a spectrum analysis of synoptic scale disturbances in the itcz abstract spectral characteristics of convective signals in synoptic scale disturbances along the intertropical convergence zone itcz are examined using a 20 yr daily outgoing longwave radiation dataset a new analysis method which combines conventional wavenumber frequency spectrum analysis and wavelet analysis is developed to explore the longitudinal seasonal and interannual variations in these disturbances within the itcz whose seasonal migration varies in different parts of the tropics the analysis focuses on three longitudinal sectors where the itcz can be clearly identified the western central pacific the central eastern pacific and the atlantic west africa the most striking results are the evident zonal variability in the spectral properties of westward propagating synoptic scale disturbances the zonal variability exists not only in their dominant frequencies and zonal wavenumbers but also in their seasonal and interannual variations eastward propagating synoptic scale disturbances in

tropical sst forcing on the anomalous wnp subtropical high during july august 2010 and the record high sst in the tropical atlantic in summer of 2010 the western north pacific subtropical high wnpsh was extremely strong and exhibited unusual westward extension which resulted in record breaking warmth in japan and considerably below normal and westward shifted tropical cyclone activity in the western north pacific wnp although a moderate la nina occurred the sea surface temperature sst in the northern indian ocean nio and tropical atlantic ta was considerably high in this study we argued that the la nina cold sst alone was not sufficient to maintain the strong wnpsh of 2010 and that the unusually warm ssts in the nio and ta markedly contributed to the enhancement and westward shift of the wnpsh in the boreal summer of that year we focused on the effects of sea surface temperature anomalies in the tropical atlantic ta sstas which have been seldom explored and are poorly understood compared with the effects of sstas in the tropical pacific and nio the warm ta sst forced a westward extending overturning circulation with a sinking branch over the central pacific ocean which produced a remote response similar to the la nina condition and enhanced the wnpsh the warm ta sst also induced the cyclonic anomaly in the tropical eastern north pacific a distinct phenomenon not observed in a canonical la nina event furthermore we demonstrated that the anomalous near surface circulation associated with the negative north atlantic oscillation might play a more dominant role than that of the 2009 el nino in inducing the record high sst in the ta in 2010

a numerical simulation of the variability in the tropical atlantic ocean 1980 88 abstract the authors have examined a numerical simulation of the tropical atlantic ocean circulation forced by the european centre for medium range weather forecasts ecmwf surface wind stress during 1980 88 the mean state and annual cycle of the ocean are realistically simulated by the model the simulated interannual variability of sea surface temperature sst is also remarkably consistent with the observations particularly the observed patterns of the basinwide warm cold periods and the variation of dipole pattern and the associated meridional sst gradient discrepancies between observed and simulated sst anomalies are large early in the simulation which seems caused by errors in the ecmwf wind analysis during that period the low frequency fluctuations of the meridional sst gradient associated with the dipole pattern during 1980 88 were caused by opposite sst anomalies between hemispheres forced by out of phase fluctuations of the trade winds specifically the southeast trade winds were anomalo

delineation of saltwater intrusion zones using the time domain electromagnetic method the nabeul hammamet coastal aquifer case study ne tunisia the time domain electromagnetic method tdem is applied to monitor to delineate and to map the saltwater intrusion zones in the mediterranean plio quaternary aquifer forty two tdem soundings were carried out in the coastal plain of nabeul hammamet region ne tunisia tdem resistivity data were correlated with the existing borehole logging data to assign them to a particular lithology and to provide information about the position of the freshwater seawater transition zone the geoelectric sections showing the vertical configuration of seawater intrusion with the brackish salty saturated zones have a resistivity ranging from 0 1 to 5 m and are detected at a depth lower than 1 5 m the salinized zones are located at nabeul sidi moussa sidi el mahrsi al gasba and mrazgua and at hammamet touristic zone of hammamet north and south baraket essahel and reached a distance of 4 km from the coastline indicating a severe state for the aquifer in these zones these tdem results are confirmed by the increase of chloride concentration content in the analysed water samples of monitoring wells moreover in the northeastern part the presence of a saltwater front located far from the coast and along the nw se major surface fault can be explained by two hypothesis i this fault seems to provide a conduit for seawater to move readily towards the water wells and ii the clay and gypsum infiltration of marine messinian deposits through the fault plane leads to low resistivities finally it comes out from this study that tdem survey has successfully depicted salinized zones of this coastal aquifer copyright 2012 john wiley sons ltd

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

frequency response properties of forced climatic sst anomaly variability in the north atlantic abstract frequency response properties of north atlantic 5 57 n sea surface temperature anomaly tsa variability with periods of several months to 20 years are characterized using the comprehensive ocean atmosphere data set coads significant direct forcing of tsa variability by the anomalous wind field primarily through the resulting anomalous surface turbulent heat flux is observed in the westerly wind and trade wind belts to characterize properties of the large scale climatic tsa response to this forcing over the entire frequency band resolved it is necessary to consider the dual role of anomalous surface heat flux as both the dominant local forcing mechanism and the dominant damping mechanism the latter through a negative linear feedback newtonian relaxation at frequencies where wind forcing is important good agreement exists between the frequency response function estimated from data and the same function theoretically predicted by a simple stochastic forcing model where the locally fo

the inversion of time domain airborne electromagnetic data using the plate model airborne electromagnetic em methods were developed in the early 1950s mostly by canadian mining exploration companies as a means of economically carrying out prospecting for sulfide deposits associated with volcanics in resistive shield areas present interpretation techniques are based on the use of nomograms but the approach is easily amenable to digital processing for highly accurate interpretation however it is necessary to develop quantitative interpretation techniques that can make full use of all the data available inverse theory has been used for interpretation with great success in most geophysical disciplines however in airborne em surveying inversion has only been used for the interpretation of airborne em data using half space and one layer models by introducing some approximations to the rectangular thin plate model it is now possible to apply inverse theory to the interpretation of time domain em data this approach provides estimates of the parameter errors the correlation matr

teleconnections of the southern oscillation in the tropical atlantic sector in the osu coupled upper ocean atmosphere gcm abstract the oregon state university coupled upper ocean atmosphere gcm has been shown to qualitatively simulate the southern oscillation a composite analysis of the warm and cold events simulated in this 23 year integration has been performed during the low phase of the southern oscillation when warm anomalies occur in the eastern pacific the model simulates for the atlantic region during march may 1 a deficit of precipitation over the tropical south american continent 2 caribbean and gulf of mexico sea level pressure and sea surface temperature are in phase with the eastern pacific anomalies while those east of the nordeste region are out of phase and 3 northeast trade winds are anomalously weak and southwest trade winds are anomalously strong as inferred from surface current anomalies the anomalies in the oceanic processes are induced by perturbations in the atmospheric circulation over the atlantic and are coupled to changes in the walker circulation during the high phase of the simulate

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

dynamics of the shallow meridional circulation around intertropical convergence zones the generally accepted view of the meridional circulation in the tropical east pacific is that of a single deep overturning cell driven by deep convective heating in the intertropical convergence zone itcz similar to the zonal mean hadley circulation however recent observations of the atmosphere from the tropical eastern pacific have called this view into question in several independent datasets significant meridional return flows out of the itcz region were observed not only at high altitudes but also at low altitudes just above the atmospheric boundary layer this paper presents a theory and idealized simulations to understand the causes and dynamics of this shallow meridional circulation smc fundamentally the smc can be seen as a large scale sea breeze circulation driven by sea surface temperature gradients when deep convection is absent in the itcz region a simple model of this circulation is presented using observed values the sea breeze model shows that the pressure gradient above the boundary can indeed reverse leading to the pressure force that drives the shallow return flow out of the itcz the weather research and forecast model wrf is used to simulate an idealized hadley circulation driven by moist convection in a tropical channel the smc is reproduced with reasonable similarity to the circulation observed in the east pacific the simulations confirm that the smc is driven by a reversal of the pressure gradient above the boundary layer and that the return flow is strongest when deep convection is absent in the itcz and weakest when deep convection is active the model also shows that moisture transport out of the itcz region is far greater in the low level shallow return flow than in the high altitude return flow associated with the deep overturning and that a budget for water transport in and out of the itcz region is grossly incomplete without it much of the moisture carried in the shallow return flow is recycled into the boundary layer but does not appear to contribute to enhanced cloudiness in the subtropical stratocumulus poleward of the itcz

atlantic seasonal hurricane frequency part i el nino and 30 mb quasi biennial oscillation influences abstract this is the first of two papers on atlantic seasonal hurricane frequency in this paper seasonal hurricane frequency as related to e1 nino events during 1900 82 and to the equatorial quasi biennial oscillation qbo of stratospheric zonal wind from 1950 to 1982 is discussed it is shown that a substantial negative correlation is typically present between the seasonal number of hurricanes hurricane days and tropical storms and moderate or strong 15 cases el nin off the south american west coast a similar negative anomaly in hurricane activity occurs when equatorial winds at 30 mb are from an easterly direction and or are becoming more easterly with time during the hurricane season this association of atlantic hurricane activity with el nino can also be made with the southern oscillation index by contrast seasonal hurricane frequency is slightly above normal in non el nino years and substantially above normal when equatorial stratospheric winds blow from a westerly direction and or are bec

interdecadal change in the south china sea summer monsoon withdrawal around the mid 2000s in this study a significant interdecadal change in the south china sea scs summer monsoon scssm withdrawal which occurred around the mid 2000s is revealed using ncep doe reanalysis cmap rainfall and olr data the withdrawal of the scssm occurred much later about 2 weeks after the mid 2000s the westerlies and rainfall are stronger around the scs during the period after the mid 2000s compared to those that occurred before the mid 2000s which is consistent with the delayed scssm withdrawal the robust and significant increases in rainfall and convection around the scs and philippine sea are dynamically associated with the appearance of an anomalous low level cyclone around the northern scs and the anomalous westerlies at approximately 10 n extend eastward from the indo china peninsula to the western north pacific wnp anomalous mid level ascending motion and upper level divergence were also observed around the philippine sea together with anomalous descending motion and upper level convergence over the equatorial eastern indian ocean correspondingly an anomalous zonal circulation formed between the wnp upward motion and eastern indian ocean downward motion further analysis indicates that the increasing number and frequent visits to the scs by the tropical cyclones and enhanced quasi biweekly oscillation activities may both contribute to the delayed scssm withdrawal around the mid 2000s

the poleward shift of south atlantic convergence zone in recent decades during austral summer december january february or djf intense precipitation over central eastern brazil is modulated by the south american monsoon system and the south atlantic convergence zone sacz previous studies identified spatial variability in precipitation trends over this region suggestive of a poleward shift of the sacz in recent years to identify underlying mechanisms associated with changes in the precipitation intensity and position of the sacz decadal averages of observed precipitation and the mean state of the atmosphere and ocean during three different periods from 1979 to 2014 are compared results show evidence of decreasing increasing average daily precipitation along the equatorward poleward margin of the climatological sacz likely related to a poleward shift of the convergence zone precipitation reduction along the equatorward margin of the sacz is associated with weakening of the poleward winds along the eastern brazilian coast and drying of low to mid troposphere 700 hpa over the tropical atlantic these changes in circulation and moisture are likely related to the poleward expansion of the south atlantic subtropical high

interannual and interdecadal variations of the east asian summer monsoon and tropical pacific ssts part i roles of the subtropical ridge the interannual relationship between the east asian summer monsoon and the tropical pacific ssts is studied using rainfall data in the yangtze river valley and the ncep reanalysis for 1951 96 the datasets are also partitioned into two periods 1951 77 and 1978 96 to study the interdecadal variations of this relationship a wet summer monsoon is preceded by a warm equatorial eastern pacific in the previous winter and followed by a cold equatorial eastern pacific in the following fall this relationship involves primarily the rainfall during the pre mei yu mei yu season may june but not the post mei yu season july august in a wet monsoon year the western north pacific subtropical ridge is stronger as a result of positive feedback that involves the anomalous hadley and walker circulations an atmospheric rossby wave response to the western pacific complementary cooling and the evaporation wind feedback this ridge extends farther to the west from the previous winter to the following fall resulting in an 850 hpa anomalous anticyclone near the southeast coast of china this anticyclone 1 blocks the pre mei yu and mei yu fronts from moving southward thereby extending the time that the fronts produce stationary rainfall 2 enhances the pressure gradient to its northwest resulting in a more intense front and 3 induces anomalous warming of the south china sea surface through increased downwelling which leads to a higher moisture supply to the rain area a positive feedback from the strong monsoon rainfall also appears to occur leading to an intensified anomalous anticyclone near the monsoon region this sst subtropical ridge monsoon rainfall relationship is observed in both the interannual timescale within each interdecadal period and in the interdecadal scale the sst anomalies sstas change sign in northern spring and resemble a tropospheric biennial oscillation tbo pattern during the first interdecadal period 1951 77 in the second interdecadal period 1978 96 the sign change occurs in northern fall and the tbo pattern in the equatorial eastern pacific sst is replaced by longer timescales this interdecadal variation of the monsoon sst relationship results from the interdecadal change of the background state of the coupled ocean atmosphere system this difference gives rise to the different degrees of importance of the feedback from the anomalous circulations near the monsoon region to the equatorial eastern pacific in a wet monsoon year the anomalous easterly winds south of the monsoon enhanced anomalous anticyclone start to propagate slowly eastward toward the eastern pacific in may and june apparently as a result of an atmosphere ocean coupled wave motion these anomalous easterlies carry with them a cooling effect on the ocean surface in 1951 77 this effect is insignificant as the equatorial eastern pacific sstas already change from warm to cold in northern spring probably as a result of negative feedback processes discussed in enso mechanisms in 1978 96 the equatorial eastern pacific has a warmer mean sst a stronger positive feedback between ssta and the walker circulation during a warm phase tends to keep the ssta warm until northern fall when the eastward propagating anomalous easterly winds reach the eastern pacific and reverse the ssta

shallow meridional circulations in the tropical atmosphere abstract a shallow meridional circulation smc in the tropical atmosphere features a low level e g 700 hpa flow that is in the opposite direction to the boundary layer monsoon or trade wind flow and is distinct from the meridional flow above representations of the smc in three global reanalyses show both similarities and astonishing discrepancies while the smc over west africa appears to be the strongest it also exists over the eastern atlantic and eastern pacific oceans and over the indian subcontinent with different strength and structure all smcs undergo marked seasonal cycles the smcs are summarized into two types one associated with the marine itcz and the other with the summer monsoon the large scale conditions for these two types of smcs are similar a strong meridional gradient in surface pressure linked to surface temperature distributions and an absence of deep moist convection the processes responsible for these conditions are different for the two types of smcs as are their str

on the discrepancies in tropical belt expansion between reanalyses and climate models and among tropical belt width metrics abstractthe arid subtropics are situated at the edges of the tropical belt where subsidence in the hadley cells suppresses precipitation any meridional shift in these edge latitudes could have significant impacts on surface climate recent studies have investigated past and future changes in the tropical belt width and have found discrepancies in the rates of expansion estimated with different metrics and between climate models and reanalyses here cmip5 simulations and four modern reanalyses are analyzed using an ensemble of objective tropical belt width metrics to reexamine if such inconsistencies exist the authors do not find sufficient evidence to demonstrate this discrepancy between models and reanalyses as reanalysis trends in the tropical belt width fall within the range of model trends for any given metric furthermore only metrics based on the hadley cells are found to exhibit robust historical and future expansion metrics based on the subtropical jet and the tropopause show no robust resp

the global monsoon as seen through the divergent atmospheric circulation a comprehensive description is given of the global monsoon as seen through the large scale overturning in the atmosphere that changes with the seasons and it provides a basis for delimiting the monsoon regions of the world the analysis focuses on the mean annual cycle of the divergent winds and associated vertical motions as given by the monthly mean fields for 1979 93 reanalyses from the national centers for environmental prediction national center for atmospheric research ncep ncar and european centre for medium range weather forecasts ecmwf which are able to reproduce the dominant modes a complex empirical orthogonal function analysis of the divergent circulation brings out two dominant modes with essentially the same vertical structures in all months of the year the first mode which depicts the global monsoon has a simple vertical structure with a maximum in vertical motion at about 400 mb divergence in the upper troposphere that is strongest at 150 mb and decays to zero amplitude above 70 mb and convergence in the lower troposphere with a maximum at 925 mb ecmwf or 850 mb ncep however this mode has a rich three dimensional spatial structure that evolves with the seasons it accounts for 60 of the annual cycle variance of the divergent mass circulation and dominates the hadley circulation as well as three overturning transverse cells these include the pacific walker circulation an americas atlantic walker circulation both of which comprise rising motion in the west and sinking in the east and a transverse cell over asia the middle east north africa and the indian ocean that has rising motion in the east and sinking toward the west these exist year round but migrate and evolve considerably with the seasons and have about a third to half of the mass flux of the peak hadley cell the annual cycle of the two hadley cells reveals peak strength in early february and early august in both reanalyses a second monsoon mode which accounts for 20 of the variance features relatively shallow but vigorous overturning with the maximum vertical velocities near 800 mb outflow from 750 to 350 mb and inflow peaking at 925 mb it is especially strong over africa where the shallow mostly meridional overturning migrates back and forth across the equator with the seasons it influences the middle east has a signature over australia and is also an important component of the overturning in the tropical eastern pacific and atlantic and thus of the convergence zones in these regions the relationship of the global monsoon to the regional monsoons is described over six zonal sectors africa australia asia north america south america and the pacific and atlantic oceans only the two ocean areas do not undergo a seasonal reversal required for monsoons although they have direct overturning cells and they nevertheless participate in the global monsoon through the changes in large scale overturning the regional meridional cross sections highlight the importance of the shallow overturning cell in lower troposphere monsoon activity the steadiness of the overturning circulation is determined by comparing the signal of the seasonal mean vertical motions at 500 mb with the standard deviation of the transient daily variations locations where this signal exceeds 60 of the daily noise correspond closely with the regional centers of the monsoon

damped least squares inversion of time domain airborne em data based on singular value decomposition1 airborne electromagnetic aem methods are increasingly being used as tools of geological mapping groundwater exploration and prospecting for coal and lignite in such applications quantitative interpretation is commonly based on the layered earth model a new approach a damped least squares inversion with singular value decomposition is proposed for interpretation of time domain towed bird aem data studies using theoretical and field aem data indicate that inversion techniques are dependable and provide fast converging solutions an analysis has been made of the accuracy of model parameter determination which depends on resistivity and thickness distribution in the common case of conductive overburden upper layer resistivity and thickness are usually well determined although situations exist where their separation becomes difficult in the case of a resistive layer overlying a conductive basement the layer thickness is the best determined parameter in both cases estimates of basement resistivity are the least reliable field data obtained with the chinese made m l aem system in dongling anhui province china were processed using the described inversion algorithm the survey area comprised fluvial cenozoic clays and weathered mesozoic sediments inversion of aem data resulted in accurate depth to bedrock sections and realistic estimates of the resistivities of overburden and bedrock which agree with the results of drilling and resistivity sounding

phase speed spectra and the recent poleward shift of southern hemisphere surface westerlies 1 the poleward shift of the southern hemisphere surface westerlies in recent decades is examined in reanalysis data and in the output of coupled atmosphere ocean and uncoupled atmospheric models the space time spectra of the eddy momentum fluxes in the upper troposphere reveal a trend that marks an increase in the eastward phase speed of the tropospheric eddies accompanied by a poleward displacement of the region of wave breaking in the subtropics a dynamical mechanism is suggested that may help explain the connections among the lower stratospheric wind anomalies the increased eastward propagation of tropospheric eddies and the poleward shift of the tropospheric circulation

regional changes in the annual mean hadley circulation in recent decades previous studies suggest that the zonally averaged hadley circulation zahc has experienced a robust poleward expansion and its trend in intensity displays inconsistency among different data sets this study examines changes in regional hc intensity and poleward edge using six reanalyses outgoing longwave radiation and precipitation data sets hcs in six regions including africa afhc the indian ocean iohc the western pacific wphc the eastern pacific ephc south america sahc and the atlantic athc are investigated intensity trends in the northern hemisphere nh wphc and athc and the southern hemisphere sh ephc and athc are in agreement with each other in the six reanalyses furthermore regional hcs in these domains appear to be intensifying although not all of the reanalyses show statistically significant trends for the poleward edge its trend in the nh afhc iohc ephc sahc and athc is significantly larger than zero and the northern hc poleward edge exhibits uniform poleward migrations in these five regions in the sh only the trend in the sahc poleward edge is significantly different from zero furthermore the trend in the sh sahc poleward edge is significantly larger than those in the sh afhc iohc and athc the results indicate that the poleward migration of the southern zahc poleward edge during recent decades that has been identified by previous studies may be attributed mainly to the poleward migration of the southern sahc poleward edge further analyses suggest that changes in regional hc poleward edges could have a significant impact on regional precipitation anomalies

reconstructing the western boundary variability of the western pacific subtropical high over the past 200 years via chinese cave oxygen isotope records cave oxygen isotope 18o records have been important in characterizing asian monsoon variations on a wide range of timescales the climatic significance of the 18o proxy of the cave records and its main control factors however remain hotly debated especially with respect to annual to decadal timescales in particular while the spatial and intensity variations of the western pacific subtropical high wpsh affects the east asian monsoon remarkably on annual to decadal timescales cave records up to present do not show clear evidence of the wpsh signal here we report a new high resolution average of 1 5 months 18o record from dongshiya cave qinling mountain central china the region is highly sensitive to variations in the position of the wpsh western boundary which in turn regulates the alternation of dominant moisture sources between the proximal pacific ocean and the remote indian ocean together with another cave record near the wpsh western boundary we established a new index to reconstruct variations of the wpsh western boundary over the past 200 years our new data revealed two significant periodicities 12 and 2 7 years respectively that can be causally linked to solar and enso variances correspondingly

characteristics of low frequency sea surface temperature fluctuations in the tropical atlantic abstract sea surface temperature anomalies in the tropical atlantic ocean are reexamined to investigate an apparent low frequency oscillation that has been described as a fluctuating dipole structure with poles north and south of the equator and a node near the itcz using principal components rotated by the varimax method and simple correlations of area averaged temperatures we show that during the 1964 88 interval sst anomalies north and south of the itcz are not significantly correlated therefore the low frequency variation with an apparent decadal period observed in the sst gradient across the itcz during 1964 88 does not arise from temporally coherent and out of phase fluctuations in each hemisphere and cannot be characterized as a dipole

shallow meridional circulation in the tropical eastern pacific abstract based on four independent datasets this study presents observational evidence of a shallow meridional circulation cell in the eastern tropical pacific in this shallow meridional circulation cell the northerly cross equatorial return flow from the itcz into the southern hemisphere is found immediately above the atmospheric boundary layer in contrast to the classic concept of the hadley type deep meridional circulation whose northerly return flow resides in the upper troposphere the strength and depth of this shallow meridional circulation undergo a distinct annual cycle possible causes and climatic implications of this shallow meridional circulation are discussed

variability of boreal spring hadley circulation over the asian monsoon domain and its relationship with tropical sst the variability of boreal spring hadley circulation hc over the asian monsoon domain over the last four decades is explored the climatological distribution of the regional hc is symmetric of the equator with the ascending branch around the equator and sinking branch around the subtropics in each hemisphere the first dominant mode eof1 of the regional hc is equatorial asymmetric with the main body in the southern hemisphere sh and the ascending branch to the north of the equator this mode is mainly characterized by interannual variation and is related to el nino southern oscillation enso significant negative sea surface temperature sst anomalies are observed over the tropical indian ocean tio along with the development of la nina events however the magnitude of sst anomalies in the southern indian ocean is greater than that in the northern counterpart contributing to eof1 formation the spatial distribution of the second dominant mode eof2 is with the main body lying in the northern hemisphere nh and the ascending branch located to the south of the equator the temporal variation of this mode is connected to the warming of the tio the warming rate of the southern tio sst is faster than that in the northern counterpart resulting in the southward migration of the rising branch the above result indicates the critical role of the meridional distribution of sst on the variability of the regional hc

decadal variability of the tropical atlantic ocean surface temperature in shipboard measurements and in a global ocean atmosphere model abstract numerous analyses of relatively short 25 30 years in length time series of the observed surface temperature of the tropical atlantic ocean have indicated the possible existence of decadal timescale variability it was decided to search for such variability in 100 yr time series of sea surface temperature sst measured aboard ships and available in the recently published global ocean surface temperature atlas gosta fourier and singular spectrum analyses of the gosta sst time series averaged over 11 subregions each approximately 1 106 km2 in area show that pronounced quasi oscillatory decadal 8 20 yr and multidecadal 30 40 yr timescale variability exists in the gosta dataset over the tropical atlantic motivated by the above results sst variability was investigated in a 200 yr integration of a global model of the coupled oceanic and atmospheric general circulations developed at the geophysical fluid dynamics laboratory gfdl the second 100 yr of sst in the coupled model s tropical

recent widening of the tropical belt evidence from tropopause observations 1 radiosonde measurements and reanalysis data are used to examine long term changes in tropopause behavior in the subtropics tropopause heights in the subtropics exhibit a bimodal distribution with maxima in occurrence frequency above 15 km characteristic of the tropical tropopause and below 13 km typical of the extratropical tropopause both the radiosonde and reanalysis data show that the frequency of occurrence of high tropopause days in the subtropics of both hemispheres has systematically increased during the past few decades so that tropical characteristics occur more frequently in recent years this behavior is consistent with a widening of the tropical belt and the data indicate an expansion of about 5 8 latitude during 1979 2005

poleward shift of subtropical jets inferred from satellite observed lower stratospheric temperatures abstractone pronounced feature in observed latitudinal dependence of lower stratospheric temperature trends is the enhanced cooling near 30 latitude in both hemispheres the observed phenomenon has not to date been explained in the literature this study shows that the enhanced cooling is a direct response of the lower stratospheric temperature to the poleward shift of subtropical jets furthermore this enhanced lower stratospheric cooling can be used to quantify the poleward shift of subtropical jets using the lower stratospheric temperatures observed by satellite borne microwave sounding units it is shown that the subtropical jets have shifted poleward by 0 6 0 1 and 1 0 0 3 latitude in the southern and northern hemispheres respectively in last 30 years since 1979 indicating a widening of tropical belt by 1 6 0 4 latitude

influence of el nino on the upper ocean circulation in the tropical atlantic ocean abstract this study investigates the influence of el nino on the upper ocean circulation in the tropical atlantic ocean via changes in the atlantic trade winds by analyzing observed sea surface temperature sst together with an ocean general circulation model integration forced by the ncep ncar reanalysis during periods with anomalously warm cold eastern equatorial pacific sst the southern atlantic tropical cell is strengthened weakened the difference of the cell strength between el nino and la nina years is about 20 of the mean cell strength however the variability of the cell is not dominated by the remote forcing from the eastern equatorial pacific but seems to be caused by intrinsic tropical atlantic variability a strengthening weakening for periods with anomalously warm cold eastern equatorial pacific sst is also found for the zonal surface and subsurface currents topex poseidon altimetry data are used to validate the results based on the ogcm integration

tropical atlantic sea surface temperature variability and its relation to el nino southern oscillation past analyses of tropical atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics across the intertropical convergence zone itcz by analyzing an improved 43 year 1950 1992 record of sst smith et al 1996 and other data derived from the comprehensive ocean atmosphere data set coads it is shown that the regions north and south of the itcz are statistically independent of each other at the seasonal to interannual timescales dominating the data confirming the conclusions of houghton and tourre 1992 some dipole behavior does develop weakly during the boreal spring season when there is a tendency for sst anomaly west of angola to be opposite of that in the tropical north atlantic it is further shown that tropical atlantic sst variability is corre lated with pacific e1 nifio southern oscillation enso variability in several regions the ma jor region affected is the north atlantic area of ne trades west of 40ow along 10on 20on and extending into the caribbean there about 50 80 of the anomalous sst variability is associ ated with the pacific enso with atlantic warmings occurring 4 5 months after the mature phases of pacific warm events an analysis of local surface flux fields derived from coads data shows that the enso related atlantic warmings occur as a result of reductions in the surface ne trade wind speeds which in turn reduce latent and sensible heat losses over the region in ques tion as well as cooling due to entrainment this enso connection is best developed during the boreal spring following the most frequent season of maximum enso anomalies in the pacific a region of secondary covariability with enso occurs along the northern edge of the mean itcz position and appears to be associated with northward migrations of the itcz when the north at lantic warmings occur although easterly winds are intensified in the western equatorial atlantic in response to pacific warm events they do not produce strong local changes in sst contrary to expectations from studies based on equatorial dynamics these teleconnected wind anomalies do not give rise to significant correlations of sst in the gulf of guinea with the pacific enso as the teleconnection sequence matures strong se trades at low southern latitudes follow the de velopment of the north atlantic sst anomaly and precede by several months the appearance of weak negative sst anomalies off angola and stronger positive anomalies extending eastward from southern brazil along 15o 30os

the interplay of internal and forced modes of hadley cell expansion lessons from the global warming hiatus the poleward branches of the hadley cells and the edge of the tropics show a robust poleward shift during the satellite era leading to concerns over the possible encroachment of the globe s subtropical dry zones into currently temperate climates the extent to which this trend is caused by anthropogenic forcing versus internal variability remains the subject of considerable debate in this study we use a joint eof method to identify two distinct modes of tropical width variability 1 an anthropogenically forced mode which we identify using a 20 member simulation of the historical climate and 2 an internal mode which we identify using a 1000 year pre industrial control simulation the forced mode is found to be closely related to the top of the atmosphere radiative imbalance and exhibits a long term trend since 1860 while the internal mode is essentially indistinguishable from the el nino southern oscillation together these two modes explain an average of 70 of the interannual variability seen in model edge indices over the historical period since 1980 the superposition of forced and internal modes has resulted in a period of accelerated hadley cell expansion and decelerated global warming i e the hiatus a comparison of the change in these modes since 1980 indicates that by 2013 the signal has emerged above the noise of internal variability in the southern hemisphere but not in the northern hemisphere with the latter also exhibiting strong zonal asymmetry particularly in the north atlantic our results highlight the important interplay of internal and forced modes of tropical width change and improve our understanding of the interannual variability and long term trend seen in observations

mapping lateral changes in conductance of a thin sheet using time domain inductive electromagnetic data abstractwith the inductive electromagnetic geophysical method the laterally varying conductance of thin sheet models can be estimated either through a direct transform of the measured data or through inversion the direct transform called the simplified solution does not require grid or line data and is simple enough to be performed in the field because the conductance at a location is calculated directly from the ratio of two measured magnetic fields the vertical spatial and temporal derivative of the vertical magnetic field at that location however the simplified solution assumes that the secondary horizontal magnetic fields are zero and or that the sheet has a uniform conductance our nonapproximate solution called the full inversion does not make these assumptions but requires gridded data measurements of the secondary horizontal magnetic fields and more complicated inversion algorithms through forward modeling we found that the full inversion provides better results than the simplified

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

weakened anomalous western north pacific anticyclone during an el nino decaying summer under a warmer climate dominant role of the weakened impact of the tropical indian ocean on the atmosphere abstractthe western north pacific subtropical anticyclone wnpac is the most prominent atmospheric circulation anomaly over the subtropical northern hemisphere during the decaying summer of an el

interannual relationship between the boreal spring arctic oscillation and the northern hemisphere hadley circulation extent abstractthis study investigates the interannual relationship and the dynamical linkage between the boreal spring arctic oscillation ao and the northern hemisphere hadley circulation extent hce

enhanced relationship between the tropical atlantic sst and the summertime western north pacific subtropical high after the early 1980s the western north pacific subtropical high wnpsh in boreal summer shows a remarkable enhancement after the early 1980s whereas the sea surface temperature sst in the north indian ocean nio and the equatorial eastern pacific had been noted to have remarkable local or remote effects on enhancing the wnpsh the influence of the atlantic sst so far is hardly explored this article reports a new finding enhanced relationship between the tropical atlantic ta sst and the wnpsh after the early 1980s regression study suggests that the warm ta sst produced a zonally overturning circulation anomaly with descending over the equatorial central pacific and ascending over the tropical atlantic eastern pacific the anomalous descending over the equatorial central pacific likely induced low level anticyclonic anomaly to the west and therefore enhanced the wnpsh one implication of this new finding is for predictability the well known spring predictability barrier i e the influence of el nino southern oscillation enso falls dramatically during boreal spring does not apply to the ta sst wnpsh relationship the ta sst shows consistently high correlation starting from boreal spring when the enso influence continues declining the ta sst extends the predictability of the wnpsh in boreal summer approximately one season earlier to boreal spring

probabilistic inversion of airborne electromagnetic data for basement conductors abstractprobabilistic inversion of airborne electromagnetic data is often approximated by a layered earth using a computationally efficient 1d kernel if the underlying framework accounts for prior beliefs on spatial correlation the inversion will be able to recover spatially coherent interfaces and associated uncertainties greenfield exploration using airborne electromagnetic data however often seeks to identify discrete economical targets in mature exploration provinces such bodies are frequently obscured by thick conductive regolith and the response of such economic basement conductors presents a challenge to any layered earth inversion a well known computationally efficient way to approximate the response of a basement conductor is to use a thin plate here we have extended a bayesian parametric bootstrap approach so that the basement of a spatially varying layered earth can contain a thin plate the resulting bayesian framework allowed for the inversion of basement conductors and associated

three dimensional inversion of airborne time domain electromagnetic data with applications to a porphyry deposit we inverted airborne time domain electromagnetic atem data over a porphyry deposit in central british columbia canada and recovered the 3d electrical conductivity structure full 3d inversion was required because of the circular geometry of the deposit typical analysis which assumes a homogeneous or layered earth produces conductive artifacts that are contrary to geologic expectations a synthetic example showed that those misleading artifacts arise by assuming a 1d layered earth and that a 3d inversion can successfully solve the problem because of the computational challenges of solving the 3d inversion with many transmitters of airborne survey we introduced a work flow that uses a multimesh strategy to handle the field data in our inversion a coarse mesh and a small number of soundings are first used to rapidly reconstruct a large scale distribution of conductivity the mesh is then refined and more soundings are incorporated to better resolve small scale features this strategy significantly

three pattern decomposition of global atmospheric circulation part ii dynamical equations of horizontal meridional and zonal circulations the three pattern decomposition of global atmospheric circulation tpdgac partitions three dimensional 3d atmospheric circulation into horizontal meridional and zonal components to study the 3d structures of global atmospheric circulation this paper incorporates the three pattern decomposition model tpdm into primitive equations of atmospheric dynamics and establishes a new set of dynamical equations of the horizontal meridional and zonal circulations in which the operator properties are studied and energy conservation laws are preserved as in the primitive equations the physical significance of the newly established equations is demonstrated our findings reveal that the new equations are essentially the 3d vorticity equations of atmosphere and that the time evolution rules of the horizontal meridional and zonal circulations can be described from the perspective of 3d vorticity evolution the new set of dynamical equations includes decomposed expressions that can be used to explore the source terms of large scale atmospheric circulation variations a simplified model is presented to demonstrate the potential applications of the new equations for studying the dynamics of the rossby hadley and walker circulations the model shows that the horizontal air temperature anomaly gradient atag induces changes in meridional and zonal circulations and promotes the baroclinic evolution of the horizontal circulation the simplified model also indicates that the absolute vorticity of the horizontal circulation is not conserved and its changes can be described by changes in the vertical vorticities of the meridional and zonal circulations moreover the thermodynamic equation shows that the induced meridional and zonal circulations and advection transport by the horizontal circulation in turn cause a redistribution of the air temperature the simplified model reveals the fundamental rules between the evolution of the air temperature and the horizontal meridional and zonal components of global atmospheric circulation

a closer comparison of early and late winter atmospheric trends in the northern hemisphere abstract decadal trends are compared in various fields between northern hemisphere early winter november december nd and late winter february march fm months using reanalysis data it is found that in the extratropics and polar region the decadal trends display nearly opposite tendencies between nd and fm during the period from 1979 to 2003 dynamical trends in late winter fm reveal that the polar vortex has become stronger and much colder and wave fluxes from the troposphere to the stratosphere are weaker consistent with the positive trend of the arctic oscillation ao as found in earlier studies while trends in nd appear to resemble a trend toward the low index polarity of the ao in the tropics the hadley circulation shows significant intensification in both nd and fm with stronger intensification in fm unlike the hadley cell the ferrel cell shows opposite trends between nd and fm with weakening in nd and strengthening in fm comparison of the observational results with general circul

on the speed of the eddy driven jet and the width of the hadley cell in the southern hemisphere a strong correlation between the speed of the eddy driven jet and the width of the hadley cell is found to exist in the southern hemisphere both in reanalysis data and in twenty first century integrations from the intergovernmental panel on climate change ipcc fifth assessment report multimodel archive analysis of the space time spectra of eddy momentum flux reveals that variations in eddy driven jet speed are related to changes in the mean phase speed of midlatitude eddies an increase in eddy phase speeds induces a poleward shift of the critical latitudes and a poleward expansion of the region of subtropical wave breaking the associated changes in eddy momentum flux convergence are balanced by anomalous meridional winds consistent with a wider hadley cell at the same time faster eddies are also associated with a strengthened polewardeddymomentumflux sustainingastronger westerlyjet in midlatitudes the proposedmechanismis consistent with the seasonal dependence of the interannual variability of the hadley cell width and appears to explain at least part of the projected twenty first century trends one of the most salient features of earth s general circulation is the presence of hadley cells hcs in the tropical belts of both hemispheres associated with their large scale motions are some of the main characteristics of tropical and subtropical climates the intertropical convergence zone in the rising branch and the subtropical dry zones in the descending branches e g hartmann 1994 studying the factors determining the meridional extent of these overturning circulations is therefore essential to understand the spatial distribution of tropical and subtropical climates and its changes the role of the hcs is particularly crucial in the context of climate change and the observed widening of the atmospheric circulation observations show a poleward shift of the eddy driven jets and an expansion of the hcs in recent decades particularly in the southern hemisphere hu and fu 2007 johanson and fu 2009 lu et al 2009 and the role of radiative forcings induced by greenhouse gases and stratospheric ozone has been shown to be crucial in this context polvani et al 2011b

expansion of the hadley cell under global warming 1 a consistent weakening and poleward expansion of the hadley circulation is diagnosed in the climate change simulations of the ipcc ar4 project associated with this widening is a poleward expansion of the subtropical dry zone simple scaling analysis supports the notion that the poleward extent of the hadley cell is set by the location where the thermally driven jet first becomes baroclinically unstable the expansion of the hadley cell is caused by an increase in the subtropical static stability which pushes poleward the baroclinic instability zone and hence the outer boundary of the hadley cell

low frequency variability of the indian monsoon enso relationship and the tropical atlantic the weakening of the 1980s and 1990s abstract the indian monsoon el nino southern oscillation enso relationship according to which a drier than normal monsoon season precedes peak el nino conditions weakened significantly during the last two decades of the twentieth century in this work an ensemble of integrations of an atmospheric general circulation model agcm coupled to an ocean model in the indian basin and forced with observed sea surface temperatures ssts elsewhere is used to investigate the causes of such a weakening the observed interdecadal variability of the enso monsoon relationship during the period 1950 99 is realistically simulated by the model and a dominant portion of the variability is associated with changes in the tropical atlantic ssts in boreal summer in correspondence to enso the tropical atlantic ssts display negative anomalies south of the equator in the last quarter of the twentieth century and weakly positive anomalies in the previous period those anomalies in turn produce heating anomalies which excit

interdecadal change in the relationship between enso and the intraseasonal oscillation in east asia abstract the northward propagating intraseasonal oscillation npiso during the boreal summer is closely linked to the onset retreat and intensity of the east asian summer monsoon easm in this study interdecadal variability in the relationships between the npiso and el nino southern oscillation enso was investigated using long term outgoing longwave radiation data obtained from the 40 yr ecmwf re analysis era 40 for a 44 yr period 1958 to 2001 it was found that before the late 1970s the preceding winter enso influenced the early summer i e may to june npiso activity whereas after the late 1970s a strong relationship appeared during the later summertime i e july to august the may june npiso before the late 1970s was modulated by springtime indian ocean sea surface temperature warming and central north pacific suppressed convection anomalies and was consequently related to the enso induced west pacific wp pattern which shows a north south dipole structure over the north pacific from

climate model biases in the width of the tropical belt abstractearth s arid subtropics are situated at the edges of the tropical belt which encircles the planet along the equator and covers half of its surface area the climate of the tropical belt is strongly influenced by the hadley cells with their subsidence and easterly trade winds both sustaining the aridity at the belt s edges the understanding of earth s past present and future climates is contingent on understanding the dynamics influencing this region an important but unanswered question is how realistically climate models reproduce the mean state of the tropical belt this study augments the existing literature by examining the mean width and seasonality of the tropical belt in climate models from phase 5 of cmip cmip5 and experiments from the second phase of the chemistry climate model validation ccmval 2 activity of the stratospheric processes and their role in climate sparc project while the models overall reproduce the structure of the tropical belt width s seasonal cycle they und

relationship between enso and northward propagating intraseasonal oscillation in the east asian summer monsoon system 1 observational studies are presented on the relationship between el nino southern oscillation enso and the northward propagating intraseasonal oscillation npiso in the east asian summer monsoon easm system the summer npiso activity shows a significant correlation with the preceding winter extreme phase of enso cycles a higher correlation appears during late summer which is consistent with frequent heavy rainfall events at that time as revealed in some previous case studies the westward expansion of broad anticyclonic circulation over the western north pacific and the smaller cyclonic circulation around korea and japan are found to be associated with the npiso activity enso affects the late summer npiso activity through an atmospheric bridge and wave propagation the springtime indian ocean sea surface temperature warming induced by enso through the walker circulation leads to the downward motion and suppressed convection over the philippine sea and this generates the forced rossby wave train forming the above south to north low level circulation anomalies

remote forcing of the northern tropical atlantic sst anomalies on the western north pacific anomalous anticyclone this study uses both observations and numerical modeling experiments to investigate the lead lag relationship and the associated physical mechanism of the western north pacific anomalous anticyclone wnpac with sea surface temperature sst anomalies over the northern tropical atlantic nta the results show that the wnpac from late spring to the middle of autumn has a significant in phase relationship with the nta sst anomalies up to two seasons ahead this relationship reaches a peak when the nta sst leads by approximately 1 2 months and is nearly independent of the el nino southern oscillation variability diagnosis based on observations and numerical experiments using the community atmospheric model version 5 3 reveals that the nta warming favors intensified local convection activity during the spring autumn seasons causing enhanced low level convergence and upper level divergence i e ascending motion over the nta and opposite flow anomalies over the central tropical pacific the enhanced subsidence over the central tropical pacific in turn triggers an anomalous low level anticyclone over the western north pacific moreover the intensity of the anomalous local convection activity that is associated with the nta sst is closely related to the seasonal migration of the atlantic intertropical convergence zone itcz as the atlantic itcz migrates northward the nta sst induced local convection activity extends northward from a narrow band near the equator during early spring to nearly the entire nta region during the middle of summer leading to the strongest remote effect of the nta sst anomalies on the wnpac during late summer and early autumn

enhanced influences of tropical atlantic sst on wnp nio atmosphere ocean coupling since the early 1980s abstractthis paper reports a new finding and related mechanism the forcing effect of the tropical atlantic ta sea surface temperature sst on the atmosphere ocean coupling in the western north pacific wnp and northern indian ocean nio since the early 1980s the ta sst has increased and notably exhibited an enhanced interannual statistical relationship with the wnp subtropical high and nio sst in boreal summer empirical diagnostics reveal the following spatial pattern linking the ta sst and the atmosphere ocean coupling in the pacific and indian ocean 1 a cyclonic anticyclonic circulation pair straddling the equator over the eastern pacific 2 an anticyclonic cyclonic circulation pair straddling the equator in the wnp and indian ocean 3 overturning circulation with ascending descending and descending ascending anomalies over the ta and tropical western pacific respectively and 4 positive negative sst anomaly in the ta and nio the characteristics of this pattern are consistent

impact of the indian ocean sst basin mode on the asian summer monsoon 1 following an el nino event a basin wide warming takes place over the tropical indian ocean peaks in late boreal winter and early spring and persists through boreal summer our observational analysis suggests that this indian ocean warming induces robust climatic anomalies in the summer indo west pacific region prolonging the el nino s influence after tropical east pacific sea surface temperature has returned to normal in response to the indian ocean warming precipitation increases over most of the basin forcing a matsuno gill pattern in the upper troposphere with a strengthened south asian high near the ground the southwest monsoon intensifies over the arabian sea and weakens over the south china and philippine seas an anomalous anticyclonic circulation forms over the subtropical northwest pacific collocated with negative precipitation anomalies all these anomaly patterns are reproduced in a coupled model simulation initialized with a warming in the tropical indian ocean mixed layer indicating that the indian ocean warming is not just a passive response to el nino but important for summer climate variability in the indo west pacific region the implications for seasonal prediction are discussed

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

climatic anomalous patterns associated with the arctic and polar cell strength variations the arctic cell as a reversed and closed loop next to the polar cell has been recently revealed in the northern hemisphere nh in this paper we study the interannual variability of the arctic and polar cell strengths during 1979 2012 and their influence on surface air temperature sat precipitation and sea ice concentration sic at mid and high latitudes of the nh we show that there is a significant negative correlation between the arctic and polar cell strengths both the arctic and polar cell strengths can well indicate the recurring climatic anomalies of sat precipitation and sic in their extreme winters the surface large scale cold warm and dry wet anomalous patterns in these extreme winters are directly linked with the vertical structure of height and temperature anomalies in the troposphere results suggest that the past climatic anomalies are better indicated by the strength anomalies of the polar and arctic cells than the traditional indices of mid high latitude pattern such as the arctic oscillation and north atlantic oscillation this study illustrates a three dimensional picture of atmospheric variable anomalies in the troposphere that result in surface climatic anomalies

decadal variation of summer precipitation over china and associated atmospheric circulation after the late 1990s abstractin this study the authors found that the summer precipitation over china experienced different decadal variation features from north to south after the late 1990s in northeastern and north china and the lower middle reaches of the yangtze river precipitation decreased after 1999 while precipitation experienced a significant reduction over south and southwestern china and a significant increase over the southern parts of hetao region and huaihe river valley after 2003 the authors next analyzed the associated decadal variation of the atmospheric circulation and attempted to identify the mechanisms causing the two decadal variations of precipitation the wind anomalies for the former exhibit a barotropic meridional dipole pattern with anticyclonic anomalies over mongolia to northern china and cyclonic anomalies over the southeastern chinese coast to the northwestern pacific for the latter there is a southeast northwest oriented dipole pattern in the middle and lower troposphere with cyclonic

the early 1950s regime shift in temperature in taiwan and east asia a summer climate regime shift in temperature in taiwan and east asia during the early 1950s was identified in this study the event was characterized by a cooling land warming ocean dipole in east asia and the western north pacific marking the decreasing land sea thermal contrast from the 1940s to the 1950s the corresponding sea surface temperature sst anomaly was characterized by the sign flipping of a north south dipole in the western north pacific from north cool south warm to north warm south cool indicating a weakening north south sst gradient in the area the corresponding change in mean sea level pressure was characterized by the rising pressure in continental east asia and the philippine sea and the falling pressure over the extratropical western north pacific to the east of japan this change was the reflection of a weakening thermal low in the continental east asia a weakening monsoon trough in the tropical western north pacific a strengthening and southwestward expanding ridge in the subtropical western north pacific and a deepening mid latitude trough over eastern china and japan the phase reversal of the sst anomaly in the western north pacific exhibited the characteristics of the pacific decadal oscillation pdo but lagged behind the phase reversal of the pdo in the extratropical north pacific by several years the connection with the pdo is speculated although the mechanism is not understood

spatial patterns of atmosphere ocean interaction in the northern winter abstract the variability of monthly mean sea surface temperature sst anomalies over the extratropical north atlantic and pacific and its relation to atmospheric circulation anomalies over the northern hemisphere during wintertime is investigated by applying eigenvector analysis to a 39 year dataset and correlating the time series of the resulting expansion coefficients with the hemispheric 500 mb height and sea level pressure fields in agreement with previous studies the simultaneous correlation between the tone series of the expansion coefficient of the first empirical orthogonal function eof 1 of north pacific sea surface temperature sst and the hemispheric 500 mb height field resembles the pacific north american pattern and the corresponding pattern for atlantic sst resembles the north atlantic oscillation in the vicinity of the conters of action of thew patterns the sst fluctuations associated with these modes explain on the order of half the variance of 500 mb height and slightly less of

seasonal to multidecadal variability of the width of the tropical belt 1 an expansion of the tropical belt has been extensively reported in observations reanalyses and climate model simulations but there is a great deal of uncertainty in estimates of the rate of widening as different diagnostics give a wide range of results this study critically examines robust diagnostics for the width of the tropical belt to explore their seasonality interannual variability and multidecadal trends the width based on the latitudes of the maximum tropospheric dry bulk static stability measuring the difference in potential temperature between the tropopause and the surface is found to be closely coupled to the width based on the subtropical jet cores on all time scales in contrast the tropical belt width and northern hemisphere edge latitudes based on the latitudes at which the vertically averaged stream function vanishes a measure of the hadley circulation s poleward edges lag those of the other diagnostics by approximately 1month the tropical belt width varies by up to 10 latitude among the diagnostics with trends in the tropical belt width ranging from 0 5 to 2 0 per decade over the 1979 2012 period nevertheless in agreement with previous studies nearly all diagnostics exhibit a widening trend although the stream function diagnostic exhibits a significantly stronger widening than either the jet or dry bulk stability diagnostics finally gps radio occultation observations are used to assess the ability of the reanalyses to reproduce the tropical belt width finding that they better situate the latitudes of maximum bulk stability versus those of the subtropical jets

early summer southern china rainfall variability and its oceanic drivers rainfall in southern china reaches its annual peak in early summer may june with strong interannual variability using a combination of observational analysis and numerical modeling the present study investigates the leading modes of this variability and its dynamic drivers a zonal dipole pattern termed the southern china dipole scd is found to be the dominant feature in early summer during 1979 2014 and is closely related to a low level anomalous anticyclone over the philippine sea psac and a eurasian wave train pattern over the mid high latitudes linear regressions based on observations and numerical experiments using the cam5 model suggest that the associated atmospheric circulation anomalies in early summer are linked to decaying el nino southern oscillation like sea surface temperature sst anomalies in the tropical pacific basin scale sst anomalies in the tropical indian ocean and meridional tripole like sst anomalies in the north atlantic in the previous winter to early summer the tropical pacific and indian ocean sst anomalies primarily exert an impact on the scd through changing the polarity of the psac while the north atlantic tripole like sst anomalies mainly exert a downstream impact on the scd by inducing a eurasian wave train pattern the north atlantic tripole like sst anomalies also make a relatively weak contribution to the variations of the psac and scd through a subtropical teleconnection modeling results indicate that the three basin combined forcing has a greater impact on the scd and associated circulation anomalies than the individual influence from any single oceanic basin

trends in the local hadley and local walker circulations the linear trend in the local hadley and walker circulations from 1979 to 2009 is calculated these local circulations are defined through a decomposition of the vertical mass flux into its zonal and meridional components defining the local circulation this way ensures that the two orthogonal circulations the local hadley and walker circulations sum to the original circulation even after averaging the circulations regionally large regional differences in changes in the local hadley and walker circulations over a 31 year period are found for example the local hadley circulation has shifted southward over africa the maritime continent and the western and central pacific by about 1 over the americas and the atlantic the local hadley circulation has strengthened by about 1 5 the zonal component of the vertical mass flux has increased by about 10 20 in the tropics over all continents and decreased over the adjacent oceans by about 10 20 although the local walker circulations in the indian ocean and the atlantic have weakened the circulation in the pacific has changed little about 1 2 the local walker circulations in all ocean basins have shifted westward by about 1 2 on average