sea ice models for climate study retrospective and new directions scientific observations of sea ice began more than a century ago but detailed sea ice models appeared only in the latter half of the last century the high albedo of sea ice is critical for the earth s heat balance and ice motion across the ocean s surface transports fresh water and salt the basic components in a complete sea ice model must include vertical thermodynamics and horizontal dynamics including a constitutive relation for the ice advection and deformational processes this overview surveys topics in sea ice modeling from the global climate modeling perspective emphasizing work that significantly advanced the state of the art and highlighting promising new developments

the granular sea ice model in spherical coordinates and its application to a global climate model abstract the granular sea ice model gran from tremblay and mysak is converted from cartesian to spherical coordinates in this conversion the metric terms in the divergence of the deviatoric stress and in the strain rates are included as an application the gran is coupled to the global earth system climate model from the university of victoria the sea ice model is validated against standard datasets the sea ice volume and area exported through fram strait agree well with values obtained from in situ and satellite derived estimates the sea ice velocity in the interior arctic agrees well with buoy drift data the thermodynamic behavior of the sea ice model over a seasonal cycle at one location in the beaufort sea is validated against the surface heat budget of the arctic ocean sheba datasets the thermodynamic growth rate in the model is almost twice as large as the observed growth rate and the melt rate is 25 lower than observed the larger growth rate is due to thinner ice at the beginning of

nonlinear tide surge wave interaction at a shallow coast with large scale sequential harbor constructions abstract the southwestern part of bohai bay in northeastern china is a shallow water coast with a long fetch for water to pile up to produce large storm surge under strong wind action during the extreme weather condition in addition the coastline along the bay has experienced significant environmental impacts from large scale harbor constructions in the past two decades consequently there is a pressing need to better understand the effects of two local large scale sequential harbor constructions on storm surge and coastal vulnerability in the bay area the extreme cold front weather on 10 13th october 2003 caused a 1 31 billion yuan damage a two way coupled tide surge wave delft3d model is used to investigate the impact of the harbor constructions from 2003 to 2016 on the interaction of tide storm surge and wave during a storm like that the wind field by the newly released global reanalysis wind product era5 of european centre for medium range weather forecasts ecmwf has been improved by assimilation with field observations at a higher resolution than previous version and is used to drive the tide surge and wave modelling framework the model results indicate that the storm surge in the study area is dominated by the wind induced surge before and after the constructions whereas the maximum contribution from wave induced surge wave setup is increased from 5 15 to 8 20 by the harbor constructions between 2003 and 2016 it is found that semi diurnal modulation of storm surge is generated by nonlinear tide surge interaction which is mainly attributed to local tidal acceleration in the offshore zone and bottom stress in the nearshore zone respectively the harbor constructions affect the coastal storm surge mainly through nonlinear tide surge wave interaction in addition the quarter diurnal variation of storm surge induced by the harbor constructions is due to the influences of the harbor constructions on the local quarter diurnal tidal constituents and their modulation of wave momentum transfer to coastal circulation

four stages of pressure ridging the pressure ridging process is simulated using a two dimensional particle model blocks are broken from an intact sheet of relatively thin lead ice pushed against a thick multiyear floe at a constant speed the blocks of ice rubble accumulate to form the ridge sail and keel during the simulations the energy consumed in ridge growth including dissipation is explicitly calculated on the basis of the results of simulations performed with the model the ridging process can be divided into four distinct stages the first stage begins with an intact sheet of lead ice impacting a floe and ends when the sail reaches its maximum height in the second stage the ridge keel deepens and widens the stage ends when the maximum keel draft is reached in the third stage the direction of growth is leadward creating a rubble field of more or less uniform thickness the third stage ends when the supply of thin ice is exhausted in the fourth stage the rubble field is compressed between converging floes the results of simulations establish the dependence of ridging energetics in the first and second stages on the thickness of the ice sheet and the amount of ice pushed into the ridge the average profiles of the simulated ridges delineate the growth process in the first second and third stages the energetics and profiles of the fourth stage were described by hopkins et al 1991 lead ice extents of up to 1300 m are pushed into ridges to determine maximum sail heights keel drafts and ridging forces

why the western pacific subtropical high has extended westward since the late 1970s the western pacific subtropical high wpsh is closely related to asian climate previous examination of changes in the wpsh found a westward extension since the late 1970s which has contributed to the inter decadal transition of east asian climate the reason for the westward extension is unknown however the present study suggests that this significant change of wpsh is partly due to the atmosphere s response to the observed indian ocean western pacific iwp warming coordinated by a european union s sixth framework programme understanding the dynamics of the coupled climate system dynamite five agcms were forced by identical idealized sea surface temperature patterns representative of the iwp warming and cooling the results of these numerical experiments suggest that the negative heating in the central and eastern tropical pacific and increased convective heating in the equatorial indian ocean maritime continent associated with iwp warming are in favor of the westward extension of wpsh the sst changes in iwp influences the walker circulation with a subsequent reduction of convections in the tropical central and eastern pacific which then forces an enso gill type response that modulates the wpsh the monsoon diabatic heating mechanism proposed by rodwell and hoskins plays a secondary reinforcing role in the westward extension of wpsh the low level equatorial flank of wpsh is interpreted as a kelvin response to monsoon condensational heating while the intensified poleward flow along the western flank of wpsh is in accord with sverdrup vorticity balance the iwp warming has led to an expansion of the south asian high in the upper troposphere as seen in the reanalysis

distinct quasi biweekly features of the subtropical east asian monsoon during early and late summers using global precipitation climatology project daily rainfall and era interim reanalysis data we investigate the distinct characteristic of quasi biweekly variation qbv 12 20 days over east asia ea during early june 10 july 20 and late july 21 august 31 summer the qbv maximum variance is found over the core region of ea 30 40 n 110 130 e which includes eastern china lower reaches of the yellow huaihe and yangtze rivers and the korean peninsula at both its peak wet and dry phases qbv over the core region has a baroclinic structure but with different spatial distributions different lower level prevalent wind anomalies and different upper level major circulation anomalies in the two subseasons meanwhile the two subseasons have different propagating tracks prior to reaching the peak phase and different precursors associated with the local genesis of qbv furthermore during the transition from the peak dry to peak wet phase of qbv the major monsoon circulations have different behaviors that tropical monsoon trough extends eastward in early summer but retreats westward in late summer and the south asia high sah and western north pacific wnp subtropical high move toward away from each other in early late summer the abrupt change of mean state in mid to late july which includes the northward migration of westerly jet sah and wnp and the weakening and broken of westerly jet is considered the root cause of the change in behavior of qbv finally we indicate that the tropical monsoon trough and midlatitude westerly jet are possible sources of qbv over subtropical ea in both subseasons and provide useful guidance for 2 3 week predictions over ea

synoptic scale characteristics and atmospheric controls of summer heat waves in china summer heat waves with persistent extreme high temperatures have been occurring with increasing frequency in recent decades these extreme events have disastrous consequences for human health economies and ecosystems in this study we examine three summers with intense and protracted heat waves the summers of 2003 2006 and 2013 with high temperatures located mainly in southeastern southwestern and eastern china respectively the synoptic scale characteristics of these heat waves and associated atmospheric circulation anomalies are investigated in the early heat wave episode of 2003 a heat center was located in the southeast coastal provinces during the first 20 days of july the maximum southward displacement of the east asian jet stream eajs induced anticyclonic anomalies to the south associated with southwestward intensification of the western north pacific subtropical high wnpsh and extreme high temperatures were found only to the south of the yangtze river in the later episode a poleward displacement of the eajs and an enhanced wnpsh over the midlatitudes of eastern china resulted in a heat dome over the region and the heat wave extended northward to cover a larger area of eastern china the coupling between the westward enhanced wnpsh and poleward displaced eajs was found in the east china heat wave of 2013 as well but the area of high temperatures reached far to the north in august 2013 with below normal temperatures located in a small region of south china in the 2006 southwestern drought and heat wave extreme poleward displacement of the eajs associated with extraordinary westward extension of the wnsph resulted in further blocking of the moisture supply from the southwest monsoon large scale moisture deficiencies dry conditions and downslope winds were common features of all investigated heat wave episodes but in 2006 low level heat lows associated with a well mixed layer due to intensive daytime heating and atmospheric turbulence were emphasized

large scale circulation anomalies and intraseasonal oscillations associated with long lived extreme heat events in south china abstractsouth china experiences extreme heat eh most frequently in eastern china this study specifically explores the large scale circulation anomalies associated with long lived eh events in south china the results show that there is an anomalous cyclone anticyclone and active inactive convection over south china the western pacific before the eh onset then an anticyclone develops and moves northwestward and dominates over south china on the onset day the anomalous anticyclone maintains its strength over south china and then diminishes and is replaced by another cyclone migrating from the western pacific after the final day of the eh event consequently the temperature increases over south china around the onset day and is anomalously warm for approximately 10 days on average and then decreases shortly thereafter the fluctuating anomalies over south china and the western pacific are intimately related to two intraseasonal oscillation iso modes namely the 5 25 and 30 90 day oscillation

indian ocean capacitor effect on indo western pacific climate during the summer following el nino significant climate anomalies persist through the summer june august after el nino dissipates in spring over the equatorial pacific they include the tropical indian ocean tio sea surface temperature sst warming increased tropical tropospheric temperature an anomalous anticyclone over the subtropical northwest pacific and increased mei yu baiu rainfall over east asia the cause of these lingering el nino effects during summer is investigated using observations and an atmospheric general circulation model gcm the results herein indicate that the tio warming acts like a capacitor anchoring atmospheric anomalies over the indo western pacific oceans it causes tropospheric temperature to increase by a moist adiabatic adjustment in deep convection emanating a baroclinic kelvin wave into the pacific in the northwest pacific this equatorial kelvin wave induces northeasterly surface wind anomalies and the resultant divergence in the subtropics triggers suppressed convection and the anomalous anticyclone the gcm results support this kelvin wave induced ekman divergence mechanism in response to a prescribed sst increase over the tio the model simulates the kelvin wave with low pressure on the equator as well as suppressed convection and the anomalous anticyclone over the subtropical northwest pacific an additional experiment further indicates that the north indian ocean warming is most important for the kelvin wave and northwest pacific anticyclone a result corroborated by observations these results have important implications for the predictability of indo western pacific summer climate the spatial distribution and magnitude of the tio warming rather than simply whether there is an el nino in the preceding winter affect summer climate anomalies over the indo western pacific and east asia

drought reconstructions for the continental united states abstract the development of a 2 lat 3 long grid of summer drought reconstructions for the continental united states estimated from a dense network of annual tree ring chronologies is described the drought metric used is the palmer drought severity index pdsi the number of grid points is 154 and the reconstructions cover the common period 1700 1978 in producing this grid an automated gridpoint regression method called point by point regression was developed and tested in so doing a near optimal global solution was found for its implementation the reconstructions have been thoroughly tested for validity using pdsi data not used in regression modeling in general most of the gridpoint estimates of drought pass the verification tests used in addition the spatial features of drought in the united states have been faithfully recorded in the reconstructions even though the method of reconstruction is not explicitly spatial in its design the drought reconstructions show that the 1930s dust bow

interannual and interdecadal variability of the summertime western north pacific subtropical high 1 the western north pacific subtropical high wnpsh in summer exhibits significant 2 3 years and 3 5 years oscillations with interdecadal variability the 2 3 year oscillation is most evident after 1990 it is accompanied by anomalous meridional overturning circulation characterized by warm sst anomalies ssta and ascending motion in the maritime continent and anomalous descending motion near the philippine sea and by evolving warm to cold ssta in the central eastern pacific from the preceding winter to the summer the 3 5 year oscillation is most pronounced during the 1980s it is accompanied by anomalous descending motion over the maritime continent and warm ssta in the central eastern equatorial pacific that persists from the preceding winter to the summer the complementary cooling and descending motion in the western pacific are related to anomalous east west circulation associated with enso

high frequency fall off of source spectra of deep focus earthquakes from wigner distribution estimation abstract using wigner distribution estimation the high frequency fall off of source spectra was estimated the technique was applied to the analysis of the source spectra of the vladivostok m 6 4 deep focus earthquake of 22 july 1994 and the northern japan sea m 5 7 deep focus earthquake of 22 july 1994 it is shown that the high frequency fall off of the source spectra of these two earthquakes may be characterized by two parts between the first corner frequency f1 and the second corner frequency f2 the high frequency fall off of the source spectra can be represented by f 5 above f2 the high frequency fall off can be represented by f 2

temperature variations in the southern great lakes during the last deglaciation comparison between pollen and gdgt proxies abstract our understanding of deglacial climate history in the southern great lakes region of the united states is primarily based upon fossil pollen data with few independent and multi proxy climate reconstructions here we introduce a new well dated fossil pollen record from stotzel leis oh and a new deglacial temperature record based on branched glycerol dialkyl glycerol tetraethers brgdgts at silver lake oh we compare these new data to previously published records and to a regional stack of pollen based temperature reconstructions from stotzel leis silver lake and three other well dated sites the new and previously published pollen records at stotzel leis are similar but our new age model brings vegetation events into closer alignment with known climatic events such as the younger dryas yd brgdgt inferred temperatures correlate strongly with pollen based regional temperature reconstructions with the strongest correlation obtained for a global soil based brgdgt calibration r2 0 88 lending confidence to the deglacial reconstructions and the use of brgdgt and regional pollen stacks as paleotemperature proxies in eastern north america however individual pollen records show large differences in timing rates and amplitudes of inferred temperature change indicating caution with paleoclimatic inferences based on single site pollen records from 16 0 to 10 0ka both proxies indicate that regional temperatures rose by 10 c roughly double the 5 c estimates for the northern hemisphere reported in prior syntheses change point analysis of the pollen stack shows accelerated warming at 14 0 1 2ka cooling at 12 6 0 4ka and warming from 11 6 0 5ka into the holocene the timing of bolling allerod b a warming and yd onset in our records lag by 300 500 years those reported in syntheses of temperature records from the northern mid latitudes this discrepancy is too large to be attributed to uncertainties in radiocarbon dating and correlation between pollen and brgdgt temperature reconstructions rules out vegetation lags as a cause however the yd termination appears synchronous among the brgdgt record regional pollen stack and northern hemisphere stack the cause of the larger and lagged temperature changes in the southern great lakes relative to northern hemisphere averages remains unclear but may be due to the effects of continentality and ice sheet extent on regional climate evolution

interdecadal change on the relationship between the mid summer temperature in south china and atmospheric circulation and sea surface temperature south china suffers from high temperature frequently in mid summer and this study aims to explore the interdecadal change of interannual variation of the mid summer temperature in south china it is revealed that the relationship between south china temperature and atmospheric circulation and sea surface temperature anomaly ssta experiences an interdecadal change around the early 1990s before the early 1990s warmer summer in south china is associated with the mid latitude teleconnection featured by higher pressure over the ural mountains and the korean peninsula and lower pressure around the lake baikal south china is located at the southern flank of an anomalous high pressure after the early 1990s south china temperature is prominently influenced by the tropical ssta and meanwhile the mid latitude teleconnection becomes much weaker warmer summer is associated with higher pressure centered over south china and the el nino to la nina transition phase the higher pressure influencing south china is located more southwards after the early 1990s and it is favored by the tropical ssta the warmer sst in summer over the western tropical pacific enhances the local convection and triggers an anomalous local hadley cell with stronger subsidence over south china directly leading to higher pressure over south china moreover the colder sst over the central eastern pacific induces an anomalous walker circulation and further strengthens the convection over the western tropical pacific exerting an indirect impact on the higher pressure over south china the relative role of the western pacific warming and central eastern pacific cooling is verified by cam4 simulations the intimate relationship between the tropical ssta and south china temperature occurs during the el nino to la nina transition phase which is the case after the early 1990s and suggests higher predictability for south china temperature in the recent decades

evolution of the circulation anomalies and the quasi biweekly oscillations associated with extreme heat events in southern china abstractsouthern china located in the tropical subtropical east asian monsoonal region presents a unique anticyclonic cyclonic circulation pattern during extreme heat eh obviously different from the typical anticyclone responsible for eh in many other regions associated with the evolution of eh in southern china the anticyclonic cyclonic anomalies propagate northwestward over the philippines and southern china before the eh onsets the anticyclonic anomaly dominates southern china resulting in stronger subsidence over southern china and stronger southerly southwesterly flow over the western northern margins of southern china the southerly southwesterly flow transports more water vapor to the north of southern china thus together with the local stronger subsidence resulting in drier air condition and accordingly favoring the occurrence of eh conversely after the eh onsets the cyclonic component approaches southern china and offsets the high temperature the oscillations of temperature

northwestward propagation of the intraseasonal oscillation in the western north pacific during the boreal summer structure and mechanism abstract the convection of the intraseasonal timescale in the western north pacific during the boreal summer tends to propagate northwestward in the philippine sea to near 20 n and then continues propagating westward the formation of enhanced convection in the western north pacific is a result of the merging of a convective system moving eastward along the equator and a westward propagating low level convergence anomaly which is located to the east of a vortex in the subtropics a positive feedback between the anomalous circulation and convection leads to a rapid enhancement of the system the strengthened southwesterly associated with the vortex enhances evaporation over the oceans e g the eastern indian ocean the bay of bengal and the south china sea and transports moisture northeastward the moisture converges at the northwestern corner of the convection and results in a potentially unstable atmosphere the result is the northwestward propagation of the coupled circulation convection system in

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

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

influences of northward propagating 25 90 day and quasi biweekly oscillations on eastern china summer rainfall the present study reveals that rainfall anomalies associated with the 25 90 day quasi biweekly tropical convective activity propagates northward northwestward into northern china the yangtze river enhanced rainfall over southern china results directly from enhanced convection propagating northward from the south china sea scs western north pacific wnp strengthened northward water vapor transport and intensified upper level divergence the anomalous anticyclone over scs wnp which is induced by local lower sea surface temperature provides a favorable condition for transporting more moisture to southern china stronger subtropical westerly jet and south asia high strengthen upper level divergence the northward propagating 25 90 day oscillation over eastern china reaches farther north than the quasi biweekly oscillation qbwo the intensity of qbwo in summer rainfall has significantly strengthened over southern china after 1993 but not for the 25 90 day oscillation this is mainly contributed by an interdecadal increase in rainfall over southern china and the yangtze river basin in the wet phases of qbwo the interdecadal enhancement of rainfall associated with the qbwo is attributed to three factors one is lower tropospheric convergence caused by anomalous anticyclone over the wnp and anomalous cyclone over korean peninsula and japan the second is upper tropospheric divergence resulting from strengthening of subtropical westerly jet and the south asia high the last is enhanced ascent over south china through meridional vertical circulation

mechanisms of meridional propagating high frequency intraseasonal oscillation associated with a persistent rainfall over south china abstractthe present study divides the intraseasonal variations into high frequency intraseasonal oscillation hf iso with a 5 20 day period and low frequency iso lf iso with a 30 60 day period here defined hf iso is heavily different from some previous work because over south china persistent rainfall pr is not only related to the quasi biweekly oscillation 10 20 day period but also connected with the quasi weekly oscillation 5 10 day period associated with a pr over south china during the first half of june 2016 pr1606 the propagating components of the convections are largely attributed to the hf isos moreover both southward and northward propagating hf isos are found in this case over southern china the moisture advection dominated by anomalous flow and mean water vapor plays an important role in the southward propagation of the hf iso and the cloud radiation effect may be also at least partially responsible for the southward shift of the associated convective zone neverthele

a model study of heat waves over north america meteorological aspects and projections for the twenty first century abstractthe characteristics of summertime heat waves in north america are examined using reanalysis data and simulations by two general circulation models with horizontal resolution of 50 and 200 km several key regions with spatially coherent and high amplitude fluctuations in daily surface air temperature are identified the typical synoptic features accompanying warm episodes in these regions are described the averaged intensity duration and frequency of occurrence of the heat waves in various key regions as simulated in the two models for twentieth century climate are in general agreement with the results based on reanalysis data the impact of climate change on the heat wave characteristics in various key regions is assessed by contrasting model runs based on a scenario for the twenty first century with those for the twentieth century both models indicate considerable increases in the duration and frequency of heat wave episodes and in number of heat wave days per year during the twenty firs

roles of enso and pdo in the link of the east asian winter monsoon to the following summer monsoon abstractthe present study investigates the roles of el nino southern oscillation enso and the pacific decadal oscillation pdo in the relationship between the east asian winter monsoon eawm and the following east asian summer monsoon easm the variability of the eawm is divided into an enso related part named eawmen and an enso unrelated part named eawmres corresponding to a weak eawmen an anomalous low level anticyclone forms over the western north pacific wnp and persists from winter to the following summer this anticyclone enhances southerlies over the coast of east asia in summer hence a weak eawmen tends to be followed by a strong easm and vice versa as such a link is established between the eawmen and the easm the persistence of this wnp anticyclone may be mainly attributed to the sea surface temperature anomalies associated with the enso related eawm part in the tropical indian ocean and the extratropical north pacific in contrast corresponding to a weak eawmres the anomalous wn

a model for attenuation and scattering in the earth s crust the mechanisms contributing to the attenuation of earthquake ground motion in the distance range of 10 to 200 km are studied with the aid of laboratory data coda waves rg attenuation strong motion attenuation measurements in the northeast united states and canada and theoretical models the frequency range 1 10 hz has been studied the relative contributions to attenuation of anelasticity of crustal rocks constant q fluid flow and scattering are evaluated scattering is found to be strong with an albedo b 0 0 8 0 9 and a scattering extinction length of 17 32 km the albedo is defined as the ratio of the total extinction length to the scattering extinction length the rg results indicate that q increases with depth in the upper kilometer or two of the crust at least in new england coda q appears to be equivalent to intrinsic anelastic q and indicates that this q increases with frequency as q q 0 f n where n is in the range of 0 2 0 9 the intrinsic attenuation in the crust can be explained by a high constant q 500 q 0 2000 and a frequency dependent mechanism most likely due to fluid effects in rocks and cracks a fluid flow attenuation model gives a frequency dependence q q 0 f0 5 similar to those determined from the analysis of coda waves of regional seismograms q is low near the surface and high in the body of the crust

multi stage onset of the summer monsoon over the western north pacific the climatological summer monsoon onset displays a distinct step wise northeastward movement over the south china sea and the western north pacific wnp 110 160 e 10 20 n monsoon rain commences over the south china sea philippines region in mid may extends abruptly to the southwestern philippine sea in early to mid june and finally penetrates to the northeastern part of the domain around mid july in association three abrupt changes are identified in the atmospheric circulation specifically the wnp subtropical high displays a sudden eastward retreat or quick northward displacement and the monsoon trough pushes abruptly eastward or northeastward at the onset of the three stages the step wise movement of the onset results from the slow northeastward seasonal evolution of large scale circulation and the phase locked intraseasonal oscillation iso the seasonal evolution establishes a large scale background for the development of convection and the iso triggers deep convection the iso over the wnp has a dominant period of about 20 30 days this determines up the time interval between the consecutive stages of the monsoon onset from the atmospheric perspective the seasonal sea surface temperature sst change in the wnp plays a critical role in the northeastward advance of the onset the seasonal northeastward march of the warmest sst tongue sst exceeding 29 5 c favors the northeastward movement of the monsoon trough and the high convective instability region the seasonal sst change in turn is affected by the monsoon through cloud radiation and wind evaporation feedbacks

pacific east asian teleconnection how does enso affect east asian climate observational evidence is presented to show a teleconnection between the central pacific and east asia during the extreme phases of enso cycles this pacific east asian teleconnection is confined to the lower troposphere the key system that bridges the warm cold events in the eastern pacific and the weak strong east asian winter monsoons is an anomalous lower tropospheric anticyclone cyclone located in the western north pacific the western north pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures the anomalies persist until the following spring or early summer causing anomalously wet dry conditions along the east asian polar front stretching from southern china northeastward to the east of japan kuroshio extension using atmospheric general circulation and intermediate models the authors show that the anomalous philippine sea anticyclone results from a rossby wave response to suppressed convective heating which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central pacific warming the development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling both the anticyclone and the cooling region propagate slowly eastward the development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades the rapid establishment of the philippine sea wind and sst anomalies implies the occurrence of extratropical tropical interactions through cold surge induced exchanges of surface buoyancy flux the central pacific warming plays an essential role in the development of the western pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone sst interaction and midlatitude tropical interaction in the western north pacific

zonal oscillation of western pacific subtropical high and subseasonal sst variations during yangtze persistent heavy rainfall events abstractthis study examines the relationship between the zonal oscillation of the western pacific subtropical high wpsh and underneath sea surface temperature sst variation on a subseasonal time scale associated with the persistent heavy rainfall phr events over the middle and lower reaches of the yangtze river valley mlyrv in china a total of 76 phr events and 45 break events in the summers of 1979 2011 are first identified over the mlyrv and divided into early and late summer groups during the phr events over the mlyrv for both groups the wpsh stretches more westward accompanied by the positive anomalies of the 500 hpa geopotential height field over east asia and its coastal region south of 30 n and the subseasonal warmer ssts beneath the wpsh western edge the time lagged composites suggest that the wpsh western edge exhibits westward then eastward migration on a subseasonal time scale for the phr events the zonal changes of the wpsh and anomalous circulation and sst anomaly ssta signal

influences of enso induced indo western pacific sst anomalies on extratropical atmospheric variability during the boreal summer the causes for the observed occurrence of anomalous zonally symmetric upper level pressure ridges in the midlatitude belts of both hemispheres during the year after warm el nino southern oscillation enso events have been investigated sea surface temperature sst anomalies in the indo western pacific iwp sector were simulated by allowing an oceanic mixed layer model for that region to interact with local atmospheric changes forced remotely by observed enso episodes in the eastern central tropical pacific the spatiotemporal evolution of these sst conditions through a composite enso cycle was then inserted as lower boundary conditions within the iwp domain in an ensemble of atmospheric general circulation model gcm integrations this experimental setup is seen to reproduce zonally symmetric geopotential height anomalies with maximum amplitudes being attained over the extratropics in the boreal summer after the peak phase of enso the model evidence hence supports the notion that these globalscale atmospheric changes are primarily responses to sst perturbations in iwp which are in turn linked to enso variability in the equatorial pacific by the atmospheric bridge mechanism experimentation with a stationary wave model indicates that the eastern hemisphere portion of the aforementioned atmospheric signals are attributable to forcing by tropical heat sources and sinks associated with precipitation anomalies in the iwp region which are closely related to the underlying sst changes diagnosis of the output from the gcm integrations reveals that these circulation changes due to diabatic heating are accompanied by alterations of the propagation path and intensity of the high frequency eddies at locations farther downstream the geopotential tendencies associated with the latter disturbances bear some resemblance to the anomalous height pattern in the western hemisphere such local eddy mean flow feedbacks hence contribute to the zonal symmetry of the atmospheric response pattern to forcing in the iwp region analysis of zonally averaged circulation statistics indicates that the mean meridional circulation induced by divergence of anomalous transient eddy momentum fluxes in enso events could also generate zonally symmetric perturbations in midlatitudes the model simulated precipitation and surface temperature anomalies in the north american sector in response to sst changes in iwp suggest an increased frequency of droughts and heat waves in that region during the summer season after warm enso events

on the numerical simulation of the sea ice ridging process a two dimensional particle simulation model of the sea ice ridging process is developed in this model ridges are formed from a floating layer of rubble compressed between converging multiyear floes the energy consumed in ridge growth including dissipation is explicitly calculated a series of experiments are performed to establish the dependence of the energy consumed in ridging on the velocity of the multiyear floes and on the shape the friction coefficient and the inelasticity of the rubble blocks the experiments show that shape and friction between ice blocks are the most significant factors in determining the energy required to ridge ice in large scale sea ice modeling using a variable thickness approach it is convenient to parameterize total ridging work in terms of the increase of potential energy the results of the ridging simulations with block shaped rubble suggest that the total ridging work may be 4 5 times the increase in potential energy at the same time an analytical model of the ridging process is developed from classical mohr coulomb rankine theory for a cohesionless granular material the predictions of this model using values of porosity and the passive pressure coefficient derived from the ridge simulations are in fair agreement with the numerical experiments however several violations of the basic assumptions underlying the mohr coulomb rankine model are noted in the ridge simulations

elastic decohesive constitutive model for sea ice 1 one of the dominant characteristics of arctic ice is the development and persistence of leads leads are critically important for climate modeling since they are a source for new ice and an avenue for heat exchange between the atmosphere and ocean therefore a specific representation for leads in a constitutive model for pack ice is considered essential presented here is an elastic decohesive constitutive model whose purpose is to specifically indicate when a lead is initiated to provide the orientation of the lead to give the mode of failure and to allow for the numerical determination of the width of leads both laboratory and in situ data of sea ice provide the motivation for the basic structure of the model sample paths in stress and strain space are used to illustrate how the model can simulate failure the model can predict multiple failure planes a feature that is necessary to simulate crack branching preexisting planes of weakness such as those formed from previous leads can also be accommodated

influence of sea surface temperature on the intraseasonal variability of the south china sea summer monsoon the objective of this study is to examine based on recently available high resolution satellite and observational data the evolution and role of sea surface temperature sst in influencing the intraseasonal variability of the south china sea scs summer monsoon sm the study focuses on the 30 60 day timescale when the northward propagating anomalies are dominant over the scs composite analysis of the sst maximum events during scs sm shows that increased sst anomalies over the scs are significantly influenced by the downward shortwave radiation flux anomalies with the suppressed surface latent heat flux anomalies supplementing to it a thermal damping of the positive sst anomalies induces positive upward heat fluxes which then destabilize the lower atmosphere between 1 000 and 700 hpa the positive sst anomalies lead the positive precipitation anomalies over the scs by 10 days with a significant correlation r 0 44 between the sst precipitation anomalies the new findings here indicate an ocean to atmosphere effect over the scs where underlying sst anomalies tend to form a favorable condition for convective activity and sustain enhanced precipitation during the scs sm it is also argued based on our observations that the negative sea level pressure anomalies induced by the positive sst anomalies play a role in enhancing the northward propagation of the intraseasonal anomalies over the scs

on large scale shifts in the arctic ocean and sea ice conditions during 1979 98 results from a regional model of the arctic ocean and sea ice forced with realistic atmospheric data are analyzed to understand recent climate variability in the region the primary simulation uses daily averaged 1979 atmospheric fields repeated for 20 years and then continues with interannual forcing derived from the european centre for medium range weather forecasts for 1979 98 an eastward shift in the ice ocean circu lation fresh water distribution and atlantic water extent has been determined by compar ing conditions between the early 1980s and 1990s a new trend is modeled in the late 1990s and has a tendency to return the large scale sea ice and upper ocean conditions to their state in the early 1980s both the sea ice and the upper ocean circulation as well as fresh water export from the russian shelves and atlantic water recirculation within the eurasian basin indicate that the arctic climate is undergoing another shift this suggests an oscillatory behavior of the arctic ocean system interannual atmospheric variability appears to be the main and sufficient driver of simulated changes the ice cover acts as an effective dy namic medium for vorticity transfer from the atmosphere into the ocean

arctic ice dynamics joint experiment aidjex assumptions revisited and found inadequate 1 this paper revisits the arctic ice dynamics joint experiment aidjex assumptions about pack ice behavior with an eye to modeling sea ice dynamics the aidjex assumptions were that 1 enough leads were present in a 100 km by 100 km region to make the ice isotropic on that scale 2 the ice had no tensile strength and 3 the ice behavior could be approximated by an isotropic yield surface these assumptions were made during the development of the aidjex model in the 1970s and are now found inadequate the assumptions were made in part because of insufficient large scale 10 km deformation and stress data and in part because of computer capability limitations upon reviewing deformation and stress data it is clear that a model including deformation on discontinuities and an anisotropic failure surface with tension would better describe the behavior of pack ice a model based on these assumptions is needed to represent the deformation and stress in pack ice on scales from 10 to 100 km and would need to explicitly resolve discontinuities such a model would require a different class of metrics to validate discontinuities against observations

high frequency spectral falloff of earthquakes fractal dimension of complex rupture b value and the scaling of strength on faults the high frequency falloff omega sup minus gamma of earthquake displacement spectra and the b value of aftershock sequences are attributed to the character of spatially varying strength along fault zones the author assumes that the high frequency energy of a main shock is produced by a self similar distribution of subevents where the number of subevents with radii greated than r is proportional to r sup minus d d being the fractal dimension in this model an earthquake is composed of a hierarchical set of smaller earthquakes the static stress drop is parameterized to be proportional to r sup eta and strength is assumed to be proportional to static stress drop he finds that a distribution of subevents with d 2 and stress drop independent of seismic moment eta 0 produces a main shock with an omega sup minus 2 falloff if the subevent areas fill the rupture area of the main shock by equating subevents to islands of high stress of a random self similar stress field on a fault he relates d to the scaling of strength on a fault such that d 2 minus eta thus d 2 corresponds to constant stress drop scaling eta 0 and scale invariant fault strength amore self similar model of aftershock rupture zones on a fault is used to determine the relationship between the b value the size distribution of aftershock rupture zones and the scaling of strength on a fault the b value for aftershock sequences on a fault is found to equal 3 minus 1 5 eta 3 eta therefore this model indicates that the typically observed spectral falloffs of omega sup minus 2 and b values of 1 can be entirely caused by scale invariant strength eta 0 along fault zones less

two centuries temperature variations over subtropical southeast china inferred from pinus taiwanensis hayata tree ring width high resolution long term temperature reconstructions in subtropical southeast china ssc are very scarce yet indispensable for the comprehensive understanding of climate change in china even in east asia we reconstructed the first previous growth season temperature in the sanqingshan mountains sqs southeast china since 1806 based on tree ring width data the reconstruction accounts for 56 4 of the total variance in the instrumental record over 1954 2009 unlike the northern hemispheric warming during recent two centuries the reconstruction captured a slowly cooling trend from 1806 to 1980 followed by a rapid warming afterward 2003 2009 was the warmest period in the reconstruction 1970 2000 was colder than the last stage of the little ice age lia most of the warm and cold periods in this reconstruction could be found in the tree ring based temperature reconstructions of vicinity area indicating that the temperature variations in ssc were almost synchronous at least at decadal scale this regional coherence of temperature variation was further confirmed by the spatial correlation patterns with the cru ts3 22 grid dataset a strong positive relationship between the temperature over sqs region and sea surface temperature sst over the north pacific ocean np has been noted suggesting that sst variations over np and the related pacific decadal oscillation significantly influenced the temperature variability over ssc to better understand the climate variability during the lia and the regional differences in temperature variations over sqs and northern hemisphere long data sets from more diverse areas of southern china are needed

intraseasonal variations of the yangtze rainfall and its related atmospheric circulation features during the 1991 summer the intraseasonal variations of the yangtze rainfall over eastern china and its related atmospheric circulation characteristics during the 1991 summer are examined based on the gauge observed rainfall and the ncep ncar reanalysis data wavelet analysis shows that during the 1991 summer the active and break sequences of rainfall over the middle and lower yangtze basin are mainly regulated by an oscillatory mode with a period of 15 35 days an investigation of the circulation features suggests that the 15 35 day oscillation is associated with an anomalous low level cyclone anticyclone appearing alternatively over the northern south china sea scs and the philippine sea and related to a northeastward southwestward shift of the western pacific subtropical anticyclone over the scs leading to a lower tropospheric divergence convergence over the yangtze basin in the upper troposphere the 15 35 day oscillation exhibits a dipole anomaly characterized by an anomalous cyclone anticyclone over eastern china and an anomalous anticyclone cyclone over the northern tibetan plateau resulting in a southwestward shrinking northeastward extending of the south asian anticyclone and forming a convergence divergence over eastern china such a coupled anomalous flow pattern between the lower and upper troposphere favors large scale descending ascending motion and hence reduced enhanced rainfall over the yangtze basin dynamically the intraseasonal variations in the yangtze rainfall are mainly determined by the coupling between the low level relative vorticity and the upper level divergence in the middle troposphere the 15 35 day oscillation of the subtropical high is originated over the central north pacific north of hawaii then propagates westward to the scs philippine sea and finally modulates the intraseasonal variations of the yangtze rainfall

decadal variations in the relationship between the western pacific subtropical high and summer heat waves in east china abstractthe western pacific subtropical high wpsh is regarded as the key circulation system that dominates the summer heat waves over eastern china but whether the wpsh summer heat wave connecti

modeling sea ice transport using incremental remapping sea ice models contain transport equations for the area volume and energy of ice and snow in various thickness categories these equations typically are solved with first order accurate upwind schemes which are very diffusive with second order accurate centered schemes which are highly oscillatory or with more sophisticated second order schemes that are computationally costly if many quantities must be transported e g multidimensional positive definite advection transport algorithm mpdata here an incremental remapping scheme originally designed for horizontal transport in ocean models is adapted for sea ice transport this scheme has several desirable features it preserves the monotonicity of both conserved quantities and tracers it is second order accurate except where the accuracy is reduced locally to preserve monotonicity and it efficiently solves the large number of equations in sea ice models with multiple thickness categories and tracers remapping outperforms the first order upwind scheme and basic mpdata scheme in several simple test problems in realistic model runs remapping is less diffusive than the upwind scheme and about twice as fast as mpdata

a new modeling framework for sea ice mechanics based on elasto brittle rheology we present a new modeling framework for sea ice mechanics based on elasto brittle eb behavior the eb framework considers sea ice as a continuous elastic plate encountering progressive damage simulating the opening of cracks and leads as a result of long range elastic interactions the stress relaxation following a damage event can induce an avalanche of damage damage propagates in narrow linear features resulting in a very heterogeneous strain field idealized simulations of the arctic sea ice cover are analyzed in terms of ice strain rates and contrasted to observations and simulations performed with the classical viscous plastic vp rheology the statistical and scaling properties of ice strain rates are used as the evaluation metric we show that eb simulations give a good representation of the shear faulting mechanism that accommodates most sea ice deformation the distributions of strain rates and the scaling laws of ice deformation are well captured by the eb framework which is not the case for vp simulations these results suggest that the properties of ice deformation emerge from elasto brittle ice mechanical behavior and motivate the implementation of the eb framework in a global sea ice model

ground surface temperature reconstruction for the jinggangshan mountains interpreting the hydro thermal coupling pattern in southeastern china abstract understanding the spatial temporal variations of climatic factors and hydro thermal coupling patterns htcp is crucial to forecasting and preparing for future climate change based on accurately dated tree rings we developed the first dekad 10 days 6 to dekad 27 minimum ground surface temperature gstmin6 27 reconstruction for the jinggangshan mountains jgsm in southeastern china sc spanning the period 1791 2014 ad this reconstruction explains 57 9 of observed temperature during the instrumental period 1960 2014 ad our record exhibits a slow cooling trend before 1834 ad followed by drastic fluctuations between 1835 and 1850 ad and progressive warming r2 0 31 thereafter the highest gstmin6 27 variance occurs during the 1820s 1840s and from the 1900s to the early 1930s our reconstruction not only captures the characteristics of temperature variability over a large portion of sc but also reveals decadal scale temperature fluctuations that are approximately synchronous with conditions across north china and the northern hemisphere this research suggests that the western pacific subtropical high wpsh was likely the primary control of gstmin6 27 variability in the jgsm while the pacific decadal oscillation pdo tropical indian and western pacific ocean sea surface temperatures along with the north atlantic oscillation nao indirectly influenced decadal scale temperature variations based on our new reconstruction we identified regional decadal scale differences in the htcp over sc with an insignificant warm dry cold wet coupling pattern dominating the jgsm and a significant warm wet cold dry pattern in coastal areas

source retrieval for mantle earthquakes by iterative deconvolution of long period p waves abstract long period p waves of eighteen deep and intermediate depth earthquakes in a moment range 1 10 26 3 10 28 dyn cm are analysed by the method of kikuchi and fukao this issue to iteratively derive point dislocations on a plane the fault plane is defined as the plane of point dislocations that gives the best fit between the synthetic and observed waveforms for dip slip type earthquakes the fault plane is found to dip more steeply than the auxiliary plane in general point dislocations tend to cluster into one or a few subevents we characterize the largest subevent by its maximum moment rate m 0 m and its half duration from which the associated stress drop can be roughly estimated for earthquakes shallower than 400 km half duration is approximately constant 5 s so that stress drop increases from 1000 bar as m 0 m increases the value of for the great banda sea earthquake of 1963 h 100 km is exceptionally large 10 s for which 700 bar for earthquakes deeper than 400 km increases from 3 s to 9 s as m 0 m increases so that is approximately constant 700 bar stress drop so obtained approximates to an overall stress drop with a possible exception of the several largest earthquakes the distribution of point dislocations and the moment rate function indicate that rupture most often expands in a fan shaped fault area and that a large part of the rupture front ceases propagation in a coherent manner a sharp contrast in stress drop behavior across a depth of 400 km may be related to the olivine spinel transition within the downgoing slab of lithosphere

a new lagrangian model of arctic sea ice a new lagrangian sea ice model for the arctic ocean has been developed to accommodate the assimilation of integral measures of ice displacement over periods of days or weeks the model is a two layer thick ice and open water dynamic model with 600 700 cells spaced at roughly 100 km the force balance equation is solved for each cell with standard wind and water stress terms a coriolis term and an internal ice stress term the internal stress is found using a viscous plastic rheology and an elliptical yield curve the strain rate is determined by the smoothed particle hydrodynamics formalism which determines the spatial derivatives of the velocity by a weighted summation of the velocities of adjacent cells a length scale of 150 km is used the model is driven with observed geostrophic winds and climatological mean ocean currents ice growth and melt are found from a seasonal and thickness based lookup table because the current focus is on the model dynamics the model ice velocity simulations are compared to observed buoy motion over the 5 yr period 1993 97 the correlation of the daily averaged model velocity with buoy velocities is r 5 0 76 n 5 42 553 rms difference 5 0 072 m s21 speed bias 51 0 009 m s21 angle bias 5 8 08 this compares favorably with the correlation of a state of the art eulerian coupled ice ocean model where r 5 0 74 in the summer and 0 66 in the winter over the same 5 yr period

decadal variations of the relationship between the summer north atlantic oscillation and middle east asian air temperature 1 the relationship between the summer july september north atlantic oscillation snao and simultaneous east asian air temperature is investigated the results show that the snao is related to middle east asian summer air temperature however this linkage varies with time on decadal timescale a strong connection appears after the late 1970s but a weak connection before the late 1970s further analysis indicates that this instable relationship may have resulted from the shift of the snao mode around the late 1970s in the period of 1979 2003 the centers of the snao mode are located more eastward a positive phase negative phase snao produces a strong lower level divergence convergence over the asian jet entrance region in turn stimulates a strong upper level convergence divergence via the ekman pumping such a convergence divergence then excites a zonally oriented quasi stationary barotropical rossby wave train along the asian upper level jet thus the snao signal is transported eastward to east asia resulting in an anomalous summer air temperature over middle east asia however in the period of 1951 1975 the centers of the snao mode are located more westward the associated upper level divergence convergence is away from the asian jet entrance region and the snao signal cannot be transported eastward to east asia hence the connection is broken

a strengthened influence of enso on august high temperature extremes over the southern yangtze river valley since the late 1980s abstractthe present study investigates the decadal change in the relationship between china high temperature extremes htes and el nino southern oscillation enso it is found that the relationship between the august htes in the southern yangtze river valley syrv and enso has strengthened since the late 1980s before the late 1980s the relationship is weak whereas after the late 1980s the august hot day numbers in the syrv region tend to be more than normal during el nino decaying years during 1988 2008 el nino induced august warm sst anomalies are mainly located in the eastern tropical and north indian ocean as a response to the north indian ocean warming the south asia high extends eastward and the syrv is overlain by upper level easterly anomalies the cold horizontal temperature advection induced by upper level easterly anomalies leads to anomalous descent which is conducive to the occurrence of htes through adiabatic warming during 1966 86 el nino induced august warm sst anomalies are

using sea ice deformation fields to constrain the mechanical strength parameters of geophysical sea ice we investigate the ability of viscous plastic vp sea ice models with an elliptical yield curve and normal flow rule to reproduce the shear and divergence distributions derived from the radarsat geophysical processor system rgps in particular we reformulate the vp elliptical rheology to allow independent changes in the ice compressive shear and isotropic tensile strength parameters p s t respectively in order to study the sensitivity of the deformation distributions to changes in the ice mechanical strength parameters our 10 km vp simulation with standard ice mechanical strength parameters p 27 5 knm 2 s 6 9 knm 2 and t 0 knm 2 ellipse aspect ratio of e 2 does not reproduce the large shear and divergence deformations observed in the rgps deformation fields and specifically lacks well defined active linear kinematic features lkfs probability density functions pdfs for the shear and divergence of are nonetheless not gaussian simulations with a reduced compressive or increased shear strength are in good agreement with rgps derived shear and divergence pdfs with relatively more large deformations compared to small deformations the isotropic tensile strength of sea ice on the other hand does not significantly affect the shear and divergence distributions when considering additional metrics such as the ice drift error mean ice thickness fields and spatial scaling of the deformations our results suggest that reducing the ice compressive strength is a better solution than increasing the shear strength when performing arctic wide simulations of the sea ice cover with the vp elliptical rheology

the effect of ice pressure on marginal ice zone dynamics to evaluate the role of compressive ice pressure in marginal ice zone dynamics a cavitating fluid model with periodic boundaries is developed and subjected to a fixed wind field and both cyclonic and anticyclonic wind vortices in this model ice interaction is approximated by assuming that sea ice has no resistance to divergence or shear but has some compressive strength which is taken to be a linear function of compactness time scales of ice pressure effects are examined and their relevance to ocean eddies is discussed

introduction to special section small scale sea ice kinematics and dynamics 1 away from the ice margins the response of the ice cover to large scale gradients in atmospheric and oceanic forcing is concentrated along narrow zones of failure up to tens of kilometers in width resulting in openings closings or shears in winter openings dominate the local brine production and heat exchange between the underlying ocean and the atmosphere convergence of the pack ice forces the ice to raft or pile up into pressure ridges and to be forced down into keels increasing the ice ocean and ice atmosphere drag a combination of openings and closings is typical when irregular boundaries are sheared relative to one another these processes shape the unique character of the thickness distribution of the ice cover and have profound impacts on the strength of the ice and its deformation properties over a wide range of temporal and spatial scales understanding the basin scale mechanical character of the sea ice cover is thus of importance in modeling its behavior in a changing climate and in facilitating operational applications 2 in widely used models of sea ice the representation of these processes is typically included in an aggregate and parameterized form based on simplifying assumptions in the past progress in model validation and improvements has been slowed by the lack of suitable observations except for focused field campaigns observations of the above processes from buoy drift are limited by spatial sampling that is typically several hundred kilometers only with sea ice kinematics derived from high resolution synthetic aperture radar sar imagery have we been able to approach the spatial length scale required to observe these processes in the late 1980s and most of the 1990s the availability of small volumes of ice motion data from the european sar satellites ers 1 2 have allowed examination of sea ice strain rates at 5 10 km length scales and demonstrated the utility of these measurements for sea ice studies however the narrow swath of these early sar missions obscures the spatial extent of the deformation patterns beyond 100 km launched in november of 1996 the wide swath coverage of the radarsat imaging radar offers a tool capable of providing high resolution 100 m observations of the arctic ice cover since 1997 routine 3 day radarsat data of the arctic ocean have been acquired and processed into imagery at the alaska satellite facility the nasa funded radarsat geophysical processing system rgps kwok 1998 a joint project of the alaska satellite facility and the jet propulsion laboratory is a program for producing fine scale sea ice motion products the program objective is to provide a dataset suitable for understanding the basin scale behavior of sea ice kinematics on a seasonal and inter annual time scale and for improving ice dynamics thus far four winters and three summers of the radarsat acquisitions have been processed and the data products are posted at the following website http www radar jpl nasa gov rgps working2 radarsat html 3 the availability of ice motion data from the rgps program has allowed a more detailed and unprecedented look at the small scale time varying deformation of the ice cover kwok 2001 the rgps observations point to the importance of understanding the consequence of ice pack as an anisotropic material with large scale oriented fracture patterns with the increasing resolution of coupled iceocean models that approaches the widths of leads high resolution observations like that of the rgps are needed for model development and validation simulation results can now be examined in detail for climate studies the impact of an anisotropic ice cover on surface heat and mass balance is not well understood the rgps dataset is a crucial component in the testing of new models that accounts for the spatial and temporal characteristics of these patterns 4 at the 2004 rgps science working group meeting in seattle the participants showed that there were sufficient potential papers and new results to justify a journal of geophysical research special section to showcase recent work on this topic they highlight the importance of highresolution satellite observations for sea ice studies there are also of course other papers that discuss these topics in other issues of jgr as well as other journals we encourage interested readers to examine these sources the resulting collection is a special section that contains a mix of eight papers addressing a range of topics in modeling and observations of small scale kinematics and dynamics of the sea ice cover five papers address the issues of smallscale modeling and three summarize the laboratory in situ and satellite observations that describe the small scale behavior of the sea ice cover journal of geophysical research vol 111 c11s21 doi 10 1029 2006jc003877 2006 click here for full article

more intense more frequent and longer lasting heat waves in the 21st century a global coupled climate model shows that there is a distinct geographic pattern to future changes in heat waves model results for areas of europe and north america associated with the severe heat waves in chicago in 1995 and paris in 2003 show that future heat waves in these areas will become more intense more frequent and longer lasting in the second half of the 21st century observations and the model show that present day heat waves over europe and north america coincide with a specific atmospheric circulation pattern that is intensified by ongoing increases in greenhouse gases indicating that it will produce more severe heat waves in those regions in the future

role of mediterranean sst in enhancing the european heat wave of summer 2003 1 during summer 2003 europe was affected by one of the driest and most persistent heat waves during this event the mediterranean sea surface temperature sst was exceptionally warm sst anomalies of 2 4 c we investigate the possible role of the mediterranean sst in enhancing the amplitude of the heat wave several atmospheric general circulation model agcm sensitivity experiments were conducted with and without mediterranean sst anomalies first it was found that the agcm was able to simulate the evolution and structure of the heat wave using observed global sst anomalies the experiment with sst anomalies over the mediterranean only was also able to simulate the upper level anticyclone over central europe even though it was weaker and about half of the amplitude of the heat wave of the global sst anomaly experiment

20 50 day oscillation of summer yangtze rainfall in response to intraseasonal variations in the subtropical high over the western north pacific and south china sea the spatio temporal variability in summer rainfall within eastern china is identified based on empirical orthogonal function eof analysis of daily rain gauge precipitation data for the period 1979 2003 spatial coherence of rainfall is found in the yangtze basin and a wavelet transform is applied to the corresponding principal component to capture the intraseasonal oscillation iso of yangtze rainfall the ensemble mean wavelet spectrum representing statistically significant intraseasonal variability shows a predominant oscillation in summer yangtze rainfall with a period of 20 50 days a 10 20 day oscillation is pronounced during june and july this finding suggests that the 20 50 day oscillation is a major agent in regulating summer yangtze rainfall composite analyses reveal that the 20 50 day oscillation of summer yangtze rainfall arises in response to intraseasonal variations in the western north pacific subtropical high wnpsh which in turn is modulated by a rossby wave like coupled circulation convection system that propagates northward and northwestward from the equatorial western pacific when an anomalous cyclone associated with this rossby wave like system reaches the south china sea scs and philippine sea the wnpsh retreats northeastward due to a reduction in local pressure under these conditions strong monsoonal southwesterlies blow mainly toward the scs philippine sea while dry conditions form in the yangtze basin with a pronounced divergent flow pattern in contrast the movement of an anomalous anticyclone over the scs philippine sea results in the southwestward extension of the wnpsh consequently the tropical monsoonal southwesterlies veer to the northeast over the scs and then converge toward the yangtze basin producing wet conditions therefore the 20 50 day oscillation of yangtze rainfall is also manifest as a seesaw pattern in convective anomalies between the yangtze basin and the scs philippine sea a considerable zonal shift in the wnpsh is associated with extreme dry wet episodes in the yangtze basin with an abrupt eastward westward shift in the wnpsh generally leading the extreme negative positive yangtze rainfall anomaly by a 3 8 period of the 20 50 day oscillation this finding may have implications for improving extended range weather forecasting in the yangtze basin

tree ring stable carbon isotope based may july temperature reconstruction over nanwutai china for the past century and its record of 20th century warming growth anomaly of trees in some regions was detected under current episode of rapid warming thisraises a dilemma for temperature reconstructions by using tree ring width which is believed to be themost important proxy on inter annual temperature reconstruction during the past millenniums here weemployed the tree ring d13c to reconstruct temperature variations for exploring their potential oncapturing signals of rapid warming and to test how its difference with the tree ring width basedreconstruction in this study the mean mayejuly temperature tmej was reconstructed over the pastcentury by tree ring d13c of chinese pine trees growing in the nanwutai region the explained varianceof the reconstruction was 43 3 42 1 after adjusting the degrees of freedom compared to a ring widthtemperature reconstruction mayejuly from the same site the tree ring d13c based temperaturereconstruction offered two distinct advantages 1 it captured a wider range of temperature variability i e at least mayejuly even over a longer part of the year januaryeseptember and 2 the reconstructionpreserved more low frequency climate information than that of ring width did the 20th century warming was well represented in the nanwutai tree ring d13c temperature reconstruction which implied that stable carbon isotope of tree rings potentially represents temperaturevariations during historical episodes of rapid warming a spatial correlation analysis showed that ourtemperature reconstruction represented climate variations over the entire loess plateau in north centralchina significant positive correlations p 0 1 were found between the temperature reconstruction andenso as well as ssts in the pacific and indian oceans the reconstruction showed the periodicities of22 78 4 16 3 45e3 97 and 2 04e2 83 year quasi cycles at a 95 confidence level our results suggestedthat temperature variability in the nanwutai region may be linked to pacific and indian ocean sstvariations and solar activity less

genesis of the south asian high and its impact on the asian summer monsoon onset abstractthe formation of the south asian high sah in spring and its impacts on the asian summer monsoon onset are studied using daily 40 yr ecmwf re analysis era 40 data together with a climate mean composite technique and potential vorticity diabatic heating pv q analysis results demonstrate that about 2 weeks before the asian summer monsoon onset a burst of convection over the southern philippines produces a negative vorticity source to its north the sah in the upper troposphere over the south china sea is then generated as an atmospheric response to this negative vorticity forcing with the streamline field manifesting a gill type pattern afterward the persistent rainfall over the northern indochinese peninsula causes the sah to move westward toward the peninsula consequently a trumpet shaped flow field is formed to its southwest resulting in divergence pumping and atmospheric ascent just over the southeastern bay of bengal bob near the surface as a surface anticyclone is formed over t

general characteristics of temperature variation in china during the last two millennia three alternate china wide temperature composites covering the last 2000 years were established by combining multiple paleoclimate proxy records obtained from ice cores tree rings lake sediments and historical documents five periods of temperature variation can be identified a warm stage in ad 0 240 a cold interval between ad 240 and 800 a return to warm conditions from ad 800 1400 including the medieval warm period between ad 800 1100 the cool little ice age period between 1400 1920 and the present warm stage since 1920 regional temperature variation is found during ad 800 1100 when warm conditions occurred in eastern china and in the northeastern tibetan plateau and in ad 1150 1380 when the southern tibetan plateau experienced a warm interval in contrast evidence for cool conditions during the lia is more consistent among the proxy records the temperature reconstructions for china and the northern hemisphere show good agreement over the past millennium

continental scale temperature variability during the past two millennia past global climate changes had strong regional expression to elucidate their spatio temporal pattern we reconstructed past temperatures for seven continental scale regions during the past one to two millennia the most coherent feature in nearly all of the regional temperature reconstructions is a long term cooling trend which ended late in the nineteenth century at multi decadal to centennial scales temperature variability shows distinctly different regional patterns with more similarity within each hemisphere than between them there were no globally synchronous multi decadal warm or cold intervals that define a worldwide medieval warm period or little ice age but all reconstructions show generally cold conditions between ad 1580 and 1880 punctuated in some regions by warm decades during the eighteenth century the transition to these colder conditions occurred earlier in the arctic europe and asia than in north america or the southern hemisphere regions recent warming reversed the long term cooling during the period ad 1971 2000 the area weighted average reconstructed temperature was higher than any other time in nearly 1 400 years

interannual relationships between the tropical sea surface temperature and summertime subtropical anticyclone over the western north pacific 1 the interannual variability of the western north pacific subtropical high wnpsh in boreal summer is investigated with the use of the ncep ncar reanalysis data the most significant change of the 500 hpa geopotential height field appears at the western edge of the wnpsh with dominant 2 3 year and 3 5 year power spectrum peaks the 2 3 year oscillation of the wnpsh and associated circulation and sea surface temperature sst patterns possess a coherent eastward propagating feature with a warm sst anomaly ssta and anomalous ascending motion migrating from the tropical indian ocean in the preceding autumn to the maritime continent in the concurrent summer of a strong wnpsh a strong wnpsh is characterized by anomalous anticyclonic circulation and maximum subsidence in the western north pacific wnp the anomalous wnpsh circulation has an equivalent barotropic vertical structure and resides in the sinking branch of the local hadley circulation triggered by enhanced convection over the maritime continent a heat budget analysis reveals that the wnpsh is maintained by radiative cooling the 3 5 year oscillation of the wnpsh exhibits a quasi stationary feature with a warm ssta anomalous ascending motion located in the equatorial central eastern pacific and indian ocean and a cold ssta anomalous descending motion located in the western pacific the anomaly pattern persists from the preceding winter to the concurrent summer of a high wnpsh the greatest descent is located to the southeast of the anomalous anticyclone center where a baroclinic vertical structure is identified the zonal phase difference and the baroclinic vertical structure suggest that the anomalous anticyclone on this timescale is a rossby wave response to a negative latent heating associated with the persistent local cold ssta echam4 model experiments further confirm that the 2 3 year mode is driven by the ssta forcing over the maritime continent while the 3 5 year mode is driven by the local ssta in the wnp

the material point method for unsaturated soils the paper describes a three phase single point material point method formulation of coupled flow water and air for hydro mechanical analysis of geotechnical problems involving unsaturated soils the governing balance and dynamic momentum equations are discretised and adapted to material point method characteristics an eulerian computational mesh and a lagrangian analysis of material points general mathematical expressions for the terms of the set of governing equations are given a suction dependent elastoplastic mohr coulomb model expressed in terms of net stress and suction variables is implemented the instability of a slope subjected to rain infiltration inspired from a real case is solved and discussed the model shows the development of the initial failure surface in a region of deviatoric strain localisation the evolution of stress and suction states in some characteristic locations the progressive large strain deformation of the slope and the dynamics of the motion characterised by the hi

relation between indian monsoon variability and sst abstract the relation between the intraseasonal modes of the south asian monsoon and the sea surface temperature sst in the tropical oceans on a daily time scale has been investigated long lead lag relations of the daily sst anomalies with the dominant monsoon modes obtained from a multichannel singular spectrum analysis mssa of the daily outgoing longwave radiation olr over the south asian monsoon region are presented the dominant mssa monsoon modes consisting of two oscillatory modes at 45 and 28 day time scales and two seasonally persistent modes are found to have varying degrees of lead lag relation with the ssts in the indian and pacific oceans while the 45 day oscillatory mode has weak correlations with the ssts in the pacific and indian ocean it also reveals a possible 45 day oscillation in the sst in the northwestern pacific and northern indian ocean the 28 day oscillatory mode has negligible correlation with the tropical sst one of the persistent monsoon modes has a very strong r

quasi 4 yr coupling between el nino southern oscillation and water vapor transport over east asia wnp abstractthe summer moisture circulation anomaly over east asia and the western north pacific wnp couples well with the el nino southern oscillation enso in a quasi 4 yr period the moisture circulation is dominated by two well separated modes the first mode exhibits an anticyclonic cyclonic moisture circulation over tropical subtropical east asia wnp with an easterly westerly transport over the tropical wnp indian ocean the second mode displays an alternating pattern with an anticyclonic cyclonic moisture circulation over the subtropical wnp layered between two cyclonic anticyclonic circulations both modes couple well with the enso signal during its quasi 4 yr cycle within the cycle in the summer of a developing warm episode the positive phase of the second mode plays a key role while in the transitional summer between a decaying warm episode and a developing cool episode the positive phase of the first mode tends to take effect in the summer of a developing cool episode the negative

interdecadal changes in the major modes of asian australian monsoon variability strengthening relationship with enso since the late 1970s abstract the present paper develops an integral view of the year to year variability across the entire asian australian monsoon a am system which covers one third of the global tropics between 40 and 160 e using season reliant empirical orthogonal function s eof analysis the authors identified two major modes of variability for the period 1956 2004 the first exhibits a prominent biennial tendency and concurs with the turnabout of el nino southern oscillation enso providing a new perspective of the seasonally evolving spatiotemporal structure for tropospheric biennial oscillation the second mode leads enso by one year the remote el nino forcing the monsoon warm pool ocean interaction and the influence of the annual cycle are three fundamental factors for understanding the behavior of the first mode the monsoon ocean interaction is characterized by a positive feedback between the off equatorial convectively coupled rossby waves and the underlying sea surface temperature sst dipole anoma

using the material point method to model sea ice dynamics 1 the material point method mpm is a numerical method for continuum mechanics that combines the best aspects of lagrangian and eulerian discretizations the material points provide a lagrangian description of the ice that models convection naturally thus properties such as ice thickness and compactness are computed in a lagrangian frame and do not suffer from errors associated with eulerian advection schemes such as artificial diffusion dispersion or oscillations near discontinuities this desirable property is illustrated by solving transport of ice in uniform rotational and convergent velocity fields moreover the ice geometry is represented by unconnected material points rather than a grid this representation facilitates modeling the large deformations observed in the arctic as well as localized deformation along leads and admits a sharp representation of the ice edge mpm also easily allows the use of any ice constitutive model the versatility of mpm is demonstrated by using two constitutive models for simulations of wind driven ice the first model is a standard viscous plastic model with two thickness categories the mpm solution to the viscous plastic model agrees with previously published results using finite elements the second model is a new elastic decohesive model that explicitly represents leads the model includes a mechanism to initiate leads and to predict their orientation and width the elastic decohesion model can provide similar overall deformation as the viscous plastic model however explicit regions of opening and shear are predicted furthermore the efficiency of mpm with the elastic decohesive model is competitive with the current best methods for sea ice dynamics

long term summer warming trend during the holocene in central asia indicated by alpine peat α cellulose δ13c record abstract the long term cooling or warming trend is one of the most important aspects of holocene paleoclimatic research however there are currently significant discrepancies among climatic simulation results sedimentary and synthesized holocene temperature records these discrepancies call for new holocene temperature records with a robust chronology and unambiguous indicative significance here we present a ca 45 year resolution alpine peat cellulose carbon isotopic 13c record from the altai mountains in central asia the chronology of the record has been well constrained by 22 ams 14c dates of the peat cellulose samples based on detailed modern process study results the indicative significance of the record has been carefully determined as summer temperature indicator the record reveals an overall trend of increasing summer temperature for the past ca 11 ka with a warmer early from ca 8 6 ka bp and late from ca 4 0 ka bp holocene and colder middle holocene from ca 6 4 ka bp the general pattern of a warmer early and late holocene and colder middle holocene is consistent with previously reported temperature records from central asia the tibetan plateau and north china the long term warming trend in our summer temperature record is consistent with recently reported winter temperature records from high latitudes of continental eurasia all these results further support the reliability of our summer temperature record from central asia the better understandings about the holocene temperature history and its possible driven mechanism s can be benefited potentially from more reliable holocene temperature records including our record reported in this paper

biweekly and 21 30 day variations of the subtropical summer monsoon rainfall over the lower reach of the yangtze river basin abstract the lower reach of the yangtze river basin lyrb is located at the central region of the mei yu and baiu front which represents the subtropical east asian ea summer monsoon based on the newly released daily rainfall data two dominant intraseasonal variation isv modes are identified over the lyrb during boreal summer may august with spectral peaks occurring on day 15 the biweekly mode and day 24 the 21 30 day mode these two modes have comparable intensities and together they account for above about 57 of the total intraseasonal variance both isv modes exhibit baroclinic structures over the lyrb at their extreme phases however the genesis and evolutions associated with the two modes are different considering the genesis of their extreme wet phases over the lyrb the biweekly mode is initiated by a midlatitude jet stream vorticity anomaly moving southeastward while the 21 30 day mode is primarily associated with a low level westward propagation of an anticyclonic anomaly from

on modeling the anisotropic failure and flow of flawed sea ice the failure and flow of sea ice on scales small and large is characterized by the propagation of oriented leads and cracks in this paper a theory for the dynamical treatment of anisotropic oriented flaws in sea ice is developed and used to examine the interaction of these oriented flaws under idealized stress forcing the essential idea of the theory is to take one or more oriented weak leads imbedded in thick ice a constitutive law for both the thin and thick ice is taken to be similar to laboratory observations which are consistent with mohr coulomb like failure application of normal continuum mechanics boundary conditions leads to anisotropic flow and failure characteristics of this anisotropic composite under both near and far field forcing the local failure characteristics show that there is a preferred orientation for failure with the intersection between leads increasing as confinement increases for spatially separated interacting flaws the theory predicts a preference for the weakening of flaws in a narrow range of angles of 10 20 relative to the principal far field stress imbedding isolated flaws leads to simulated damage directions consistent with local failure characteristics in the case where the ice is considered to have available flaws in all directions fracture propagation is found to proceed by picking out oriented flaws alternating in direction along large scale damage strikes with individual flaw alignments of 20 relative to far field principal stresses the mechanisms responsible for these results and how this anisotropic sea ice rheology might be implemented in current dynamic thermodynamic sea ice models are discussed