the link between the north pacific climate variability and the north atlantic oscillation via downstream propagation of synoptic waves abstractthe north atlantic oscillation nao response to the northeast pacific climate variability is examined using the era 40 dataset the main objective is to validate a mechanism involving downstream wave propagation processes proposed in a recent idealized companion study a low frequency planetary scale ridge trough anomaly located in the eastern pacific north american sector induces more equatorward poleward propagation of synoptic scale wave packets on its downstream side which favors the occurrence of anticyclonic cyclonic wave breakings in the atlantic sector and the positive negative nao phase the mechanism first provides an interpretation of the canonical impact of the el nino southern oscillation on the nao in late winter the wintertime relationship between the pacific north american oscillation pna and the nao is also investigated for out of phase fluctuations between the pna and nao indices i e the most recurrent situation in late winter the eastern pacific pna ridge trou

understanding the contrasting north atlantic oscillation anomalies of the winters of 2010 and 2014 the present study investigates the two contrasting winters of 2010 and 2014 during which the north atlantic oscillation nao was mainly negative and positive respectively in the north pacific contrasting anomalies were also present with a straight zonal pacific jet in 2010 and a strong poleward deviation of the pacific jet in its exit region in 2014 using reanalysis data sets and adopting a nonlinear initial value approach with a quasi geostrophic model we show that the pacific north american anomalies are responsible for shaping synoptic wave trains propagating across north america this in turn largely determines the nature of wave breaking and the synoptic eddy feedback onto the mean flow in the north atlantic and finally the nao phase in such a proposed mechanism synoptic wave activity forms the cornerstone of the dynamical relationship between the north pacific and north atlantic large scale anomalies during the contrasting winters of 2010 and 2014

the role of synoptic waves in the formation and maintenance of the western hemisphere circulation pattern abstractprevious studies have demonstrated that the nao the leading mode of atmospheric low frequency variability over the north atlantic could be linked to northeast pacific climate variability via the downstream propagation of synoptic waves in those studies the nao and the northeast pacific climate variability are considered as two separate modes that explain the variance over the north atlantic sector and the east pacific north american sector respectively a newly identified low frequency atmospheric regime the western hemisphere wh circulation pattern provides a unique example of a mode of variability that accounts for variance over the whole north atlantic north american north pacific sector the role of synoptic waves in the formation and maintenance of the wh pattern is investigated using the ecmwf reanalysis datasets persistent wh events are characterized by the propagation of quasi stationary rossby waves across the north pacific north american north atlantic regions and by associated s

a new perspective toward cataloging northern hemisphere rossby wave breaking on the dynamic tropopause abstractrossby wave breaking rwb events are a common feature on the dynamic tropopause and act to modulate synoptic scale jet dynamics these events are characterized on the dynamic tropopause by

dynamical evolution of north atlantic ridges and poleward jet stream displacements the development of a particular wintertime atmospheric circulation regime over the north atlantic comprising a northward shift of the north atlantic eddy driven jet stream and an associated strong and persistent ridge in the subtropics is investigated several different methods of analysis are combined to describe the temporal evolution of the events and relate it to shifts in the phase of the north atlantic oscillation and east atlantic pattern first the authors identify a close relationship between northward shifts of the eddydriven jet the establishment and maintenance of strong and persistent ridges in the subtropics and the occurrence of upper tropospheric anticyclonic rossby wave breaking over iberia clear tropospheric precursors are evident prior to the development of the regime suggesting a preconditioning of the atlantic jet stream and an upstream influence via a large scale rossby wave train from the north pacific transient 2 6 days eddy forcing plays a dual role contributing to both the initiation and then the maintenance of the circulation anomalies during the regime there is enhanced occurrence of anticyclonic rossby wave breaking which may be described as low latitude blocking like events over the southeastern north atlantic a strong ridge is already established at the time of wave breaking onset suggesting that the role of wave breaking events is to amplify the circulation anomalies rather than to initiate them wave breaking also seems to enhance the persistence since it is unlikely that a persistent ridge event occurs without being also accompanied by wave breaking

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

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

comparisons of the circulation anomalies associated with extreme heat in different regions of eastern china abstractthe circulation associated with extreme heat eh typically shows an anomalous anticyclone that enhances temperature through adiabatic heating but this study indicates obvious spatial variation in eastern china the eh related circulation pattern in eastern china can be classified into three categories typical extratropical pattern monsoonal pattern and foehn pattern eh over northeastern china and eastern north china is characterized by a typical pattern involving an anomalous anticyclone and subsidence and the air temperature increases throughout almost the entire troposphere in contrast eh over the yangtze river valley and south china is associated with the monsoonal pattern over these regions the air temperature only increases in the lower troposphere as a result of anomalous subsidence and lower humidity that has resulted from a farther north transportation of water vapor by a stronger monsoonal southwesterly meanwhile the air temperature decreases in the upper troposphere because

tropospheric rossby wave breaking and the nao nam objective analysis of several hundred thousand anticyclonic and cyclonic breaking rossby waves is performed for the northern hemisphere nh winters of 1958 2006 a winter climatology of both anticyclonic and cyclonic rossby wave breaking rwb frequency and size zonal extent is presented for the 350 k isentropic surface over the nh and the spatial distribution of rwb is shown to agree with theoretical ideas of rwb in shear flow composites of the two types of rwb reveal their characteristic sea level pressure anomalies upper and lower tropospheric velocity fields and forcing of the upper tropospheric zonal flow it is shown how these signatures project onto the centers of action and force the velocity patterns associated with the north atlantic oscillation nao and northern hemisphere annular mode nam previous studies have presented evidence that anticyclonic cyclonic breaking leads to the positive negative polarity of the nao and this relationship is confirmed for rwb over the midlatitudes centered near 50 n however an opposite and statistically significant relationship in which cyclonic rwb forces the positive nao and anticyclonic rwb forces the negative nao is shown over regions 20 to the north and south centered at 70 and 30 n respectively on a winter mean basis the frequency of rwb over objectively defined regions covering 12 of the area of the nh accounts for 95 of the nao index and 92 of the nam index a 6 hourly analysis of all the winters indicates that rwb over the objectively defined regions affects the nao nam without a time lag details of the objective wave breaking analysis method are provided in the appendix

on double rossby wave breaking in the north atlantic we discuss the dynamical features associated with double rossby wave breaking dwb concurrent cyclonic and anticyclonic breakings over the north atlantic with a focus on the north atlantic oscil

on climate model simulations of the large scale meteorology associated with california heat waves previous work considered how well the large scale meteorological patterns lsmps associated with california central valley heat waves are captured by a climate model recent work found two distinct types of lsmps and key parcel trajectories occurring prior to heat wave onset this study searches for those two types of heat waves in two additional reanalyses and in historical simulations by 14 climate models the reanalyses develop both types with similar properties their differences are used as a conservative estimate of acceptable differences between data sets all the models develop heat waves of both types but the models vary quite a bit in the separation between the two types the magnitudes of the two types and the frequency of occurrence of the two types the best models match a third to a half of the properties found in reanalyses models tend to have lower valued projections onto the two types than reanalyses consistent with a systematic tendency to center the hottest 850 hpa temperatures onshore instead of just offshore models of higher horizontal resolution tend to simulate better the two types there is some evidence that models with a low top with relatively poorly resolved stratosphere also simulate the clusters better

the north atlantic oscillation response to large scale atmospheric anomalies in the northeastern pacific abstractingredients in the north pacific flow influencing rossby wave breakings in the north atlantic and the intraseasonal variations of the north atlantic oscillation nao are investigated using both reanalysis data and a three level quasigeostrophic model on the sphere first a long term run is shown to reproduce the observed relationship between the nature of the synoptic wave breaking and the phase of the nao furthermore a large scale low frequency ridge anomaly is identified in the northeastern pacific in the days prior to the maximum of the positive nao phase both in the reanalysis and in the model a large scale northeastern pacific trough anomaly is observed during the negative nao phase but does not systematically precede it then short term linear and nonlinear simulations are performed to understand how the large scale ridge anomaly can act as a precursor of the positive nao phase the numerical setup allows for analysis of the propagation of synoptic waves in the eastern pacific in the p

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

a climatology of heat waves from a multimillennial simulation abstract a 10 000 yr unforced simulation with the commonwealth scientific and industrial research organisation csiro mark 2 coupled global climatic model has been used to investigate the occurrence of heat waves over the globe results are presented for both seasonal summer mean and daily heat waves geographical distributions of the occurrence rates of these heat waves are shown for various magnitudes of surface temperature anomalies the heat waves have specific geographical preferences with regions where relatively frequent intense and long lasting heat waves occur time series over all 10 000 yr of the heat waves for the selected model grid boxes illustrate the differing temporal variabilities at these locations as well as identifying the occurrences of extreme heat waves to this end the observed european heat wave of 2003 was simulated remarkably well in its overall characteristics it occurs once in this simulation heat waves for various continental locations are shown to occur as isolated

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

factors contributing to record breaking heat waves over the great plains during the 1930s dust bowl abstractrecord breaking summer heat waves were experienced across the contiguous united states during the decade long dust bowl drought in the 1930s using high quality daily temperature observations the dust bowl heat wave characteristics are assessed with metrics that describe variations in heat wave activity and intensity despite the sparser station coverage in the early record there is robust evidence for the emergence of exceptional heat waves across the central great plains the most extreme of which were preconditioned by anomalously dry springs this is consistent with the entire twentieth century record summer heat waves over the great plains develop on average 15 20 days earlier after anomalously dry springs compared to summers following wet springs heat waves following dry springs are also significantly longer and hotter indicative of the importance of land surface feedbacks in heat wave intensification a distinctive anomalous continental wide circulation pattern accompanied exceptio

reconstructing sea level pressure variability via a feature tracking approach abstractthe aim of this paper is to quantify the contribution of synoptic transients to the full spectrum of space time variability of sea level pressure slp in middle latitudes in previous work by the authors it was shown that tracking cyclones and anticyclones in an idealized atmospheric model allows one to reconstruct a surprisingly large fraction of the model s variability including not only synoptic components but also its large scale low frequency component motivated by this result the authors performed tracking of cyclones and anticyclones and estimated cyclone and anticyclone size and geometry characteristics in the observed slp field using the 1948 2008 ncep ncar reanalysis dataset the reconstructed synoptic field was then produced via superimposing radially symmetrized eddies moving along their actual observed trajectories it was found that similar to earlier results for an idealized model the synoptic reconstruction so obtained accounts for a major fraction of the full observed slp v

contributions of downstream eddy development to the teleconnection between enso and the atmospheric circulation over the north atlantic abstractthe spatiotemporal evolution of various meteorological phenomena associated with el nino southern oscillation enso in the north pacific north american north atlantic sector is examined using both ncep ncar reanalyses and output from a 2000 yr integration of a global coupled climate model particular attention is devoted to the implications of downstream eddy developments on the relationship between enso and the atmospheric circulation over the north atlantic the el nino related persistent events are characterized by a strengthened pacific subtropical jet stream and an equatorward shifted storm track over the north pacific the wave packets that populate the storm tracks travel eastward through downstream development the barotropic forcing of the embedded synoptic scale eddies is conducive to the formation of a flow that resembles the negative phase of the north atlantic oscillation nao the more frequent and higher persistence of those episodes during el nino winters contribute to the prevale

observed changes in baroclinic wave activity during the life cycles of low frequency circulation anomalies abstract anomalous baroclinic wave activity during the onset and decay of blocking patterns in the northern hemisphere winter is investigated based upon a 30 year record of 500 mb height and sea level pressure a slowly varying envelope function is defined at each gridpoint in order to represent the modulation of the amplitude of baroclinic wave activity by the low frequency circulation anomalies related to blocking the envelope function fields and the low frequency circulation fields are composited relative to the onset and decay times of four persistent dipole patterns in low frequency circulation anomalies located downstream of the climatological mean stormtracks one polarity of the anomaly patterns corresponds to dipole or modon like blocking patterns over the eastern oceans and the other to strong zonal flow patterns each of the eight composites is comprised of more than 50 persistent blocking or zonal flow episodes the most striking common feature observed during the onset of blocking over th

how rossby wave breaking over the pacific forces the north atlantic oscillation 1 anticyclonic rossby wave breaking rwb over a well defined limited area region of the east pacific leads to the positive polarity of the north atlantic oscillation nao by locally piling up wave activity where it may be advected downstream resulting in increased wave activity flux and anticyclonic rwb over the subtropical atlantic a composite time series shows that pacific rwb occurs several days prior to the atlantic rwb and the peak of the nao index following pacific rwb a channel of increased pseudomomentum flux extends from the pacific wave breaking region northeastward toward midlatitudes of eastern north america where pseudomomentum density accumulates for several days prior to moving eastward and leading to anticyclonic rwb over the atlantic

multiscale variability in north american summer maximum temperatures and modulations from the north atlantic simulated by an agcm abstractsix recurrent thermal regimes are identified over continental north america from june to september through a k means clustering applied to daily maximum temperature simulated by echam5 forced by historical ssts for 1930 2013 and validated using ncep doe amip ii reanalysis over the 1980 2009 period four regimes are related to a synoptic wave pattern propagating eastward in the midlatitudes with embedded ridging anomalies that translate into maximum warming transiting along two other regimes associated with broad continental warming and above average temperatures in the northeastern united states respectively are characterized by ridging anomalies over north america europe and asia that suggest correlated heat wave occurrences in these regions their frequencies are mainly related to both la nina and warm conditions in the north atlantic removing all variability beyond the seasonal cycle in the north atlantic in echam5 leads to a significant drop in the occurrences of the regime associated w

anatomy of synoptic eddy nao interaction through eddy structure decomposition abstracta method of eddy structure decomposition is proposed to detect how low frequency flow associated with the north atlantic oscillation nao organizes systematically synoptic eddy se activity to generate in phase and upstream feedbacks in this method a statistical eddy streamfunction ses field defined by the three point covariance of synoptic scale streamfunction is introduced to characterize spatiotemporal se flow structures the ses field is decomposed into basic and anomalous parts to represent the climatological se flow structure and its departure these two parts are used to calculate the basic and anomalous eddy velocity eddy vorticity and thus eddy vorticity flux fields in order to elucidate those two se feedbacks onto the nao this method is validated by the fact that the observed anomalous eddy vorticity flux field can be reproduced well by two linear terms the basic eddy velocity field multiplied by anomalous eddy vorticity field and the anomalous eddy velocity field multiplied

the shift of the northern node of the nao and cyclonic rossby wave breaking abstractseveral studies have found an eastward shift in the northern node of the north atlantic oscillation nao during the winters of 1978 97 compared to 1958 77 this study focuses on the connection between this shift of the northern node of the nao and rossby wave breaking rwb for the period 1958 97 it is found that the region of frequent cyclonic rwb underwent a northeastward shift at high latitudes in the latter 20 yr period on a year to year basis the cyclonic rwb region moves along a southwest northeast sw ne directed axis both latitude and longitude of the winter maximum frequency of cyclonic rwb occurrence are positively correlated with the nao index to investigate the role of location of cyclonic rwb in influencing the nao pattern the geographical location of frequent cyclonic rwb is divided into two subdomains located along the sw ne axis to the south sw domain and east ne domain of greenland two composites are assembled as one cyclonic rwb occurrence is detected in one of the t

synoptic view of the north atlantic oscillation abstract this article investigates the synoptic characteristics of individual north atlantic oscillation nao events by examining the daily evolution of the potential temperature field on the nominal tropopause the 2 pvu surface this quantity is obtained from the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis dataset for the winter season for both phases the nao is found to originate from synoptic scale waves as these waves evolve into the low frequency nao pattern they break anticyclonically for the positive phase and cyclonically for the negative phase the results of this analysis suggest that it is the remnants of these breaking waves that form the physical entity of the nao throughout the nao events for both phases the nao is maintained by the successive breaking of upstream synoptic scale waves when synoptic scale disturbances are no longer present mixing processes play an important role in the nao decay as in other recent

model simulation and projection of european heat waves in present day and future climates abstractthe synoptic behavior of present day heat waves hw over europe is studied using the gfdl high resolution atmospheric model hiram with 50 km grid spacing three regions of enhanced and coherent temperature variability are identified over western russia eastern europe and western europe the simulated hw characteristics are compared with those derived from climate forecast system reanalysis products composite charts for outstanding hw episodes resemble well known recurrent circulation types the hw region is overlain by a prominent upper level anticyclone which blocks the passage of synoptic scale transients the altered eddy vorticity transports in turn reinforce the anticyclone the anticyclone is part of a planetary scale wave train the successive downstream development of this wave train is indicative of rossby wave dispersion additional runs of hiram are conducted for the time slices of 2026 35 and 2086 95 in the climate scenario corresponding to representative concentration pathway

tropical and subtropical north atlantic vertical wind shear and seasonal tropical cyclone activity abstractgiven recent insights into the role of anticyclonic rossby wave breaking awb in driving subseasonal and seasonal north atlantic tropical cyclone tc activity this study further examines

impact of midlatitude stationary waves on regional hadley cells and enso 1 stationary planetary waves are excited in the midlatitudes propagate equatorward and are absorbed in the subtropics the impact these waves have on the tropical climate has yet to be fully unraveled previous work has shown that interannual variability of zonal mean stationary eddy stress is well correlated with interannual variability in hadley cell strength a separate line of research has shown that changes in midlatitude planetary waves local to the pacific strongly affect enso variability here we show that the two phenomena are in fact closely connected interannual variability of wave activity flux impinging on the subtropical central pacific affects the local hadley cell the associated changes in subtropical subsidence affect the surface pressure field and wind stresses which in turn affect enso as a result a winter with an anomalously weak hadley cell tends to be followed a year later by an el nino event

relation of substorm breakup arc to other growth phase auroral arcs 1 high resolution canopus meridian scanning photometer and all sky imager observations of preonset and expansion phase auroral arcs are analyzed for expansion phase onsets that evolve into full substorms and into pseudobreakups one or more arcs are seen across the sky throughout the growth phase prior to onset the onsets we have examined indicate that auroral breakup at onset does not generally occur along one of these arcs but instead often occurs along a thin breakup arc that forms equatorward of all growth phase arcs a few minutes prior to onset the intensity of this breakup arc increases monotonically for the few minutes prior to the time normally identified as substorm onset and then typically increases dramatically these results imply that the processes responsible for auroral breakup initiate a few minutes prior to the time normally identified as substorm expansion phase onset we also find that arcs poleward of the arc that breaks up appear to be unaffected by substorm onset until expansion phase auroral activity moves poleward to the location of such arcs arcs poleward of the poleward most extent of pseudobreakup auroral activity show no apparent effects of a pseudobreakup these results imply that the process that initiates the onset of substorms does not require the occurrence of plasma sheet changes significant enough to affect magnetosphere ionosphere electrodynamics along field lines that cross the equator tailward of the substorm onset region

time variation of 500 mb height fluctuations with long intermediate and short time scales as deduced from lag correlation statistics abstract the time variation of northern hemisphere wintertime 500 mb height fluctuations with short intermediate and long time scales is investigated using lag correlation patterns derived from time filtered data fluctuations with short 2 5 6 day periods time scales propagate eastward at a rate consistent with the notion of a steering level around 700 mb which supports an interpretation in terms of baroclinic waves the mobile teleconnection patterns associated with the intermediate 10 30 day periods time scales exhibit a pattern of time variation suggestive a rossby wave dispersion with a predominance of southward dispersion from middle latitudes into the tropics the geographically fixed teleconnection patterns characteristic of the longer time scales do not show a well defined pattern of time variation but their horizontal structure resembles that of the fastest growing normal mode associated with barotropic instability of the climatological mean wintertime flow

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

a new parameterization for shallow cumulus convection and its application to marine subtropical cloud topped boundary layers part i description and 1d results abstract a new parameterization of shallow cumulus convection is presented the parameterization consists of a mass flux scheme based on a buoyancy sorting entrainment detrainment plume model the mass flux scheme is coupled to a 1 5 order turbulence closure model with an entrainment closure for convective boundary layers model performance is verified using single column model simulations at relatively high vertical resolution of pure trade cumulus convection and a cumulus to stratocumulus transition mixing rates cloud cover and vertical flux profiles as deduced from previously published large eddy simulation studies are well reproduced by the parameterization the model is used to demonstrate that height variations of lateral mixing rates can be successfully captured by a simple implementation of a buoyancy sorting mechanism in the updraft cloud model a companion paper describes the implementation of the scheme in a mesoscale model

the role of dynamic tropopause rossby wave breaking for synoptic scale buildups in northern hemisphere zonal available potential energy abstractzonal available potential energy az measures the magnitude of meridional temperature gradients and static stability of a domain here the role of northern hemisphere dynamic tropopause 2

heat waves in china definitions leading patterns and connections to large scale atmospheric circulation and ssts based on the daily maximum temperatures tmax from 587 surface observation stations in china during 1959 2013 heat waves are detected using both absolute and relative definitions the spatiotemporal variations of heat wave occurrence duration amplitude are compared between the two definitions considering the significant differences in regional climatology relative threshold is more meaningful to detect the local extremes by utilizing the empirical orthogonal function the integral index heat wave total intensity is decomposed into three dominant modes interdecadal id interannual tripole ia tr and interannual dipole ia dp modes the id mode shows uniform anomalies over the whole china with the maximum in north and its corresponding time series depict notable interdecadal variations with a turning point around mid 1990s the ia dp mode exhibits opposite signed anomalies over north and south china the ia tr mode shows an anomalous tripole pattern with negative anomalies over central china and positive anomalies over north and south china in its positive phase both the ia dp and ia tr patterns are more obvious since mid 1990s with mainly year to year variations before that all the three modes are controlled by anomalous high pressure systems which are accompanied by local scale dry land conditions the diabatic heating associated with anomalous convective activities over tropical western pacific triggers rossby wave trains propagating northward along the east asia which causes abnormal heat waves through descending motion over the high pressure nodes in turn the severe convections are generated by enhanced walker circulation in the tropical pacific due to warming and or cooling sea surface temperature sst anomalies in the tropical western and eastern pacific respectively

linking atmospheric river hydrological impacts on the u s west coast to rossby wave breaking abstractatmospheric rivers ars have significant hydrometeorological impacts on the u s west coast this study presents the connection between the characteristics of large scale rossby wave breaking rwb over the eastern north pacific and the regional scale hydrological impacts associated with landfalling ars on the u s west coast 36 49 n ars associated with rwb account for two thirds of the landfalling ar events and 70 of total ar precipitation in the winter season the two regimes of rwb anticyclonic wave breaking awb and cyclonic wave breaking cwb are associated with different directions of the vertically integrated water vapor transport ivt awb ars impinge in a more westerly direction on the coast whereas cwb ars impinge in a more southwesterly direction most of the landfalling ars along the northwestern coast of the united states states of washington and oregon are awb ars because of their westerly impinging angles when compared to cwb ars awb ars arrive more orthogonally to the

anatomy of great plains protracted heat waves especially the 1980 u s summer drought abstract the protracted heat wave and drought of the great plains during summer 1980 was a manifestation of an abnormal form of the general circulation an upper level continental high developed rapidly over the southern plains in late may and persisted with only small changes throughout the summer the associated subsidence dry soil lack of cloud and high insolation led to unrelenting heat descriptions of several interlocking features are given followed by an attempt to ascribe the development and maintenance of the drought producing cell to several physical factors strong low latitude westerlies expanded circumpolar vortex over the north pacific north america and north atlantic during spring 1980 led to latitudinally depressed storm tracks relative to normal combined with normal seasonal forcing this anomalous pattern was stable in spring but unstable in summer after the climatologically dependable northward march of the westerlies moreover normal spring to summer mid tropospheric height chang

a multisatellite study of a pseudo substorm onset in the near earth magnetotail this paper reports the multisatellite and ground observations of two pseudo substorm onset events that occurred successively at 0747 ut and 0811 ut may 30 1985 with more attention to the 0747 ut onset the distinguishing features of the 0747 ut event are as follows 1 the substorm associated tail reconfiguration started in a very localized region in the near earth magnetotail 2 the magnitude of the current disruption decreased markedly as the disruption region expanded tailward 3 on the ground the onset of a very small negative bay 40 nt was observed simultaneously with the onset of the current disruption but over a much wider local time sector than the near earth tail reconfiguration positive bay onsets at mid latitudes also had a longitudinally wide distribution from these features we infer that in the present event the current disruption took place filamentarily near ampte cce at 8 8 re it is also inferred that pseudo substorm onsets are distinguished from standard substorm onsets by the absence of a global expansion of the current disruption and that the spatial scale of the onset region in the magnetosphere is not a major difference between the two the present study suggests that the spatial distribution of the magnetic distortion before onsets is an important factor to determine the expansion scale of the current disruption it is also suggested that the current disruption is basically an internal process of the magnetosphere

characteristics of the atlantic storm track eddy activity and its relation with the north atlantic oscillation abstract this study focuses on feedbacks of the high frequency eddy activity onto the quasi stationary circulation particularly with regard to the north atlantic oscillation nao the methodology consists of analyzing ncep ncar reanalysis data and sensitivity runs from a high resolution nonhydrostatic regional model consistent with recent studies results show that the jet displacement characteristic of the nao phenomenon depends strongly on the dynamics of the synoptic scale waves and the way they break positive and negative phases of the nao are closely related to anticyclonic and cyclonic wave breaking respectively indeed the high frequency momentum flux whose sign is directly related to the type of wave breaking is correlated with the nao index over the atlantic the peak of the momentum flux signal precedes that of the nao by a few days suggesting that wave breaking is triggering nao events two examples illustrate the significant impact of single storms in particular those occurring in the e