role of rossby wave breaking in the west pacific teleconnection 1 the dynamical link between the west pacific wp teleconnection and rossby wave breaking rwb events is analyzed during winter months using era40 reanalysis data from 1957 to 2002 the wp pattern which is characterized by latitudinal fluctuations of the pacific jet is closely linked to variations in the nature of rwb similarly to the north atlantic oscillation more anticyclonic cyclonic rwbs than usual occur in the central pacific during the positive negative wp phase when the pacific jet is more to the north south than usual time lag daily composites show that before the occurrence of an anticyclonic rwb event wp anomalies close to the positive phase preexist that are then reinforced during the breaking leading to an increase of the wp index even few days after the peak of the event cyclonic rwb events have similar but opposite effects on the wp pattern since they trigger and maintain the negative phase finally a comparison with the rwb anomalies of the pacific north american pna teleconnection is provided

mesoscale impacts of explicit numerical diffusion in a convection permitting model abstractin convection permitting simulations the spectrum of resolved motions is truncated near scales where convection is active an energy gap between resolved and unresolved motions does not exist such that the upscale and downscale fluxes of energy across the spectrum are affected by the representation of turbulence as well as implicit and explicit numerical diffusion in the current study a systematic analysis is undertaken of the role of explicit numerical diffusion in simulations of diurnal convection over a large alpine region using the consortium for small scale modeling cosmo mesoscale model results are explored by using energy spectra and by diagnosing the physical and dynamical contributions to the bulk mesoscale heat budget in addition a linear analytical model is employed to assess different formulations of numerical diffusion consistent with previous studies the authors find that diffusion may strongly affect the energy spectrum and the formation of precipitation besides the d

relationship between cyclone tracks anticyclone tracks and baroclinic waveguides abstract this study presents observational results concerning the structure and evolution of high frequency fluctuations with periods shorter than 6 days in the geopotential height field the results are based on a statistical analysis of 1000 500 and 250 mb height fields derived from twice daily nmc final analyses over the northern hemisphere for the 20 winters 1964 65 through 1983 84 the disturbances assume the form of waves elongated in the meridional direction with a mean wavelength of 4000 km a westward tilt with height and a mean eastward phase propagation of 12 1 5 m s 1 these results support an interpretation in terms of finite amplitude baroclinic waves whose structure and evolution varies with geographical location over the continents and especially along the eastern slopes of the rockies and the tibetan plateau the waves show marked departures in structure and evolution from those over the oceans in particular we find evidence of a systematic influence of the terrain in steering the

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

cloud resolving model simulations of multiply banded frontal clouds an idealized two dimensional cloud resolving model is used to investigate the formation and temporal evolution of multiply banded clouds in frontal zones radar observations often show both upright and slantwise convection in the circulations associated with such bands the aim is to examine the interaction between upright and slantwise convection and to determine the mechanisms leading to multiple banding a warm bubble is used to initiate convection in the frontal zone which has an initial thermodynamic profile based on observations further triggering occurs and banded clouds evolve the initially upright plumes become tilted due to the so called am adjustment process upscale development observed multiple bands in frontal zones are frequently attributed to the release of conditional symmetric instability csi however in these simulations there is no evidence of the release of csi despite the fragmentation of slantwise bands into multiple layers in the mid troposphere successive triggering of upright convection is instead associated with a spreading cold pool driven by evaporative cooling in the slanted downdraughts triggering can occur on both the warm and cold air sides of the frontal zone and is sensitive to the microphysical parametrization used

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

the link between rossby wave breakings and weather regime transitions abstractthe link between rossby wave breaking rwb and the four wintertime weather regimes over the north atlantic domain is studied in this paper using the 40 yr ecmwf re analysis era 40 data frequencies of occurrence of anticyclonic and cyclonic wave breaking awb and cwb respectively events are computed each weather regime has its own characteristic pattern of rwb frequencies cwb events are found to be most frequent for the greenland anticyclone weather regime whereas awb events occur more for the atlantic ridge and the zonal regimes time lagged composites show that the rwb events characterizing each weather regime occur more often during the formation of the regime rather than during its decay this suggests a reinforcement of the weather regime by rwb an exception is the blocking weather regime which is destroyed by an increase of cwb events south of greenland weather regime transitions are then studied using the low frequency streamfunction tendency budget two types of precursors for th

large scale variabilities of wintertime wind stress curl field in the north pacific and their relation to atmospheric teleconnection patterns 1 wintertime wind stress curl wsc field in the north pacific is investigated to reveal large scale variabilities and their relation to atmospheric teleconnection patterns it is found that the leading empirical orthogonal function eof and the next three rotated eof modes of wintertime wsc anomalies well correspond to those of atmospheric teleconnection patterns i e pacific north american pna western pacific wp tropical northern hemisphere tnh and eastern pacific ep teleconnection patterns respectively time coefficient of the first eof mode well correlates with the north pacific index and does with the pacific decadal oscillation index to some degree it is also found that sverdrup transports in the two zonal bands of 25 n 30 n and 42 5 n 47 5 n have highly negative correlation and these variations can be represented by the forcing field of the first eof mode the pna forcing makes both subtropical and subpolar gyres spin up spin down simultaneously

an idealized nonlinear model of the northern hemisphere winter storm tracks abstract in this paper a nonlinear dry model forced by fixed radiative forcing alone has been constructed to simulate the northern hemisphere winter storm tracks a procedure has been devised to iterate the radiative equilibrium temperature profile such that at the end of the iterations the model climate closely resembles the desired target climate this iterative approach is applied to simulate the climatological storm tracks in january it is found that when the three dimensional temperature distribution in the model resembles the observed distribution the model storm tracks are much too weak it is hypothesized that this is due to the fact that eddy development is suppressed in a dry atmosphere owing to the lack of latent heat release in the ascending warm air to obtain storm tracks with realistic amplitudes the static stability of the target climate is reduced to simulate the enhancement in baroclinic energy conversion due to latent heat release with this modification the storm tracks in the

mesoscale dynamics of a deepening secondary cyclone in fastex iop16 three dimensional structure retrieved from dropsonde data the mesoscale dynamics of a secondary cyclone sampled during the field phase of the fronts and atlantic storm track experiment fastex intensive observation period iop 16 are documented using airborne dropsonde data the method proposed to recover the mesoscale analytical three dimensional 3 d dynamic fields from the dropsonde measurements is evaluated using simulated fields airborne in situ measurements and airborne doppler radar measurements these simulations and comparisons indicate that the method is able to resolve the mesoscale structures within the studied secondary cyclone both in the regions of clear air and precipitation it appears however that the most accurate description of the 3 d dynamic fields in both these regions would be obtained by combining doppler and dropsonde measurements the studied secondary cyclone is a fast moving frontal wave that developed on the trailing cold front of a parent low situated over greenland using the dropsonde derived 3 d fields the mesoscale flows involved in the organization of the secondary cyclone are described the potential vorticity and equivalent potential vorticity fields deduced from the basic analytical fields indicate that the atmosphere is roughly neutral to moist slantwise instability this configuration is known to significantly promote frontogenesis the vertical configuration of the jets and circulations within this secondary cyclone are compared with the coupling uncoupling scheme of shapiro a slight coupling is found between the thermally indirect circulation and the ageostrophic circulation the obtained coupling is however not as developed as in the ideal case described by shapiro which may explain the small upward velocities in our case airborne doppler radar and dropsonde measurements are combined so as to infer the multi scale processes involved in the mesoscale and convective scale organization of the atlantic secondary cyclones and to evaluate the new emerging theoretical interpretations of secondary cyclogenesis

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

significance of a midlatitude sst frontal zone in the formation of a storm track and an eddy driven westerly jet abstract in a set of idealized aquaplanet experiments with an atmospheric general circulation model to which zonally uniform sea surface temperature sst is prescribed globally as the lower boundary condition an assessment is made of the potential influence of the frontal sst gradient upon the formation of a storm track and an eddy driven midlatitude polar front jet pfj and on its robustness against changes in the intensity of a subtropical jet stj in experiments with the frontal midlatitude sst gradient as that observed in the southwestern indian ocean transient eddy activity in each of the winter and summer hemispheres is organized into a deep storm track along the sst front with an enhanced low level baroclinic growth of eddies in the winter hemisphere another storm track forms just below the intense stj core but it is confined to the upper troposphere with no significant baroclinic eddy growth underneath the near surface westerlies are strongest near the midlatitude sst front as observe

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

response of northern hemisphere storm tracks to indian western pacific ocean warming in atmospheric general circulation models with 40 years integration output of two atmospheric general circulation models gamil iap and hadam3 ukmo forced with identical prescribed seasonally varying sea surface temperature this study examines the effect of the observed indian western pacific ocean iwp warming on the northern hemisphere storm tracks both models indicate that the observed iwp warming tends to cause both the north pacific storm track npst and the north atlantic storm track nast to move northward such a consistent effect on the two storm tracks is closely associated with the changes in the low level atmospheric baroclinicity high level jet stream and upper level geopotential height the iwp warming can excite a wavelike circum global teleconnection in the geopotential height that gives rise to an anticyclonic anomaly over the midlatitude north pacific and a positive phase nao anomaly over the north atlantic these geopotential height anomalies tend to enhance upper level zonal westerly winds north of the climatological jet axes and increase low level baroclinicity and eddy growth rates thus favoring transient eddy more active north of the climatological storm track axes responsible for the northward shift of the both storm tracks the iwp warming induced northward shift of the nast is quite similar to the observed suggesting that the iwp warming can be one of the key factors to cause decadal northward shift of the nast since the 1980s however the iwp warming induced northward shift of the npst is completely opposite to the observed implying that the observed southward shift of the npst since the 1980s would be primarily attributed to other reasons although the iwp warming can have a cancelling effect against those reasons

the role of mesoscale instabilities in the sting jet dynamics of windstorm tini sting jets sj occur as an additional region of low level strong winds in some shapiro keyser type extra tropical cyclones while sjs are widely accepted as being distinct from the warm and cold conveyor belts the mechanisms responsible for their occurrence are still not fully understood here we determine the relative importance of the release of mesoscale instabilities and synoptic scale cyclone dynamics so addressing an area of current debate numerical weather prediction simulations of a sj containing windstorm are analysed and lagrangian trajectories used to assess the evolution of and mesoscale atmospheric instabilities e g symmetric and inertial instabilities in the descending airstream the sj undergoes a two stage descent cooling via sublimation followed by a large acceleration accompanied by instability release combined tilting and stretching of vorticity play a major role in the local onset of instability on the airstream vorticity and frontogenesis fields have a narrow slantwise banded structure in the cloud head and around the sj the descending sj modifies the widespread frontolysis expected from the large scale dynamics alone in the frontal fracture region a coarser resolution simulation also generates strong winds in the frontal fracture region although these are significantly weaker than in the higher resolution simulation the sj airstream in the coarser resolution simulation undergoes a weaker descent without instability generation and descends in a widespread frontolytic region hence while the sj undergoes a process of destabilisation that enhances its descent and acceleration in the higher resolution simulation enhancing the strong winds already generated by the synoptic scale cyclone dynamics this destabilisation does not occur in the sj produced by a coarser resolution simulation resulting in weaker winds this analysis reveals the synergy between the paradigms of sj occurrence through the release of mesoscale instabilities and synoptic scale cyclone dynamics and demonstrates that the current debate may in part be a consequence of the model resolutions used by different studies

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

applicability of large scale convection and condensation parameterization to meso γ scale hirlam a case study of a convective event abstract this paper presents a case study of a single cold air outbreak event with widespread convective precipitation over southern finland on 25 may 2001 the purpose of the study is to investigate the applicability of the convection and condensation scheme of the high resolution limited area model hirlam on meso scales the study concentrates on the issue of grid size dependent convection parameterization an explicit approach without the convection scheme is also examined at the same time the performance of an experimental nonhydrostatic version of hirlam is evaluated model simulations are conducted with three different horizontal grid spacings 11 5 6 and 2 8 km model results are compared to observed radar reflectivity data utilizing a radar simulation model which calculates radar reflectivities from three dimensional model output the best results are obtained using nonhydrostatic dynamics and a grid size dependent convection scheme with a 5 6 km grid interval however even the best conf

the effects of changing resolution on mesocale modelling of line convection and slantwise circulations in fastex iop16 data are presented from modelling a rapidly developing cyclone in intensive observation period 16 of the fronts and atlantic storm tracks experiment using the new non hydrostatic version of the met office unified model at a number of different horizontal and vertical resolutions the model produces a good representation of the system including multiple fronts with line convection cloud heads and slantwise cross frontal circulations similar to those seen in the observations results from the model with various grid lengths from 60 km nested down to 2 km with 45 vertical levels show that more realistic detail is produced as the grid length is reduced but that the large scale structures remain consistent by spectral analysis it is found that structures on scales shorter than approximately five grid lengths are attenuated the line convection at the fronts is aliased onto the grid length scale except in the 2 km model where evidence of a three dimensional structure starts to appear the 2 and 4 km models have also been run with enhanced vertical resolutions it is concluded that whilst a 24 km 45 level model is sufficient to represent the overall frontal structure a model with resolution at least 2 km in the horizontal and 90 vertical levels is required to represent small scale multiple slantwise circulations similar to those observed in the dropsonde data crown copyright 2003

the annual cycle of northern hemisphere storm tracks part i seasons abstractin this paper and part ii a comprehensive picture of the annual cycle of the northern hemisphere storm tracks is presented and discussed for the first time it is based on both feature trac

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

the sting at the end of the tail model diagnostics of fine scale three dimensional structure of the cloud head this is the second in a series of papers on the sting at the end of the tail a mesoscale region of potentially damaging surface winds that can occur close to the evaporating tip of a cloud head wrapped around the bent back front of an extratropical cyclone in the first paper the sting phenomenon was identified from a purely observational study of the great storm of october 1987 in the present paper an observationally validated forecast run from a high resolution numerical weather prediction model is used to examine the evolving three dimensional structure of the sting phenomenon it is shown that the damaging surface winds in the october 1987 storm were due to a well defined mesoscale sting jet sj identifiable as a coherent ensemble of trajectories originating in cloudy air at about 650 hpa there is evidence of multiple mesoscale slantwise circulations and the sj appears to form within the descending part of these circulations air within the sj descends to the 900 hpa level over a period of about 4 h during which time it accelerates from less than 20 to above 45 m s 1 with extremes greater than 50 m s 1 although the wet bulb potential temperature of air in the sj remains constant during its descent to 900 hpa evaporation leads to a reduction of up to 5 k or more in dry bulb potential temperature in some parts of the jet the sj is situated behind the primary cold front and is distinct from the associated warm conveyor belt low level jet it is also distinct from the cold conveyor belt low level jet which remains below and behind it as the sj skirts the bent back front crown copyright 2005

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

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

bidimensional diagnostics variability and trends of northern hemisphere blocking abstractin this paper northern hemisphere winter blocking is analyzed through the introduction of a set of new bidimensional diagnostics based on geopotential height that provide information about the occurrence the duration the intensity and the wave breaking associated with the blocking this analysis is performed with different reanalysis datasets in order to evaluate the sensitivity of the index and the diagnostics adopted in this way the authors are able to define a new category of blocking placed at low latitudes that is similar to midlatitude blocking in terms of the introduced diagnostics but is unable to divert or block the flow furthermore over the euro atlantic sector it is shown that it is possible to phenomenologically distinguish between high latitude blocking occurring over greenland north of the jet stream and dominated by cyclonic wave breaking and the traditional midlatitude blocking localized over europe and driven by anticyclonic wave breaking these latter events are uniform

a new boundary layer mixing scheme part i scheme description and single column model tests a new boundary layer turbulent mixing scheme has been developed for use in the ukmo weather forecasting and climate prediction models this includes a representation of nonlocal mixing driven by both surface fluxes and cloud top processes in unstable layers either coupled to or decoupled from the surface and an explicit entrainment parameterization the scheme is formulated in moist conserved variables so that it can treat both dry and cloudy layers details of the scheme and examples of its performance in single column model tests are presented

three dimensional acoustic scattering from a penetrable layered cylindrical obstacle in a horizontally stratified ocean waveguide in this work a normal mode solution is presented for the three dimensional problem of acoustic scattering from a penetrable horizontally layered cylindrical obstacle in a shallow water waveguide the ocean environment around the obstacle is considered horizontally stratified and the bottom is assumed to be rigid in the general case of depth dependent sound speed and density profiles ssdp the total acoustic field is calculated numerically while an analytic solution is obtained in the special case of depth independent ssdp numerical results concerning the transmission loss outside and inside single or double layered cylindrical structures made of acoustic materials are given for a typical depth dependent ocean environment comparisons with the cases of ideally soft and ideally hard cylindrical obstacles j acoust soc am 100 206 218 1996 are also made illustrating the effect of acoustic properties of the obstacle an important feature which clearly emerges from the theoretical analysis and th

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

thermally driven and eddy driven jet variability in reanalysis two important dynamical processes influence the extratropical zonal wind field angular momentum transport by the thermally direct hadley circulation thermal driving t and momentum flux convergence by atmospheric waves eddies that develop in regions of enhanced baroclinicity eddy driving e the relationship between extratropical zonal wind variability and these driving processes is investigated using 40 yr european centre for medium range weather forecasts re analysis era 40 data indices representing the processes it and ie are defined based on vertically integrated diabatic heating and meridional convergence of the meridionalflux of zonal momentum by eddies respectively zonal wind signatures associated with these indices are identified via composite analysis in the atlantic sector zonal wind variability is mainly associated with momentum flux convergence by baroclinic eddies supporting the established view that the atlanticjetis primarilyeddydriven inthe pacificsector zonal windvariability isassociatedwith bothdriving processes evidence that the pacific jet is both thermally driven and eddy driven the thermally driven pacific signature reflects changes in jet strength intensity and longitudinal extent with some resemblance to the zonal wind anomalies of the pacific north america pna pattern the eddy driven signature reflects a latitudinal shift of the jet exit region in both sectors that resembles the zonal wind anomalies of the north atlantic oscillation nao or west pacific wp patterns

the impact of wave packets propagating across asia on pacific cyclone development abstract in this paper ecmwf 40 yr reanalysis data have been examined to study the influence of upper level wave packets propagating across asia into the pacific on surface cyclone development over the pacific previous studies have shown that in winter wave packets propagate across asia over two branches a northern branch over siberia and a southern branch along the subtropical jet across southern asia results presented here show that subsequent to the presence of wave packets on either branch the frequency of occurrence of deep cyclones defined as cyclones with central pressure below 960 hpa as well as explosively deepening cyclones those with a deepening rate of 1 bergeron or more are significantly enhanced this enhancement also clearly follows the wave packet eastward as it propagates across the pacific wave packets from the two branches are found to interfere with each other such that if wave packets of the appropriate configuration are present on both the northern and southern branch s

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones part xv a numerical modeling study of frontogenesis and cold frontal rainbands abstract a two dimensional hydrostatic primitive equation model is used to investigate the dynamics of frontogenesis in a moist atmosphere the development of a cold front is simulated through shear deformation associated with the non linear evolution of an eady wave simulations are performed with 5 10 40 and 80 km horizontal resolutions and 14 levels in the vertical four in the boundary layer compared to the dry case the inclusion of moisture in the model produces a stronger low level jet ahead of the front and a stronger upper level jet moisture also produces a stronger ageostrophic circulation across the front and a more concentrated updraft just ahead of the surface front the updraft develops a banded structure above and behind the surface front with a wavelength of about 70 km bands form near the back edge of the cloud shield and move toward the surface front with a relative velocity of 1 m s 1 these characteristics agree with observations of wide cold frontal rainbands the banded str

possible modification of atmospheric circulation over the northwestern pacific induced by a small semi enclosed ocean 1 the surface conditions of a small semi enclosed ocean the japan sea largely controlled by the volume transport of the warm current influence the monthly mean atmospheric circulation over the northwestern pacific via active cyclogenesis the new dynamical processes induced by the japan sea are proposed in this letter when the surface temperature in the japan sea is lowered in a regional atmospheric model the monthly mean potential vorticity is increased over the japanese islands and the monthly mean okhotsk low is intensified at the 500 hpa level in the case of an amplified okhotsk low the mean cyclonic flow transports a cold air over the japan sea toward the pacific and transports relatively warm air over the bering sea toward siberia such westerly easterly air mass advections over the northwestern pacific area could produce the japan siberia temperature anomaly in the lower level troposphere via enhancement of the okhotsk low which contributes to the weakness of the synoptic scale north south temperature gradient at 120 180 e this newly found westerly cold easterly warm ocean air mass advection enhanced by the amplified quasi stationary eddy that acts to reduce the temperature gradient is distinct from poleward heat transport by well known transient baroclinic waves or annual mean ferrel circulation

structure and dynamics of the summertime pacific japan teleconnection pattern convective activity over the tropical western pacific is known to influence the extratropical circulation over east asia in the boreal summer in the form of teleconnection called the pacific japan pj pattern but its structure and dynamics have not yet been studied in depth in this study a composite analysis is performed for 32 monthly events of enhanced convection observed to the east of the philippines the composited monthly mean vorticity anomalies associated with the pj pattern are elongated zonally with a distinct poleward tilt with height this structure differs fundamentally from a combination of the first baroclinic mode in the tropics and the barotropic structure in midlatitudes as has widely been accepted as a conceptual model of the pj pattern a wave activity flux points polewards only in the lower troposphere indicating that rossby wave teleconnection occurs primarily through a low level south westerly jet those tilted anomalies over the western pacific can effectively gain kinetic energy in the exits of the mean jet streams in the upper and lower troposphere and available potential energy ape in the presence of the vertically sheared jets the enhanced convection can generate ape effectively and the associated low level anomalous circulation acts to increase moisture supply into the convective region while enhancing evaporation from the pre warmed ocean surface it is thus hypothesized that the pj pattern may be regarded as a dynamical mode that can be effectively excited in the zonally asymmetric baroclinic mean flow associated with the asian summer monsoon with an efficient self sustaining mechanism through moist processes copyright 2006 royal meteorological society

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

low frequency variability in the northern hemisphere winter geographical distribution structure and time scale dependence abstract low frequency variability in wintertime 500 mb height is examined with emphasis on its structure geographical distribution and frequency dependence a 39 year record of 500 mb geopotential height fields from the nmc analyses is time filtered to partition the fluctuations into frequency bands corresponding to periods of 10 60 days 60 180 days and 180 days winter is defined as the six month period november through april variance teleconnectivity and anisotropy fields and selected loading vectors derived from orthogonal and oblique rotations of the eigenvectors of the temporal correlation matrix for each band are shown and discussed the variability in all frequency bands exhibits substantial anistropy with meridionally elongated features arranged as zonally oriented wave trains prevailing over the continents and zonally elongated features organized in the form of north south oriented dipole patterns prevailing over the oceanic sectors of the hemisphere the wave trains are most pronounc

influence of the meridional shifts of the kuroshio and the oyashio extensions on the atmospheric circulation abstract the meridional shifts of the oyashio extension oe and of the kuroshio extension ke as derived from high resolution monthly sea surface temperature sst anomalies in 1982 2008 and historical temperature profiles in 1979 2007 respectively are shown based on lagged regression analysis to significantly influence the large scale atmospheric circulation the signals are independent from the enso teleconnections which were removed by seasonally varying asymmetric regression onto the first three principal components of the tropical pacific sst anomalies the response to the meridional shifts of the oe front is equivalent barotropic and broadly resembles the north pacific oscillation western pacific pattern in a positive phase for a northward frontal displacement the response may reach 35 m at 250 hpa for a typical oe shift a strong sensitivity since the associated sst anomaly is 0 5 k however the amplitude but not the pattern or statistical significance strongly depends on the lag and an

synoptic behavior of baroclinic eddies during the blocking onset abstract synoptic behavior of individual baroclinic eddies in the course of their interactions with amplifying blocking anticyclones is examined based upon a 30 year record of the tropospheric circulation in the northern hemisphere winter high pass filtered as well as unfiltered fields of geopotential height and potential vorticity were composited relative to the onset of the five different types of blocking patterns before the compositing the entire sequence of the fields was slightly shifted in time and space in such a way that the strongest baroclinic eddy during the onset of each blocking event occupies a prescribed position in the upstream storm track when it reaches its maximum intensity since this shifting considerably reduces the cancellation between the individual high frequency migratory eddies this type of compositing can present a more synoptically oriented view of those interactions than conventional compositing in our composite results one or two pairs of cyclonic and anticyclonic

multiscale dynamical processes underlying the wintertime atlantic blockings abstractthe wintertime atmospheric blocking over the atlantic is investigated using a newly developed methodology namely localized multiscale energy and vorticity analysis ms eva and the theory of canonical energy transfer through a multiscale window transform mwt the atmospheric fields from the era 40 data are reconstructed on three scale ranges or scale windows basic flow window blocking window and synoptic window the blocking event is obtained by compositing the wintertime blocking episodes and a clear westward retrograding signal is identified on the blocking window likewise the local multiscale energetics following the signal are composited it is found that a life cycle of the blocking scale kinetic energy ke may be divided into three phases onset phase amplification phase and decay phase different phases have different mechanisms in play in general pressure work and the canonical transfer from the synoptic eddies initiate the generation of the blocking while the latter contri

intraseasonal variations of the british baikal corridor pattern abstractthe british baikal corridor bbc pattern is the dominant waveguide mode trapped along the summertime polar front jet over northern eurasia it consists of four geographically fixed centers

development and decay processes of dual inversion layers in winter over the northwest coast of the south china sea abstractinversion layers in the lower troposphere appear centered at two heights 1 5 and 4 km over the northwestern coast of the south china sea in late boreal winter the mechanisms of these dua

the dynamics of low frequency variability in a simple model of the global atmosphere abstract we examine the dynamics of low frequency variability in a simple global model with zonally homogeneous boundary conditions low frequency structure comprises trains of nearly equivalent barotropic rossby waves with weak eastward phase velocities and strong eastward group velocities these low frequency eddies are strongly coupled to synoptic activity the flux of vorticity by synoptic waves acts both to reinforce the low frequency eddies and to retard their eastward propagation mechanistic experiments with an imposed forcing show that the synoptic scale vorticity fluxes are organized by the low frequency flow the behavior is generally similar to that found in previous studies of blocks the present work shows that strong mutual interactions between the low and synoptic frequencies also characterize less dramatic low frequency flows

the dynamics of nao teleconnection pattern growth and decay this investigation performs both diagnostic analyses with ncep ncar re analysis data and forced barotropic model calculations to examine the dynamical mechanisms associated with the growth and decay of the north atlantic oscillation nao teleconnection pattern the diagnostic calculations include projection and composite analyses of each term in the stream function tendency equation the results of the analyses reveal a complete life cycle of growth and decay within approximately two weeks the positive nao phase is found to develop after anomalous wavetrain propagation across the north pacific to the east coast of north america this contrasts with the negative nao phase which appeared to develop in situ both high frequency period 10 days transient eddy fluxes drive the nao growth after the nao anomaly attains its maximum amplitude the high frequency transient eddy fluxes continue to drive the nao anomaly in a manner that is consistent with a positive feedback process the decay of the nao occurs through both the divergence term and the low frequency transient eddy fluxes the temporal and spatial properties of the divergence term are found to be consistent with ekman pumping these results illustrate many important differences between the nao and pacific north american pna teleconnection patterns perhaps most striking being that the nao life cycle is dominated by nonlinear processes whereas the pna evolution is primarily linear in addition the relation between the nao and the zonal index is discussed copyright 2003 royal meteorological society

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

heat flow in vapor dominated areas of the yellowstone plateau volcanic field implications for the thermal budget of the yellowstone caldera the yellowstone caldera the 0 11 km 2 obsidian pool thermal area opta and the 0 25 km 2 solfatara plateau thermal area spta conductive heat flux through a low permeability layer capping large vapor reservoirs is calculated from soil temperature measurements at 600 locations and from laboratory measurements of soil properties the conductive heat output is 3 6 0 4 mw and 7 5 0 4 mw from the opta and the spta respectively the advective heat output from soils is 1 3 0 3 mw and 1 2 0 3 mw from the opta and the spta respectively and the heat output from thermal pools in the opta is 6 8 1 4 mw these estimates result in a total heat output of 11 8 1 4 mw and 8 8 0 4 mw from opta and spta respectively focused zones of high heat flux in both thermal areas are roughly aligned with regional faults suggesting that faults in both areas serve as conduits for the rising acid vapor

the impact of deformation strain on the formation of banded clouds in idealized modelling experiments experiments are performed using an idealized version of an operational forecast model to determine the impact on banded frontal clouds of the strength of deformational forcing low level baroclinicity and model representation of convection line convection is initiated along the front and slantwise bands extend from the top of the line convection elements into the cold air this banding is attributed primarily to m adjustment the cross frontal spreading of the cold pool generated by the line convection leads to further triggering of upright convection in the cold air that feeds into these slantwise bands secondary low level bands form later in the simulations these are attributed to the release of conditional symmetric instability enhanced deformation strain leads to earlier onset of convection and more coherent line convection a stronger cold pool is generated but its speed is reduced relative to that seen in experiments with weaker deformational strain because of inhibition by the strain field enhanced low level baroclinicity leads to the generation of more inertial instability by line convection for a given capping height of convection and consequently greater strength of the slantwise circulations formed by m adjustment these conclusions are based on experiments without a convective parametrization scheme experiments using the standard or a modified scheme for this model demonstrate known problems with the use of this scheme at the awkward 4 km grid length used in these simulations copyright 2008 royal meteorological society

mechanisms of intraseasonal amplification of the cold siberian high mechanisms of intraseasonal amplification of the siberian high are investigated on the basis of composite anomaly evolution for its strongest events at each of the grid points over siberia at each location the amplification of the surface high is associated with formation of a blocking ridge in the upper troposphere over central and western siberia what may be called wave train atlantic origin type is common where a blocking ridge forms as a component of a quasi stationary rossby wave train propagating across the eurasian continent a cold air outbreak follows once anomalous surface cold air reaches the northeastern slope of the tibetan plateau it is found through the potential vorticity pv inversion technique that interaction between the upperlevel stationary rossby wave train and preexisting surface cold anomalies is essential for the strong amplification of the surface high upper level pv anomalies associated with the wave train reinforce the cold anticyclonic anomalies at the surface by inducing anomalous cold advection that counteracts the tendency of the thermal anomalies themselves to migrate eastward as surface thermal rossby waves the surface cold anomalies thus intensified in turn act to induce anomalous vorticity advection aloft that reinforces the blocking ridge and cyclonic anomalies downstream of it that constitute the propagating wave train the baroclinic development of the anomalies through this vertical coupling is manifested as a significant upward flux of wave activity emanating from the surface cold anomalies which may be interpreted as dissipative destabilization of the incoming external rossby waves

trapping of synoptic scale disturbances into the north pacific subtropical jet core in midwinter 1 over the northwestern nw pacific a subtropical jet stream develops at 30 n in midwinter as the east asian winter monsoon intensifies eddies with subweekly periods propagating through the midlatitude tropopause into the nw pacific storm track tend to be trapped into the jet core 1000 km away from a surface baroclinic zone at 40 n while lifted up by 3 km the trapping appears to weaken the interaction of the upper level eddies with the baroclinic zone thus acting against eddy amplification and thereby contributing to the midwinter minimum in the eddy activity as observed before the late 1980s since then under the reduced trapping effect by the weakened jet upper level eddies tended to propagate right above the surface baroclinic zone while strongly interacting it even in midwinter as in fall and spring this midwinter tendency acted to enhance the eddy amplification that led to the recent disappearance of the activity minimum

parcel theory in three dimensions and the calculation of scape slantwise convective available potential energy scape is a measure of the degree to which the atmosphere is unstable to conditional symmetric instability csi it has until now been defined by parcel theory in which the atmosphere is assumed to be nonevolving and balanced that is two dimensional when applying this two dimensional theory to three dimensional evolving flows these assumptions can be interpreted as an implicit assumption that a timescale separation exists between a relatively rapid timescale for slantwise ascent and a slower timescale for the development of the system an approximate extension of parcel theory to three dimensions is derived and it is shown that calculations of scape based on the assumption of relatively rapid slantwise ascent can be qualitatively in error for a case study example of a developing extratropical cyclone scape calculated along trajectories determined without assuming the existence of the timescale separation show large scape values for parcels ascending from the warm sector and along the warm front these parcels ascend into the cloud head within which there is some evidence consistent with the release of csi from observational and model cross sections this region of high scape was not found for calculations along the relatively rapidly ascending trajectories determined by assuming the existence of the timescale separation

observational synthesis of mesoscale structures within an explosively developing cyclone an observational case study is presented of a rapidly developing uk cyclone on 30 october 2000 to reveal the rich diversity of coexisting mesoscale structures in the vicinity of the cloud head dry slot and polar front cloud band the mesoscale structures include multiple rain bands due to upright convection originating in the boundary layer stacked slantwise convective circulations at middle levels cloud top striations due to upright convection originating at high levels above the polar front cloud band multiple sub structure within the cloud head and inertia gravity waves in the region of the tropopause fold the emphasis of the analysis synthesis is on the inter relationships between the various mesoscale structures issues raised by this study include i the interaction between upright and slantwise convection including the effects of evaporation in the dry slot ii the possible roles of inertia gravity waves and conditional symmetric instability in triggering organizing the dry slot convective rain bands and the sub structure within the cloud head and iii the relationship between the dry slot rain bands and the multiple structures within the cloud head this study is limited to documenting these relationships controlled experiments with high resolution mesoscale models will be required to establish cause and effect and to assess their importance copyright 2005 royal meteorological society

vertical structure of wintertime teleconnection patterns abstract orthogonal rotated principal component analysis of the wintertime northern hemisphere 5 day mean sea level pressure field yielded five modes which are of some dynamical interest one can be identified with the well known north atlantic oscillation and another with the pacific north american pattern three of the other modes are highly baroclinic in the sense that their sea level pressure patterns and their associated 500 mb height patterns are different in shape and opposite in polarity over substantial areas these more baroclinic patterns attain their largest amplitudes in the vicinity of the himalayas and rockies their spatial patterns evolve very differently in the lower and middle troposphere the sea level pressure patterns exhibit a distinctive eastward and or equatorward phase propagation parallel to contours of surface elevation along the northern and or eastern side of the mountain ranges while the corresponding 500 mb patterns evolve in a manner consistent with the concept of ros

the response of the pacific storm track and atmospheric circulation to kuroshio extension variability an index of the kuroshio extension front strength is produced using a maximum covariance analysis between sea surface temperature sst and sea surface height ssh gradient observations and composites of the atmospheric state are presented during its positive and negative phases using reanalysis data 1992 2011 it is found that when the kuroshio extension is less more meandering with a stronger weaker sst front the atmospheric heat transport by transient eddies is increased in the western eastern pacific region consistent with an increase decrease in low level baroclinicity analysis of the eddy mean flow interaction shows that this zonal shift in heat transport forces anomalous barotropic flow in the eastern pacific where blocking frequency is strongly influenced the above relationships cannot be reconciled with the known response of the north pacific storm track to remote forcing from the tropical pacific nor can they be explained by the response of the ocean to atmospheric forcing via surface heat fluxes or winds rather the zonal shift in the storm track highlighted here and the associated changes in the large scale circulation are interpreted as a response to the interannual variability of the kuroshio extension front

three dimensional propagation and scattering around a conical seamount a three dimensional 3d propagation and scattering model is developed for an offset acoustic source in an ocean with axisymmetric bathymetry based on the same theoretical foundation as the formulation presented by taroudakis m i taroudakis a coupled mode formulation for the solution in the presence of a conical sea mount j comput acoust 4 101 121 1996 the present approach combines a spectral decomposition in azimuth with a coupled mode theory for two way range dependent propagation however the earlier formulations were severely limited in terms of frequency size and geometry of the seamount the seabed composition and the distance between the source and the seamount and were therefore severely limited in regard to realistic seamount problems without changing the fundamental theoretical foundation the present approach applies a number of modifications to the numerical formulation leading to orders of magnitude in numerical efficiency for realistic problems further by using a st

numerical study of slantwise circulations in a strongly sheared prefrontal environment the simultaneous presence of convective symmetric and inertial instability in a prefrontal region of strong vertical wind shear was simulated with the non hydrostatic model moloch model diagnostics of absolute vorticity pseudo angular momentum saturated equivalent potential temperature and vorticity reveal a sequence of events that includes m adjustment followed by slanted ascent in symmetrically unstable regions becoming saturated in the later stages an idealized experiment without orography was performed to isolate the presence and role of instabilities characterizing the development the diagnosed circulation is reminiscent of a wavenumber two normal mode of dry symmetric instability while moist symmetric instability is confined to a very limited region despite the appearance of wider areas of negative moist potential vorticity the evaluation of moist thermodynamic quantities which give proper account of condensate loading is suggested as a possible resolution of this apparent inconsistency copyright 2011 royal meteorological society

numerical experiments of the storm track sensitivity to oceanic frontal strength within the kuroshio oyashio extensions the sensitivity of the north pacific storm track to midlatitude oceanic frontal strength within the kuroshio oyashio extensions is investigated by applying artificially changed meridional sea surface temperature sst gradients in the weather research forecasting model version 3 4 the result of sensitivity experiments further confirms the close relationship between the storm track activity and meridional sst gradient i e the storm track activity can be intensified as a response to increases in the oceanic frontal strength in order to better understand the mechanism for the storm track intensification due to increased sst gradient velocity temperature correlation and local energetics are analyzed the result indicates that the enhancement of the meridional sst gradient leads to amplitude magnification of eddy meridional velocity and temperature and their phase consistency suggesting that synoptic scale eddies tend to approach the optimum structure for the baroclinic energy conversion which is mainly responsible for the sst front induced enhancement of storm track activity in order to estimate the impact of the oceanic front on the maintenance of the near surface baroclinicity further investigation is made by the composite analysis with the increase in oceanic frontal strength the near surface baroclinicity experiences a slow but strong restoration the increase in the meridional sst gradient results in the intensification in the cross frontal differential sensible heat flux which can more effectively offset the relaxing effect of the transient eddy poleward heat transport

the north pacific oscillation west pacific teleconnection pattern mature phase structure and winter impacts abstract the north pacific oscillation npo in sea level pressure and its upper air geopotential height signature the west pacific wp teleconnection pattern constitute a prominent mode of winter midlatitude variability the npo wp its mature phase expression is identified from principal component analysis of monthly sea level pressure variability as the second leading mode just behind the pacific north american variability pattern npo wp variability primarily on subseasonal time scales is characterized by a large scale meridional dipole in slp and geopotential height over the pacific and is linked to meridional movements of the asian pacific jet and pacific storm track modulation the hemispheric height anomalies at upper levels resemble the climatological stationary wave pattern attributed to transient eddy forcing the npo wp divergent circulation is thermal wind restoring pointing to independent forcing of jet fluctuations intercomparison of sea level pressure geopotential height and zonal

energetics of the western hemisphere circulation pattern abstractthe western hemisphere wh circulation pattern identified by self organizing maps cluster analysis is a low frequency atmospheric regime that influences the fluctuations of large scale c

dynamical effects of ice sublimation in a frontal wave the dynamical role of ice sublimation in weather systems is briefly reviewed observations are presented from the fronts and atlantic storm track experiment fastex intensive observation period 16 that show variations of static stability humidity and mesoscale circulation corresponding to those associated theoretically with sublimation of ice precipitation it is thus suggested that the observations display the mechanism proposed by clough and franks in which forward mesoscale flows are associated with moist adiabatic descent supported by the sublimation cooling this mechanism was suggested as an important stage in the evolution of many mesoscale rain bands a set of three model simulations of the event has been made with versions of the mel office s unified model of these a mesoscale model integration with 11 km resolution and 45 levels clearly displays the symptoms and is diagnosed to demonstrate its consistency with the clough franks mechanism an integration omitting the cooling due to sublimation differs significantly from the full model experiment in the structure of low level wind fields frontal troughs and mesoscale precipitation distribution il is also demonstrated that the static stability transition mesoscale circulation and mid tropospheric potential vorticity perturbations are substantially weakened in this integration thus confirming that the clough franks mechanism is also operating in the numerical weather prediction nwp model we deduce from these studies that ice precipitation and its sublimation has a major role in determining mesoscale circulation and structure in mid latitude weather systems affecting stratification and the formation of features such as fronts and rain bands these are substantially affected by the fall and evaporation of ice crystals which are both important to temperature and moisture transports and the behaviour of nwp models on time scales of hours to days in our integrations dynamical feedback due to sublimation cooling coincided with extreme negative potential vorticity values and potentially conditional symmetric instability hence the anticyclonic motion occurring in the cloud head or deep cloud of the moist warm sector as in this case in moist warm sectors a substantial role for sublimation may be anticipated more generally particularly for air trajectories receiving most ice precipitation we suggest that the described phenomenon be referred to as sublimation enhanced descent or sed it is concluded that in view of tins demonstrated sensitivity substantial attention should be given to refining microphysical parametrizations in nwp models and that radar and sounding observations from the fastex experiment provide a suitable basis for validating these schemes

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

a reconstruction of subtropical western north pacific sst variability back to 1578 based on a porites coral sr ca record from the northern ryukyus japan we present a seasonal reconstruction of sea surface temperature sst from 1578 to 2008 based on a porites coral sr ca record from the northern ryukyus within the kuroshio southern recirculation gyre interannual sst anomalies are generally 0 5 c making sr ca derived sst reconstructions a challenging task replicate measurements along adjacent coral growth axes enabled by the laser ablation inductively coupled plasma mass spectrometry technique used here give evidence of rather large uncertainties nonetheless derived winter sst anomalies are significantly correlated with the western pacific atmospheric pattern which has a dominant influence on winter temperature in east asia annual mean ssts show interdecadal variations notably cold intervals between 1670 and 1700 during the maunder minimum mm and between 1766 and 1788 characterized by a negative phase of the north atlantic oscillation cold summers in 1783 and 1784 coincide with the long lasting laki eruption that had a profound impact on the northern hemisphere climate including the severe tenmei famine in japan the decades between 1855 and 1900 are significantly cooler than the first half of the twentieth century while those between 1700 and 1765 following the mm are warmer than average sst variability in the ryukyus is only marginally influenced by the pacific decadal oscillation so that external forcing remains the main driver of low frequency temperature changes however the close connection between the kuroshio extension ke and its recirculation gyre suggests that decadal sst anomalies associated with the ke front also impact the ryukyus and there is a possible additional role for feedback of the kuroshio oyashio variability to the large scale atmosphere at decadal timescale

interannual variability of the east asian winter monsoon and related modulations of the planetary waves abstractinterannual variability of the east asian winter monsoon is investigated through composite analysis applied to observational data for 50 recent years although the monsoon activity itself is confined into the lower troposphere its midwinter variability tends to accompany upper tropospheric geopotential height anomalies similar to the eurasian eu and western pacific wp teleconnection patterns the eu like pattern is characterized by a wavy signature over the eurasian continent and the north atlantic with surface temperature anomalies over the far east and north america in the wp like pattern a meridional dipole of upper level height anomalies is evident over the far east these anomaly patterns related to the anomalous winter monsoon activity are found to accompany marked modulations of the climatological development of the upper tropospheric planetary waves from late autumn to midwinter enhanced monsoon activity in january associated with the wp like pattern involves anomalous seasonal

mountain wave like spurious waves associated with simulated cold fronts due to inconsistencies between horizontal and vertical resolutions a newly developed global nonhydrostatic model is used for life cycle experiments lces of baroclinic waves and the resolution dependency of frontal structures is examined lces are integrated for 12 days with horizontal grid intervals ranging from 223 to 3 5 km in a global domain in general fronts become sharper and corresponding vertical flow strengthens as horizontal resolution increases however if the ratio of vertical and horizontal grid intervals is sufficiently small compared to the frontal slope s the overall frontal structure remains unchanged in contrast when the ratio of horizontal and vertical grid intervals exceeds 2s 4s spurious gravity waves are generated at the cold front a linear model for mountain waves quantitatively explains the mechanism of the spurious waves the distribution of the basic wind is the major factor that determines wave amplitude and propagation the spurious waves propagate up to a critical level at which the basic wind speed normal to the front is equal to the propagation speed of the front results from the linear model suggest that an effective way to eliminate spurious waves is to choose a stretched grid with a smaller vertical grid interval in lower layers where strong horizontal winds exist

sting jets in extratropical cyclones a review this paper reviews the current state of knowledge of sting jets in extratropical cyclones sting jets were formally identified in 2004 by the pioneering work of keith browning reviewing this and subsequent studies we define the sting jet as a coherent air flow that descends from mid levels inside the cloud head into the frontal fracture region of a shapiro keyser cyclone over a period of a few hours leading to a distinct region of near surface stronger winds it therefore lies above the cold conveyor belt during some stage its life but at least in some cases descends to reach the top of boundary layer ahead of the cold conveyor belt it is not attributed to a specific mechanism in this definition we conclude that it is likely that a continuum of sting jet descent and speed up mechanisms exists at one extreme is balanced descent partly associated with frontolysis in the frontal fracture region more horizontally small scale and stronger frontolytic descent may occur associated with weak stability to slantwise convective downdraughts instability to slantwise convective downdraughts may occur in some systems leading to multiple slantwise convective downdraughts associated with the release of conditional symmetric instability and even possibly symmetric instability the global climatology of sting jets and the interaction between the atmospheric boundary layer and sting jets are revealed as specific areas where more research is needed finally we describe eight myths and misunderstandings that exist in the current literature with the aim of guiding future research into the sting jet phenomenon

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

mechanisms of meridional teleconnection observed between a summer monsoon system and a subtropical anticyclone part i the pacific japan pattern abstract summertime atmospheric circulation over the midlatitude western north pacific wnp is influenced by anomalous convective activity near the philippines this meridional teleconnection observed in monthly anomalies and known as the pacific japan pj pattern is characterized by zonally elongated cyclonic and anticyclonic anomalies around the enhanced convection center and to its northeast respectively in the lower troposphere with an apparent poleward phase tilt with height the authors idealized two layer linear model whose basic state consists of a zonal subtropical jet and a pair of a monsoon system and a subtropical anticyclone can simulate a pj like response against diabatic heating located between the pair each of the observed and simulated patterns can gain energy through barotropic and baroclinic conversions from the zonally varying baroclinic mean flow in an efficiency comparable with that of energy generation due to the anomalous diabatic heating indicating a characteristic of

horizontal structure and energetics of northern hemisphere wintertime teleconnection patterns abstract the horizontal structure and dynamical properties of the teleconnection patterns in the interannual variability of the northern hemisphere wintertime 500 mb height field are investigated regression maps based on indices for the eastern atlantic ea pacific north american pna western atlantic wa western pacific wp and eurasian eu patterns defined by wallace and gutzler are used to define the geographically fixed patterns space spectrum analysis including a spherical harmonic decomposition is applied to these maps anomalous geostrophic wind fields derived from these regression maps are used to estimate the kinetic energy conversion between the climatological mean state and the wave structures associated with the teleconnection patterns the teleconnection patterns comprise seesaw and or wavelike structures in general the kinetic energy of the teleconnection patterns is concentrated in total wavenumber n 5 and 6 components with zonal wavenumbers m 0 1 and 2 which correspond

vertical resolution requirements in atmospheric simulation abstractthe role of vertical mesh spacing in the convergence of full physics global atmospheric model solutions is examined for synoptic mesoscale and convective scale horizontal resolutions usi

three dimensional acoustic scattering of a source generated field from a cylindrical island in this work an analytic solution is presented for the three dimensional 3 d problem of acoustic scattering from a nonpenetrable cylindrical island in shallow water the ocean environment around the island is considered range independent with arbitrary sound speed profile and the bottom is assumed to be rigid the total acoustic field generated by an harmonic point source is obtained as a normal mode double series expansion a systematic numerical investigation of the double series is presented results concerning the pressure field and the transmission loss around the cylindrical island are given for the case of an acoustically soft and an acoustically hard island boundary in an isovelocity environment the presented analytic solution is numerically efficient for relatively low frequencies and can serve as a 3 d benchmark solution in the appropriate frequency range

cooling of the wintertime arctic stratosphere induced by the western pacific teleconnection pattern 1 a composite analysis for extreme positive events of the western pacific wp teleconnection pattern with blocking flow configurations observed over the subpolar far east shows that such an event in winter can trigger a persistent cold period in the polar stratosphere and if it occurs in fall or early winter it augments the possibility of the formation of polar stratospheric clouds the stratospheric cooling occurs in conjunction with the weakening of upper tropospheric planetary waves and their upward propagation into the stratosphere soon after the peak time of the wp pattern synoptically this weakening of the upper tropospheric planetary waves is manifested as westward evolution of a developing blocking high into the climatological mean pressure trough over the subpolar far east this study thus presents a unique case where a blocking high can induce cooling in the polar stratosphere rather than warming

the role of the central asian mountains on the midwinter suppression of north pacific storminess abstractthe role of the central asian mountains on north pacific storminess is examined using an atmospheric general circulation model by varying the height and the areas of the mountains a series of model integrations show that the presence of the central asian mountains suppresses the north pacific storminess by 20 30 during boreal winter their impact on storminess is found to be small during other seasons the mountains amplify stationary waves and effectively weaken the high frequency transient eddy kinetic energy in boreal winter two main causes of the reduced storminess are diagnosed first the decrease in storminess appears to be associated with a weakening of downstream eddy development the mountains disorganize the zonal coherency of wave packets and refract them more equatorward as the zonal traveling distance of wave packets gets substantially shorter downstream eddy development gets weaker second the central asian mountains suppress the global baroclinic energy conversion the decre

springtime north pacific oscillation and summer sea ice in the beaufort sea we investigate the linkage between the spring april june north pacific oscillation npo and the following summer sea ice in the beaufort sea a positive npo is characterized by an intensified and northeastward extended aleutian low a strong beaufort high and enhanced easterly winds in the beaufort sea concomitantly while the deepening east asian trough steers more cyclones from siberia to the sub polar pacific and thus fewer cyclones into the western arctic ocean a weak polar vortex and weak baroclinicity in the beaufort sea does not favor cyclone activity in addition the east asian trough enhances warm air advection from the pacific to the northwestern america the spring npo accounts for 29 of interannual variability of the following september sea ice cover in the beaufort sea and can be used as a potential predictor for ice melting in the beaufort sea during a positive npo the strong easterly winds over the beaufort sea enhance ice advection and reduce ice thickness on the synoptic scale there are more occurrences of the pack ice becoming detached from the coast due to the strong easterly winds moreover increases in shortwave radiation and longwave radiations accelerate the ice melting

the anomalous merging of the african and north atlantic jet streams during the northern hemisphere winter of 2010 the north atlantic jet stream during winter 2010 was unusually zonal so the typically separated atlantic and african jets were merged into one zonal jet moreover the latitude height structure and temporal variabilityofthe northatlanticjet duringthis winterweremore characteristic ofthe northpacific this work examinesthe possibility of aflow regime changefrom an eddy driven to a mixed eddy thermally drivenjet a monthly jet zonality index is defined which shows that a persistent merged jet state has occurred in the past both at the end of the 1960s and during a few sporadic months the anomalously zonal jet is found to be associated with anomalous tropical pacific diabatic heating and eddy anomalies similar to those found during a negative north atlantic oscillation nao state a lagrangian back trajectory diagnosis of eight winters suggests the tropical pacific is a source of momentum to the atlantic and african jets and that this source was stronger during the winter of 2010 the results suggest that the combination of weak eddy variance and fluxes in the north atlantic along with strong tropical heating act to push the jet toward a merged eddy thermally driven state the authors also find significant sst anomalies in the north atlantic which reinforce the anomalous zonal winds particularly in the eastern atlantic

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

characteristics of the north pacific oscillation in cmip5 models in relation to atmospheric mean states abstractthe north pacific oscillation npo the second leading atmospheric mode in the north pacific ocean is known to be responsible for climate variability and extremes in adjacent regions the