water reaching the western scs during fall in compensation of summertime surface offshore transport associated with coastal upwelling from february to april the net transport reverses from the scs to the pacific the intruded kuroshio often forms an anticyclonic current loop west of the luzon strait the current loop separates near the dongsha islands with the northward branch continuously feeding the south china sea warm current scswc near the shelf break and the westward branch becoming the south china sea branch of kuroshio on the slope which is most apparent in the fall the scswc appears from december to february on the seaward side of the shelf break flowing eastward against the prevailing wind diagnosis shows that the onshore ekman transport due to northeasterly monsoon generates upwelling when moving upslope and the particular distributions of the density and sea level associated with the cross shelf motion supports the scswc

mesoscale eddies in the northern south china sea a fine grid resolution model with realistic bathymetry and forcing has been developed to study the characteristics of the mesoscale eddies for the northern south china sea scs the scs model derives its open boundary conditions from a larger scale model which minimizes errors related to the uncertainty of the kuroshio intrusion at the open boundaries the model results are consistent with previous observations model sea surface height anomaly demonstrates that the hydrography and circulation in the northern scs are modulated by westward propagating mesoscale eddies originating in the vicinity of the luzon strait this explains the observed intra seasonal fluctuations at the southeast asian time series study seats station the mesoscale eddies have the same propagation speed as baroclinic rossby waves 0 1 ms 1 the periods of eddy shedding estimated from strouhal number are around 40 50 days in december and 80 120 days in august respectively the seasonal variability of the kuroshio intrusion results in more eddies in winter than in summer r 2007 elsevier ltd all rights reserved

a study of the iceland faeroe frontal variability using the multiscale energy and vorticity analysis the multiscale nonlinear interactive iceland faeroe frontal iff variability during 14 22 august 1993 is investigated for complex dynamics with the localized multiscale energy and vorticity analysis ms eva in terms of multiscale window transform the cold meandering intrusion observed in the iff experiment is represented on a mesoscale window the resulting mesoscale energetics for the deep layer show an isolated center of transfer of potential energy from the large scale window into the mesoscale window in the study domain this large to mesoscale potential energy transfer or bc for short is a baroclinic instability indicator by the ms eva based stability theory signatures on other energetics maps and the reconstructed mesoscale structures all support this baroclinic instability on the bc map the transfer hotspot originally resides near the western boundary it travels along the front into the interior domain in a form of convective instability and then on 19 august changes into another instability that is absolute in character correspondingly disturbances switch from a spatial growing pattern into a time growing mode culminating on 21 august the day just before the intrusion matures the whole process lasts for about five days limited within a small horizontal region and beneath a depth of approximately 150 m by interaction analysis the energy locally gained from this process goes to the submesoscale window as well but most of it remains in the mesoscale window serving to fuel the growth of the meandering intrusion

hillslope runoff from an ice cored peat plateau in a discontinuous permafrost basin northwest territories canada peat plateaus are important landscape features of many high boreal wetland dominated drainage basins raised up to 2 m above the surrounding landscape and underlain by permafrost these forested peatlands provide meltwater drainage to the surrounding wetlands and to basin runoff understanding the factors that control the volume and timing of runoff from peat plateaus is the essential first step towards developing methods of accurately predicting basin runoff from wetland dominated basins in the region of discontinuous permafrost as well as understanding the basin response to hydrological changes brought on by the thermal degradation and thaw of permafrost peatlands in this study a water balance approach and the dupuit forchheimer equation were used to quantify sub surface runoff from a forested peat plateau at scotty creek a small 152 km2 wetland dominated discontinuous permafrost basin in northwest territories canada these two computations yielded similar results in both years of study 2004 2005 and showed that runoff accounted for approximately half of the moisture loss from the peat plateau most of which occurred in response to snowmelt inputs the melt of ground ice was also a significant source of water during the study periods which was largely detained in soil storage soil moisture conditions prior to soil freezing were a major factor controlling the volume of runoff from the hillslope sub surface drainage rates declined dramatically after the snowmelt runoff period when the majority of water inputs went to soil storage and evapotranspiration the minimal lag between rain events and hydrograph response in both years suggests that much of the runoff produced from rain events is rapidly transported to the adjacent wetlands these results give insight into how current climate warming predictions for northern latitudes could affect the hydrological response of forested peat plateaus and the basins which they occupy copyright 2008 john wiley sons ltd

the importance of high horizontal resolution and accurate coastline geometry in modeling south china sea inflow as resolution is increased from 1 2 to 1 32 in pacific ocean simulations using the nrl layered ocean model marked changes are found in the kuroshio s mean pathway as it intrudes into the south china sea scs via the luzon strait with increased horizontal resolution comes a more accurate representation of the coastline geometry associated with the batan babuyan islands within the strait and a reduction in the modeled westward intrusion of the kuroshio into the scs the 1 16 model is extremely sensitive to two very small scale shoals calayan bank and a shoal north of calayan island that are resolvable at this grid spacing the exclusion of these three model gridpoints significantly alters the mean kuroshio pathway to resemble the pathway from the 1 8 model in addition excluding all islands within the luzon strait in the 1 16 model gives a deep intrusion mean pathway as found in the 1 2 model

hydrological impacts of seismic lines in the wetland dominated zone of thawing discontinuous permafrost northwest territories canada intensive seismic exploration in the northwest territories began in the late 1960s since that time the legacy of seismic surveys i e straight lines cutting through boreal forest and tundra has remained visible throughout northern canada and alaska the removal of trees and compaction of the ground surface alter the thermophysical properties of the active i e seasonally thawed layer to such an extent that the underlying permafrost seriously degrades or even disappears completely such a transformation along linear corridors that cut indiscriminately across different terrain types with contrasting hydrological functions has potentially serious implications to the redistribution of water and energy within and among landscape units with feedbacks to permafrost thaw land cover change and run off generation this paper characterizes the flow and storage of water and energy along a seismic cut line in the high boreal zone of discontinuous permafrost in order to improve the understanding of these processes their interactions and hydrological implications as such this paper lays a conceptual foundation for the development of numerical models needed to predict the hydrological and thermal impact of seismic lines in this sensitive region we used ground penetrating radar and multi year ground temperatures and water levels along a seismic line to estimate the degree of permafrost degradation below it the seismic line studied extends from a permafrost free wetland flat bog over a permafrost body peat plateau and into another permafrost free wetland channel fen it was found that once thaw had lowered the permafrost table below the ground surface elevation of the flat bog and channel fen the seismic line forms a hydrological connection between them it was also shown that during the permafrost thaw process seismic lines develop a perennially thawed layer talik between the overlying active layer and underlying permafrost and that the talik conveys water as a conduit throughout the year the implications of such drainage through seismic lines and networks on basin drainage in peatland dominated regions with discontinuous permafrost are also discussed copyright 2015 john wiley sons ltd

wind forced variability in eddy formation eddy shedding and the separation of the east australian current the east australian current eac like many other subtropical western boundary currents is believed to be penetrating further poleward in recent decades previous observational and model studies have used steady state dynamics to relate changes in the westerly winds to changes in the separation behavior of the eac as yet little work has been undertaken on the impact of forcing variability on the eac and tasman sea circulation here using an eddy permitting regional ocean model we present a suite of simulations forced by the same time mean fields but with different atmospheric and remote ocean variability these eddy permitting results demonstrate the nonlinear response of the eac to variable nonstationary inhomogeneous forcing these simulations show an eac with high intrinsic variability and stochastic eddy shedding we show that wind stress variability on time scales shorter than 56 days leads to increases in eddy shedding rates and southward eddy propagation producing an increased transport and southward reach of the mean eac extension we adopt an energetics framework that shows the eac extension changes to be coincident with an increase in offshore upstream eddy variance via increased barotropic instability and increase in subsurface mean kinetic energy along the length of the eac the response of eac separation to regional variable wind stress has important implications for both past and future climate change studies

measurement technique for bottom scattering in shallow water sonar performance predictions of reverberation in shallow water rely upon good estimates of the bottom scattering strength however little is understood about bottom scattering in shallow water in the frequency range 400 4000 hz particularly its dependency upon frequency and its relationship to the physical properties of the seafloor in order to address these issues a new measurement technique has been developed to probe the frequency and angular dependency of bottom scattering strength the experimental technique is described which employs either coherent or incoherent sources lightbulbs in addition measurement and modeling results for two diverse shallow water sites are presented at one site the scattering appears to arise at or near the water sediment interface at the other site scattering from a 23 m sub bottom horizon is clearly apparent in the data at and below 1800 hz the fact that our measurement technique can directly reveal the presence of sub bottom scattering is a significant advance in the development of methods to explore the physical mechanisms that control bottom scattering

global observations of large oceanic eddies 1 ten years of sea surface height ssh fields constructed from the merged topex poseidon t p and ers 1 2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean the higher resolution of the merged dataset reveals that more than 50 of the variability over much of the world ocean is accounted for by eddies with amplitudes of 5 25 cm and diameters of 100 200 km these eddies propagate nearly due west at approximately the phase speed of nondispersive baroclinic rossby waves with preferences for slight poleward and equatorward deflection of cyclonic and anticyclonic eddies respectively the vast majority of the eddies are found to be nonlinear

modeling south china sea circulation response to seasonal forcing regimes 1 a three dimensional ocean model has been utilized to study circulation and its seasonal variation in the south china sea scs in response to the forcing of the asian monsoon and the kuroshio intrusion the scs ocean model has a resolution of approximately 10 km horizontal spacing and 30 vertical levels with a realistic bottom topography the model is forced with time dependent wind stress and heat flux from national center for environmental prediction reanalysis data as well as with lateral fluxes from a pacific ocean model of 40 km horizontal resolution this study reports on the analysis of the mean seasonal circulation and dynamic processes in response to monsoonal wind stress the kuroshio intrusion and other intrinsic forcing processes it is found that the seasonal circulation in the scs is mainly driven by the monsoonal wind stress and greatly influenced by the inflow from the kuroshio intrusion strong currents along the continental margin of the scs form mean basin wide cyclonic and anticyclonic circulations in the winter and summer respectively multiscale eddies are embedded in the general circulation across the basin while mainstream of the kuroshio passes through the luzon strait without intruding into the scs partial intrusion occurs in the upper 200 m near the shelf margin southwest of taiwan at times when winter dynamic conditions prevail in the north scs the intrusion of the kuroshio into the scs also occurs at depths in all seasons mainly along the continental slope the coastal current separation to the east off southern vietnam and the associated eddy formations characterize the circulation in the south scs the simulated results compare well with the corresponding observed fields dynamical processes involved in the forced flow fields are investigated by examination of the momentum balances the analyses reveal that the circulation in the scs is generally dominated by the geostrophic currents north of the luzon strait positive nonlinearity in the zonal direction is locally intensified which leads to the formation of centripetal acceleration for the mainstream of the kuroshio to turn eastward the kuroshio intrusion at depths is governed by the ageostrophic flows and highly associated with the net westward pressure gradient force coastal jet separation to the east off vietnam is mainly associated with the local wind stress field and with the shelf topography in the summer and winter respectively sensitivity study reveals that the weakening of the kuroshio markedly enhances kuroshio s intrusion and forms an anticyclonic eddy west of the luzon strait

bottom interaction of low frequency acoustic signals at small grazing angles in the deep ocean the results of a deep ocean bottom interaction experiment are presented in which the effects of both bottom refraction and subbottom reflection were observed data were obtained in the hatteras abyssal plain using a deep towed 220 hz pulsed cw source and two receivers anchored near the bottom for ranges between 1 and 6 km corresponding to bottom grazing angles less than 13 the quadrature components of the received signals were recorded digitally the observed amplitude shows a strong spatial interference pattern which is composed of the direct and bottom interacting arrivals it is shown that for small source receiver separations the bottom return is dominated by a strong subbottom reflection with increasing separation this arrival evolves into a refracted arrival due to the presence of a positive sound speed gradient in the sediment overlying the subbottom because of the gradient a caustic is formed and corresponding high intensity regions are observed in the data at the expected ranges values of sediment layer thickness sound speed gradient and sound speed drop at the water bottom interface are obtained from best fits to the data using ray theory normal mode theory and the parabolic equation method these values are consistent with those obtained in nearby locations by other workers the success of the parabolic equation method indicates that at small grazing angles the bottom interaction process may be modeled as a propagation process combined with the effect of a perfect soft subbottom reflector a value of sediment attenuation 0 0015 db m at 220 hz is also inferred from the data and is among the lowest values reported to date in the literature

gap leaping western boundary current in a circular tank model abstract an oceanographically generic problem of the interaction of a boundary current with bathymetric features such as a gap in the ridge or a strait between two islands is considered multiple flow patterns penetrating or leaping the gap and hysteresis dependence on prior evolution may exist in such systems examples include the gulf stream leaping from the yucatan to florida and the kuroshio leaping from luzon to taiwan using numerical analysis sheremet earlier found that multiple steady states can be explained by variation in the balance between the inertia which promotes leaping state and the effect which promotes penetrating state in the present work a verification of the multiple states and hysteresis in a laboratory model are offered to set up a gap leaping current a circular tank with a sloping bottom simulating the effect is used and the flow is driven using a new method of pumping fluid through sponges thus generating a sverdrup flow in the interior a semicircular ridge

kuroshio intrusion into the south china sea a review the kuroshio carrying the northwestern pacific water intrudes into the south china sea scs through the luzon strait significantly affecting the temperature salinity circulation and eddy generation in the scs thus the kuroshio intrusion makes important contributions to the momentum heat and salt budgets in the scs in the past decades much work has been done on the kuroshio intrusion this paper reviews past efforts and summarizes our current understanding of the kuroshio intruding processes from observational evidence laboratory results theoretical analyses and a range of numerical model simulations in addition discrepancies between results simulated by models as well as those between simulations and observations are presented specifically this paper addresses the following topics 1 different types of the kuroshio intrusion into the scs and their identification 2 vertical structure of the kuroshio in the luzon strait 3 an overview of the luzon strait transport resulting from observations and numerical model simulations 4 seasonal and interannual variations of the kuroshio intrusion as well as eddy generation due to the kuroshio path variation and 5 dynamical mechanisms e g wind forcing interbasin pressure gradient beta effect and hysteresis potential vorticity eddy activity controlling the kuroshio intrusion into the scs finally several future research topics for gaining a better understanding of the kuroshio intruding processes are suggested c 2014 the authors published by elsevier ltd

a mechanism for the latitudinal dependence of peak spectrum sea surface height variability previous studies have shown that the power spectrum of satellite observed sea surface height ssh variability peaks at a certain frequency or a wave number band at a given latitude lin et al 2008 attributed this latitudinal dependence to the critical frequency of the first baroclinic mode rossby waves in the tropical and subtropical oceans their study was based on the linear rossby wave theory and focused on ssh variability in the tropical and subtropical oceans since the altimetry data do not adequately resolve lengths of baroclinic rossby waves at and near the critical frequency in high latitudes in this study we expand their analysis to high latitude oceanic basins and to include nonlinear eddy effects by using a linear wave model and a high resolution model output from the ogcm for the earth simulator ofes it is found that the linear wave mechanism by and large remains valid in the tropical and subtropical oceans in higher latitudes as well as in some regions in the western tropical and subtropical oceans other mechanisms like nonlinear eddy play more important role in determining the ssh variability

nonlinear multiscale interactions and internal dynamics underlying a typical eddy shedding event at luzon strait eddy shedding is a highly nonlinear process that presents a major challenge in geophysical fluid dynamics using the newly developed localized multiscale energy and vorticity analysis ms eva this study investigates an observed typical warm eddy shedding event as the kuroshio passes the luzon strait in order to gain insight into the underlying internal dynamics through multiscale window transform mwt it is found that the loop form kuroshio intrusion into the south china sea scs is not a transient feature but a quasi equilibrium state of the system a mesoscale reconstruction reveals that the eddy does not have its origin at the intrusion path but comes from the northwest pacific it propagates westward preceded by a cyclonic cold eddy through the kuroshio into the scs as the eddy pair runs across the main current the cold one weakens and the warm one intensifies through a mixed instability in its development another cold eddy is generated to its southeast which also experiences a mixed instability it develops rapidly and cuts the warm eddy off the stream both the warm and cold eddies then propagate westward in the form of a rossby wave first baroclinic mode as the eddies approach the dongsha islands they experience another baroclinic instability accompanied by a sudden accumulation of eddy available potential energy this part of potential energy is converted to eddy kinetic energy through buoyancy conversion and is afterwards transferred back to the large scale field through inverse cascading greatly reducing the intensity of the eddy and eventually leading to its demise this article is protected by copyright all rights reserved

mapping seabed variability rapid surveying of coastal regions directional broadband reverberation can be exploited for rapidly probing seabed variability over large areas o 103 104 km2 the data need not be calibrated seabed variability thus mapped inherently combines spatial variability in geoacoustic properties that control reflection and those that control scattering it is shown that in some cases the variability can be separated the method is applied to measurements in the straits of sicily where the data indicate the existence of two provinces where the statistics of the geoparameters are distinct three attributes of each province are quantified the province boundaries measures of spatial variability and or uncertainty and the location of discrete scattering features that may lead to sonar clutter one province is quite large and exhibits remarkably little spatial variability the variability is probed on lateral scales 200 400m yet the ratio of the seabed geoparameters varies less than 3 db from 300 1600hz over 1000km2 while this result seems co

long range acoustic scattering from a shallow water mud volcano cluster analysis of reverberation measurements in the straits of sicily shows high intensity discrete scattered returns 10 20db above background reverberation these returns are due to scattering from mud volcanoes the reverberation from the mud volcanoes at ranges of 15 22km is reasonably consistent over these spatial scales i e kilometers and temporal scales of several hours measurements separated by 4years are also similar statistical characterization indicates that the reverberation associated with a mud volcano cluster is strongly non rayleigh and that the reverberation can be characterized by a single shape parameter roughly independent of frequency the non rayleigh statistics with a concomitant increase in the probability of false alarm indicate that mud volcanoes are a likely source of clutter mean target strengths were estimated at 1 11db over 160 1400hz and are consistent with target strengths measured during a different year at short direct path ranges accumulated evidence points to

an exceptional anticyclonic eddy in the south china sea in 2010 the highest sea level near the xisha islands in recent 20 years occurred during august 2010 satellite altimeter data indicated that the extreme event was largely due to an anticyclonic eddy whose amplitude exceeded 20 cm and size exceeded 400 km on 11 august 2010 cruise observations showed the eddy raised the center temperature by 7 7 degrees c at 75 m and vertically extended to 500 m eddy tracking showed it had a life span of more than 8 months and propagated far from the south of xisha islands such strong and long lasting eddy that moved northward for such a long distance was observed for the first time in the south china sea scs observational data from ctd xbt and the reconstructed three dimensional temperature and salinity were used to explore the eddy s features and vertical structure our analyses show the 2010 summer monsoon and current in the western boundary of the scs were largely altered after the 09 10 el nino event from may onward the wind blew northward and strengthened over the northwestern scs such wind drove a strong northward current along the western boundary which carried the eddy northward by advection from may to july energy budget showed during the eddy northward propagation the boundary current passed energy to the eddy which led to the continuing growth of the eddy in both strength and size