structure of a frontal cyclone a diagnostic study of a mid latitude cyclone has been carried out using routinely available numerical weather prediction model products and imagery the cyclone was intense but not exceptionally so and the results are believed to have some generality the detailed description of the cyclone structure just before it began to deepen rapidly integrates concepts from a number of researchers into a common framework a dominant feature of the cyclone close to its centre was the cloud head a region of cloud with a sharp convex outer edge which formed poleward of the main polar front cloud band the cloud head was caused by two flows that entered it from the east ascending and fanning out within it one flow the cold conveyor belt brought low wet bulb potential temperature w air back into the cloud head from low levels ahead of the warm front the other flow was due to high w air that peeled off from the base of the main warm sector airflow i e part of the warm conveyor belt and travelled in the boundary layer back towards the cyclone centre first undercutting dry air that had earlier descended from the upper troposphere called a dry intrusion and then ascending at the upper boundary of the cloud head above the cold conveyor belt the transverse circulation that gave the ascent within the cloud head also led to the cold front fracturing along its length into two separate sharp surface cold fronts with a more diffuse frontal region in between frontal fracture the two sharp surface cold fronts were associated with narrow cold frontal rainbands line convection one of the line convection segments forming the southern edge of the cloud head the overrunning of the dry intrusion in the region of the frontal fracture led to a structure known as a split front in which an upper level humidity front began to run ahead of the position of the surface cold front a feature of the cyclone at this intermediate stage in its evolution was that a large proportion of the precipitation was being generated by ascent of relatively cold air the cold conveyor belt in the cloud head as part of the thermally indirect circulation at the left exit of a developing secondary upper level jet

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

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

intrusions into the tropical upper troposphere three dimensional structure and accompanying ozone and olr distributions abstract the evolution and structure of stratospheric intrusions into the upper troposphere ut over the northern tropical pacific is examined in terms of both potential vorticity pv and ozone o3 analysis of 20 years of ncep ncar reanalysis pv shows that the intrusion events have remarkably similar evolution and structure at 350 k with all events producing narrow tongues of high pv that have an almost north south orientation and last around 3 days nearly all events extend up into the lower stratosphere but only for a small percentage is there deep downward penetration the intrusions explain a large amount of the observed variability in upper tropospheric o3 above hilo hawaii with large values occurring when a tongue of high pv passes over hilo and low values when hilo is just upstream of a high pv tongue there is also an increase in total column ozone within the pv tongues but for most intrusions the increase is relatively small the relationship between deep convection as diagnosed by sate

a trajectory based investigation of physical and dynamical processes that govern the temporal evolution of the subtropical jet streams over africa abstracttropical subtropical and extratropical dynamical processes govern the synoptic scale evolution of the subtropical jet stream s over africa however the relative importance of the respective effects is still under debate and is the focus of this study interim ecmwf re analysis era interim data are used to calculate backward trajectories from the subtropical jet over africa during winter 2005 06 the trajectories allow for studying the jet dynamics from both a potential vorticity pv and an angular momentum point of view and for linking the two theoretical frameworks three cases of synoptic scale rossby wave breaking in the extratropics and subtropics are presented in detail they illustrate basic flow configurations where i the subtropical jet is mainly forced by tropical dynamics ii extratropical forcing contributes substantially to the jet acceleration and iii strong diabatic processes in the subtropics impact the jet the case study results are then generalized for the entire wint

cross equatorial response to middle latitude forcing in a zonally varying basic state abstract a nonlinear model based on the shallow water equations is used to study cross equatorial propagation of forced waves in the presence of a longitudinally varying time mean basic state zonal wind field it is found that global scale planetary waves are unable to propagate past a critical latitude where the mean zonal wind speed vanishes however if the longitudinally asymmetric basic state includes a duet in which the zonal winds are westerly waves of zonal scale less than the zonal scale of the westerly duct may propagate from one hemisphere to the other even though the zonally symmetric mean zonal wind remains easterly in the equatorial region the amplitude of the response in one hemisphere to forcing in the opposite hemisphere increases strongly with the magnitude of the westerlies in the equatorial duct the existence and annual variations of a westerly duct region in the upper troposphere in the eastern pacific appear to account for some features of the low frequency variability in the no

cloud components of the intertropical convergence zone 1 this study explores the roles of different synoptic scale cloud systems in the making of the intertropical convergence zone itcz outgoing longwave radiation olr data are used to represent both the mean itcz and cloud systems an olr threshold of 205 w m 2 is used to distinguish daily mean deep convective clouds from nondeep clouds zonally moving synoptic scale cloud systems are identified through a cloud tracking method mean olr of the itcz is decomposed into five components westward and eastward moving synoptic scale deep convective clouds random nonpropagating deep convective clouds nondeep clouds and clear sky backgrounds hypothetical itczs each composed of one of the cloud components and the clear sky background are constructed and compared the largest synoptic scale cloud constituents of the itcz are nondeep clouds and deep clouds with no persistent tendency of zonal propagation each of the two comprises about 40 45 of total cloud signals in the itcz a weak itcz could exist solely because of westward propagating synoptic scale deep convective clouds in reality these westward propagating clouds contribute 25 40 of deep convective clouds and 10 20 of total clouds in the itcz contributions from eastward propagating synoptic scale clouds are much smaller 8 of the deep convective clouds and less than 5 of total clouds in the itcz an itcz without any zonally propagating synoptic scale deep convective clouds would be diffused in latitude the cloud compositions in the itcz and other tropical convective zones are compared their discrepancies indicate fundamental characteristics in large scale environments for the cloud components in different regions

connections between potential vorticity intrusions and convection in the eastern tropical pacific abstract the connections between intrusions of stratospheric air into the upper troposphere and deep convection in the tropical eastern pacific are examined using a combination of data analysis potential vorticity pv inversion and numerical simulations analysis of ncep ncar reanalyses and satellite measurements of outgoing longwave radiation during intrusion events shows increased cloudiness lower static stability upward motion and a buildup of convective available potential energy cape at the leading edge of the intruding tongue of high pv potential inversion inversion calculations show that the upper level pv makes the dominant contribution to the changes in the quantities that characterize convection this supports the hypothesis that upper level pv anomalies initiate and support convection by destabilizing the lower troposphere and causing upward motion ahead on the pv tongue the dominant role of the upper level pv is confirmed by simulations using the fifth generation pennsylvania state u

convective forcing in the intertropical convergence zone of the eastern pacific abstract one of the goals of the east pacific investigation of climate year 2001 process study epic2001 was to understand the mechanisms controlling the forcing of deep atmospheric convection over the tropical eastern pacific an intensive study was made of convection in a 4 4 square centered on 10 n 95 w in september and october of 2001 this is called the intertropical convergence zone itcz study region because it encompasses the eastern pacific intertropical convergence zone starting from an analysis of the theoretical possibilities and a plethora of dropsonde in situ radar and satellite data it is found that newly developing convection occurs where a deep layer of air of order 1 km deep or deeper is conditionally unstable with only weak convective inhibition shallower conditionally unstable layers are associated with numerous small clouds but do not seem to produce deep convection the occurrence of deep convection over the itcz study region is presumably related to the propensity

convective destabilization by upper level troughs the approach of an upper level trough is accompanied by a local ascent of the isentropic surfaces in the troposphere the associated cooling and moistening destabilizes the atmosphere to convection in this paper we attempt to quantify the maximum amount of destabilization as a function of the amplitude and horizontal scale of the trough the trough is represented by an elongated potential temperature perturbation on the tropopause its structure including the isentrope displacement it produces is calculated from the balanced shear line solutions of juckes these solutions are used to estimate the amount by which mid and lower tropospheric air masses are lifted when an upper tropospheric trough passes overhead on the assumption that isentropic potential vorticity anomalies are localized in the upper troposphere the amount of destabilization is characterized by the maximum change in convective available potential energy cape and convective inhibition cin brought about by the passage of the trough the calculations seek to isolate one aspect of the interaction between an upper level trough and a tropical cyclone we show that the changes in cape are significant in the tropics up to 83 for the soundings examined and even more so in the middle latitudes up to 130 and that the cin may be completely removed

effect of the arakan mountains in the northwestern indochina peninsula on the late may asian monsoon transition by simulations using a global climate model with and without the arakan mountains in the northwest of myanmar we demonstrated that this mesoscale meridionally elongated mountain range has a substantial effect on anchoring and enhancing precipitation in the region during the bay of bengal bob monsoon onset in late may in this period the presence of the arakan mountains in the model significantly improves the simulation of the thermal and dynamical atmospheric structure of the monsoon by substantially enhancing precipitation deepening the midtropospheric trough and the southwesterly flow over the bob and strengthening the upper tropospheric anticyclone atop the trough these mountain induced changes essentially improve the simulation of the late may asian summer monsoon transition prior to the bob monsoon onset the blocking and deflecting effects of the arakan mountains on the low level flow are marked which enhance the moisture convergence and also probably influence the oceanic forcing over the bob as well as the mountain effect on the moisture convergence inclusion of the arakan mountains apparently initiates an upstream troughing effect which in turn enhances the synoptic and large scale circulation during the monsoon transition furthermore the presence of the arakan mountains induces a large scale wavelike perturbation which likely leads to an improvement of meiyu baiu simulation this study reveals that a narrow mountain like the arakan mountains likely contributes markedly to the characteristics of the asian summer monsoon during its early seasonal march such effects need to be reasonably resolved in the models

using piecewise potential vorticity inversion to diagnose frontogenesis part i a partitioning of the q vector applied to diagnosing surface frontogenesis and vertical motion abstract the technique of piecewise potential vorticity pv inversion is used to identify the nondivergent wind fields attributed to upper middle and lower tropospheric pv anomalies in addition to the irrotational wind with the goal of diagnosing the respective wind fields frontogenetic potentialities frontogenesis is diagnosed using a piecewise separation of the q vector into parts associated with the partitioned wind field partitioned geostrophic q vectors are used to diagnose the vertical motion attributed to the upper middle and lower tropospheric pv anomalies insight gained from this new diagnostic technique is demonstrated by examining a particular case of extratropical marine cyclogenesis resulting from the interaction of an upper tropospheric short wave trough with a surface thermal wave in the early stages of development the largest contributor to surface frontogenesis was associated with winds attributed to the lower tropospheric thermal wave as the cyclone matured the contribut

a potential vorticity based study of the role of diabatic heating and friction in a numerically simulated baroclinic cyclone abstract a particularly intense case of western atlantic baroclinic cyclogenesis was investigated in this study specifically the roles of latent heat of condensation and surface friction were examined from the potential vorticity or pv thinking perspective the methodology used for this study involves three key components 1 a full physics mesoscale model which provides a continuous and dynamically consistent dataset and provides full user control over physical processes 2 a partitioned pv integration which temporally integrates the accumulation of pv due to various physical processes in the model s eulerian framework and 3 the piecewise inversion method of davis and emanuel which calculates the balanced wind and mass field associated with particular pv anomalies potential vorticity features obtained through the partitioned integration technique were inverted to yield their direct contributions to the total circulation in addition sensitivity studies were carried out to determine the overal

north atlantic extratropical rossby wave breaking during the warm season wave life cycle and role of diabatic heating abstractthis study investigates the life cycle of anticyclonic rossby wave breaking during the extended warm season july october over the north atlantic basin it was found that upper tropospheric breaking waves are coupled with lower level perturbations and can be traced back to a wave train that extends from the north pacific the overturning of potential vorticity pv contours during wave breaking is associated with the rapid development of an upper level ridge which occurs along the east coast of north america and over a warm and moist airstream the ridge development is investigated using the pv budget analysis and trajectory analysis the pv budget analysis suggests that the horizontal advection of pv by the perturbed flow dictates the movement and the later decay of the ridge the ridge amplification opposed by the horizontal advection of pv is driven by the vertical advection and the diabatic production of pv both of which are connected to diabatic heating the vital role of diabatic heatin

effects of cloud diabatic heating on the early development of the fastex iop17 cyclone a set of numerical simulations is used to study the first development phase of the fastex cyclone a particularly well sampled frontal cyclone system that developed on the trailing front of a primary large scale baroclinic wave during intensive observation period 17 iop17 of fastex the fronts and atlantic storm track experiment the role of diabatically induced vertical circulations is investigated with a combination of diagnostic tools including a generalized omega equation and keyser s psi vector technique applied to the model outputs the full physics simulation shows a good agreement with observed data particularly the splitting of the upper level flow into a pair of jet streaks analysis of the contributions to the vertical ageostrophic transverse circulations near the jet streak pair structure shows that a positive feedback exists between the storm s dynamical configuration and the diabatic processes in the second part of the paper this interpretation is confirmed by a sensitivity analysis excluding cloud processes results suggest that after initial baroclinic growth the storm evolves towards a purely diabatic deepening regime leading to a diabatic rossby wave mechanism as proposed by recent wave cisk conditional instability of the second kind theoretical studies

electromagnetic to seismic conversion a new direct hydrocarbon indicator we present novel methods that directly detect hydrocarbons based on conversions between electromagnetic and seismic energy we first introduce the subject and then discuss the experimental methods in three field tests next we present the results of the tests and then end with a few model results and thoughts about future applications

the structure and evolution of heat waves in southeastern australia abstractthe underlying large scale dynamical processes responsible for the development of heat waves in victoria southeastern australia in summer are presented here heat waves are defined as periods of at least three days and two nights for which daily maximum and minimum temperatures exceed the 90th percentile for a particular location and month using a station daily temperature dataset composites of upper level potential vorticity anomalies from the interim ecmwf re analysis era interim reveal that heat waves in southeastern australia are associated with propagating rossby waves which grow in amplitude and eventually overturn the process of overturning generates an upper level anticyclone over southern australia and an upper level trough to the northeast with maximum amplitudes near the tropopause the northerly flow associated with the circulation around the surface anticyclone advects hot air from the continental interior over the southeast of australia leading to extreme surface temperatur

the extratropical transition of hurricane irene 1999 a potential vorticity perspective extratropical transition et of tropical cyclones is common in all ocean basins where tropical cyclones recurve polewards after the tropical cyclone experiences et a rapid deepening can take place resulting in the development of a very large and deep extratropical cyclone the et of hurricane irene 1999 was an example of such an explosive et irene formed in the caribbean and experienced et as it moved poleward resulting in a low pressure system which deepened 39 hpa in 24 hours according to the met office analyses the extent to which the hurricane was responsible for the explosive extratropical development has been determined by performing met office unified model forecasts from initial states with and without the hurricane the circulation and temperature anomalies associated with the hurricane were removed from the initial state using potential vorticity inversion the moisture anomaly co located with the hurricane core was also removed the results show that an extratropical cyclogenesis event takes place regardless of the presence of the hurricane in the initial conditions however the hurricane makes a significant difference to the track and central mean sea level pressure evolution of the resulting extratropical cyclone when irene was present the track of the extratropical cyclone was more zonal and the cyclone deepening rate was twice as fast as when irene was not present these effects appear to be particularly associated with a negative potential vorticity anomaly and enhanced divergent flow in the region of the upper level outflow of the transforming hurricane rather than with the hurricane vortex results also show that the presence of the hurricane resulted in a significant downstream surface low development in the eastern atlantic copyright 2004 royal meteorological society

climatology of intrusions into the tropical upper troposphere regions of upper tropospheric equatorial westerly winds observed over the pacific and atlantic oceans during northern fall to spring are important for extratropical tropical interactions this paper focuses on one feature of these westerly ducts that has received relatively little attention to date the occurrence of rossby wave breaking events that transport tongues of extratropical air deep into the tropics mix tropical and subtropical air and can affect deep convection a climatology of these intrusion events formed from 20 years of meteorological analyses shows a strong dependence on the basic state flow notably intrusion events are found to occur almost exclusively within westerly ducts with more events in the presence of stronger equatorial westerlies it is also found that there is strong interannual variability in the frequency of pacific events with fewer events during the warm phases of enso consistent with the changes in the basic flow since these intrusion events laterally mix trace constituents and have been linked to tropical convection their spatial and temporal variability may cause related variability in the distribution of trace constituents and tropical convection

the role of upper level dynamics and surface processes for the pakistan flood of july 2010 in july and august 2010 floods of unprecedented impact afflicted pakistan the floods resulted from a series of intense multi day precipitation events in july and early august at the same time a series of blocking anticyclones dominated the upper level flow over western russia and breaking waves i e equatorward extrusions of stratospheric high potential vorticity pv air formed along the downstream flank of the blocks previous studies suggested that these extratropical upper level breaking waves were crucial for instigating the precipitation events in pakistan here a detailed analysis is provided of the extratropical forcing of the precipitation piecewise pv inversion is used to quantify the extratropical upper level forcing associated with the wave breaking and trajectories are calculated to study the pathways and source regions of the moisture that precipitated over pakistan limited area model simulations are carried out to complement the lagrangian analysis the precipitation events over pakistan resulted from a combination of favourable boundary conditions with strong extratropical and monsoonal forcing factors above normal sea surface temperatures in the indian ocean led to an elevated lower tropospheric moisture content surface monsoonal depressions ensured the transport of moist air from the ocean towards northeastern pakistan along this pathway the air parcel humidity increased substantially 60 90 of precipitated moisture via evapotranspiration from the land surface extratropical breaking waves influenced the surface wind field substantially by enhancing the wind component directed towards the mountains which reinforced the precipitation

impact of rossby wave breaking on u s west coast winter precipitation during enso events abstractthis study demonstrates that water vapor transport and precipitation are largely modulated by the intensity of the subtropical jet transient eddies and the location of wave breaking events during the different phases of enso clear differences are found in the potential vorticity pv meteorological fields and trajectory pathways between the two different phases rossby wave breaking events have cyclonic and anticyclonic regimes with associated differences in the frequency of occurrence and the dynamic response during la nina there is a relatively weak subtropical jet allowing pv to intrude into lower latitudes over the western united states this induces a large amount of moisture transport inland ahead of the pv intrusions as well as northward transport to the west of a surface anticyclone during el nino the subtropical jet is relatively strong and is associated with an enhanced cyclonic wave breaking this is accompanied by a time mean surface cyclone which brings zonal moisture tran

upper tropospheric forcing on late july monsoon transition in east asia and the western north pacific abstractby investigating the large scale circulation in the upper troposphere it is demonstrated that the rapid late july summer monsoon transition in the east asia and western north pacific ea wnp is associated with a weakened westerly at the exit of the east asian jet stream eajs even in a normally stable atmosphere under the influence of the north pacific np high in late july convection rapidly develops over the midoceanic region of the western np 15 25 n 150 170 e prior to the rapid transition the eajs weakens and shifts northward which induces a series of changes in downstream regions the northeastern stretch of the asian high weakens upper tropospheric divergence in the region southwest of the mid np trough increases and convection is enhanced at the monsoon transition upper level high potential vorticity intrudes southward and westward convection expand from the mid np westward to cover the entire subtropical western np the lower tropospheric monsoon trough deepens surface

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

the link between cut off lows and rossby wave breaking in the southern hemisphere the climatological link between cut off low col pressure systems that occur from 20 to 50 s and rossby wave breaking rwb in the southern hemisphere sh is examined for 1979 2008 it is shown that cols are associated with either rwb events 89 or with potential vorticity pv intrusions where there is north south advection of high pv air 11 in the vast majority of cols the rwb events occur upstream on or before the day of the col formation the evolution of the pv geopotential heights static stability absolute vorticity and temperature advection fields during the cols are consistent with the formation of high pv anomalies that induce cyclonic circulations as predicted by theory rwb plays a key role in producing the split flow associated with cols in the sh which in turn produces absolute vorticity anomalies by shear curvature vorticity conversion and creates static stability anomalies the cols associated with rwb at 330 k are deeper and more persistent than those associated with 350 k rwb and surface processes differ depending on the isentropic surface on which the associated rwb occurs the seasonality of the rwb and cols are similar and is linked to the seasonal march of the westerly jets copyright 2010 royal meteorological society

modulation of the extratropical circulation by combined activity of the madden julian oscillation and equatorial rossby waves during boreal winter abstracttime indices of the madden julian oscillation mjo are often used to generate empirical forecasts of the global atmospheric circulation moist deep convection associated with the mjo initiates eastward propagating rossby waves that disperse into the midlatitudes the background circulation then guides extratropical waves back into the tropics of the eastern pacific ocean previous works have shown that equatorial rossby er waves occur following intrusion of extratropical rossby waves into the tropics westward propagating er waves and the mjo modulate the total convection this convection modulates the zonal wind which influences the location and existence of westerly wind ducts these wind ducts in turn guide extratropical waves into the tropics this paper demonstrates through a simple composite analysis that a simultaneous assessment of mjo and er waves yields more information about the extratropical circulation during boreal winter than can be obtained based on either type of disturbance

tropical upper tropospheric potential vorticity intrusions during sudden stratospheric warmings abstractthe intrusion of lower stratospheric extratropical potential vorticity into the tropical upper troposphere in the weeks surrounding the occurrence of sudden stratospheric warmings ssws is examined the analysis reveals that ssw related pv intrusions are significantly stronger penetrate more deeply into the tropics and exhibit distinct geographic distributions compared to their climatological counterparts while climatological upper tropospheric and lower stratospheric utls pv intrusions are generally attributed to synoptic scale rossby wave breaking it is found that ssw related pv intrusions are governed by planetary scale wave disturbances that deform the extratropical meridional pv gradient maximum equatorward as these deformations unfold planetary scale wave breaking along the edge of the polar vortex extends deeply into the subtropical and tropical utls in addition the material pv deformations also reorganize the geographic structure of the utls waveguide which alters where synopti

a technique for diagnosing three dimensional ageostrophic circulations in baroclinic disturbances on limited area domains abstract the methodology developed by keyser et al for representing and diagnosing three dimensional vertical circulations in baroclinic disturbances using a two dimensional vector streamfunction referred to as the psi vector is restricted to f plane channel model geometry the vertical circulation described by the psi vector consists of the irrotational or divergent part of the ageostrophic wind and the vertical velocity a key property of the psi vector is that its projections onto arbitrarily oriented orthogonal vertical planes yield independent vertical circulations allowing separation of a three dimensional vertical circulation into two two dimensional components and thus objective assessment of the extent to which a three dimensional vertical circulation is oriented in a preferred direction here the methodology for determining the psi vector is modified to be suitable for real data applications the modifications consists of reformulating the diagnostic equations to apply to conformal map pr

invigoration and capping of a convective rainband ahead of a potential vorticity anomaly abstractdeep convection frequently occurs on the eastern side of upper level troughs or potential vorticity pv anomalies this is consistent with uplift ahead of a cyclonic pv anomaly and consequent reduction in static stability and increase of convective available potential energy cape nevertheless the causal link between upper level pv and deep convection has not been proven and given that lift moisture and instability must all be present for deep convection to occur it is not clear that upper level forcing is sufficient in this paper a convective rainband that intensified ahead of a cyclonic pv anomaly in an environment with little cape 10 j kg 1 is examined to determine the factors responsible for its intensification the key feature was a low level convergence line arising from the remnants of an occluded front embedded in the low level cyclonic flow the rainband s intensity and morphology was influenced by the remnants of a tropopause fold that capped convection at midlevels in the

dynamics of the intertropical convergence zone of the east pacific abstract the dynamical factors controlling the mean state and variability of the east pacific intertropical convergence zone itcz and the associated cross equatorial boundary layer flow are investigated using observations from the east pacific investigation of climate epic2001 project the tropical east pacific exhibits a southerly boundary layer flow that terminates in the itcz this flow is induced by the strong meridional sea surface temperature sst gradient in the region away from the equator and from deep convection it is reasonably well described on a day to day basis by an extended ekman balance model variability in the strength and northward extent of this flow is caused by variations in free tropospheric pressure gradients that either reinforce or oppose the pressure gradient associated with the sst gradient these free tropospheric gradients are caused by easterly waves tropical cyclones and the madden julian oscillation convergence in the boundary layer flow is often assumed to be r

quasi biweekly oscillations of the south asian monsoon and its co evolution in the upper and lower troposphere the upper tropospheric quasi biweekly oscillation uqbw of the south asian monsoon is studied using the potential vorticity field on the 370 k isentrope the uqbw is shown to be a common occurrence in the upper troposphere during the monsoon and its typical evolution is described we suggest that the uqbw is a phenomenon of both the middle and tropical latitudes owing its existence to the presence of the planetary scale upper tropospheric monsoon anticyclone the uqbw is first identified as rossby waves originating in the northern flank of the monsoon anticyclone these rossby waves break when reaching the pacific ocean and their associated cyclonic pv anomalies move southward to the east of asia and then westward across the indian ocean and africa advected by the monsoon anticyclone a strong correlation or co evolution between the uqbw and quasi biweekly oscillations in the lower troposphere qbw is also found in particular analysis of vertically integrated horizontal moisture transport 850 hpa geopotential and outgoing long wave radiation show that the uqbw is usually observed at the same time as and co evolves with the lower tropospheric qbw over south asia we discuss the nature of the uqbw and its possible physical link with the qbw

layer wise attribution of vertical motion and the influence of potential vorticity anomalies on synoptic development a methodology is presented for attributing vertical motion to potential vorticity pv in a explicit manner using the quasi geostrophic omega equation the methodology is then used to determine the contribution individual pv anomalies make to the synoptic development it is shown how the total vertical motion may be decomposed into self generating and interaction terms the former correspond to vertical motion that arises from one pv region alone whilst each of the interaction terms represent vertical motion due to the interaction of two different regions of pv the method is applied to a number of cyclones studied in the fronts and atlantic storm tracks experiment in order to determine the dynamical role of individual pv regions in cyclogenesis for purposes of comparison cyclones were chosen to be representative of the types a b and c of an extended petterssen smebye scheme devised by deveson browning and hewson in terms of our new pv method the type a and b cyclones exhibit only subtle differences with the upper level layer of pv playing a larger role in the case of the type b cyclone a much larger difference is apparent between the type a and b cyclones on the one hand and the type c cyclone on the other in the type c cyclone the upper level pv self generating term plays an important role whereas in the type a and b cases the influence of the upper level pv is largely restricted to the interaction terms in all of the cases the vertical motion attributable to the interaction between the low level pv and boundary thermal gradient was found to be large hence from the viewpoint of instantaneous attribution we conclude that the low level pv is always important copyright 2003 royal meteorological society

classification of atmospheric river events on the u s west coast using a trajectory model author s ryoo jm waliser de waugh dw wong s fetzer ej fung i abstract 2015 american geophysical union all rights reserved we investigate transport pathways of water vapor associated with landfalling atmospheric river ar events that result in precipitation along the west coast of the u s for winters of 1997 2010 the water vapor transport pathways are determined by computing back trajectories with a trajectory model using the modern era retrospective analysis for research and applications reanalysis data set the majority of ar events 86 over the west coast of the u s are grouped into three trajectory types and two of them are closely associated with the ar events we designate the first type as ascending near landfall and of tropical origin at the second type as ascending near landfall and of extratropical origin ae and the third type as descending or parallel near landfall and of extratropical origin de which is accompanied but not directly associated with the ar events the magnitude and spatial distribution of precipitation of a given ar event are found to be strongly determined by the type of trajectories in general ar events composed of both at and ae trajectories have more frequent precipitation over a broad region of the western u s and ar events composed of both at and de trajectories have intense precipitation over the southwestern u s due to at trajectories ar events of at only trajectories have intense precipitation especially over the northwestern u s but are less frequent compared to those of at ae trajectories in addition different patterns of trajectory types among ar events are closely linked to upper level potential vorticity pv anomalies 66 of ar events are associated with anticyclonic rossby wave breaking events

a subtropical cyclonic gyre associated with interactions of the mjo and the midlatitude jet abstractthis paper describes a large cyclonic gyre that lasted several days in the northwest pacific during july 1988 cyclonic winds at 850 hpa extended beyond the 2000 km radius with a radius of maximum winds of 700 800 km the gyre exhibited clear skies within and north of its center active convection extended 4000 km in longitude to its south the madden julian oscillation mjo was in its active phase in the indian ocean prior to gyre formation consistent with earlier studies diabatic heating in the mjo was associated with an anomalous upper tropospheric westerly jet over the northeast asian coast and a jet exit region over the northwest pacific repeated equatorward wave breaking events developed downwind of the jet exit region one such event left behind a region of lower tropospheric cyclonic vorticity and convection in the subtropics that played a key role in the gyre formation a second wave breaking event produced strong subsidence north of the mature gyre that contributed to its convective a

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

fastex iop17 cyclone introductory synoptic study with field data this paper introduces the study of the early development phase of the iop17 frontal cyclone of the fastex field experiment fronts and atlantic storm track experiment with the support of observations from fastex observing platforms a synoptic description highlights the development of mesoscale features of interest in the operational meteo france arpege action de recherche petite echelle grand echelle analysis cycle i e cloud head dry wedge and upper level jet outflow a discussion attempts to isolate two significant differences of the present cyclone life cycle compared with previous well known conceptual models of maritime cyclone life cycles i the indirect role of an upper level precursor in triggering the surface low ii the existence of a diabatic regime taking over from the baroclinic development to sustain the deepening rate of the cyclone these two mechanisms are the subject of two companion papers

disentangling the forcing mechanisms of a heavy precipitation event along the alpine south side using potential vorticity inversion extreme precipitation events along the alpine south side as are often forced by upper level positive potential vorticity pv anomalies over western europe these so called pv streamers go along with a dynamical forcing for upward motion a reduction of the static stability in the troposphere hence facilitating convection and are associated with low level winds that transport moisture toward the alps a case of heavy precipitation is examined using the 40 yr ecmwf re analysis data piecewise pv inversion ppvi and the limited area climate high resolution model chrm are used to assess the influences of mesoscale parts of the streamer on the precipitation event the impacts on the vertical stability are quantified by the convective available potential energy cape and an index of static stability very sensitive areas in terms of the stability are located beneath the southern tip of the streamer smaller changes in the stability are observed in the alpine region the moisture transport toward the alps is sensitive to the amplitude of the streamer which influences the amount of water that can be transported along its eastern flank the impacts of the topography on the flow are assessed by calculating an average inverse froude number whether or not the air parcels are blocked by or lifted over the barrier going along with suppressed and enhanced precipitation respectively depends on the vertical stability and the impinging wind velocity two parameters that are inherently linked to the pv streamer and its substructure

attribution and its application to mesoscale structure associated with tropopause folds it is important in meteorology to be able to establish a link between various features this link in its strongest form would be referred to as cause and effect but this is extremely difficult to establish for atmospheric flows a weaker but nonetheless powerful link is attribution which attempts to provide a way to associate various fundamental features such as potential vorticity anomalies to weather events involving regions of ascent attribution is not new and it is implicit in the way that atmospheric evolution is usually described in this paper an attempt is made to define more precisely what are the steps and assumptions being made in such a method these ideas become more concrete by applying them to a simple model of a two dimensional front at which there is a tropopause fold the aim is to find the vertical motion attributable to the descended tropopause fold in an extra tropical cyclone this is the first step in a longer programme of research designed to provide a test of the hypothesis that such a descended tropopause can trigger mesoscale phenomena such as convection and cyclones

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