variations of the east asian jet stream and asian pacific american winter climate anomalies in this study the authors apply the ncep ncar reanalysis and other observations to depict the association of the asian pacific american climate with the east asian jet stream eajs with an emphasis on boreal winter seasons and on interannual timescales they analyze the variations of the eajs and their relationships with el nino southern oscillation enso and extratropical north pacific sea surface temperature sst and assess the relative connections of the eajs and enso to the anomalies of atmospheric circulation surface temperature and precipitation in the asian pacific american region it is found that the eajs is coupled to a teleconnection pattern spanning the entire asian pacific american region with the strongest signals over east asia and the western pacific this pattern differs significantly from that associated with enso which influences the earth s climate extensively with a strongest impact on the climate over the central pacific and east a strong eajs is associated with an intensification of the weather and climate systems in asia and over the pacific such as deepening of the east asian trough and the aleutian low and strengthening of the east asian winter monsoon it is linked to colder and drier conditions in east asia and stronger convection over the tropical asia australia sector compared with enso the eajs seems to link to the climate signals of asia and the pacific more strongly an intensified eajs is also associated with anomalies of temperature and precipitation in north america due to the related changes in stationary wave patterns while the eajs does not strongly link to the tropical central eastern pacific sst it is significantly associated with the extratropical north pacific sst more specifically the second most dominant mode of the empirical orthogonal function analysis of the sst in addition a strong weak eajs seems to follow a large small meridional gradient of the western pacific sst associated with warming cooling in the tropics subtropics and cooling warming in the extratropics

drought in late spring of south china in recent decades late spring 21 april 20 may precipitation to the south of the yangtze river in china along the east asian front is a salient feature of the global climate the present analysis reveals that during 1958 2000 south china 26 31 n 110 122 e has undergone a significant decrease in late spring precipitation since the late 1970s the sudden reduction of the precipitation concurs with a notable cooling in the upper troposphere over the central china 30 40 n 95 125 e the upper level cooling is associated with an anomalous meridional cell with descending motions in the latitudes 26 35 n and low level northerly winds over southeastern china 22 30 n 110 125 e causing deficient rainfall over south china the late spring cooling in the upper troposphere over the central china is found to strongly link to the north atlantic oscillation nao in the preceding winter during winters with a positive nao index the upper tropospheric cooling occurs first to the north of the tibetan plateau in early middle spring then propagates southeastward to central china in late spring it is suggested that the interdecadal change of the winter nao is the root cause for the late spring drought over south china in recent decades

connections between wintertime jet stream variability oceanic surface heating and transient eddy activity in the north pacific 1 a set of statistical analyses of the fields from the european center for medium range weather forecasts reanalysis era 40 are carried out to investigate the connections between three selected fields namely the wintertime western pacific jet stream wpjs as represented by the zonal wind at 200 hpa the oceanic surface heating represented by the latent and sensible heat fluxes and the synoptic scale transient eddy activity stea over the north pacific first empirical orthogonal function eof analysis is performed to characterize the wintertime wpjs variability further analyses yield the following conclusions 1 the most dominant relationship among the three selected fields is strongly linked to the el nino southern oscillation enso during enso events anomalous zonal wind at 200 hpa downstream of the wpjs main body shown in the first eof is accompanied by stea anomalies around the region of the anomalous midlatitude zonal wind 2 the strengthening weakening of the wintertime wpjs main body shown in the second eof is connected to the surface heating anomalies in the kuroshio and its extension region as well as to stea anomalies in the region downstream of the wpjs main body 3 the northward southward shift of the wintertime wpjs represented in the third eof is closely related to the south north dipolar structure of the surface heating anomalies in the western north pacific the stea spatial displacement is in conjunction with the shift of the jet stream in the same direction due to the dynamical connection between the winds and the eddies furthermore the stea anomalies in winter may cause the wpjs anomalies on the submonthly timescale as a consequence the northward southward shift of the stea is harmoniously in favor of the similar jet shift

the role of barents sea ice in the wintertime cyclone track and emergence of a warm arctic cold siberian anomaly abstractsea ice variability over the barents sea with its resultant atmospheric response has been considered one of the triggers of unexpected downstream climate change for example east asia has experienced several major cold events while the underlying temperature over the arctic has risen steadily to understand the influence of sea ice in the barents sea on atmospheric circulation during winter from a synoptic perspective this study evaluated the downstream response in cyclone activities with respect to the underlying sea ice variability the composite analysis including all cyclone events over the nordic seas revealed that an anticyclonic anomaly prevailed along the siberian coast during light ice years over the barents sea this likely caused anomalous warm advection over the barents sea and cold advection over eastern siberia the difference in cyclone paths between heavy and light ice years was expressed as a warm arctic cold siberian wacs anomaly the lower baroclinicity over the barents se

interannual and decadal modulations recently observed in the pacific storm track activity and east asian winter monsoon abstract interannual variability of the north pacific storm track observed over 17 recent winters is documented the local storm track activity is measured by a meridional flux of sensible heat associated with the lower tropospheric subweekly fluctuations the interannual variability in the heat flux over the northwestern nw pacific is found to be strongest in midwinter the first empirical orthogonal function of the interannual variability in midwinter captures the decadal tendency toward the enhanced storm track activity in midwinter over the nw pacific in association with the decadal weakening of the east asian winter monsoon siberian high and the aleutian low that occurred in the late 1980s the most marked signature of this enhancement is that the midwinter minimum in the storm track activity which had been apparent in the early to mid 1980s almost disappeared afterward as opposed to linear theory of baroclinic instability the enhanced activity occurred despite the weakening of the pacific j

transient investigation of saltwater upconing in laboratory scale coastal aquifer abstract the objective of this research was to examine the response of seawater intrusion and retreat to freshwater abstraction from a well in laboratory scale coastal aquifer under transient conditions this has been done experimentally and numerically through qualitative and quantitative analysis the laboratory experiments were completed in a two dimensional laboratory tank for two beads sizes namely 1090 m and 780 m the seawat code was used for the numerical simulations the experimental results showed that the vulnerability of the pumping well to salinization was higher for the low permeability aquifer whereby the saltwater upconing process was observed at an abstraction rate 40 smaller in the lower permeability aquifer compared to the high permeability aquifer in the lower permeability scenario the inland penetration of the saline plume was up to 41 larger than in the higher permeability scenario for an equivalent pumping rate increment in addition the process of decay after the abstraction had ceased of the wedge was slower in the lower permeability aquifer which suggests a slower retreat of the wedge the qualitative comparison of the shape of the saline plume and the quantitative comparison of the transient toe length data between experimental and numerical results showed excellent agreement the flow velocity field analysis revealed that the local reduction of the magnitude of the flow velocity along the upper part of the interface was a major factor contributing to the saltwater upconing mechanism

variable density flow and solute transport simulation of regional aquifers containing a narrow freshwater saltwater transition zone variable density flow and solute transport simulation of aquifer systems containing narrow transition zones between freshwater and saltwater requires particular attention to certain aspects of the numerical method and its application to be successful typically only cases involving wide transition zones have been simulated with variable density transport models possibly because of inaccuracies in the modeling approaches used the major components of a successful approach are threefold first functionally consistent approximation of terms involved in fluid velocity calculations is necessary in the case of galerkin finite element methodology a significant modification is required to the standard approach in order to achieve consistency second the simulator must be verified in a particular series of tests the usual tests using henry s problem for verification of density dependent transport simulators are inadequate to check for consistency of the velocity approximations and for the accuracy of simulating flow driven by bouyancy forces third adequately fine spatial discretization is required when applying the simulator for spatial stability of the numerical transport solution and to allow accurate representation of narrow transition zones and the effects of low transverse dispersivity the effectiveness of this approach is demonstrated through simulation of the flow of fresh and saline groundwater in the layered basalt aquifer of southern oahu hawaii the transition zone in this regional flow system is narrow except near the discharge area where it is broadly dispersed simulation of this common situation with an inconsistent approximation gives grossly incorrect results while simulation with a consistent model provides a robust tool for analysis of system hydrology

mesoscale aspects of a dry intrusion within a vigorous cyclone the results of a diagnostic study using radar and satellite imagery together with surface reports and output from regional and mesoscale models are presented for an occasion of a rapidly deepening cyclone that crossed the british isles the study shows how air descended from near tropopause level in the form of mesoscale dry intrusions which appeared to overrun parts of the warm conveyor belt ahead of a surface cold front one of the dry intrusions is analysed in detail because it is thought to have led to the large changes that were observed in the character of the wide frontal rain band in some places the precipitation was entirely suppressed whilst in other places the precipitation became convective with a tornadic squall line developing although the effect of the dry intrusion was seen most clearly in the precipitation distribution as determined by radar the approach of the dry intrusion was also clearly detected in the satellite water vapour imagery and foreshadowed in the model forecasts the mesoscale model despite some limitations reproduced many of the observed mesoscale features it also provided insight into the detailed behaviour of the dry intrusion associated with the tornadic squall line it showed that the dry intrusion was characterized by a mesoscale filament of high potential vorticity pv which was extruded from the lower part of a large region of high pv near a low tropopause the extruded pv anomaly plunged to within a kilometre of the surface where it overran part of the warm conveyor belt the dry intrusion was also characterized by relatively low wet bulb potential temperature w and it led to potential instability where it overran the warm air the warm conveyor belt itself was characterized not only by a high w but also by a separate strip of high pv generated locally mainly by condensation the quality of the mesoscale model simulation gives grounds for optimism that such models are capable in principle of predicting severe mesoscale weather events when as in this case they are orchestrated by resolved larger scale dynamics

numerical modelling of saltwater up coning comparison with experimental laboratory observations summary in this study previous interpretations of the density dependent flow and transport processes induced by pumping freshwater above denser saltwater in four laboratory sand tank experiments are extended using numerical modelling the numerical model captured the transition in dispersiveness of up coning plumes observed in the laboratory i e highly dispersive at early times tending to sharp interfaces after saltwater reaches the well this demonstrates the applicability of the velocity dependent dispersion of the modelling code in all four experiments head dependent flux boundary conditions were used to simulate the sand tank side boundary conditions the experimentally derived boundary conductance values indicate non linear variations in the resistance to flow through side inflow ports between the different experiments nonetheless linear boundary head inflow relationships adequately reproduced laboratory up coning the numerical model was able to reproduce the laboratory results within a reasonable level of accuracy and with minimal calibration of model parameters for three of the four experiments this serves to validate those particular laboratory observations the double peak up coning observed late in the fourth laboratory experiment was not reproduced by the model further analysis considering adsorption of the rhodamine tracer is suggested to explore the cause of this effect numerical modelling results were compared to an existing sharp interface analytical solution which corresponded well with the numerical modelling results for early stages of the four up coning experiments despite the dominant influence of dispersion at early times

the concurrent variability of east asian subtropical and polar front jets and its implication for the winter climate anomaly in china the variability of east asian upper level westerly jets in winter is studied with regard to the concurrent existence of subtropical jet east asian subtropical jet easj and polar front jet east asian polar front jet eapj using the national centers for environmental prediction national center for atmospheric research reanalysis in the distribution of jet occurrence revealed in 6 hourly data two jet branches along 30 n and 55 n corresponding to locations of easj and eapj respectively are separated over the tibetan plateau the leading two modes of zonal mean zonal wind in east asia extracted from a mass weighted empirical orthogonal function analysis are characterized by the intensity changes and location displacements of two jets the key regions for easj and eapj are then defined to represent variabilities of these two jets correlation analysis indicates that the subseasonal variation of eapj precedes easj by around 5 days which can be interpreted as wave mean flow interactions via synoptic scale transient eddy activities based on the pentad intensity indices of two jets the concurrent variabilities of easj and eapj are investigated with typical temperature and precipitation anomalies in china the results suggest that by taking account of the two jets we are able to get a more comprehensive understanding of the winter climate

role of indian ocean warming in the development of philippine sea anticyclone during enso 1 the anomalous low level anticyclone near the philippines and suppressed convection over the western pacific associated with the mature warm phase of el nino southern oscillation enso have been suggested as important elements in the interaction between enso and the east asian monsoon we examined the causes of these anomalies in the circulation and convection using a newly developed linear baroclinic model that includes interactive moist processes of the cumulus convection and surface heat fluxes a conventional version of the linear model forced by prescribed heating indicates that the diabatic cooling due to suppressed convection over the maritime continent generates the philippine sea anticyclone from a series of the moist linear model experiments we found that the modest warming of the indian ocean in addition to the strong warming in the central eastern pacific and weak cooling in the western pacific is significant to suppress the convection over the maritime continent observed data also show a coincidence of the development between the philippine sea anticyclone indian ocean warming and the ascending motion over the indian ocean supporting the model results the above results indicate that the atmosphere ocean system in the indian ocean may be one of important factors to improve predictability of the east asian climate during enso

zonal jet structure and the leading mode of variability an observational analysis of the northern hemisphere circulation during winter reveals that the leading mode of variability depends on longitude in particular the first eof of the zonal mean circulation differs over the atlantic and pacific sectors these results provide motivation for a series of model runs where a simple gcm is used to investigate the effects of the zonal jet structure on the leading mode of variability in the northern hemisphere model results indicate that the leading mode of variability depends on the distance between the eddy driven and subtropical jets when the jets are well separated the leading mode of variability describes latitudinal shifting of the eddy driven jet however when the two jets are nearly collocated pulsing of the combined jet dominates the variability this change coincides with a weakening of the positive feedback between the eddies and zonal flow anomalies these results provide a possible explanation for the reduced amplitude of the northern annular mode in the pacific sector relative to that in the atlantic sector during northern hemisphere winter

variations in the east asian winter monsoon from 3500 to 1300 cal yr bp in northern china and their possible societal impacts abstract changes in paleoenvironments from 3500 to 1300 cal yr bp have been documented by a high resolution grain size and organic carbon isotope record in core z8 from the shandong mud wedge in the southern yellow sea ys the sensitive grain size component sorting coefficients and 13corg values were used to identify the paleohydrologic variations and the intensity of the east asian winter monsoon eawm the coarse fraction of sediment together with organic isotope and sea surface temperature sst data shows a weak eawm during 3500 2300 cal yr bp a gradual increase in the eawm from 2300 to 1700 cal yr bp and an enhanced eawm since 1700 cal yr bp superimposed on this general trend several prominent short lived strong eawm episodes peaked at approximately 3300 3100 2900 2750 2620 2220 1900 1700 and 1400 cal yr bp the paleoenvironmental record matches ancient chinese historical climate records as well as socioeconomic changes with lower economic levels occurring during stronger eawm episodes the results show that prosperous stages of ancient chinese dynasties mainly occurred in weak eawm periods while collapses and or changes in ancient chinese dynasties generally occurred during cold periods with a strong eawm we suggest that the persistent short lived strengthening of the eawm could have exerted a remarkable influence on ancient agricultural societies through decreases in both winter temperature and monsoonal precipitation

double difference elastic waveform inversion with prior information for time lapse monitoring abstractquantitative time lapse seismic monitoring can provide crucial information for enhanced oil recovery geologic carbon storage and enhanced geothermal systems recently developed double difference elastic waveform inversion has the potential to quantitatively monitor reservoirs using seismic reflection data because the approximate location of a reservoir or a target monitoring region is usually known we incorporated this knowledge as prior information into double difference elastic waveform inversion using numerical examples of synthetic time lapse models we found that our new method can quantitatively monitor the changes of elastic properties within reservoirs therefore the double difference elastic waveform inversion with prior information on the location of a monitoring region is a promising tool for quantitatively monitoring reservoir properties changes

blocky regularization schemes for full waveform inversion with ill posed inverse problems such as full waveform inversion regularization schemes are needed to constrain the solution whereas many regularization schemes end up smoothing the model an undesirable effect with fwi where high resolution maps are sought blocky regularization does not it identifies and preserves strong velocity contrasts leading to step like functions these models might be needed for imaging with wave equation based techniques such as reverse time migration or for reservoir characterization enforcing blockiness in the model space amounts to enforcing a sparse representation of discontinuities in the model sparseness can be obtained using the 1 norm or cauchy function which are related to long tailed probability density functions detecting these discontinuities with vertical and horizontal gradient operators helps constraining the model in both directions blocky regularization can also help recovering higher wavenumbers that the data used for inversion would allow thus helping controlling the cost of fwi while the cauchy function yields blockier models both 1 and cauchy attenuate illumination and inversion artifacts

experimental observations of saltwater up coning summary the proper management of coastal aquifers commonly requires an understanding of the behaviour of saltwater plumes underlying production wells the current understanding of saltwater up coning i e the pumping induced rise in the freshwater saltwater interface is based predominantly on theoretical constructs of salinity and flow responses to groundwater pumping plus a limited number of field scale and laboratory investigations there is a need to produce direct observations of saltwater up coning given the considerable and inherent uncertainties associated with the prediction of density dependent flow and dispersive solute transport behaviour in this study time series observations of saltwater up coning were made using controlled sand tank experiments of a two dimensional aquifer cross section a range of mixed convection ratios was tested by invoking different groundwater abstraction rates and saltwater densities the temporal development of up coning was characterised in terms of the height of the interface apex the width of the salt plume and the salinity of the pumping well experimental results were compared to an existing sharp interface analytical solution and close agreement was obtained for two of the cases higher freshwater saltwater density differences and lower pumping appeared to induce the largest deviations from theoretical up coning dispersive transport processes dominated during phases of near well up coning causing gradual increases in pumped water salinity although plumes became non dispersive after the interface made contact with the bore an interesting departure from the classical up coning shape was obtained for the situation of highest saltwater density and lowest pumping in which up coning occurred as an almost horizontal interface for the majority of the experiment eventually producing a double apex shape as the interface neared the well the experimental results could form a useful basis for the testing of density dependent groundwater flow and transport models since they offer controlled laboratory analogues of saltwater up coning

structure and evolution of baroclinic waves as inferred from regression analysis abstract the structure of transient disturbances with periods shorter than a week is documented an the basis of one point regression maps and longitude height sections derived from the national meteorological center nmc operational analyses for nine winter seasons the reference time series for the regression coefficients is highpass filtered normalized 500 mb height at a grid point in the pacific stormtrack the field variables that were regreesed on the reference time series were not filtered the regression statistics yield quantitative estimates of the amplitudes of the high frequency fluctuations in the geopotential height temperature wind ageostrophic wind vorticity divergence vertical velocity and outgoing longwave radiation fields the observed high frequency fluctuations exhibit a vertical and meridional structure suggestive of baroclinic waves evolving through the mature phase of their life cycle most of the results are in qualitative agreement with previous studies but the ageostrop

relationship between stationary planetary wave activity and the east asian winter monsoon 1 the variability of both the stationary planetary wave activity and the east asian winter monsoon is strongly associated with the thermal contrast between oceans and landmasses in this study we explore the interannual relationship between the monsoon and the wave activity defined by an index of the difference in the divergence of eliassenpalm flux between 50 n at 500 hpa and 40 n at 300 hpa it is found that compared to the winters of low wave activity the equatorward propagation of planetary waves in the middle and upper troposphere is stronger in the high wave activity winters during these high activity winters the upward wave propagation from the troposphere into the stratosphere becomes weaker this is accompanied by a smaller perturbation in the polar vortex which tends to be colder and stronger in the meantime the east asian westerly jet stream the east asian trough the siberian high and the aleutian low all become weaker apparently in particular the weakening of the siberian high and the aleutian low decreases the northeasterly wind over east asia leading to a warming condition in the region especially in northeastern asia a further analysis reveals that the zonal wavenumber 2 pattern of planetary waves contributes dominantly to the variability of the east asian winter monsoon

the linkage between upper level jet streams over east asia and east asian winter monsoon variability abstractthis study investigates the linkage between east asian winter monsoon eawm variability and upper level jets with particular focus on the east asian polar front jet pj and its concurrent variation with the subtropical jet located to the south of the tibetan plateau tsj the winter upper level zonal wind variations over the asian landmass 70 120 e are dominated by two principal modes i e meridional displacement of the pj and out of phase variation in the intensity of the tsj and pj and they are closely linked to the eawm northern mode and southern mode respectively southward shifting of the pj concurs with northwestward displacement of the siberian high sh an enhanced northern east asian trough leading to cold winter in northern east asia meanwhile the simultaneous tsj intensification and pj weakening is linked to an amplified sh a southward shift of the aleutian low al a strengthened southern east asian trough and a wavelike anomaly pattern extending from western barents s

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

why is there an early spring cooling shift downstream of the tibetan plateau abstract the temperature shift over the eastern flank of the tibetan plateau is examined using the last 50 yr of chinese surface station observations it was found that a strong cooling shift occurs in early spring march and april and late summer july august and september in contrast to the warming shift in other seasons the cause of the march april ma cooling is investigated in this study the ma cooling shift on the lee side of the tibetan plateau is found to be not a local phenomenon but rather it is associated with an eastward extension of a cooling signal originating from north africa that is related to the north atlantic oscillation nao in the previous winter the midtropospheric westerlies over the north atlantic and north africa tend to intensify during positive nao phases the enhanced westerlies after passing over the tibetan plateau result in strengthened ascending motion against the lee side of the plateau which favors the formation of midlevel stratiform clouds the increased a

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

how does layered heterogeneity affect the ability of subsurface dams to clean up coastal aquifers contaminated with seawater intrusion abstract the main purpose of this work was to examine how aquifer layering impacts the ability of subsurface dams to retain seawater intrusion swi and to clean up contaminated coastal aquifers using both experimental and numerical techniques four different layering configurations were investigated including a homogeneous case case h and three different layered cases where a low permeability layer was set at the top of the aquifer case lh at the middle part of the aquifer as interlayer case hlh and at the lower part of the aquifer case hl the subsurface dam was able to retain the saltwater wedge associated with a drop of the hydraulic gradient from 0 0158 down to 0 0095 in all the cases thereby achieving up to 78 reduction in the saltwater toe length in cases lh and hlh the start of the saltwater spillage was delayed compared to the homogeneous case and the time taken for the freshwater zone to be fully contaminated post spillage was twice and three times longer respectively by contrast the existence of a low k layer at the bottom of the aquifer case hl considerably weakened the ability of dams to retain the intrusion allowing for quicker saltwater spillage past the wall the natural cleanup of swi contaminated coastal aquifers was for the first time evidenced in heterogeneous settings depending on the stratification pattern the presence of stratified layers however prolonged the cleanup time to various degrees compared to the homogeneous scenario particularly in case hl where the cleanup time was nearly 50 longer

circulations of the west pacific jet stream abstract the jet stream of the west pacific is a very steady feature of the winter circulation with almost continuousintensification over east china and japan and weakening in the central pacific in this study the national meteorological center spectral forecast model with normal mode initialization is used as a tool to provide diagnostic elements in a region of nonstandard data sources cross sections transverse to the jet stream in its intensification zone show a deep single celled direct solenoidal circulation around a single frontal zone to be producing large increases of kinetic energy farther east in the central pacific a strong indirect solenoidal circulation produces a strong decrease of kinetic energy the irrotational wind components at jet stream levels are suggestive of an inertial cycle as part of the jet stream dynamics a simple model of a modified inertial cycle is integrated in which the geostrophicwind is allowed to vary as a function of the ageostrophic flow transverse to the jet a

observed trends in the global jet stream characteristics during the second half of the 20th century 1 in this paper we propose a new method based on the detection of jet cores with the aim to describe the climatological features of the jet streams and to estimate their trends in latitude altitude and velocity in the national centers for environmental prediction ncep national center for atmospheric research ncar and 20th century reanalysis data sets due to the fact that the detection method uses a single grid point to define the position of jet cores our results reveal a greater latitudinal definition allowing a more accurate picture of the split flow configurations and double jet structures to the best of our knowledge these results provide the first multiseasonal and global trend analysis of jet streams based on a daily resolution 3 d detection algorithm trends have been analyzed over 1958 2008 and during the post satellite period 1979 2008 we found that in general trends in jet velocities and latitudes have been faster for the southern hemisphere jets and especially for the southern polar front jet which has experienced the fastest velocity increase and poleward shift over 1979 2008 during the austral summer and autumn results presented here show an acceleration and a poleward shift of the northern and southern winter subtropical jets over 1979 2008 that occur at a faster rate and over larger zonally extended regions during this latter period than during 1958 2008

asian jet waveguide and a downstream extension of the north atlantic oscillation abstract anomalous atmospheric fields associated with the north atlantic oscillation nao are analyzed on interannual and intraseasonal time scales in order to examine the extent to which the nao is a regional phenomenon analyses on the interannual time scale reveal that the nao signal is relatively confined to the euro atlantic sector in december while it extends toward east asia and the north pacific in february the difference is most clearly seen in the meridional wind anomaly which shows a wave train along the asian jet collocated with an anomalous vorticity source near the jet entrance diagnoses using a linear barotropic model indicate that this wave train is interpreted as quasi stationary rossby waves trapped on the asian jet waveguide and effectively excited by the anomalous upper level convergence over the mediterranean sea it is found that when the nao accompanies the mediterranean convergence mc anomaly most frequently seen in february the nao indeed has a much wider horizontal str

flow dynamics and age stratification of freshwater lenses experiments and modeling the development and flow dynamics of freshwater lenses are investigated by physical experiments on a laboratory scale using an acrylic glass box and a combination of different tracers we were able to simulate a cross section of an infinite strip island and visualize its groundwater flow patterns for validating our model results of the generation and degeneration of the freshwater lens were compared to analytical and numerical models using recharge water of different colors we were able to visualize flow paths as well as the age stratification within a freshwater lens flow paths in the lens could be demonstrated to remain in contact to the outflow zone at all times during the experiments analytical solutions are in good accordance to our findings additional experiments show the differences between pumping from a horizontal and a vertical well on the interface these experiments with identical boundary conditions confirm former presumptions a horizontal well shows less up coning of the interface and therefore allows a higher sustainable yield than a vertical well

the different configurations of the east asian polar front jet and subtropical jet and the associated rainfall anomalies over eastern china in summer abstractto investigate the concurrent impacts of the east asian polar front jet eapj and subtropical jet easj on the summer rainfall over eastern china positive strengthened eapj with weakened easj and negative weakened eapj with strengthened easj configurations are identified in the positive configuration rainfall decreases in the northern part of eastern china and increases in the southern part vice versa in the negative configuration the possible mechanisms maintaining the two jet configurations are further proposed from the perspectives of sea surface temperature sst and synoptic scale transient eddy activities stea in the positive configuration meridional distributed cold warm sst anomalies over the eastern north pacific may induce regional circulation and meridional temperature gradient anomalies which can strengthen the eapj and weaken the easj the central pacific la nina like sst anomalies are related with the arctic vortexlike anomalies in the stratosphere which may strength

wave equation reflection traveltime inversion with dynamic warping and full waveform inversion abstractin reflection seismology full waveform inversion fwi can generate high wavenumber subsurface velocity models but often suffers from an objective function with local minima caused mainly by the absence of low frequencies in seismograms these local minima cause cycle skipping when the low wavenumber component in the initial velocity model for fwi is far from the true model to avoid cycle skipping we discovered a new wave equation reflection traveltime inversion werti to update the low wavenumber component of the velocity model while using fwi to only update high wavenumber details of the model we implemented the low and high wavenumber inversions in an alternating way in werti we used dynamic image warping diw to estimate the time shifts between recorded data and synthetic data when compared with correlation based techniques often used in traveltime estimation diw can avoid cycle skipping and estimate the time shifts accurately even when shifts vary rapidly hence by minimizing tr

experimental saltwater intrusion in coastal aquifers using automated image analysis applications to homogeneous aquifers summary this paper presents the applications of a novel methodology to quantify saltwater intrusion parameters in laboratory scale experiments the methodology uses an automated image analysis procedure minimising manual inputs and the subsequent systematic errors that can be introduced this allowed the quantification of the width of the mixing zone which is difficult to measure in experimental methods that are based on visual observations glass beads of different grain sizes were tested for both steady state and transient conditions the transient results showed good correlation between experimental and numerical intrusion rates the experimental intrusion rates revealed that the saltwater wedge reached a steady state condition sooner while receding than advancing the hydrodynamics of the experimental mixing zone exhibited similar traits a greater increase in the width of the mixing zone was observed in the receding saltwater wedge which indicates faster fluid velocities and higher dispersion the angle of intrusion analysis revealed the formation of a volume of diluted saltwater at the toe position when the saltwater wedge is prompted to recede in addition results of different physical repeats of the experiment produced an average coefficient of variation less than 0 18 of the measured toe length and width of the mixing zone

impact of layered heterogeneity on transient saltwater upconing in coastal aquifers abstract this research investigated the effect of layered heterogeneity on transient saltwater upconing in a laboratory scale coastal aquifer the experiments were conducted in a 2d laboratory flow tank and the response of the saltwater wedge to pumping was analysed in a heterogeneous aquifer system where a low permeability layer was constructed in the middle of the aquifer the seawat code was used for validation and to perform additional simulations to explore the sensitivity of the critical pumping rate and the critical time to the main parameters characterising the low permeability layer which included its permeability thickness and position the experimental results showed that the presence of layered heterogeneity noticeably altered the shape and the intrusion length of the upconing wedge without inducing a change in the abstraction rate triggering saltwater upconing mechanism compared to the homogeneous case the numerical results of the layered aquifer provided excellent agreement with the experimental data for both the transient toe length and the shape of the steady state saltwater wedges the sensitivity analysis revealed that the critical pumping rate and the critical time was found to decrease considerably with decreasing hydraulic conductivity and thickness of the middle layer which evidences the higher vulnerability of such layered aquifer systems to the saltwater upconing in comparison to idealised homogeneous systems the results nonetheless showed that varying the position of the interlayer induced very little change on the critical pumping rate but the critical time would tend to decrease as the low permeability layer was moved deeper away from the pumping well particularly for smaller middle layer thickness

interannual variations of east asian trough axis at 500 hpa and its association with the east asian winter monsoon pathway interannual variations of the east asian trough eat axis at 500 hpa are studied with the european centre for medium range weather forecasts 40 yr reanalysis data the associated circulation pattern and pathway of the east asian winter monsoon eawm with the eat axis tilt are specially investigated with a trough axis index which is closely related to the midlatitude baroclinic process and mainly represents the intensity of the eddy driven jet over the east asia north pacific sector when the tilt of eat is smaller than normal the eawm prefers to take the southern pathway and less cold air moves to the central north pacific however the eawm prefers the eastern pathway and brings more cold air to the north pacific when the tilt of eat is larger than normal these differences induce pronounced changes in both the precipitation and the surface air temperature over east and southeast asia furthermore the tilt status of the eat has a significant modulation effect on the regional climate anomalies related to the intensity of the eawm the findings suggest an increase in the temperature anomaly associated with the eawm intensity and a clear northward southward shift in its pattern in anomalous tilt phase of the eat in addition the modulation tends to be confined mainly to east asia and expanded to a larger area during the weak and the strong eawm winters respectively the possible reasons for interannual variations of the eat tilt are discussed and it is speculated that the midlatitude air sea interaction in the north pacific plays a dominant role this study on the eat tilt may enrich knowledge of the east asian winter monsoon beyond the conventional intensity index and may be helpful to improve regional climate prediction in east asia

influence of low arctic sea ice minima on anomalously cold eurasian winters 1 influence of low arctic sea ice minima in early autumn on the wintertime climate over eurasia is investigated observational evidence shows that significant cold anomalies over the far east in early winter and zonally elongated cold anomalies from europe to far east in late winter are associated with the decrease of the arctic sea ice cover in the preceding summer to autumn seasons results from numerical experiments using an atmospheric general circulation model support these notions the remote response in early winter is regarded as a stationary rossby wave generated thermally through an anomalous turbulent heat fluxes as a result of anomalous ice cover over the barents kara seas in late autumn which tends to induce an amplification of the siberian high causing colder conditions over the far east the late winter cold anomalies over eurasia are also reproduced in our experiment which is associated with the negative phase of the north atlantic oscillation

a new physical barrier system for seawater intrusion control abstract the construction of subsurface physical barriers is one of various methods used to control seawater intrusion swi in coastal aquifers this study proposes the mixed physical barrier mpb as a new barrier system for seawater intrusion control which combines an impermeable cutoff wall and a semi permeable subsurface dam the effect of the traditionally used physical barriers on transient saltwater wedge dynamics was first explored for various hydraulic gradients and the workability of the mpb was thereafter thoroughly analysed a newly developed automated image analysis based on light concentration conversion was used in the experiments which were completed in a porous media tank the numerical code seawat was used to assess the consistency of the experimental data and examine the sensitivity of the performance of the barriers to various key parameters the results show that the mpb induced a visible lifting of the dense saline flux upward towards the outlet by the light freshwater this saltwater lifting mechanism observed for the first time induced significant reduction to the saline water intrusion length the use of the mpb yielded up to 62 and 42 more reduction of the saltwater intrusion length than the semi permeable dam and the cutoff wall respectively the performance achieved by the mpb with a wall depth of 40 of the aquifer thickness was greater than that of a single cutoff wall with a penetration depth of 90 of the aquifer thickness about 13 extra reduction this means that the mpb could produce better seawater intrusion reduction than the traditionally used barriers at even lower cost

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

mechanisms of intraseasonal amplification of the cold siberian high mechanisms of intraseasonal amplification of the siberian high are investigated on the basis of composite anomaly evolution for its strongest events at each of the grid points over siberia at each location the amplification of the surface high is associated with formation of a blocking ridge in the upper troposphere over central and western siberia what may be called wave train atlantic origin type is common where a blocking ridge forms as a component of a quasi stationary rossby wave train propagating across the eurasian continent a cold air outbreak follows once anomalous surface cold air reaches the northeastern slope of the tibetan plateau it is found through the potential vorticity pv inversion technique that interaction between the upperlevel stationary rossby wave train and preexisting surface cold anomalies is essential for the strong amplification of the surface high upper level pv anomalies associated with the wave train reinforce the cold anticyclonic anomalies at the surface by inducing anomalous cold advection that counteracts the tendency of the thermal anomalies themselves to migrate eastward as surface thermal rossby waves the surface cold anomalies thus intensified in turn act to induce anomalous vorticity advection aloft that reinforces the blocking ridge and cyclonic anomalies downstream of it that constitute the propagating wave train the baroclinic development of the anomalies through this vertical coupling is manifested as a significant upward flux of wave activity emanating from the surface cold anomalies which may be interpreted as dissipative destabilization of the incoming external rossby waves

an intensity index for the east asian winter monsoon the thermal contrast betweenthe asian continentand the adjacent oceans is the primary aspect of the east asian winter monsoon eawm that can be well represented in the sea level pressure slp field based on this consideration a new slp based index measuring the intensity of the eawm is proposed by explicitly taking into account both the east west and the north south pressure gradients around east asia the new index can delineate the eawm related circulation anomalies well including the deepened shallow midtropospheric east asian trough sharpened and accelerated widened and decelerated upper tropospheric east asian jet stream and enhanced weakened lower tropospheric northerly winds in strong weak eawm winters compared with previous indices the new index has a very good performance describing the winter mean surface air temperature variations over east asia especially for the extreme warm or cold winters the index is strongly correlated with several atmospheric teleconnections including the arctic oscillation theeurasianpattern andthenorthpacificoscillation westernpacificpattern implyingthepossible internal dynamics of the eawm variability meanwhile the indexis significantly linked to el ni oscillation enso and the sea surface temperature sst over the tropical indian ocean moreover the sst anomalies over the tropical indian ocean are more closely related to the index than enso as an independent predictor this adds further knowledge to the prediction potentials of the eawm apart from enso the predictability of the index is high in the hindcasts of the centre national de recherches m cnrm model from development of a european multimodel ensemble system for seasonal to interannual prediction demeter hence it would be a good choice to use this index for the monitoring prediction and research of the eawm

distinguishing interannual variations of the northern and southern modes of the east asian winter monsoon abstractthe east asian winter monsoon eawm related climate anomalies have shown large year to year variations in both the intensity and the meridional extent the present study distinguishes the interannual variations of the low latitude and mid to high latitude components of the eawm to gain a better understanding of the characteristics and factors for the eawm variability through composite analysis based on two indices representing the northern and southern components modes of the eawm variability the present study clearly reveals features unique to the northern and southern mode the northern mode is associated with changes in the mid to high latitude circulation systems including the siberian high the aleutian low the east asian trough and the east asian westerly jet stream whereas the southern mode is closely related to circulation changes over the global tropics the north atlantic and north america a strong northern mode is accompanied by positive negative and positive surface temp

analysis of saltwater upconing beneath a pumping well abstract aquifer systems that contain freshwater and saltwater are usually stratified with the more dense saltwater underlying the freshwater a groundwater well discharging from the freshwater zone causes the saltwater to move upwards towards the well this phenomenon is known as saltwater upconing two methods of analysis the sharp interface method and the fluid density dependent solute transport method are used to simulate saltwater upconing numerical experiments including comparisons of the two methods indicate 1 for low to moderate pumpages the 50 isochlor and sharp interface correlate well 2 the well can discharge significant concentrations of saltwater even though a stable cone according to the sharp interface method exists below the well screen 3 an almost linear relationship exists between the well discharge rate and the concentration of the discharge at low pumping rates that maintain a stable cone and 4 upconing is sensitive to transverse dispersivity whereas it is insensitive to longitudinal dispersivity a simulation of upconing at test site no 4 truro cape cod massachusetts indicates that the appropriate field value of transverse dispersivity is very small this supports the validity of the sharp interface assumption for analyzing the behavior of systems with thin saltwater freshwater transition zones

an analysis of the large scale climate anomalies associated with the snowstorms affecting china in january 2008 abstract extraordinarily frequent and long lasting snowstorms affected china in january 2008 causing above normal precipitation below normal temperature and severe icing conditions over central southern china these snowstorms were closely linked to the change in the middle east jet stream mejs which intensified and shifted southeastward the change in mejs was accompanied by southeastward shifts of the ridge and the trough over europe and western asia the intensified mejs also strengthened the trough embedded in the southern branch of the subtropical westerlies over the southern tibetan plateau enhancing the water vapor transport from western asia and the bay of bengal to china in the meantime the subtropical western pacific high swph was stronger and its ridgeline was farther north than normal the anomalous high slowed down the eastward propagation of weather systems to the pacific and favored convergence of water vapor over central southern china the mejs is usually strong when the arctic

saltwater upconing in unconfined aquifers the need for skimming of fresh groundwater above a saline water body without producing an unacceptable contamination in the pumped water calls for the investigations carried out in this research work two axisymmetric models namely the steady state and the transient upconing models are developed with the assumption of an abrupt interface finite element method with an iterative scheme is employed in solving the steady state model whereas a method of finite element in space and finite differences in time is used with iterative schemes for the transient model the models are calibrated with the analytical solutions for the case of radial flow to a fully penetrating well in an unconfined aquifer a method of superimposing the effects of hydrodynamic dispersion on the upconing is discussed the simulation results of both models together with the technique of dimensional analysis provide information for establishing design criteria for optimal pumping or choice of well depth or both

storm tracks and zonal mean flow variability a comparison between observed and simulated data a statistical technique is used to analyze the relation between monthly mean zonal flow and storm tracks activity in the observations and numerical simulations echam4 model the singular value decomposition technique svd has been used to correlate storm tracks and monthly mean wintertime anomaly fields the analysis has been performed on data from january 1980 to december 1989 nmc analyses and on an ensemble of agcm simulations with prescribed sst for the same period separately in the euro atlantic and pacific sectors we found good correlation between storm tracks activity and zonal flow in both regions in both data and simulations the dominant svd modes show that the storm tracks spatial displacement is in conjunction with jet shifts in the same direction our analysis suggests that the model is highly sensitive to the equatorial ocean forcing although the model produces an excessive response to el nino and la nina phases it shows good capability of simulating the dynamical connection between storm tracks and jet

another look at interannual to interdecadal variations of the east asian winter monsoon the northern and southern temperature modes abstract this study investigates the causes of interannual to interdecadal variability of the east asian ea 0 60 n 100 140 e winter monsoon eawm over the past 50 yr 1957 2006 the winter mean surface air temperature variations are dominated by two distinct principal modes that together account for 74 of the total temperature variance the two modes have notably different circulation structures and sources of variability the northern mode characterized by a westward shift of the ea major trough and enhanced surface pressure over central siberia represents a cold winter in the northern ea resulting from cold air intrusion from central siberia the southern mode on the other hand features a deepening ea trough and increased surface pressure over mongolia representing a cold winter south of 40 n resulting from cold air intrusion from western mongolia the cold northern mode is preceded by excessive autumn snow covers over southern siberia mongolia whereas the cold southern mode is preceded b

seasonality and interannual variability of the westerly jet in the tibetan plateau region abstract in this study 40 yr ecmwf re analysis era 40 data are used for the description of the seasonal cycle and the interannual variability of the westerly jet in the tibetan plateau region to complement results based on the analysis of monthly mean horizontal wind speeds an occurrence based jet climatology is constructed by identifying the locations of the jet axes at 6 hourly intervals throughout 1958 2001 thus a dataset describing the highly transient and localized features of jet variability is obtained during winter and summer the westerly jet is located respectively to the south and north of the tibetan plateau during the spring and autumn seasons there are jet transitions from south to north and vice versa the median dates for these transitions are 28 april and 12 october the spring transition is associated with large interannual variations while the fall transition occurs more reliably within a 3 week period the strength of the jet exhibits a peculiar seasonal cycle during northw

two dimensional full wavefield inversion of wide aperture marine seismic streamer data summary a 2 d full wavefield inversion method is presented for the processing of wide aperture data the diversity of information contained within such datasets may be handled in a complete manner by first matching the traveltimes of the main events and then progressing to waveform fitting of the data through explicit full wavefield modelling our wavefield inversion scheme is based upon a finite difference solution of the 2 d elastic wave equation in the time distance domain the strength of adopting such an approach is the ability to generate all possible wave types within a given 2 d model multiples converted waves etc and thus to simulate and accurately model complex seismic wavefields the aim of the inversion is to find the 2 d p wave velocity model that minimizes the least squared difference between the observed and synthetic data across the full range of offsets following extensive testing on synthetic data the wavefield inversion scheme has been applied to wide aperture real marine seismic streamer datasets we present results from the synthetic testing and the wavefield inversion of wide aperture real data out to 12 km offset that was recorded on a single streamer even though current computational restrictions allow only a small subsection of the data to be analysed these examples demonstrate the potential value of wide aperture 2 d full wavefield inversion

regionality of record breaking low temperature events in china and its associated circulation extreme cold events frequently occur around the world in recent several years and arouse widespread concern in this study 17 record breaking event processes rbeps of low temperature during 1981 2012 are identified by using daily minimum temperature at 1897 meteorological stations in china these rbeps are classified into two types based on the occurring area at northern or southern china to compositely examine the associated circulations although the correspondence between arctic oscillation ao and rbeps is not linearly stable there still exist relationship between them i e under ao negative phase the rbeps tend to occur at northern china nor the southern part where the rbeps prefer to happen under ao positive phase in the rbeps occurring at southern china the continent high pressure over mongolia area is extremely intensified and the east asian polar front jet stream is enhanced accompanied with strong synoptic scale eddy kinetic energy transports correspondingly the cold air masses break out and unobstructed southward intrude to low latitudes causing severe cooling effect in southern china in the rbeps occurring at northern china however the extremely intensified high pressure over northern siberian area combining with the northward enhanced subtropical jet stream lead to the cold air mass accumulation and blockage at mid latitudes and therefore rbeps of low temperature at this area further study implies that interdecadal change of the ao phase and differences of synoptic scale eddy activity might synthetically attribute to the different regional preference of those rbeps of low temperature that are mostly located at southern china in 1990s but concentrated in northern china in 2000s

the winter concurrent meridional shift of the east asian jet streams and the associated thermal conditions abstractin this study the concurrent meridional shift of the east asian polar front jet eapj and the east asian subtropical jet easj and the associated thermal conditions have been investigate

el nino modoki and its possible teleconnection 1 using observed data sets mainly for the period 1979 2005 we find that anomalous warming events different from conventional el nino events occur in the central equatorial pacific this unique warming in the central equatorial pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly ssta on both sides along the equator empirical orthogonal function eof analysis of monthly tropical pacific ssta shows that these events are represented by the second mode that explains 12 of the variance since a majority of such events are not part of el nino evolution the phenomenon is named as el nino modoki pseudo el nino modoki is a classical japanese word which means a similar but different thing the el nino modoki involves ocean atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution analogous to the southern oscillation in the case of el nino hence the total entity is named as el nino southern oscillation enso modoki the enso modoki events significantly influence the temperature and precipitation over many parts of the globe depending on the season the impacts over regions such as the far east including japan new zealand western coast of united states etc are opposite to those of the conventional enso the difference maps between the two periods of 1979 2004 and 1958 1978 for various oceanic atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline this appears to be a cause of more frequent and persistent occurrence of the enso modoki event during recent decades

oscillating relationship between the east asian winter monsoon and enso abstractthis work investigates the interdecadal variations of the relationship between the el nino southern oscillation enso and the east asian winter monsoon eawm further explores possible mechanisms and finally considers a recent switch in the enso eawm relationship the 23 yr sliding correlation between the nino 3 4 index and the eawm index reveals an obvious low frequency oscillation with a period of about 50 yr in the enso eawm relationship warm enso events during high correlation periods are associated with an unusually weak east asian trough a positive phase of the north pacific oscillation npo significant southerly wind anomalies along coastal east asia and warmer east asian continent and adjacent oceans however there are no robust and significant anomalies in the eawm related circulation during low correlation periods because of the southeastward shift of the walker circulation the area of anomalously high pressure in the western pacific retreats south of 25 n confining it to the

interannual variability of the east asian winter monsoon and related modulations of the planetary waves abstractinterannual variability of the east asian winter monsoon is investigated through composite analysis applied to observational data for 50 recent years although the monsoon activity itself is confined into the lower troposphere its midwinter variability tends to accompany upper tropospheric geopotential height anomalies similar to the eurasian eu and western pacific wp teleconnection patterns the eu like pattern is characterized by a wavy signature over the eurasian continent and the north atlantic with surface temperature anomalies over the far east and north america in the wp like pattern a meridional dipole of upper level height anomalies is evident over the far east these anomaly patterns related to the anomalous winter monsoon activity are found to accompany marked modulations of the climatological development of the upper tropospheric planetary waves from late autumn to midwinter enhanced monsoon activity in january associated with the wp like pattern involves anomalous seasonal

concurrent variation between the east asian subtropical jet and polar front jet during persistent snowstorm period in 2008 winter over southern china 1 the concurrent variation features between the east asian subtropical jet and polar front jet were investigated during persistent snowstorm period in 2007 2008 winter over southern china the east asian subtropical jet was divided into two parts 1 the plateau jet located along the southern side of the tibetan plateau and 2 the ocean jet situated at the southeastern japan island the concurrent intensity variation among the polar front jet plateau jet and ocean jet and the associated atmospheric anomalous signals were examined a possible mechanism for concurrent variation among the three jets was also investigated from a perspective of synoptic scale transient eddy activities stea the enhanced plateau jet was simultaneously correlated with the weakened polar front jet while the variation of the ocean jet lagged the variation of the plateau jet polar front jet about 5 days the concurrent variation between the plateau jet and the polar front jet acted as an important bridge that linked the snowstorm to the atmospheric anomalous signals associated with the cold and warm air activities due to the opposite trends of stea variation over the southern and northern sides of the tibetan plateau the plateau jet and the polar front jet exhibited a significant concurrent variation feature the stea anomalies over the plateau jet and polar front jet regions propagated downstream to the east asian coast as a wave train along the southern and northern sides of the tibetan plateau respectively resulting in a 5 day lag variation relationship between the ocean jet and the plateau jet polar front jet

influence of the east asian winter monsoon on the storm track activity over the north pacific 1 we investigate the relationship between the east asian winter monsoon eawm and synoptic eddy activity over the north pacific ocean it is well known that the subtropical pacific jet becomes stronger during strong monsoon periods than during weak monsoons the storm track is generally expected to be active when the eawm is strong owing to the enhanced subtropical jet contrary to this expectation synoptic eddy activity is significantly reduced in strong eawm years and conversely significantly increased during weak years in addition we found that eawm induced lower level cooling brings about the reverse relationship a stronger jet but with weaker storm activities it is suggested that the local baroclinicity induced by the eawm modulates the variation of both the jet and north pacific storm track simultaneously in the interannual time scale because major lower level cooling is located in the western parts of both the subtropical jet and the storm track in longitudes and between the two central axes in latitudes it induces the opposite sign of anomalous local baroclinicity at the two active regions and causes this reverse relationship the wave seeding from east asia to the north pacific storm track is weakened owing to the anomalous lower level cooling in the northwestern pacific which also results in reduction of eddy generation and storm track activities

a dynamical index for the east asian winter monsoon abstract a new index measuring the east asian winter monsoon is defined using the mean wind shears of upper tropospheric zonal wind based on the belief that the physical processes of both higher and lower latitudes and at both lower and upper troposphere should be considered to depict the variability of monsoon when the index is high low the westerly jet is strong weak the east asian trough is deep shallow the siberian high is strong weak and anomalous low level northerlies southerlies prevail over east asia as a result the surface and lower tropospheric temperature over east asia decreases increases and the cold surges over southeast asia and tropical western pacific are more less active the index which exhibits distinct interannual variations is also strongly correlated with the arctic oscillation and nino 3 4 sea surface temperature sst index compared to previous indexes this index takes into account more influencing factors and better elucidates the physical processes ass

the shape propagation and mean flow interaction of large scale weather systems abstract for a zonal average operator the eliassen palm flux provides a diagnostic of both eddy behavior and the feedback of the eddies onto the mean flow this paper addresses the diagnosis problem for other averaging operators and in particular for time averaging which has proved in recent years such a powerful means of viewing the three dimensional tropospheric flow the horizontal velocity correlation tensor gives a measure of the characteristic horizontal eddy shape at a point it also implies the direction of the group velocity relative to the mean flow in cases where such a concept is valid however the major emphasis here is on the mean flow feedback of eddies in this respect the eddy vorticity flux is determined by derivatives of the components of the anisotropic part of the tensor making a reasonable approximation allows the eddy vorticity flux convergence to be written in terms of e v 2 u 2 u v a simple interpretation of the mean flow feedback of eddies is then possible a sligh

key controls on the seasonal and interannual variations of the carbonate system and air sea co2 flux in the northeast atlantic bay of biscay 1 biogeochemical variations of surface water in the northeast atlantic bay of biscay were examined using high frequency underway measurements combined with monthly sampling of carbon related variables the mechanisms controlling seasonal co2 variability were investigated by distinguishing the contributions of biological and physical processes to the monthly changes in dissolved inorganic carbon dic and partial pressure of co2 pco2 the seasonality of dic 47 81 mol kg 1 had a single peak with a winter maximum primarily driven by vertical mixing and a summer minimum driven by spring biological removal non redfield c n uptake was observed in the nutrient depleted summer but not during the spring bloom in the north atlantic pco2 seasonality shows a latitudinal transition from the temperature dominated oligotrophic subtropical gyre to the subpolar region where pco2 is dominated by changing concentrations of dic in the midlatitude bay of biscay the annual cycle of pco2 61 75 atm showed a double peak distribution the summer pco2 peak was mainly driven by temperature increase while the winter peak resulted from the dominant effect of entrainment of subsurface water interannual variations of dic were more pronounced in winter and were driven by the changes in the strength of winter mixing higher wintertime concentrations and seasonal amplitudes of dic were observed in cold years when the mixed layer depths were deeper which appears to be associated with negative phases of the north atlantic oscillation the bay of biscay shows a decrease of co2 uptake in 2008 2010 0 97 and 0 75 mol m 2 yr 1 compared to 2002 2004 1 47 and 1 68 mol m 2 yr 1

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

assessment of sharp interface approach for saltwater intrusion prediction in an unconfined coastal aquifer exposed to pumping water over exploitation becomes a common problem in coastal aquifers as it disarranges the dynamic equilibrium of saltwater and freshwater and causes saltwater intrusion swi mathematical simulations become a necessary tool nowadays to predict swi under future pumping scenarios this study aims to assess the validity of sharp interface approach for an unconfined coastal aquifer subjected to pumping by comparison with sand tank observation and dispersive approach results the comparison was in terms of 1 transient movement of saltwater toward the well screen and 2 prediction of well salinity in times the sharp interface approach produced acceptable results although it over predicted the toe position of saltwater wedge salinity of extracted water was less predicted by sharp interface modeling the sharp interface approach was then applied for a synthetic field scale unconfined aquifer in steady condition with different pumping rates and well placements to explore the sensitivity of the modeling the results were compared with salinity contours of dispersive modeling the sharp interface approach produced better result for higher pumping rates where the saltwater was reached to the well screen additionally the results of fully penetrating wells compare to partially penetrating one and also closer location of well to shoreline matched better with the dispersive modeling outputs in real cases where the saltwater may wend a long distance toward the well screen the sharp interface modeling weakly matched with the dispersive modeling specially in terms of well salinities that is attributed to wider mixing zone

the effect of boreal late autumn snow cover over western and central china on the northern hemisphere wintertime blocking frequency abstractthe impact of snow cover in western and central china during late autumn on wintertime blocking occurrence is investigated using reanalysis data the study results show that wintertime atmospheric circulations affected by late autumn snow cover anomalies form favorable conditions for increased blocking frequency bf especially in the north pacific and north atlantic evidence is also presented that the stratosphere troposphere interactions are the key mechanism of the lag response of wintertime north pacific and north atlantic bfs to the late autumn snow cover that is positive anomalous snow cover can induce a dipole anomaly in the geopotential height field over the lower stratosphere due to the decrease of the 300 1000 hpa thickness and the concurrent variation between the east asian plateau jet and the polar front jet the associated positive geopotential height anomalies are located over northwestern eurasia meanwhile western and central china features remarkably negative geopotential he

on the existence of storm tracks abstract given that middle latitude weather systems transport heat in a manner such as to weaken the baroclinicity that is thought to be crucial to their growth it is perhaps surprising that concentrated regions of such eddy activity i e storm tracks are found in the northern hemisphere winter the existence and possible self maintenance of storm tracks is investigated using a linear stationary wave model with storm track region forcings taken from data averaged over a number of winters it is found that the direct thermal effect of the eddies does indeed act against the existence of the storm track their vorticity fluxes lead to some reduction of this effect it is argued that the mean diabatic heating in the storm track region is an indirect eddy effect this heating is found to maintain the mean maximum in baroclinicity in the region further the mean low level flow induced by the eddy effects is such as to enhance the warm western oceanic boundary currents that are crucial to the existence of t

seasonal variations of the synoptic scale transient eddy activity and polar front jet over east asia abstract seasonal variations of the synoptic scale transient eddy activity stea and the jet streams over east asia are examined through analysis of the 40 yr european centre for medium range weather forecasts ecmwf re analysis era 40 data extracted from the 6 hourly upper level wind fields the distribution of the jet core numbers exhibits a distinct geographical border for the east asian subtropical jet easj and the east asian polar front jet eapj at the latitudes of the northern tibetan plateau tp in the cool seasons two branches of the stea and low level baroclinicity exist over the east asian landmass accompanied by the two jet state of the easj and eapj in the warm seasons a single jet pattern of the easj along the north flank of the tp is accompanied by the weakened stea over the mid to high latitudes of east asia further analysis shows two distinct features of the seasonal variations of the stea over east asia compared with that over the north pacific first during the transit

seasonal evolution of the upper tropospheric westerly jet core over east asia the location change of the westerly jet core at upper troposphere in june and july is investigated by using the ncep ncar reanalysis data the results show that the location of the westerly jet core changes rapidly from 140 e to 90 e during 35th 39th pentads which corresponds to the plum rain period over east asia the location change of the jet core is actually the relative intensity change of the different westerly jet centers the meridional temperature contrast in the troposphere is associated with the rapid location change of the jet core the diabatic heating changes are the primary factor determining the seasonal evolution of the westerly jet core over east asia

concurrent variations in the location and intensity of the asian winter jet streams and the possible mechanism this study investigates the concurrent variations in the location and intensity of the east asian subtropical jet easj and polar front jet eapj with a focus on the relationship between the variations and the atmospheric circulation in the mid latitude region the possible mechanisms for the concurrent variations of the easj and eapj are explored the wintertime upper level zonal wind variation over the landmass 50 100 e is characterized by two principal modes i e the out of phase variations in the intensity and the meridional displacements of the easj eapj the easj and eapj are intensified weakened when they are located close to far away from each other corresponding to a weakened intensified east asian trough over the northern pacific region and a decreased increased geopotential height in the mid latitude over central asia the spatial pattern of 500 hpa geopotential height anomaly is similar to the eurasian teleconnection pattern while the pattern of sea level pressure anomaly shows a feature similar to the arctic oscillation analyses of related thermal dynamical processes indicate that the increased decreased diabatic heating and horizontal heat transport lead to a larger smaller meridional temperature gradient over the easj eapj regions which subsequently intensifies weakens the east asian jets severe weak convective activities accompanied with warmer colder sst in the tropics also contribute to the intensification weakening of the easj and eapj dynamically the strong weak divergence of the eddy vorticity flux along the northern tibetan plateau and that of the eliassen palm flux of the synoptic scale stationary waves are favorable for the intensification weakening of zonal winds through the wave mean flow interactions as a result the easj and eapj are intensified weakened

eddy zonal flow feedback in the northern hemisphere winter abstract the variability of the zonal mean zonal wind in the northern hemisphere winter december march is studied using eof analysis and momentum budget diagnostics of ncep ncar reanalysis data 1976 2001 the leading eof of the zonal mean zonal wind is well separated from the remaining eofs and represents the north south movement of the midlatitude westerlies analysis of the momentum budget shows that a positive feedback between the zonal mean wind anomalies and the eddy momentum fluxes selects the leading eof of midlatitude variability like the southern hemisphere the baroclinic eddies reinforce the zonal wind anomalies while external rossby waves damp the wind anomalies in the northern hemisphere the quasi stationary eddies also reinforce the zonal wind anomalies but the baroclinic eddies are most important for the positive eddy zonal flow feedback the observations support the following feedback mechanisms 1 above normal baroclinic wave activity is generated in the region of enhanced wester

experimental and numerical investigation of saltwater intrusion dynamics in flux controlled groundwater systems 1 sea level rise and reduction of groundwater fluxes due to changes in rainfall patterns are the two major climate change induced hydrological variables that can severely affect saltwater intrusion in coastal aquifers in this study we use a combination of laboratory experiments and numerical simulations to study the impacts of changes in one of these climate change induced hydrological variables groundwater flux on saltwater intrusion process we have completed experiments in a laboratory scale model to study the changes in two types of groundwater fluxes areal recharge flux and regional flux the experimental results were modeled using the numerical code seawat the transient data sets reported in this study are useful benchmarks for testing numerical models that employ flux type boundary conditions also based on the experimental observations we hypothesize that when the fluxes are perturbed it would require relatively less time for a salt wedge to recede from an aquifer when compared to the time required to advance into the aquifer this rather counterintuitive hypothesis implies that saltwater intrusion and receding processes are asymmetric and the timescales associated with these processes will be different we use a combination of laboratory and numerical experiments to test this hypothesis and use the resulting data set to explain the reason for the difference in intrusion rates