intraseasonal variability of the saharan heat low and its link with midlatitudes abstract the saharan heat low shl is thought to be a key feature of the west african monsoon and its variations during the summer season have not yet been systematically assessed to characterize the intraseasonal variations of the shl real and complex empirical orthogonal function analyses were applied to the 850 hpa potential temperature field over northern africa and the mediterranean using ncep department of energy doe atmospheric model intercomparison project amip ii reanalysis results a robust quasi propagative mode was highlighted over north africa and the mediterranean this mode consists of two phases the west phase corresponds to a maximum temperature over the coast of morocco mauritania propagating southwestward and a minimum between libya and sicily propagating southeastward the east phase corresponds to the opposite temperature structure which propagates as in the west phase a lag composite analysis revealed that this shl mode was preceded by large scale midlatitude intrase

stationary rossby wave propagation in a baroclinic atmosphere observational studies of teleconnections in both soisticial seasons have suggested various patterns of behaviour linked mainly to westerly jets and equatorial westerlies these have been interpreted using barotropic rossby wave theory and simulated using stationary forcing in barotropic models linearized about 300 hpa flows in this paper the relevant propagation behaviour is investigated using a baroclinic model with three dimensional climatological basic states time integrations are performed using localized thermal forcing as a wavemaker the propagation results are qualitatively very similar to those obtained with the barotropic model though there are quantitative differences the westerly jets still act as strong waveguides the shorter wavelengths and smaller wave activity speeds found with the baroclinic model are generally in better agreement with observation propagation into and from the upper tropospheric equatorial westerlies in the east pacific propagation across north america and propagation from europe across the arabian gulf are all found the extent to which upper tropospheric westerlies reach towards the equator influences the propagation into those regions barotropic models can only represent such behaviour if the basic state reflects the near equatorial upper tropospheric zonal wind structure

why do baroclinic waves tilt poleward with height theoretical and modeling studies of nongeostrophic effects in baroclinic waves predict that baroclinic waves should tilt poleward with height with a larger tilt in total meridional wind than in geostrophic quantities regression analysis of ncep ncar reanalysis 6 hourly data demonstrates that observed baroclinic waves do indeed tilt poleward with height although the observed tilt is smaller than predicted by previous studies the meridional ageostrophic wind enhances the poleward tilt of meridional wind perturbations despite being smaller in amplitude than the meridional geostrophic wind by a factor of 5 an improved estimate of the structure of the meridional ageostrophic wind in baroclinic waves is calculated assuming force balance several important terms in this estimate have been left out of previous estimates of the meridional ageostrophic wind three terms in the improved estimate produce nearly all of the poleward tilt of the meridional wind 1 the advection of geostrophic zonal wind perturbations by the mean zonal wind 2 the convergence of the eddy momentum flux and 3 the effect of friction the poleward tilt with height of baroclinic waves explains why upper level storm tracks tend to occur poleward of near surface baroclinic regions and may play a role in the midwinter suppression of the pacific storm track

causes of reduced north atlantic storm activity in a cam3 simulation of the last glacial maximum abstract the aim of this paper is to determine how an atmosphere with enhanced mean state baroclinity can support weaker baroclinic wave activity than an atmosphere with weak mean state baroclinity as a case study a last glacial maximum lgm model simulation previously documented to have reduced baroclinic storm activity relative to the modern day climate simulated by the same model despite having an enhanced midlatitude temperature gradient is considered several candidate mechanisms are evaluated to explain this apparent paradox a linear stability analysis is first performed on the jet in the modern day and the lgm simulation the latter has relatively strong barotropic velocity shear it was found that the lgm mean state is more unstable to baroclinic disturbances than the modern day mean state although the three dimensional jet structure does stabilize the lgm jet relative to the eady growth rate next feature tracking was used to assess the storm track seeding and temporal growth of distur

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

pacific north american teleconnection controls on precipitation isotope ratios across the contiguous united states large scale climate teleconnections such as the pacific north american pna pattern strongly influence atmospheric processes and continental climate here we show that precipitation 18o values in the contiguous united states are correlated with an index of the pna pattern the 18o pna relationship varies across the study region and exhibits two prominent modes with positive correlation in the western usa and negative correlation in the east this spatial pattern appears not to reflect variation in local climate variables but rather primarily reflects differences in atmospheric circulation and moisture sources associated with pna our results suggest that strong antiphase variation in paired paleo water 18o proxy records from regions characterized by the two modes of 18o pna correlation especially in the midwest and southwestern usa may provide a robust basis for reconstruction of past variation in the pna pattern

poleward deflection of storm tracks an analysis of 11 years of european centre for medium range weather forecasts data focuses primarily on the vertically averaged high frequency transients the conclusions are discussed in the context of a the winter storm track b monthly variability and c interannual variability a winter storm track results show that the pattern of the forcing by the high frequency eddies along the storm track is highly correlated with the stationary circulation and the forcing itself is primarily responsible for the location of the trough ridge system associated with the stationary flow the results also clarify the role of wind component covariance terms u9y9 and y9 2 2 u9 2 in the column averaged vorticity forcing the simpler term u9y9 has the well known effect of intensifying the anticyclonic cyclonic tendencies on the southern northern side of the jet thereby producing an increase in the barotropic component of the zonal jet the y9 2 2 u9 2 term displays a quadrupole pattern which is also approximately in phase with the trough ridge system associated with the stationary flow b monthly variability eddy activity has been shown to possess a seasonal life cycle increasing during the early fall and reaching a maximum around the month of november then decaying for most of the winter months month to month variations in eddy activity over the pacific ocean show that energy levels increase up through november decreasing thereafter at the same time the trough ridge circulation pattern is intensifying by december baroclinicity in the western pacific has increased substantially and low level eddies are found to break by the middle of the ocean upper level eddies start to break well before reaching the west coast of north america resulting in a displacement of the maximum in y9 2 2 u9 2 westward from its november position and increasing the trough ridge forcing by the high frequency eddies c interannual variability wintertime eddy kinetic energy is seen to extend further eastward through the pacific ocean during the warm phase but displays an abrupt termination during the cold phase anomalies in the eddy transient forcing tend to be quite similar to that of the pacific north american pattern itself the extension of the storm track during the warm phase resembles that of fall conditions and is present in the winter season because the source of low level baroclinicity

linear contributions of different time scales to teleconnectivity the contributions of different time scales to extratropical teleconnections are examined by applying empirical orthogonal functions and correlation analyses to reanalysis data it is shown that eddies with periods shorter than 10 days have no linear contribution to teleconnectivity instead synoptic variability follows wavelike patterns along the storm tracks interpreted as propagating baroclinic disturbances in agreement with preceding studies it is found that teleconnections such as the north atlantic oscillation nao and the pacific north america pna pattern occur only at low frequencies typically for periods more than 20 days low frequency potential vorticity variability is shown to follow patterns analogous to known teleconnections but with shapes that differ considerably from them it is concluded that the role if any of synoptic eddies in determining and forcing teleconnections needs to be sought in nonlinear interactions with the slower transients the present results demonstrate that daily variability of teleconnection indices cannot be interpreted in terms of the teleconnection patterns only the slow part of the variability

a pathway connecting the monsoonal heating to the rapid arctic ice melt abstractthis study provides a monsoonal link to the rapid arctic ice melt each year the planetary scale african asian monsoonal outflow near the tropopause carries a large anticyclonic gyre that has a longitudinal spread that occupies nearly half of the entire tropics in recent years the south asian summer monsoon has experienced increased rainfall over northwestern india and pakistan and it has also contributed to more intense local anticyclonic outflows from this region the western lobes of these intense upper high pressure areas carry outflows with large heat fluxes from the monsoon belt toward central asia and eventually to the region of the rapid ice melt of the canadian arctic in this study this spectacular pathway has been defined from airflow trajectories heat content and heat flux anomalies most of these show slow increasing trends in the last 20 years the monsoonal connection to the rapid arctic ice melt is a new contribution of this study this is shown from the passage of a vertical c

development of the palaeogeography of pangaea from late carboniferous to early permian abstract old and new well and poorly known lithofacies data of moscovian and artinskian age in the area limited by the arctic sea and central africa the atlantic ocean and the ural mountains have been plotted on present day maps the facies mapped and related environments allow the recognition of a series of different palaeogeographic palaeotectonic units including the late carboniferous to early permian deep sea to palaeo tethyan ocean west siberia kazakhstan continent and uralian kazakhstan tienshan arc uralian foredeep up to the closing arms of the uralian ocean precaspian basin russian platform donets rift basin caucasian moesian dobrogean polish oslo basinal belt syn tectonic hercynian foreland basin intramontane post hercynian basins iran anatolian hellenic dinaric carnic basin branching into the hungarian seaway apennine basin branching into the cantabrian and south portuguese basins oman iraq levantine sicily deep basin and inferred oceanic sea way south peri tethyan platform basins east arabian cratonic basin and north african intracratonic basins the subsidence sedimentation trends of these units were correlated and compared through lithostratigraphic logs bathymetric curves and uncorrected cumulative stratigraphic curves the sets of original and processed data were used to test two different palaeodynamic models a pangaea a model static from late carboniferous to triassic and a mobile pangaea b model with different dextral displacements between laurussia and gondwanaland in the same time interval the best fit for our data requires a strike slip offset of about 800 km from moscovian to artinskian time this model implies a first quasi pangaea or pangaea b assembly at the carboniferous permian transition an ephemeral pangaea b break up driven by an early permian oblique rift across the mediterranean to caribbean areas and a final pangaea a assembly in the mid to late permian the two palinspastic maps describing the model have been cross checked by comparison with an independent set of biogeographic features of late carboniferous and early permian overall floral reptile and marine benthic organism distribution is consistent with the early permian trans pangaea seaway inferred from facies and palaeodynamic analyses

the initial value problem for tropical perturbations to a baroclinic atmosphere large scale wave propagation ideas have proved extremely valuable in interpreting real and model data these ideas have been developed in the context of barotropic models and here the extension to baroclinic atmospheres is investigated the dispersion of waves from an initial large scale tropical perturbation to a baroclinic basic flow is studied using a direct approach a 15 level spectral primitive equation model is integrated forward in time even in baroclinically unstable flows it is found that for a period normally of order 12 days the model yields what can be considered to be the direct response to the tropical perturbations after this time baroclinic instability dominates the basic flows are a resting atmosphere a climatological westerly an equatorial longitudinal modification to this and a 3 d climatological december february state for the perturbations used here equatorial kelvin waves play only a very small role the large scale equatorial rossby wave shows only small dispersion and tends to move with a doppler shifted phase speed which allows it to accumulate to the east of an equatorial maximum of 10 ms 1 or more rossby wavetrains propagate into the middle and high latitude westerly regions with the climatological flow perturbations in the indian ocean west pacific sector trigger a modal structure in the north pacific and wavetrain across north america very much as barotropic theory would suggest and similar to observed pacific north america pna patterns in such a flow the middle latitude waves tend to extend to the equator in the westerly regions of the east pacific and atlantic in agreement with observed behaviour

the life cycle of the north atlantic storm track abstractthe north atlantic eddy driven jet exhibits latitudinal variability with evidence of three preferred latitudinal locations south middle and north here the authors examine the drivers of this variability and the variability of the associated storm track the authors investigate the changes in the storm track characteristics for the three jet locations and propose a mechanism by which enhanced storm track activity as measured by upstream heat flux is responsible for cyclical downstream latitudinal shifts in the jet this mechanism is based on a nonlinear oscillator relationship between the enhanced meridional temperature gradient and thus baroclinicity and the meridional high frequency periods of shorter than 10 days eddy heat flux such oscillations in baroclinicity and heat flux induce variability in eddy anisotropy which is associated with the changes in the dominant type of wave breaking and a different latitudinal deflection of the jet the authors results suggest that high heat flu

vertical structure and energetics of the western pacific teleconnection pattern abstractthe western pacific wp pattern characterized by north south dipolar anomalies in pressure over the far east and western north pacific is known as one of the dominant teleconnection patterns in the wintertime northern hemisphere composite analysis reveals that monthly height anomalies exhibit baroclinic structure with their phase lines tilting southwestward with height in the lower troposphere the anomalies can thus yield not only a poleward heat flux across the climatological thermal gradient across the strong pacific jet but also a westward heat flux across the climatological thermal gradient between the north pacific and the cooler asian continent the resultant baroclinic conversion of available potential energy ape from the climatological mean flow contributes most efficiently to the ape maintenance of the monthly wp pattern acting against strong thermal damping effects by anomalous heat exchanges with the underlying ocean and anomalous precipitation in the subtropics and by the effec

characteristics of wave packets in the upper troposphere part i northern hemisphere winter abstract gridded data produced by the ecmwf reanalysis project have been analyzed to document the properties of wave packets in the northern hemisphere winter midlatitude upper troposphere based on results from earlier investigations 300 hpa meridional wind variations were chosen for analysis wave packet envelopes were also defined by performing complex demodulation on the wind data the properties of the wave packets are mainly illustrated using time lagged one point correlation maps performed both on and wave packet envelopes the results show that over most regions in the northern hemisphere winter with the exception of the deep tropics and near the aleutian low medium scale waves dominant wavenumber 5 8 exhibit the characteristics of downstream development and occur within wave trains that propagate with eastward group velocities much faster than the phase speeds of individual phases of the waves their group velocity is highly correlated with the local time mean 200 400 hpa wind while the

40 ar 39 ar polyorogenic mineral age record within the southern mauritanide orogen m bout bakel region west africa the southern mauritanide orogen exposed between m bout and bakel is characterized by several internally imbricated polydeformed and variably metamorphosed infrastructural allochthons sup 40 ar sup 39 ar incremental release ages recorded by hornblende within undeformed granodiorite of the guidimakha complex suggest post magmatic cooling through appropriate argon closure temperatures at approx 670 ma sup 40 ar sup 39 ar ages recorded by muscovite within lithologic elements of both the guidimakha complex and the diala bouanze series suggest initial regional metamorphism associated with pan african i orogenesis was following by cooling through muscovite argon closure temperatures between approx 600 and 620 ma slight rejuvenation of muscovite argon systems occurred locally between approx 325 and 350 ma muscovite and whole rock slate phyllite argon systems within metavolcanic and metavolcaniclastic components of the infrastructural calc alkaline igneous complex easternmost sectors of the m bout series record sup 40 ar sup 39 ar plateau age of approx 300 to 320 ma muscovite and whole rock slate phyllite argon systems within westernmost portions of the study area western portions of the m bout series record sup 40 ar sup 39 ar plateau ages of approx 267 to 312 ma all foreland units within the m bout bakel area were affected by post emsian folding effects of this tectonic activity are widespread throughout the parautochthon and western metamorphic sequences these effects includemore emplacement of suprastructural allochthons and local reactivation of older thrust faults within infrastructural units less

sea surface temperature anomalies planetary waves and air sea feedback in the middle latitudes the mechanisms that contribute to the generation and damping of large scale mid latitude sea surface temperature sst anomalies are discussed the sst anomalies reflect primarily the response of the upper ocean to the changes in air sea fluxes that are associated with daily weather fluctuations heat flux forcing is dominant in the lower middle latitudes while wind driven entrainment may be most effective in the high latitudes advection by anomalous ekman current is generally less important and ekman pumping is negligible the sst anomalies decay in part because of entrainment effects associated with mixed layer deepening and oceanic mixing and in part because of heat exchanges with the atmosphere the three approaches commonly used to model the evolution of sst anomalies are reviewed case studies based on monthly or seasonal anomaly maps of the large scale sst and atmospheric anomalies numerical simulations with one dimensional mixed layer models and stochastic forcing models we stress the similarities in the different approaches and discuss their main advantages and limitations the response of the atmosphere to mid latitude sst anomalies is considered first we discuss the poorly known relationship between sst anomalies and diabatic heating using a crude assumption for the air sea coupling we consider a two layer quasi geostrophic channel model and discuss the stationary wave response to sst anomaly forcing and the resulting air sea feedback it is found that the back interaction of the sst anomalies onto the atmosphere causes a weak sst anomaly damping at large scales and a strong one at small scales the air sea coupling should also act as an eastward propagator for the sst anomalies the response of more realistic linear wave models to prescribed diabatic heating is then reviewed and it is suggested that realistic mid latitude sst anomalies have a weak influence on the atmospheric circulation corresponding to changes in the geopotential height of 10 30 m at most this order of magnitude is consistent with the results of general circulation model experiments and with the limited climate predictability associated with mid latitude sst anomalies

paleomagnetism and the evolution of pangea we present new apparent polar wandering apw paths for the latest carboniferous to middle jurassic of europe northern asia north america and gondwana the paths have been constructed by ordering the paleopoles into a time sequence and calculating running averages globally this statistical analysis cannot be carried back before the latest carboniferous because the paleomagnetic record becomes inadequate the polar paths have all been rotated along with the land masses from which they have been observed into the classical configuration of wegener pangea a as quantified by later workers the mean paleopoles agree in the early jurassic but disagree in the latest carboniferous permian and early triassic this result is insensitive to reasonable choices made regarding the arrangement of the continents within gondwana it is true either for results from gondwana as a whole or from africa and south america alone this disagreement in apw paths suggests but does not prove that pangea a lasted for only a short interval of time in the early to middle jurassic 190 170 m y and perhaps the latest triassic 200 m y alternatively we may say either that the paleomagnetic record is biassed by sampling inadequacies or by systematically incorrect age assignments or that the earth s field has been non dipolar we regard these explanations as less likely although they cannot be discounted the polar paths can be reconciled by rotating gondwana anticlockwise by about 35 relative to laurasia placing africa beneath europe and south america beneath eastern north america this configuration is called pangea b pangea b could be a valid reconstruction for the latest carboniferous and early permian approximately 290 260 m y pangea b provides a statistically satisfactory resolution of the paleomagnetic problem it also provides a symmetrical arrangement of the continents bordering the appalachian hercynian fold belt for the late paleozoic which pangea a does not it provides a satisfactory framework for the early evolution of the gulf of mexico and it provides an explanation of the absence of geological evidence for a tethys ocean in the paleozoic the transition between b and a cannot be accurately reconstructed from the paleomagnetic data because the resolution of the record is as yet inadequate but it presumably occurred by a 3500 km minimum dextral megashear between laurasia and gondwana during the late permian and triassic approximately 250 200 m y without the formation of ocean between them and was accompanied by lesser motions between north america and europe the sense of megashear is the same as that invoked by arthaud and matte 1977 on geological grounds but the magnitude and timing are different our interpretation favors the idea that continental drift is a continuous process not confined to jurassic and later times but extending backwards into the triassic and permian we suggest that pangea was not an immobile configuration as envisaged by wegener and most subsequent workers but that it evolved more or less continuously

dynamical characterization of the fastex cyclogenesis cases summary a series of diagnostics based on the automatic tracking of cyclones is applied to the 25 life cycles captured during the fastex field experiment the tracking enables a setting of the various cases into a common frame of reference that moves with the system time filtering is used to further separate the events into a basic state and perturbations information is obtained on environmental properties such as strain or baroclinicity combining these diagnostics it is shown that instability mechanisms based on the existence of potential vorticity strips or the control of these instabilities by deformation may be involved in the initial genesis of a number of cases but do not seem to characterize specific types nor to determine a systematic behaviour on the other hand it is shown that rapid deepening phases leading eastern atlantic systems to their maximum amplitude happens suddenly and at the same time as crossing the jet stream even in the absence of a clear additional upper level feature for cold air systems development means meeting a diffluent zone this is unlike the american east coast systems that are associated with an exit entrance complex another remarkable feature is the generation of a frontal waveas a re sult of the parent vorticity maximum being apparently stretched and split this has occurred in 25 of cases a number of other properties of the fastex cases are shown such as several occurrences of large

space time spectral analysis of the southern hemisphere daily 500 hpa geopotential height in this paper the authors use the ncep department of energy doe reanalysis 2 ncep2 data from 1979 to 2004 to expand the daily 500 hpa geopotential height in the southern hemisphere sh 908 208s into a double fourier series and analyze the temporal frequency characteristics of the expansion coefficients over various spatial scales for the daily series over the whole year the coefficient series of the extratropical mean heightischaracterizedbyasignificantlow frequency 10 30day variation forzonalwaveswith k l 5 1 5

horizontal structure of 500 mb height fluctuations with long intermediate and short time scales abstract maps of standard deviations and one point correlation maps based on twice daily data subjected to a variety of temporal filters are presented in order to document the horizontal structure of 500 mb height fluctuations with different time scales the filters have been chosen to isolate fluctuations with long time scales periods much longer than 30 days intermediate time scales 10 30 day periods and short time scales 2 5 6 day periods the one point correlation maps for long time scales resemble the teleconnection patterns described by wallace and cutzler these patterns are strongly regionally dependent with meridionally oriented dipole structures in the jet exit regions over the oceans indicative of strong fluctuations in the zonal wind for intermediate time scales the dominant patterns consist of more zonally oriented wave trains which originate in the jet entrance regions and cross the jet streams as they curve southeastward into the tropics another important distinction between th

patterns of wintertime jet stream variability and their relation to the storm tracks abstract a new approach is put forward for defining extratropical teleconnection patterns the zonal wind field at 250 hpa is analyzed separately in the north atlantic and north pacific ocean sectors during the winter season december march teleconnectivity of this field is found to be particularly strong eof analysis of the zonal wind field yields patterns that i are robust with respect to the range of frequencies included in the data ii relate clearly to the position of the climatological mean jets and iii are broadly consistent with their traditionally defined counterparts in terms of climatic impacts the patterns are characterized by a north south shifting or an extension retraction of the eddy driven jet in its exit region and similar changes at the entrance region of the subtropical jet the patterns also reflect the degree of separation between the subtropical and eddy driven jets atlantic eofs 1 and 2 are counterparts of the north atlantic oscillation nao and eastern atlantic patter

cross frequency coupling skewness and blocking in the northern hemisphere winter circulation abstract variability in daily wintertime december february djf 500 hpa heights on low l 6 day 1 frequencies is examined using 40 yr ecmwf re analysis era 40 data leading eofs of l correspond to planetary scale teleconnection patterns those of m to retrograding eastward dispersing long waves oriented along great circle routes and those of h to baroclinic waves in the climatological mean storm tracks in the atlantic sector eof 1 of m appears to be embedded in eof 1 of l cross frequency coupling between l and m exhibits distinctive patterns in the atlantic sector the negative polarity of the north atlantic oscillation nao with above normal heights over greenland is associated with enhanced m variability over greenland an analogous relationship is observed in the pacific sector between an nao like pattern and the variance of m over alaska cross frequency coupling between l and h in both sectors is indicative of a reinforcement

quasi biweekly oscillation over the tibetan plateau and its link with the asian summer monsoon abstract intraseasonal variation isv is especially prominent and unique in the asian summer monsoon region in this work the dominant isv mode over the tibetan plateau tp in the summer monsoon season june august together with its structure and evolution is identified using station observations global precipitation climatology project precipitation data and era interim during 1979 2011 results indicate that quasi biweekly oscillation qbwo is the dominant mode of isv over the tp and is significant in terms of the circulation precipitation and diabatic heating fields in particular the qbwo is closely related to the onset and active break phases of the tp summer monsoon in most cases the qbwo originates from the equatorial western pacific and first propagates northwestward to the bay of bengal and northern india then northward to the southeastern tp and finally eastward to the east asian area showing a clockwise propagation pathway two main mechanisms are responsible for the northward

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

afro eurasian intermediate frequency teleconnection and modulation by enso abstractthe afro eurasian intermediate frequency atmospheric teleconnection conveys meteorological signals zonally leads to various atmospheric variations and causes extreme events along its path

interannual variations and future change of wintertime extratropical cyclone activity over north america in ccsm3 climatology and interannual variations of wintertime extratropical cyclone frequency in ccsm3 twentieth century simulation are compared with the ncep ncar reanalysis during 1950 1999 ccsm3 can simulate the storm tracks reasonably well although the model produces slightly less cyclones at the beginning of the pacific and atlantic storm tracks and weaker poleward deflection over the pacific as in the reanalysis frequency of cyclones stronger than 980 hpa shows significant correlation with the pacific north america pna teleconnection pattern over the pacific region and with the north atlantic oscillation nao in the atlantic sector composite maps are constructed for opposite phases of el nino southern oscillation enso and the nao and all anomalous patterns coincide with observed one ccsm3 twenty first century a1b scenario realization indicates there is significant increase in the extratropical cyclone frequency on the us west coast and decrease in alaska meanwhile cyclone frequency increases from the great lakes region to quebec and decreases over the us east coast suggesting a possible northward shift of the atlantic storm tracks under the warmer climate the cyclone frequency anomalies are closely linked to changes in seasonal mean states of the upper troposphere zonal wind and baroclinicity in the lower troposphere due to lack of 6 hourly outputs we cannot apply the cyclone tracking algorithm to the other eight ccsm3 realizations based on the linkage between the mean state change and the cyclone frequency anomalies it is likely a common feature among the other ensemble members that cyclone activity is reduced on the east coast and in alaska as a result of global warming

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

daily scale planetary wave patterns and the modulation of cold season weather in the northern extratropics tropospheric planetary waves often linked to asymmetries in lower boundary forcing significantly modulate atmospheric blocking and storm track structures that are in turn linked to extreme surface weather events day to day variability in the planetary scale circulation taken as wavenumbers 1 to 5 in the daily 500 hpa geopotential heights and the associated impact on storm tracks and regional weather are studied for the period 1950 2005 six boreal cold season distinct planetary wave patterns are identified via hierarchical cluster analysis the first second and sixth patterns feature a prominent zonal wavenumber 1 structure while the fourth and fifth patterns resemble the negative and positive phases of northern annular mode respectively the second pattern represents an amplification of the climatological mean wave structure while the third pattern resembles the zonal wavenumber 3 pattern a multi taper spectral analysis of the daily projection indices indicates that the planetary wave patterns are primarily intraseasonal in nature the first sixth pattern combines the positive negative phase of the pacific north american teleconnection pattern and negative positive phase of the north atlantic oscillation inducing poleward equatorward shifts in the pacific storm track and a weakened strengthened atlantic storm track in contrast the fourth fifth pattern results in a simultaneous equatorward poleward displacement of both storm tracks extreme cold waves over the continental united states us are favored during occurrences of the fourth and sixth patterns during episodes of the first pattern increased rainfall prevails over much of the us while precipitation anomalies induced by the other patterns are more regional in nature

the intraseasonal oscillation of eastern tibetan plateau precipitation in response to the summer eurasian wave train abstractthis study examines the characteristics and mechanisms associated with the dominant intraseasonal oscillation iso that controlled eastern tibetan plateau summer rainfall etpsr over the period 1979 2011 the results of both power and wavelet spectrum analysis reveal that etpsr follows a significant 7 20 day oscillation during most summers the vertical structure of the etpsr iso in the dry phase is characterized by a vertical dipole pattern of geopotential height with a positive center on the eastern tibetan plateau tp and a negative center on the western tp the wet phase shows the opposite characteristics to the dry phase the transitions between the dry and wet phases during an etpsr iso cycle are related to a rossby wave train that presents as large anomalous anticyclonic and cyclonic centers that alternate along the pathway from the eastern atlantic to southern china via the tp it corresponds to the evolution of the phase independent wave activity w which implies an eastward southeastw

permian circumpacific deep water faunas from the western tethys sicily italy new evidences for the position of the permian tethys abstract circumpacific deep water faunas characterized mainly by radiolarians paleopsychrospheric ostracods and conodonts were found in the early middle and late permian deposits pertaining to the sicanian paleogeographic domain of western sicily near the western end of the eurasiatic tethys similar permian deep water faunas are known from the phyllite unit of crete and from oman in the latter area partly above oceanic crust all these occurrences indicate the presence of a late paleozoic tethys ocean immediately north of gondwana

horizontal structure and seasonality of large scale circulations associated with submonthly tropical convection the relationship between deep tropical convection and large scale atmospheric circulation in the 6 30 day period range is examined regression relationships between filtered outgoing longwave radiation at various locations in the tropics and 200 and 850 mb circulation are mapped for the standard seasons and the spatial structure and seasonal dependence of the results are interpreted in view of the basic state circulation in regions where the convection is embedded in upper level easterlies anomalous equatorial easterly flow is typically present at 200 mb within and to the west of the convective signal along with patterns of meridional outflow into subtropical anticyclonic perturbations lagged relationships suggest that the convection is forcing the circulation in many of these cases the outflow and subtropical circulations are strongest into the winter hemisphere during the solstitial seasons with more symmetric signals about the equator seen in the equinoctial seasons the longitudinal positioning of the subtropical features with respect to the convection varies but is generally located due poleward or just to the east of the convection there tends to be a first baroclinic mode vertical structure to these circulations such that equatorial westerlies are present at 850 mb within the convection with closed circulations on either side of the equator resembling equatorial rossby modes especially common over the atlantic and pacific sectors as a contrast in regions located within upper level westerlies or along the margin of influence of upper westerly disturbances convection appears to be forced by upper level wave energy propagating into the deep tropics with the heating located in the upward motion region ahead of upper level troughs this occurs over the atlantic and eastern pacific sectors during northern winter and spring and over australia the south pacific and south america during southern summer when upper westerlies are at relatively low latitudes where they can interact with deep tropical convection the results confirm theoretical and modeling ideas that suggest that rossby wave energy is able to propagate into the deep tropics in regions where upper level westerlies exist in the tropics

subseasonal variations in warm season moisture transport and precipitation over the central and eastern united states abstract subseasonal variations in warm season may august precipitation over the central and eastern united states are shown to be strongly linked to variations in the moisture entering the continent from the gulf of mexico within a longitudinally confined channel referred to here as the texas corridor or tc these variations reflect the development of low level southerly wind maxima or jets on a number of different timescales in association with distinct subcontinental and larger scale phenomena on the diurnal timescale the tc moisture flux variations are tied to the development of the great plains low level jet the composite nighttime anomalies are characterized by a strong southerly moisture flux covering northeast mexico and the southern great plains and enhanced boundary layer convergence and precipitation over much of the upper great plains the strongest jets tend to be associated with an anomalous surface low over the great plains reflecting a predilection for periods when midlatitude

a general circulation model study of the atmospheric response to extratropical sst anomalies observed in 1950 79 abstract a 30 year experiment with an atmospheric general simulation model has been performed the lower boundary condition at all oceanic grid points between 38 s and 60 n has been prescribed to follow the observed month to month variation of the sea surface temperature sst field during the 1950 79 period much of the model diagnosis presented here pertains to the midlatitude atmospheric response to recurrent sst patterns in the north pacific and north atlantic in winter the principal modes of variability of the seasonally averaged 515 mb height and sst fields have been identified using rotated principal component rpc analysis the extrema of the first atmospheric mode reside over the north atlantic and eurasia whereas the second mode is associated with height anomalies in the north pacific north american sector cross correlation analysis reveals that these two atmospheric modes am linked to leading patterns of the sst field in the north atlantic and north pacific respectively it is also demonst

the spring relationship between the pacific north american pattern and the north atlantic oscillation the pacific north american pattern pna and north atlantic oscillation nao are two dominant modes of low frequency variability in the northern hemisphere winter generally these two patterns are separable and uncorrelated in both space and time however dating back to the 1970s there have been studies which have linked the aleutian and icelandic low intensities and shown that a significant temporal correlation does on occasion occur each of these semi permanent low pressure systems is a part of the pna and nao patterns respectively and therefore given a link between the two semi permanent low pressure systems we explore whether a link between the pna and nao also appears recently studies have found such a link during the winters of certain decades the present study documents an observed relationship between the pna and nao which is consistently present during the spring and early summer this relationship is shown to be due to the fact that the pna and nao are spatially overlapping projections of the same pattern of variability given by the first eof of 500 hpa geopotential height both the pna and nao patterns correlate more strongly to the first eof s spatial pattern resembling the aleutian low icelandic low seesaw pattern than the rotated eof reof loading patterns used to compute their respective indices furthermore when the two patterns are correlated the effect of el nino on the northern hemisphere is separate from the pattern associated with the pna finally we examine a 21 year period in the winter for which the pna and nao are significantly correlated and find that the conclusions drawn from the spring hold true the results presented herein demonstrate that defining the pna and nao based upon typical loading patterns may not be the ideal approach especially given that the patterns are spatially similar and covary in time

teleconnections and low frequency variability in idealized experiments with two storm tracks low frequency variability and teleconnection patterns induced by two storm tracks in idealized experiments depend on their zonal distance a separation of about 150 which resembles the northern hemisphere storm track distribution reveals teleconnection patterns which are similar to the pacific north american pna pattern and the north atlantic oscillation nao the nao like structure is associated with retrograde travelling rossby waves barotropic stream function tendencies show that the interaction of the stationary eddies with the low frequency flow and the high frequency eddies contribute to the amplification of the pattern its decay is due to their interaction with the zonal mean flow and the low frequency contribution to the divergence term the pna like pattern has a longer memory and is linked to a quasi stationary wave the stationary wave activity flux shows the dominating influence of baroclinic processes and the other storm track further upstream the correlation between the teleconnection indices is significant for storm track distances between 180 and 160 and vanishes between 150 and 130

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

rossby wave propagation into the tropics in two gfdl general circulation models during the northern winter the eastern pacific is characterized by upper level westerly flow extending from the equator into the midlatitudes of both hemispheres theoretical and simple modeling studies suggest that such a region should favor the penetration of rossby waves into the tropics from higher latitudes observational results by kiladis and weickmann using 200 mb data indicate that rossby waves do indeed propagate freely into the tropical eastern pacific during the northern winter from the asian jet exit region they also confirmed that cross equatorial dispersion of energy from the northern into the southern hemisphere occurs frequently the present study examines these interactions in climatological runs of two gfdl gcms the northern wintertime mean states of these models are characterized by a rather realistically simulated upper level westerly regime in the tropical pacific despite the relative weakness of the asian jet and wave activity with respect to observations propagation of rossby waves into the tropics is present in both models and these waves are strongly positively tilted as seen in the observations a momentum budget of the zonal wind and e vector diagnostics over the tropical pacific indicate that these transients are an important component of the momentum balance of the equatorial westerlies in both the observations and in the models

intraseasonal variations in the southern hemisphere circulation abstract intraseasonal variations in the southern hemisphere atmospheric circulation have been examined through the application of a 10 50 day bandpass filter to daily ecmwf analyses for 1980 88 variations on this time scale contribute more than 40 of the daily variance in 500 hpa geopotential over much of the middle and high latitudes of the southern hemisphere eof analysis of the unnormalized variance for all seasons shows that 49 of this variance can be explained by zonal wave trains centered on the south pacific and southern atlantic indian oceans a high latitude mode of global extent and a wavenumber 3 pattern at midlatitudes these modes are essentially equivalent barotropic but slope westward with height so that the patterns at 100 hpa typically lag those at 1000 hpa by around 1o longitude there appears to be little interaction with the low latitude circulation all of the leading modes propagate eastward but the most consistent movement is shown by the south pacific wave train represented

the asymmetric eddy background flow interaction in the north pacific storm track using a recently developed methodology namely the multiscale window transform mwt and the mwt based theory of canonical transfer and localized multiscale energetics analysis we investigate in an eddy following way the nonlinear eddy background flow interaction in the north pacific storm track based on the era40 reanalysis data from ecwmf it is found that more than 50 of the storms occur on the northern flank of the jet stream about 40 are around the jet center and very few less than 5 happen on the southern flank for storms near or to the north of the jet center their interaction with the background flow is asymmetric in latitude in higher latitudes strong downscale canonical available potential energy transfer happens especially in the middle troposphere which reduces the background baroclinicity and decelerates the jet in lower latitudes upscale canonical kinetic energy transfer intensifies at the jet center accelerating the jet and enhancing the middle level baroclinicity the resultant effect is that the jet strengthens but narrows leading to an anomalous dipolar pattern in the fields of background wind and baroclinicity for the storms on the southern side of the jet the baroclinic canonical transfer is rather weak on average the local interaction begins from about 3 days before a storm arrives at the site of observation achieves its maximum as the storm arrives and then weakens

a survey of small scale waves and wave like phenomena in jupiter s atmosphere detected by junocam in the first 20 orbits of the juno spacecraft around jupiter we have identified a variety of wave like features in images made by its public outreach camera junocam because of juno s unprecedented and repeated proximity to jupiter s cloud tops during its close approaches junocam has detected more wave structures than any previous surveys most of the waves appear in long wave packets oriented east west and populated by narrow wave crests spacing between crests were measured as small as 30 km shorter than any previously measured some waves are associated with atmospheric features but others are not ostensibly associated with any visible cloud phenomena and thus may be generated by dynamical forcing below the visible cloud tops some waves also appear to be converging and others appear to be overlapping possibly at different atmospheric levels another type of wave has a series of fronts that appear to be radiating outward from the center of a cyclone most of these waves appear within 5 of latitude from the equator but we have detected waves covering planetocentric latitudes between 20 s and 45 n the great majority of the waves appear in regions associated with prograde motions of the mean zonal flow juno was unable to measure the velocity of wave features to diagnose the wave types due to its close and rapid flybys however both by our own upper limits on wave motions and by analogy with previous measurements we expect that the waves junocam detected near the equator are inertia gravity waves

seasonal variations in the southern hemisphere storm tracks and associated wave propagation abstract seasonal variations in the southern hemisphere sh storm track characteristics and associated wave propagation are studied using 19 years of ncep ncar gridded data it is found that the sh storm track is strongest in the austral autumn season and weakest in spring the characteristics of wave packets are studied by computing 1 point lag correlation maps with unfiltered meridional wind at 300 hpa it is found that the eastward group velocities of waves are much higher than the phase velocities in the transition seasons this shows that the downstream development occurs throughout the year and is a basic feature of upper tropospheric waves in the midlatitudes of the sh this extends previous studies made for winter and summer seasons based on the indices that show wave coherence and correlation maps it is found that the pathways in the transition seasons split into two branches east of australia in a way similar to what happens in the zonal wind distribution

role of cross equatorial waves in maintaining long periods of low convective activity over southern africa abstractperiods of low convective activity over southern africa during the peak rainy season from december to february are known to be due to the northeastward displacement of the tropical temperate trough ttt systems from the landmass in this study using interim european centre for medium range weather forecasts ecmwf re analysis era interim data the authors show that the displacement of the ttt systems during long periods of low convective activity has origins in the northern hemisphere using standardized area averaged outgoing longwave radiation olr daily anomalies over southern africa long periods of low convective activity are defined as periods of positive olr anomalies lasting consecutively for 5 or more days with a standard deviation of 1 or more an eddy streamfunction anomaly composite of the periods of low convective activity shows an upper level anomalous wave originating in the northern hemisphere and extending to southern africa from the eastern pacific and displacing the tropic

long term equilibrium tides extreme equilibrium tides or hypertides are computed in a new equilibrium tidal model combining algorithms of a version of the chapront elp 2000 82 lunar theory with the ber78 milankovitch astronomical expansions for the rerent past a high correspondence exists between computed semidiurnal tide levels and a record of coastal flooding demonstrating that astronomical alignment is a potential influence on such flooding for the holocene and near future maximum tides demonstrate cyclic variations with peaks at near 5000 b p and 4000 a p on the late quaternary timescale variations in maximum equilibrium tide level display oscillations with periods of approximately 10 000 100 000 and 400 000 years because of precessional shifts in tidal maxima between vernal and autumnal equinoxes while flooding occurs under the combined effects of tides and storms via storm surges the most extensive flooding will occur with the coincidence of storms and the rarer hypertides and is thus primarily influenced by hypertides therefore we suggest that astronomical alignment s relationship to coastal flooding is probabilistic rather than deterministic data derived from this model are applicable to 1 archaeological and paleoclimatic coastal reconstructions 2 long term planning for example radioactive waste site selection 3 sealevel change and paleoestuarine studies or 4 ocean meteorological interactions

the amplitude asymmetry between synoptic cyclones and anticyclones implications for filtering methods in feature tracking abstract the background state is commonly removed from synoptic fields by use of either a spatial or temporal filter prior to the application of feature tracking commonly used spatial and temporal filters applied to sea level pressure data admit substantially different information to be included in the synoptic fields the spatial filter retains a time mean field that has comparable magnitude to a typical synoptic perturbation in contrast the temporal filter removes the entire time mean field the inclusion of the time mean spatially filtered field biases the feature tracking statistics toward large cyclone anticyclone magnitudes in the regions of climatological lows highs the resulting cyclone anticyclone magnitude asymmetries in each region are found to be inconsistent with the unfiltered data fields and merely result from the spurious inclusion of the time mean fields in the spatially filtered data the temporally filtered fields do not suffer from the same problem and produce modest cyclone

an analysis of a relatively rare case of continental blocking planetary and synoptic scale analyses of a relatively rare continental blocking event that occurred over north america during the spring of 1980 are undertaken to determine whether or not this event was different from its counterparts which occur over oceanic regions the planetary scale analysis demonstrates that during the spring season a ridge was located further inland over the north american continent and amplified with respect to climatology the position of this ridge may have been linked to a broad region of colder than normal sea surface temperatures found over the north central pacific during the spring season and much of the previous winter simple sutcliffe type and thermodynamic analyses of the accompanying lower tropospheric warm anomaly associated with the ridging show that lower tropospheric temperature advection and subsidence associated with anticyclonic vorticity advection by the time mean thermal wind produced much of the anomalous warmth a simple synoptic scale analysis was performed using both the zwack okossi zo equation and potential vorticity pv thinking approaches these complementary analyses demonstrated that synoptic scale cyclones were instrumental in the formation and maintenance and or intensification of this blocking event the pv analysis demonstrated that low pv air was swept polewards and then was advected over the blocking region sustaining the broad region of low potential vorticity associated with the block over north america the zo analysis showed that the advection of anticyclonic vorticity was the most important mechanism forcing geopotential height rises at 500 hpa over the block centre the region of low pv and zo height rises could be associated with the anticyclonic shear side of an upstream jet maximum typically found in association with developing and or intensifying blocking events thus negative pv advection correlated significantly with calculated zo height rises finally it is suggested that a favourable phase relationship between the upstream cyclones and the large scale ridge is necessary for block development or intensification

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

a new variable threshold persistent anomaly index northern hemisphere anomalies in the era interim reanalysis abstractpersistent weather regimes characterized by anomalous temperature or precipitation are often associated with persistent anomalies pas in the tropospheric geopotential height field to ide

the large scale modulation of subtropical cyclogenesis in the central and eastern pacific ocean abstract an analysis of the composite large scale circulation associated with periods of enhanced active or diminished inactive cyclogenesis in the subtropical central and eastern pacific ocean is presented composites were constructed using surface and tropospheric analyses from the ecmwf tropical ocean global atmosphere toga dataset for 10 northern hemisphere cool seasons 1986 96 active periods of subtropical cyclogenesis were defined to be periods in which two or more cyclones developed in close succession to each other while inactive periods were defined to be periods of at least 10 days duration during which no cyclones with a subtropical origin were present in the pacific basin the analysis revealed that the occurrence of subtropical cyclones in the central and eastern pacific ocean is strongly linked to the strength and location of the asian jet with active periods characterized by a weaker zonally retracted asian jet while inactive periods are characterized by a stronger zonally elon

behavior of one to two week summertime subtropical wind maxima over the south pacific during an enso cycle abstract the behavior of subtropical jet streaks over the australian south pacific region is investigated for four consecutive 6 month summer seasons november to april during the period 1985 89 the study is an extension of a recent one by ko and vincent hereafter referred to as kv in which jet streaks during the summer season of 1984 85 were examined ko and vincent found that the upper tropospheric zonal wind behaved in a quasi periodic manner with maxima recurring over the western south pacific at intervals between one and two weeks in the present study wind maxima are found to exhibit a 1 2 week periodic oscillation over the south pacific in all four years thus substantiating the finding by kv in addition a second set of jet streaks with a similar periodicity is found over the southern australian region it is also seen that the mean summertime position of the south pacific jet and its accompanying jet streaks are much farther cast during the el nino event of 1986 87 than they are in the

interhemispheric propagation of stationary rossby waves in a horizontally nonuniform background flow abstractsignificant interhemispheric teleconnections are identified that span the tropical easterlies in the boreal summer 300 hpa streamfunction such as the north africa antarctic naa and the north pacific south america npsa patterns these patterns are not supported by traditional wave theory since stationary waves in a basic state without meridional wind would be trapped in the easterlies to describe the interhemispheric responses more realistically two dimensional spherical rossby wave theory in a horizontally nonuniform basic state is considered conditions sufficient for the existence of one propagating wave are obtained and the meridional group velocity of the wave is shown to have the same direction as the meridional basic wind at the traditional critical latitude it is concluded that stationary waves with a specific wavelength can propagate across the easterlies from south north to north south via southerly northerly flows hence energy transport by stationary waves on a horizont

quantitative reconstruction of younger dryas to mid holocene paleoclimates at le locle swiss jura using pollen and lake level data abstract pollen and lake level data from le locle in the swiss jura were used to quantitatively reconstruct climatic parameters for the younger dryas event and the first half of the holocene period the younger dryas cold event at le locle was characterized by i a general trend toward a slight increase in summer temperature and a decrease in annual precipitation and ii a marked drying phase at ca 11 900 cal yr b p that occurred between two wetter ones further phases of major deficit in moisture occured at ca 11 500 cal yr b p younger dryas holocene transition 10 800 cal yr b p 8700 cal yr b p and 6500 cal yr b p climatic parameters reconstructed here suggest that phases of higher lake level developing at ca 12 500 12 000 11 750 11 600 11 200 10 900 synchronous with the preboreal oscillation 10 400 8900 8400 8300 possibly related to the 8200 yr event and 7800 7000 cal yr b p coincided with an increase in annual precipitation a decrease in summer temperature and a shorter growing season conversely periods of low lake level corresponded to a decrease in annual precipitation an increase in summer temperature and a longer growing season this general pattern could have resulted from alternate southward northward displacements of the atlantic westerly jet

a kinematic mechanism for positive feedback between synoptic eddies and nao 1 a kinematic mechanism for the positive feedback between the north atlantic oscillation nao and synoptic eddies are depicted based on observational data analyses using three point rescaled covariance statistics of band pass filtered 2 8 days synoptic eddy fields we examined observed eddy structure changes associated with winter mean nao anomalous flow it is demonstrated that the nao flow anomalies systematically deform the structures of recurring synoptic eddies to generate seasonal mean eddy vorticity flux anomalies predominately directed to the left hand side of the nao flow anomalies these anomalous eddy vorticity fluxes converge into the cyclonic center and diverge from the anticyclonic center of the anomalous nao flow and thus enhance the nao flow

spatial and temporal characteristics of the wind forcing of the bering sea abstract the surface wind stress over the bering sea is estimated for the period 1946 90 from sea level pressure analyses empirical relationships between the geostrophic wind and the surface wind and a bulk aerodynamic formula the focus is on the propagation and variability of the stress and the curl of the stress as a function of frequency the stress at high frequencies 0 1 cpd is dominated by northward and eastward propagating disturbances with mean wavelengths of 2500 and 10 000 km respectively at periods of 10 100 days the mean propagation is near zero there are however significant interannual variations in the zonal propagation wind driven ocean transports estimated by the sverdrup method for the deep bering basin account for 6 sv or roughly one half of the observed transport within the western boundary current along the kamchatka peninsula a low pass filtered retaining periods greater than 18 months time series of the sverdrup transport exhibits a standard deviation of 25 of th

interannual variability in north atlantic weather data analysis and a quasigeostrophic model abstractthis paper addresses the effect of interannual variability in jet stream orientation on weather systems over the north atlantic basin nab the observational analysis relies on 65 yr of ncep ncar reanalysis 1948 2012 the total daily kinetic energy of the geostrophic wind gtke is taken as a measure of storm activity over the north atlantic the nab is partitioned into four rectangular regions and the winter average of gtke is calculated for each quadrant the spatial gtke average over all four quadrants shows striking year to year variability and is strongly correlated with the north atlantic oscillation nao the gtke strength in the northeast quadrant is closely related to the diffluence angle of the jet stream in the northwest quadrant to gain insight into the relationship between the diffluence angle and its downstream impact a quasigeostrophic baroclinic model is used the results show that an initially zonal jet persists at its initial latitude over 30 days or longer while a tilted