intraseasonal modulation of the north pacific storm track by tropical convection in boreal winter abstract the modulation of the north pacific storm track by tropical convection on intraseasonal time scales 30 90 days in boreal winter december march is investigated using the ncep ncar reanalysis and noaa satellite outgoing longwave radiation olr data multivariate empirical orthogonal function meof analysis and case compositing based upon the principal components pcs of the eofs reveal substantial changes in the structure and intensity of the pacific storm track quantified by vertically 925 200 mb averaged synoptic eddy kinetic energy seke during the course of a typical madden julian oscillation mjo event the storm track response is characterized by an amplitude varying dipole propagating northeastward as the center of the anomalous tropical convection moves eastward across the eastern indian ocean and the western central pacific a diagnosis of the seke budget indicates that the storm track anomaly is induced primarily by changes in the convergence of energy flux baroclinic conversi

observations of rossby waves linked to convection over the eastern tropical pacific rossby wave activity propagating into the eastern tropical pacific from the midlatitudes during northern winter is examined in some detail these waves are associated with the intrusion of high potential vorticity air into low latitudes and they modulate cloudiness stability and vertical motion in the vicinity of the itcz in the upper troposphere and lower stratosphere the horizontal phase and group propagation of the wave activity are qualitatively like those of a nondivergent barotropic rossby wave as the waves move equatorward they become more shallow and propagate upward into the stratosphere the horizontal and vertical propagation is consistent with the tilts of the waves the large scale three dimensional background flow and with the signatures of momentum and heat fluxes associated with the wave activity in the lower troposphere paired cyclonic anomalies on either side of the equator accompany the upper level wave activity to the west of the itcz cloudiness signal these waves amplify following the peak in the itcz cloudiness and propagate westward along the equator this suggests that the upper level wave activity and possibly the associated convective heating can trigger the excitation of the equatorially trapped rossby modes the transient wave activity appears to be a crucial component of the momentum balance of the eastern tropical pacific circulation there is substantial interannual variability in the wave activity consistent with observed changes in the large scale basic state associated with the southern oscillation

the equatorial response to higher latitude forcing abstract the classic view following charney and webster and holton is that significant midlatitude forcing of the tropics can be expected only in regions with westerly winds in the upper troposphere because it is only in these regions that stationary rossby waves will be able to propagate toward the equator here it is shown that higher latitude forcing can project directly onto equatorial waves and give a significant tropical response in both easterly and westerly tropical flow the equatorial response to higher latitude forcing is considered in the context of a dry atmosphere and a localized higher latitude forcing with eastward or westward phase speed previous ideas of the doppler shifting of equatorial waves by zonal flows are extended to include consideration of a forcing involving a range of zonal wavenumbers a gill type model suggests that there can be significant forcing of equatorial waves by either vorticity forcing or heating in higher latitudes in agreement with the theory the kelvin wav

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

circulation anomalies associated with tropical convection during northern winter abstract lagged cross correlations between outgoing longwave radiation olr and national meteorological center global analyses are utilized to isolate the preferred upper level and surface circulation anomalies associated with tropical convection during northern winter three intraseasonal time scales are studied 30 70 14 30 and 6 14 days in the 30 70 day band the upper level circulation signals are zonally elongated with zonal wavenumbers 0 2 dominant higher frequency signals are dominated by zonal wavenumbers 5 and 6 in the 14 30 day band convection over the eastern hemisphere is associated with upper level anticyclones in the subtropics and appears to be linked in some cases to midlatitude wave trains the strongest signals are for convection over africa australia and the eastern indian ocean only weak signals are seen for convection over indonesia in these regions of upper level easterlies olr anomalies peak prior to the maximum anomalies in wind suggesting forcing of the circulation b

the atmospheric angular momentum cycle during the tropical madden julian oscillation abstract global scale wind and outgoing longwave radiation anomalies are documented during the atmospheric angular momentum aam cycle associated with the madden julian oscillation cross spectral and compositing techniques are applied to 150 and 850 mb national meteorological center wind data and outgoing longwave radiation olr data during ten northern winter and summer seasons coherent wind and olr signals are found in the tropics and in the winter hemisphere and are dominated by zonal wavenumbers 0 2 at the time of zero aam anomaly anomalous zonal winds are found over the western hemisphere tropics during northern winter while convection anomalies tend to be collocated with the seasonal mean australasian convection zonal mean olr anomalies are small as the aam anomaly increases the anomalous zonal winds move eastward and poleward while dipole convection anomalies become established over the oceanic warm pool and result in an east west shift of the australasian monsoon zonal mean olr ano

tropical extratropical geopotential height teleconnections during the northern hemisphere winter abstract simultaneous and lagged correlation statistics have been calculated between time series of seasonal height anomalies at selected stations and extratropical grid point anomalies in both hemispheres the tropical stations in two major tropical precipitation zones the indo china maritime continent and africa are well correlated with each other these stations are also correlated with stations in the north pacific and australia but the coefficients are smaller the correlations between height anomalies at any of these stations and northern hemisphere height anomalies show a well defined global pattern depending upon the location of the stations the pattern is either a pacific north american pna a tropical northern hemisphere tnh pattern or a mixed pattern having both elements all three patterns pna tnh and wpo western pacific oscillation have been linked to tropical variations the correlations between height anomalies at these well correlated stations and the southern hemisphere heig

on the zonal structure of the north atlantic oscillation and annular modes abstract the zonal structure and dynamics of the dipolar patterns of intraseasonal variability in the extratropical atmosphere namely the north atlantic oscillation nao and the so called annular modes of variability are investigated in an idealized general circulation model particular attention is focused on the relationships linking the zonal structure of the stationary waves synoptic variability i e the storm tracks and the zonal structure of the patterns of intraseasonal variability large scale topography and diabatic anomalies are introduced to modify and concentrate the synoptic variability establishing a recipe for a localized storm track comparison of the large scale forcing synoptic variability and patterns of intraseasonal variability suggests a nonlinear relationship between the large scale forcing and the variability it is found that localized nao like patterns arise from the confluence of topographic and diabatic forcing and that the patterns are more localized than one would e

power law breakthrough curve tailing in a fracture the role of advection summary we offer an explanation of the strongly tailed solute breakthrough curve typically observed when a tracer test is conducted in fractured bedrock in this example we limit the model to a single planar fracture of varying aperture flow heterogeneity derives from variable fracture aperture which implies variable transmissivity t the analysis employs a physically based model well suited to strong heterogeneity and relies only upon advective transport the purely advective model is able to explain a power law trend of magnitude 2t o 3 in the breakthrough curve tail a range that has been found in field tracer experiments the principle cause of this trend is the comparatively slow transport in zones of small transmissivity tight aperture slow advection occurs when either heterogeneity variance of ln t i s strong or when the assumed heterogeneity distribution is non gaussian thus we link breakthrough tailing to the statistical parameters for the transmissivity field

thermophysical properties of the mer and beagle ii landing site regions on mars 1 we analyzed remote sensing observations of the isidis basin gusev crater and meridiani planum landing sites for beagle ii mer a spirit and mer b opportunity spacecraft respectively we emphasized the thermophysical properties using daytime and nighttime radiance measurements from the mars global surveyor mgs thermal emission spectrometer and mars odyssey thermal emission imaging system themis and thermal inertias derived from nighttime data sets themis visible images mgs mars orbiter camera moc narrow angle images and mgs mars orbiter laser altimeter mola data are incorporated as well additionally the remote sensing data were compared with ground truth at the mer sites the isidis basin surface layer has been shaped by aeolian processes and erosion by slope winds coming off of the southern highlands and funneling through notches between massifs in the gusev region surface materials of contrasting thermophysical properties have been interpreted as rocks or bedrock duricrust and dust deposits these are consistent with a complex geological history dominated by volcanic and aeolian processes at meridiani planum the many layers having different thermophysical and erosional properties suggest periodic deposition of differing sedimentological facies possibly related to clast size grain orientation and packing or mineralogy

variability of the observed midlatitude storm tracks in relation to low frequency changes in the circulation pattern abstract the principal modes of month to month variability of the wintertime storm tracks over the north pacific and north atlantic are identified by empirical orthogonal function analysis of the root mean square statistics of bandpass 2 5 6 day filtered geopotential height data for 19 yr one of the two leading modes depicts fluctuations in the level of synoptic scale activity without any noticeable spatial displacement of the storm track axes whereas the other mode is associated with meridional shifts of the storm tracks from their time averaged positions higher order modes are indicative of diversion or truncation of cyclone tracks in particular geographical regions it is demonstrated that the leading storm track modes are linked to some of the best known monthly averaged teleconnection patterns the dipolar western pacific and western atlantic patterns for the monthly mean flow are seen to be accompanied by marked changes in the intensity of the storm tracks over the western oceans whereas the m

life cycles of persistent anomalies ii the development of persistent negative height anomalies over the north pacific ocean abstract the present study extends our previous work on the life cycles of persistent anomalies by providing more comprehensive analyses of the synoptic and dynamical characteristics associated with the developments of the anomalies we focus here on the developments of major cases of persistent negative height anomalies over the extratropical central north pacific pac region during wintertime these ewes are generally manifested at the surface by an anomalously intense and eastward displaced aleutian low and at upper levels by an abnormally strong zonal jet that extends across most of the western and central pacific at midlatitudes the associated flow anomalies usually resemble particularly strong realizations of the pacific north american pna teleconnection pattern the large scale flow anomalies are typically preceded by a buildup of anomalously cold air over asia and an intensification of the upper level jet over southeastern asia and the fox western pacific a few days prior to the larger scal

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

midwinter suppression of baroclinic wave activity in the pacific abstract seasonal variations in baroclinic wave activity and jet stream structure in the northern hemisphere are investigated based upon over 20 years of daily data baroclinic wave activity at each grid point is represented for each day by an envelope function the lowpass filtered time series of the squared highpass filtered geopotential height baroclinic wave activity over the atlantic exhibits a single maximum in january whereas in the pacific it exhibits peaks in late autumn and in early spring and a significant weakening in midwinter which is more evident at the tropopause level than near the surface this suppression occurs despite the fact that the low level baroclinity and the intensity of the jet stream are strongest in midwinter based on the analysis of 31 day running mean fields for individual winters it is shown that over both the oceans baroclinic wave activity is positively correlated with the strength of the upper tropospheric jet for wind speeds up to 45 m s 1 when the strength of t

nature of the differences in the intraseasonal variability of the pacific and atlantic storm tracks a diagnostic study abstract on the basis of an intraseasonal variability index of storm track evaluated for 40 winters 1963 64 through 2003 04 of ncep ncar reanalysis data it is found that well defined midwinter minimum mwmin midwinter maximum mwmax occurs in 21 8 winters over the north pacific in contrast mwmin mwmax occurs in 4 25 of the 40 winters over the north atlantic the power spectrum of such an index for the pacific has a broad peak between 5 and 10 yr whereas the spectrum of the index for the atlantic has comparable power in two spectral bands 2 2 8 and 3 5 8 yr over the north pacific the increase in the zonal asymmetry of the background baroclinicity as well as in the corresponding horizontal deformation of the time mean jet from early late winter to midwinter is distinctly larger in an mwmin winter associated with these changes there is a distinctly stronger barotropic damping rate in the january of an mwmin winter the increase in the net conversion rate of eddy kinetic energy from early

interactions between the tropical iso and midlatitude low frequency flow in this study we investigate the interaction between the tropical intraseasonal oscillation iso and midlatitude atmospheric low frequency variability using observational data and numerical models with a special emphasis on the role of the synoptic eddy feedback a statistical closure for the synoptic eddy to low frequency flow feedback is constructed based on a singular value decomposition svd method with observational data applying this statistical closure to a barotropic model and a baroclinic 2 layer model we study the role of the synoptic eddy feedback in the midlatitude response to the tropical iso forcing both observational and modeling studies show that the strongest synoptic eddy forcing appears at the pacific and atlantic storm track regions and the synoptic eddy exerts a positive feedback to the midlatitude low frequency flow induced by tropical iso forcing our numerical experiments demonstrate the possible role of midlatitude disturbance forcing in the iso initiation at the equator the signal of the midlatitude perturbations propagates southeastward in the form of a rossby wave package it may reach the equator within several days under either easterly or westerly basic flow regimes the response at the equator has observed iso like structure and eastward propagation characteristics

an idealized model study relevant to the dynamics of the midwinter minimum of the pacific storm track the synoptic variability of a two level quasigeostrophic flow in response to plausible changes in the forcing of a localized baroclinic jet is investigated in the context of the midwinter minimum of the pacific storm track mwm the changes in the model forcing are introduced in terms of a reference potential vorticity field that is associated with plausible changes in the global baroclinicity zonal variation of the baroclinicity and horizontal deformation over the pacific from early winter to midwinter conditions it is found that the modal instability growth rate of perturbation in such a localized jet is significantly reduced in spite of an increase in the local baroclinicity the dynamical nature of such an effect can be interpreted as a generalized barotropic governor effect on localized baroclinic instability the existence of three instability regimes is established on the basis of energetics characteristics the intensity of the nonlinear model storm track is reduced by about 30 in response to a change in the forcing condition from early to midwinter the characteristics of the linear model storm track and nonlinear model storm track are compared the overall results support a hypothesis that mwm could stem from a sufficiently large increase in the stabilizing influence of the local barotropic process in spite of a simultaneous increase in its local baroclinicity in the pacific jet from early to midwinter

persistent north pacific circulation anomalies and the tropical intraseasonal oscillation abstract a composite analysis of multiyear 1985 93 global reanalyses produced by the ncep ncar and the nasa dao is used to show that the development of persistent north pacific pnp circulation anomalies during nh winter is linked to tropical intraseasonal oscillations the development is initiated over the tropical west pacific by anomalous convection characterized by an east west dipole structure one to two weeks prior to the extratropical onset time in both reanalyses as tropical heating moves eastward toward the central pacific anomalous divergent outflow associated with the local hadley circulation generates an anomalous rossby wave sink source in the subtropics consistent with the retraction extension of the pacific jet prior to onset the signature of the forced anomalies is a pair of cyclonic anticyclonic circulation anomalies centered near the node of the tropical heating dipole wave trains extending from the region of anomalous convection into the extratropics set the stage for th

organization of extratropical transients during el nino abstract four observed el nino southern oscillation enso events are studied to determine the mechanisms responsible for the anomalous extratropical atmospheric circulation during northern winter a parallel analysis of a gcm s response to el nino is performed in order to assess if similar mechanisms are operative in the model atmosphere the observed stationary wave anomalies over the pacific north american pna region are found to he similar during the four winters despite appreciable differences in sea surface temperatures the anomalous transient vorticity fluxes are remarkably robust over the north pacific during each event with an eastward extension of the climatological storm track leading to strong cyclonic forcing near 40 n 150 w this forcing is in phase with the seasonal mean aleutian trough anomaly suggesting the importance of eddy mean flow interactions by comparison the intersample variability of the gcm response over the pna region is found to exceed the observed inter el nino variabi

variations of midlatitude transient dynamics associated with enso abstract the winter response of the atmosphere to el nino events in the pacific is studied both from a 14 year integration of the center for ocean land atmosphere gcm using observed ssts from january 1979 to february 1993 and from the corresponding analyses of ecmwf emphasis is put on the shift in the high frequency transients that define the pacific storm track during warm events warm and normal ensembles are defined on the basis of the gcm s diabatic heating field in the tropical pacific which falls in one of two states during the winters of 1982 83 1986 87 and 1991 92 the heating averaged between 6 s and 6 n lies in the range of 100 200 w m 2 all the way across the basin the remaining 10 normal years all show no large tropical diabatic heating anomalies in the mid or eastern pacific the difference between warm and normal ensembles for the mean fields of zonal wind u and height z indicates an eastward and equatorward extension of the midlatitude pacific jet associated with a similar extensio

the global response to tropical heating in the madden julian oscillation during the northern winter a life cycle of the madden julian oscillation mjo was constructed based on 21 years of outgoing long wave radiation data regression maps of ncep ncar reanalysis data for the northern winter show statistically significant upper tropospheric equatorial wave patterns linked to the tropical convection anomalies and extratropical wave patterns over the north pacific north america the atlantic the southern ocean and south america to assess the cause of the circulation anomalies a global primitive equation model was initialized with the observed three dimensional 3d winter climatological mean flow and forced with a time dependent heat source derived from the observed mjo anomalies a model mjo cycle was constructed from the global response to the heating and both the tropical and extratropical circulation anomalies generally matched the observations well the equatorial wave patterns are established in a few days while it takes approximately two weeks for the extratropical patterns to appear the model response is robust and insensitive to realistic changes in damping and basic state the model tropical anomalies are consistent with a forced equatorial rossby kelvin wave response to the tropical mjo heating although it is shifted westward by approximately 20 longitude relative to observations this may be due to a lack of damping processes cumulus friction in the regions of convective heating once this shift is accounted for the extratropical response is consistent with theories of rossby wave forcing and dispersion on the climatological flow and the pattern correlation between the observed and modelled extratropical flow is up to 0 85 the observed tropical and extratropical wave patterns account for a significant fraction of the intraseasonal circulation variance and this reproducibility as a response to tropical mjo convection has implications for global medium range weather prediction copyright 2004 royal meteorological society

an observed connection between the north atlantic oscillation and the madden julian oscillation abstract based on the bivariate madden julian oscillation mjo index defined by wheeler and hendon and 25 yr 1979 2004 of pentad data the association between the north atlantic oscillation nao and the mjo on the intraseasonal time scale during the northern hemisphere winter season is analyzed time lagged composites and probability analysis of the nao index for different phases of the mjo reveal a statistically significant two way connection between the nao and the tropical convection of the mjo a significant increase of the nao amplitude happens about 5 15 days after the mjo related convection anomaly reaches the tropical indian ocean and western pacific region the development of the nao is associated with a rossby wave train in the upstream pacific and north american region in the atlantic and african sector there is an extratropical influence on the tropical intraseasonal variability certain phases of the mjo are preceded by the occurrence of strong naos a significant change of upper zonal

does enso force the pna abstract the primary effect of el nino southern oscillation enso sea surface temperature sst anomalies is to force distinct midlatitude patterns and not only to modify the probability of the internal variability patterns such as the pacific north american pna pattern of wallace and gutzler both the spatial structure and probability distribution of the external enso pattern are distinct from the pna pattern ensemble general circulation model gcm integrations for 30 winters have been analyzed in the pacific north america region these winters span the recent period of 1981 82 through 1998 99 plus 12 earlier winters the entire dataset includes six el nino warm and seven la nina cold events the ensemble size is nine simulations empirical orthogonal function eof analysis is carried out for all gcms and observed seasonal means for the gcm ensemble means and for the gcm deviations about the ensemble means eof 1 of the gcm 200 hpa height z ensemble mean agrees well with eof 1 of all gc

interdecadal variations in northern hemisphere winter storm track intensity abstract in this paper the interannual variations in the northern hemisphere winter storm tracks have been examined based on 51 winters december january february of ncep ncar reanalysis data the leading empirical orthogonal function eof corresponds to the simultaneous strengthening weakening of both the pacific and atlantic storm tracks interannual and month to month variations in the pacific and atlantic storm tracks are found to be significantly correlated the principal component associated with the leading hemispheric eof exhibits pronounced interdecadal variability there appears to be a transition during the early 1970s from a weak storm track state prior to 1972 73 to a strong storm track state subsequently decadal mean storm track intensity during the 1990s is about 30 stronger than that during the late 1960s and early 1970s the relationship between variations in storm track intensity and low frequency seasonal mean flow anomalies has also been examined it is shown that storm track va

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

extratropical forcing of tropical pacific convection during northern winter abstract statistical evidence is presented to support the notion that tropical convection in the eastern pacific and atlantic intertropical convergence zone itcz during northern winter can be forced by disturbances originating in the extratropics the synoptic scale transients in these regions are characterized at upper levels by strong positive tilts in the horizontal and appear to induce vertical motions ahead of troughs as in midlatitude baroclinic systems two case studies of such interactions are examined one for the eastern north pacific itcz and another somewhat different type of interaction for the south pacific convergence zone spcz over the western south pacific both cases are associated with upper level troughs strong cold advection deep into the tropics and the formation of a frontal boundary at low levels the itcz case is characterized by the advection of anomalously high isentropic potential vorticity air southward a strong poleward flux of heat and westerly momentum and the devel

horizontal and vertical structure of cross equatorial wave propagation abstract observational evidence of interhemispheric wave propagation through the equatorial upper tropospheric mean westerlies in the eastern pacific ocean is found in nine years 1980 81 to 1988 89 of european centre for medium range weather forecasts analyses during boreal winter using time mean standard deviation and one point correlation fields of potential vorticity on isentropic surfaces ipv it is found that waves associated with local fluctuations with periods between 6 and 30 days propagate from the northern hemisphere extratropics cross the equator and continue into the southern hemisphere extratropics this result is in agreement with hypotheses that claim regions of time mean westerlies in the tropics act as ducts allowing extratropical rossby waves to propagate into and through the tropics horizontal structure of the waves appears to change little during the course of the interhemispheric propagation however in the lower troposphere where the mean zonal wind is easterly the lowe

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