midlatitude atmospheric transient eddy feedbacks influenced enso associated wintertime pacific teleconnection patterns in two pdo phases the el nino southern oscillation enso associated wintertime atmospheric teleconnection patterns in two pacific decadal oscillation pdo phases are investigated using era 20c reanalysis data for 1950 2010 a strengthened enso associated pacific north american pna teleconnection pattern presents in pdo positive phase while a west pacific wp pattern over northwestern pacific and a squeezed pna pattern coexist when enso occurs in pdo negative phase the dynamical role of atmospheric transient eddy feedbacks to the teleconnection patterns are highlighted in the present study when enso occurs in pdo positive phase the uniform strengthened westerly jet anomalies downstream of the climatological main body of jet accompany with energetic transient eddy anomalies over northeastern pacific the transient eddy feedbacks largely enhance and favor the strengthened pna pattern when enso occurs in pdo negative phase the strengthened westerly jet anomalies appear to separate into two parts one locating north of the climatological main body of jet and the other at the downstream the accompanied transient eddy anomalies also split into two parts under such conditions the transient eddy feedbacks are limited over northeastern pacific and favor a weak pna pattern however the transient eddy anomalies over northwestern pacific strengthen and the feedbacks also strengthen and largely contribute to the wp pattern moreover the transient eddy anomalies over northwestern pacific seem to be anchored along the anomalously poleward strengthened oceanic subarctic frontal zone safz in pdo negative phase the enhanced atmospheric baroclinicity anomalies coupled with the strengthened safz energize atmospheric transient eddy anomalies and work as the potential maintenance in shaping the wp pattern

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

life cycles of persistent anomalies i evolution of 500 mb height fields abstract we have conducted observational analysts to identify systematic aspects of the life cycles of persistent anomalies of the extratropical northern hemisphere wintertime circulation in the present study we focus on the typical characteristics of the 500 mb height anomaly and flow patterns accompanying the development and breakdown of large scale flow anomalies in two key regions the eastern north atlantic atl and the northern soviet union nsu and then compare the results for these regions with results described previously for cases located over the north pacific pac region throughout their life cycles the positive anomaly and negative anomaly cases for a given region display a number of striking similarities the primary anomaly center develop rapidly with little indication of a significant anomaly over the key region until just prior to onset following establishment of the major anomaly center over the key region anomaly centers develop and intensify in sequence downstream leading t

contrasting mechanisms of summer blocking over western eurasia the formation of summer blocking events appears to have been mostly studied for a few individual events often associated with heat waves here we investigate summer blocking event dynamics in three areas over western eurasia in order to draw some more general conclusions mostly in terms of high and low frequency processes a 2 d blocking event detection algorithm is applied to the 500 hpa geopotential field from the era 40 and era interim reanalyses over the 1958 2017 period it is shown that both high and low frequency processes are important to initiate blocking events over southern central europe blocking events over western russia are preceded by a significant low frequency large scale wave train and their formation and maintenance are dominated by low frequency processes only finally it is shown that the risk of extreme seasons such as summer 2010 cannot be accurately estimated from the poisson statistics of past events

rise and fall of an isolated unstable carbonate platform the cambrian of southwestern sardinia strong effects of tensional tectonics dominate the lower and middle cambrian sequence of southwestern sardinia a thinning of the continental crust and the possible development of a passive margin in the cambrian is indicated by different stages of evolution of a mainly carbonatic platform a clastic carbonatic homoclinal ramp with algal archaeocyathan mounds epiphyton renalcis in the west clastic shallow marine to tidal sequences in the east b carbonatic clastic ramp or rimmed shelf with an ooid shoal complex prograding towards the west the back shoal area contains peloidal mudstones algal archaeocyathan biostromes girvanella and increasingly tidal deposits clastic and carbonatic towards the east c isolated platform aggraded to sea level rimmed by slope deposits with slumps and breccia beds in the southeast and northwest d isolated flooded platform barriers towards the open sea partly broke down e isolated platform with raised rims and deep interior often with thick breccia beds in uppermost parts f break down of the platform late early cambrian marked by nodular limestones and limestoneshale intercalations g terrigenous clastics cover the former platform

features of rossby wave propagation associated with the evolution of summertime blocking highs with different configurations over northeast asia abstractthis study categorized blocking high bh episodes during the boreal summer in northeast asia 40 70 n 100 150 e into four types according to their wave breaking features at the dynamic tropopause on the initial day anticyclonic warm cyclonic warm anticyclonic cold and cyclonic cold based on the results of a statistical analysis it was shown that 1 the anticyclonic warm type tended to occur in eastern russia 55 70 n 127 5 142 5 e whereas the other three types preferentially occurred in the vicinity of lake baikal 2 the two cold types generally were more common than the two warm types and 3 the average life spans of the two anticyclonic types were longer than those of the two cyclonic types according to a composite analysis the four bh types were preceded by different wave train like anomalies over the eurasian continent over approximately one week correspondingly each bh type was characterized by distinct rossby wave propagation features interestingly a northeastward pro

simulated life cycles of persistent anticyclonic anomalies over the north pacific role of synoptic scale eddies abstract this study examines the role of synoptic scale eddies during the development of persistent anticyclonic height anomalies over the central north pacific in a general circulation model under perpetual january conditions the gcm replicates the basic characteristics of the evolution of the anomaly patterns found in observations the life cycle is characterized by the rapid establishment of the major anomaly center and considerably longer maintenance and decay phases which include the development of downstream anomaly centers the simulation also shows a realistic evolution of synoptic scale activity beginning with enhanced activity off the east coast of asia prior to onset followed by a northward shift of the pacific storm track which lasts throughout the maintenance phase the initial enhancement of synoptic scale eddy activity is associated with a large scale cyclonic anomaly that develops over siberia several days prior to the onset of the main anticyclonic anomaly over the central north pacif

upward and downward injection of rossby wave activity across the tropopause a new aspect of the troposphere stratosphere dynamical linkage propagation of zonally confined rossby wave activity between the troposphere and lower stratosphere of the southern hemisphere during austral winter and spring of 1997 is studied by using a wave activity flux and refractive index both defined for stationary rossby waves on a zonally asymmetric time mean flow a particular event of large scale quasi stationary cyclogenesis in the troposphere is discussed to which downward wave activity injection from anticyclonic anomalies upstream that had developed in the exit region of the lower stratospheric polar night jet pnj contributed substantially consistent with that downward injection phase lines of observed stream function anomalies exhibited a distinct eastward tilt with height the development of the anticyclonic anomalies occurred at the leading edge of a quasi stationary rossby wave train propagating along the pnj that had originated from a tropospheric blocking ridge farther upstream though less common than upward wave activity injection across the tropopause similar events of downward wave activity injection occurred several times during that season primarily in the regions south of australia and over the central south pacific over each of which the pnj exit overlapped with a tropospheric subpolar jet to form a vertical waveguide locally it is argued that the downward wave activity propagation is essentially due to refraction in the vertically sheared westerlies and the zonal asymmetries in the time mean flow are a likely factor for the observed geographical preference of the downward wave activity injection copyright 2005 royal meteorological society

on the dynamics of austral heat waves this work examines summer heat wave events in four different regions of australia southwest central southeast and northeast to assess similarities and differences in the circulations that precede accompany and follow the heat wave events a series of circulation composites are constructed for days from 10 days prior to 5 days following onset of each heat wave event the composites of geopotential height anomalies and wave activity flux vectors show that heat waves in southwest and southeast australia are preceded by coherent wave train structures in the indian ocean region accompanied by blocking in the australian region as an amplified node of the wave train structure and followed by coherent responses of wave train patterns in the pacific and south america regions the heat wave blocking high is maintained by convergence of wave activity in a well defined wave channel the concentration of wave activity in the block is aided by the formation of a subtropical jet branch and wave barrier on the equatorward side of the block heat waves in central and northeast australia show similar wave train life cycle responses but with a proximate ridge in the midtroposphere and a trough in the nearby waveguide region heat waves in australia can be viewed as an element of successive expression of the planetary waveguide modes in the southern hemisphere and serve as signifiers of organized active phases of these modes

on the interpretation of eddy fluxes during a blocking episode abstract using twice daily synoptic charts objectively analyzed at the national meteorological centre horizontal eddy fluxes of temperature and quasi geostrophic potential vorticity are computed for the month of july 1976 when a blocking anticyclone was centered over western europe the local time averaged eddy variance equations are used to provide a dynamical basis for interpreting the spatial pattern of eddy fluxes and their relation to mean gradients it is shown that a rotational non divergent flux can be identified the cross gradient component of which balances the mean flow advection of eddy variance the remaining flux is the dynamically significant one which helps maintain the block and can be understood in terms of a response to sources and sinks of eddy variance

the dynamics of large scale cyclogenesis over the north pacific ocean abstract earlier studies of persistent large scale flow anomalies have been extended with the aim of identifying the primary mechanisms for persistent anomaly development in this study the focus is on wintertime cases of persistent cyclonic flow anomalies over the north pacific these cases are typically manifested by an abnormally intense cyclonic circulation extending over the north pacific basin an unusually strong and eastward extended east asian jet and a well defined pacific north american teleconnection pattern we have conducted extensive diagnostic analyses in order to determine the mechanisms responsible for development in particular these diagnostics examine the processes influencing the time evolution of eddy potential enstrophy and potential vorticity anomalies the cases are preceded by a buildup of anomalously high potential vorticity air at upper levels over eastern asia this high potential vorticity air is initially advected eastward in association with synoptic scale cyclogenesis

influence of the vertical and zonal propagation of stratospheric planetary waves on tropospheric blockings 1 case studies are used to elucidate the relationship between stratospheric planetary wave reflection and blocking formation in the troposphere the enhanced upward propagation of a planetary scale wave packet from the eurasian sector involving a euro atlantic blocking leads to a stratospheric sudden warming ssw following the weakening of the stratospheric westerly jet due to polar warming the stratospheric planetary wave packet then propagates downward over the american sector inducing a ridge over the north pacific as well as a trough over eastern canada in the upper troposphere the ridge promotes the formation of a pacific blocking this result explains why pacific blockings tend to form after ssw and why they are associated with suppressed upward propagation of planetary waves

northern hemisphere winter atmospheric transient eddy heat fluxes and the gulf stream and kuroshio oyashio extension variability abstractspatial and temporal covariability between the atmospheric transient eddy heat fluxes i e t and q in the northern hemisphere winter january march and the paths of the gulf stream gs kuroshio extension ke and oyashio extension oe are examined based on an atmospheric reanalyses and ocean observations for 1979 2009 for the climatological winter mean the northward heat fluxes by the synoptic 2 8 days transient eddies exhibit canonical storm tracks with their maxima collocated with the gs and ke oe the intraseasonal 8 days 3 months counterpart while having overall similar amplitude shows a spatial pattern with more localized maxima near the major orography and blocking regions lateral heat flux divergence by transient eddies as the sum of the two frequency bands exhibits very close coupling with the exact locations of the ocean fronts linear regression is used to examine the lead lag relationship between interannual changes in the northward heat fluxes by the transient

impacts of the aleutian icelandic low seesaw on surface climate during the twentieth century abstract an interannual seesaw between the intensities of the icelandic and aleutian lows and its impact on surface climate observed during the twentieth century are investigated in a recent period from the late 1960s to the early 1990s their seesaw relationship was particularly apparent in late winter the associated anomalies in surface air temperature were significant in many regions over the extratropical northern hemisphere except in central portions of the continents the seesaw also modified the ocean atmosphere exchange of heat and moisture extensively over the north atlantic and north pacific by changing evaporation and precipitation since the seesaw formation was triggered by eastward propagation of stationary rossby wave trains from the north pacific into the north atlantic anomalous circulation over the north pacific in january was identified as a good precursor for february surface air temperatures in the euro atlantic sector during that period the seesaw relationship between the two low

planetary and synoptic scale dynamic control of extreme cold wave patterns over the united states the roles of planetary and synoptic scale waves in extreme cold wave ecw events over the southeastern se and northwestern nw united states us are studied using a spherical harmonic decomposition in conjunction with piecewise tendency diagnosis ptd planetary waves and synoptic waves jointly work together to initiate ecw events notably the planetary waves not only provide a direct contribution to circulation field enacting ecw events but also alter the background circulation field in such a manner that promotes synoptic waves growth via increases in regional barotropic deformation the se ecw events concurrent with the northern hemisphere annular mode nam negative phase feature high latitude intensification and subsequent southeastward movement of cold surface air temperature sat anomalies the planetary scale pattern provides a sizable contribution to the total wave pattern on both sea level pressure slp and upper level moreover the negative nam planetary anomaly acts to displace the jet equatorward and thereby increases the barotropic deformation of the synoptic scale anomaly over southeastern us ptd confirms that the planetary scale barotropic deformation plays a key role in deepening the negative height anomaly with a secondary contribution from baroclinic growth in contrast nw ecw events feature a regional sat cold anomaly that intensified in situ in association with a quasi stationary positive slp anomaly with a substantial planetary scale wave component the upper level circulation is characterized by a pronounced anomalous ridge over the gulf of alaska and a northeast southwest tilted negative height anomaly to its east the negative height anomaly axis is orthogonal to the planetary scale dilatation result in a stronger planetary barotropic deformation of the incipient negative height anomaly

geographical dependence of upper level blocking formation associated with intraseasonal amplification of the siberian high abstract intraseasonal amplification events of the surface siberian high in winter are generally associated with blocking ridge formation in the upper troposphere composite analysis applied to the 20 strongest intraseasonal events of upper level anticyclonic anomalies at every grid point over siberia reveals that the blocking formation differs fundamentally between the east and west of the climatological upper level trough over the far east to the west what can be called wave train atlantic origin type is common where a blocking ridge develops from anomalies as a component of a quasi stationary rossby wave train propagating across the eurasian continent under modest feedback forcing from transient eddies to the east of the trough what can be called pacific origin type dominates where a blocking ridge forms in association with westward development of anticyclonic anomalies from the north pacific under stronger feedback forcing from the pacific storm track regardless of a particular type of bl

transient eddy forcing of blocking flows abstract the net forcing of blocking flows by transient eddies having synoptic time scales is examined within the framework of quasi geostrophic theory temporal filtering is used to distinguish the effects of transients having synoptic lime scales i e periods less than approximately seven days from those having longer time scales convergences of transient eddy transports of heat and vorticity during blocking conditions are computed from highpass filtered time series the eddy flux convergences for individual blocking events are then composited according to the locations of the blocks the quasi geostrophic potential vorticity equation relating geopotential tendency and the eddy flux convergences of heat and vorticity is solved for composite blocking conditions the diagnosis is performed for both observed blocks and blocks simulated by a general circulation model the net quasi geostrophic geopotential tendencies due to transports by the synoptic scale transient eddies exhibit a quadrature relations

an assessment of the impact of transient eddies on the zonal flow during a blocking episode using localized eliassen palm flux diagnostics abstract the eliassen palm e p flux applied to zonal men flows is an indicator of both the flux of eddy activity and the eddy forcing of the zonal mean flow for time mean flows a localized e p flux is derived and used diagnostically to assess the impact of transient eddies on a major blocking episode that occurred over the south pacific during the southern hemisphere winter of 1979 in contrast to previous studies that have focused on the mean quasi geostrophic potential vorticity equation the focus here is on the mean momentum equations eddy transports and the associated induced meridional circulation and other internal adjustments necessary to maintain the thermal wind balance are gathered together allowing the residual circulation and the effects of the eddies to be determined the time mean equations of motion are thus transformed to consist of mean terms the residual circulation and the divergence of a localized e p flux vector the latter is a measure of the eddy forcing of the mean flow

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

the role of high and low frequency dynamics in blocking formation time evolutions of prominent blocking flow configurations over the north pacific and europe are compared based upon composites for the 30 strongest events observed during 27 recent winter seasons fluctuations associated with synoptic scale migratory eddies have been filtered out before the compositing a quasi stationary wave train across the atlantic is evident during the blocking amplification over europe while no counterpart is found to the west of the amplifying blocking over the north pacific correlation between the tropopause level potential vorticity pv and meridional wind velocity associated with the amplifying blocking is found to be negative over europe in association with the anticyclonic evolution of the low pv center but it is almost zero over the north pacific feedback from the synoptic scale eddies as evaluated in the form of 250 mb geopotential height tendency due to the eddy vorticity flux convergence accounts for more than 75 of the observed amplification for the pacific blocking and less than 45 for the european blocking this difference is highlighted in two types of contour advection with surgery experiments in one of them pv contours observed four days before the peak blocking time were advected by composite time series of the low pass filtered observational wind and in the other experiment they were advected by the low pass filtered wind from which the transient eddy feedback evaluated as above had been removed at every time step hence the latter data should be dominated by low frequency dynamics for the european blocking both experiments can reproduce the anticyclonic evolution of low pv air within a blocking ridge as observed for the pacific blocking in contrast the observed intrusion of low pv air into the higher latitudes cannot be reproduced without the transient feedback furthermore in a barotropic model initialized with the composite 250 mb flow observed three days before the peak time a simulated blocking development over the north pacific is more sensitive to the insertion of the observed transient feedback than that over europe these results suggest that the incoming wave activity flux associated with a quasi stationary rossby wave train is of primary importance in the blocking formation over europe whereas the forcing by the synoptic scale transients is indispensable to that over the north pacific

the anomalous structures of atmospheric and oceanic variables associated with the frequency of north pacific winter blocking 1 from empirical orthogonal function eof analysis of the atmospheric and oceanic variables over the north pacific during the northern hemispheric winter 1960 2009 we were able to determine that the second mode of the eof is related to north pacific winter blocking our composite analysis reveals that the structures of the variables during winters with contrasting frequencies of blocking events are systematically different and show quite opposite pattern in the north pacific during winters with frequent blocking occurrence a north south dipole pattern of geopotential height anomaly is formed and the associated westerly winds are weakened strengthen north south of 35 n these factors bring variations of ocean advection and ocean surface heat flux resulting in a dipole pattern of sea surface temperature sst with a warm anomaly north of 35 n and a cold anomaly to the south the effect of sst on blocking is examined using an atmospheric general circulation model agcm experiment in the experiment the sst anomaly related to blocking is applied as a boundary forcing of the agcm to investigate the effect of sst on the formation of blocking from the experiment we also concluded that the winter blocking is not induced by north pacific sst forcing although consistent linkage between oceanic and atmospheric variables is evident

on the source of midlatitude low frequency variability part ii nonlinear equilibration of weather regimes abstract we present a new statistical dynamical approach to the concept of weather regimes including the effect of tralisients without any assumption other than scale separation the method is applied to a quasi geostrophic channel model without topography and forced by a local baroclinic jet baroclinic perturbations grow and decay along a storm track which is linked with a maximum of low frequency variability towards its exit in agreement with the observations the weather regimes are searched within the subspace spanned by the large scales only they are identified through the resolution of a stationary problem in which the feedback of the transients is included as an ensemble average over analogs of the large scale flow in this way the feedback is a continuous function of the large scale flow only and the system of equations is closed taking into account the whole coupling the solution is obtained using a nonlinear optimization technique several regimes are identified corresponding to zonal a

persistent anomalies blocking and variations in atmospheric predictability abstract we consider regimes of low frequency variability in large scale atmospheric dynamics the model used for the study of these regimes is the fully nonlinear equivalent barotropic vorticity equation on the sphere with simplified forcing dissipation and topography twenty five modes are retained in a spherical harmonics expansion of the streamfunction solutions are studied as a function of the nondimensional intensity of the forcing and dissipation multiple stationary solutions are obtained as a result of nonlinear interaction between waves mean flow and orography the number of modes retained in the analysis permits these multiple equilibria to appear for realistic values of the forcing the equilibria exhibit blocked and zonal flow patterns bearing a marked resemblance to synoptically defined zonal and blocked northern hemisphere midlatitude flows wave wave interactions influence strongly the stability properties of the equilibria and the time evolution of nonequilibrium solutions time depe

persistent anomaly forcing in a two level global circulation model abstract perpetual january data from a simple global two level model are used to diagnose the forcing of the model s low frequency lf large scale flow the forcing is considered within the context of a hypothetical low order model that resolves only the slowly varying planetary scale modes thus the forcing is partitioned into resolved components consisting of lf planetary scale i e autonomous processes and unresolved components that involve high frequency hf transient eddy and lf synoptic scale effects spatial patterns of the net tendencies of low pass filtered planetary scale barotropic streamfunction and vertically averaged temperature are compared with corresponding patterns of resolved and unresolved forcing during the onset maintenance and decay stages of composited persistent anomalies growth stages of positive and negative persistent anomalies that are found in both the atlantic atl and pacific pac regions are dominated by autonomous processes for positive anomalies the n

high frequency transient eddies and blocking abstract in this paper we investigate the role of high frequency transient eddies in the maintenance of the blocking high which occurred over europe on 16 25 february 1979 time filtering is used to decompose the atmospheric large scale flow into contributions from high frequency and low frequency fluctuations the separation being roughly at the period of six days the net effect on the ten day mean flow of the high frequency cyclone scale eddies is studied using several methods the vorticity flux convergence associated with the high frequency eddies although small in comparison with the dominating terms in the vertically averaged vorticity equation appears to be important for counterbalancing the effects of the time mean surface stress especially in the vicinity of the storm tracks the eddies are thus important for the distribution of the time mean surface pressure also the tendency method of illustrating the eddy effects supports this view the hemispheric average of the barotropic energy conve

barotropic wave propagation and instability and atmospheric teleconnection patterns abstract a global barotropic model linearized about the 300 mb climatological mean january flow is perturbed by applying a series of localized forcings distributed throughout the tropics and subtropics structures which resemble the observed pacific north american and east atlantic teleconnection patterns noted by wallace and gutzler 1981 tend to recur in the responses similar patterns are found to result from the dispersion of isolated initial perturbations placed at a variety of locations in the tropics and midlatitudes it is shown that these structures are related to the most rapidly growing mode associated with barotropic instability of the zonally varying climatological basic state in the absence of damping this mode has an e folding time of about a week and a period close to 50 days in localized regions the instantaneous growth rates can be competitive with those of baroclinic instability these episodes of rapid local barotropic growth are interspersed with intervals in which the local

a linkage between the north atlantic oscillation and its downstream development due to the existence of a blocking ridge 1 in this work the spatial growth of the north atlantic oscillation nao and its relationship to downstream development are examined in contrast to positive nao events which are primarily initiated over the western north atlantic negative persistent nao events tend to be preceded by a blocking ridge in the vicinity of northern europe this blocking ridge contributes to the growth of negative nao events through a low frequency eddy interaction it is also shown that a noticeable downstream development is dominant only for negative persistent nao events that are preceded by the blocking ridge while the blocking ridge exists over inland eurasia it induces anticyclonic circulation near the surface over siberia as the nao grows a stationary wave train that originates from the north atlantic transfers wave energy downstream toward siberia the surface anticyclone is then reinforced by the wave train and begins to migrate eastward this process explains the distinct impact of the negative nao on the downstream eurasian region

transient cyclone scale vorticity forcing of blocking highs abstract the forcing of northern hemisphere blocking highs by the transient vorticity transfer from the cyclone scale eddies into the planetary flow is investigated thereby a barotropic prediction model for the planetary modes is numerically integrated the time dependent cyclone scale vorticity forcing is evaluated from the observations the blocking activity in the forced model flow is examined by means of an objective analysis scheme it is found that the model flow exhibits frequent blocking with some regional preference for the atlantic and pacific oceans the mean structure of the model blocks compares well with the observations particularly in the case of atlantic blocking however the mean amplitude of the model blocks is only about two thirds of those observed furthermore it is found that the time mean part of the forcing does not support the blocking pattern so that the model blocking activity is due only to the transient forcing the significance of the cyclone scale vorticity forcing fo

a case study of atmospheric blocking using isentropic analysis abstract a particular episode of blocking that occurred in the north atlantic during december 1978 is analyzed from nmc gridpoint data using isentropic analysis the advantages of this analysis technique are outlined specifically with regard to isentropic potential vorticity analysis of the montgomery streamfunction on the 315 k isentropic surface is preferable to the more traditional analysis of geopotential height on the 300 mb surface for describing the evolution of the block the sea level pressure pattern shows several intense cyclonic storms upstream of the block prior to its development during its mature stage the block exhibits little tilt with height has a warm core throughout most of the troposphere and a high tropopause the block also significantly affected the passage of fronts through the blocking region the potential vorticity analysis is shown to be a useful framework for understanding several characteristics of the block the blocking region is characterized by a broad uniform area

piecewise tendency diagnosis of weather regime transitions abstract piecewise tendency diagnosis ptd is extended and employed to study the dynamics of weather regime transitions originally developed for adiabatic and inviscid quasigeostrophic flow on a beta plane ptd partitions local geopotential tendencies into a linear combination of dynamically meaningful source terms within a potential vorticity pv framework here ptd is amended to account for spherical geometry diabatic heating and ageostrophic processes and is then used to identify the primary mechanisms responsible for northern hemisphere weather regime transitions height tendency patterns obtained by summing the contributions of individual ptd forcing terms correspond very well to actual height tendencies composite ptd analyses reveal that linear pv advections provide the largest dynamical forcing for the weather regime development over the north pacific specifically linear baroclinic growth provides the primary forcing while barotropic deformation of pv anomalies provides a secondary contrib

the behavior of light lithophile and halogen elements in felsic magma geochemistry of the post caldera valles rhyolites jemez mountains volcanic field new mexico abstract post collapse rhyolite lava domes lava flows and pyroclastic rocks from valles caldera 1140 ka erupted from 1133 ka to approximately 520 60 ka have been sampled to study variations of light lithophile li be b and halogen f cl elements our principal objectives were 1 to examine the mobility of these elements during post eruptive devitrification and hydration and 2 to study their behavior during magma differentiation compared to fresh glassy samples devitrified rocks from the same dome are depleted in b li f and cl but not in be during devitrification be was immobile while the other elements were progressively more mobile in the order b

transient eddy forcing of the time mean flow as identified by geopotential tendencies abstract the forcing of the time mean flow by transient eddies is examined within the framework of a quasi geostrophic equation relating the geopotential tendency to the convergence of transient eddy transports of heat and vorticity the forcing functions of this equation are computed using observed circulation statistics for the wintertime northern hemisphere and solutions are sought for the three dimensional structure of geopotential and temperature tendencies associated with eddies of different time scales in general the geopotential tendencies associated with vorticity fluxes are of the same sign within a given atmospheric column whereas the polarity of the geopotential tendencies associated with heat fluxes in the lower troposphere is opposite to that in the upper troposphere the geostrophic wind tendencies associated with synoptic scale eddies with periods between 2 5 and 6 days are strongest in the vicinity of the oceanic storm tracks the enhanced poleward heat transports by active disturbanc

variability of the baroclinic and barotropic transient eddy forcing associated with monthly changes in the midlatitude storm tracks abstract the heat and vorticity transports by synoptic scale eddies at various levels between 1000 and 100 mb have been compiled for each winter month of the 1966 84 period using time filtered daily analyses produced by the u s national meteorological center these circulation statistics were used to compute the three dimensional distributions of the quasigeostrophic geopotential tendency and vertical motion induced by baroclinic and barotropic eddy processes in individual months the latter fields serve as the basis for describing the synoptic scale eddy forcing associated with the leading modes of month to month variability of the storm tracks over the north pacific and north atlantic these modes are associated with the meridional displacements of the storm track axes from their climatological positions the placement of a storm track at a certain latitude in a certain month is accompanied by enhanced convergence of eddy heat fluxes poleward of in the tropospheric column poleward of the storm tra

the gulf stream influence on wintertime north atlantic jet variability in this paper we investigate the influence of the gulf stream sst front on the north atlantic eddy driven jet and its variability by analysing the ncep cfsr dataset and a pair of agcm simulations forced with realistic and smoothed gulf stream sst boundary conditions the gulf stream sst front acts to generate stronger meridional eddy heat flux in the lower troposphere and an eddy driven jet over the eastern north atlantic that is located further polewards compared to the simulation with smoothed sst the strong gulf stream sst gradient is found to be crucial in more accurately capturing the trimodal distribution of the eddy driven jet latitude with the more poleward climatological jet being the result of the jet occupying the northern jet position more frequently in the simulation forced with observed ssts the more frequent occurence of the northern jet location is associated with periods of high eddy heat flux over the gulf stream region composite analysis of high eddy heat flux events reveals that the significantly higher heat flux is followed by larger and more persistient poleward jet excursions in the simulations with realistic ssts compared to the simulation with smoothed ssts with upper tropospheric eddy momentum fluxes acting to maintain the more poleward eddy driven jet periods of high eddy heat flux over the gulf stream region are also shown to be associated with increased blocking frequency over europe which are clearly distinct from periods with a northern jet position

upstream cyclone influence on the predictability of block onsets over the euro atlantic region abstractatmospheric blocking has been shown to be a phenomenon that models struggle to predict accurately particularly the onset of a blocked state following a more zonal flow this struggle is i

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

explosive cyclogenesis and large scale circulation changes implications for atmospheric blocking abstract large scale circulation changes attending explosive surface cyclogenesis are quantitatively examined in two cases selected from recent winter seasons both cases feature a rapidly deepening surface cyclone over the western atlantic ocean but changes in the 500 mb geopotential height field near the cyclone differ in each case one event during january 1977 is characterized by the retrogression of an anticyclonic vortex blocking high in the 500 mb height field downstream of the surface cyclone the second case in february 1978 is distinguished by the formation of a 500 mb cyclonic vortex cutoff low upstream of the surface cyclone but no downstream anticyclonic vortex is observed the retrogression of the january 1977 block over the atlantic ocean coincides with the migration of a 500 mb synoptic scale perturbation associated with the surface cyclone from a planetary scale trough over north america toward a planetary scale ridge over europe in the february 1978 case the blocking cyclo

transport out of the lower stratospheric arctic vortex by rossby wave breaking the fine scale structure in lower stratospheric tracer transport during the period of the two arctic airborne stratospheric expeditions january and february 1989 december 1991 to march 1992 is investigated using contour advection with surgery calculations these calculations show that rossby wave breaking is an ongoing occurrence during these periods and that air is ejected from the polar vortex in the form of long filamentary structures there is good qualitative agreement between these filaments and measurements of chemical tracers taken aboard the nasa er 2 aircraft the ejected air generally remains filamentary and is stretched and mixed with midlatitude air as it is wrapped around the vortex this process transfers vortex air into midlatitudes and also produces a narrow region of fine scale filaments surrounding the polar vortex among other things this makes it difficult to define a vortex edge the calculations also show that strong stirring can occur inside as well as outside the vortex

the climatology of blocking events in a perpetual january simulation of a spectral general circulation model abstract a variety of statistical comparisons is made between the fluctuations occurring in a 1200 day perpetual january simulation of a spectral general circulation model and those occurring in a 20 winter data set attention is focused on the persistent anomalies with lifetimes greater than one week over the atlantic and pacific oceans we show that there is generally good agreement between modeled and observed persistent anomalies in their frequency of occurrence and mean lifetime however we note a striking deficiency in the simulation of persistent anomalies over the soviet union we focus further on a subset of persistent anomalies blocking highs and show that the model blocks have vertical structure in agreement with observations we also show an example of the development of a blocking event which follows an episode of explosive cyclogenesis finally we show an example of the interaction of low and high frequency eddies during a period of blocking and at the termination of model blocking the

deducing anomalous wave source regions during the life cycles of persistent flow anomalies abstract anomalous wave source regions are identified during the life cycles of persistent flow anomalies occurring over the north pacific and north atlantic oceans during boreal winter these cases project strongly upon the pacific north american and eastern atlantic teleconnection patterns respectively and represent two of the primary modes of intraseasonal low frequency variability in the northern hemisphere wintertime circulation in the upper troposphere these cases are manifested by wave trains of large scale and large amplitude flow anomalies extending downstream from key regions near the aleutian islands and south of iceland respectively the occurrence of persistent flow anomalies is closely linked to persistent extremes in surface weather and to variations in the skill of extended range weather forecasts black and dole performed a detailed diagnostic analysis of the onset of persistent cyclonic flow anomalies over the north pacific a key result of their study was that wave activity flux di