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

observed and gcm simulated westward propagating planetary scale fluctuations with approximately three week periods the structural characteristics and vorticity dynamics of westward traveling patterns wtp in the troposphere are examined using the national centers for environmental prediction national center for atmospheric research ncep ncar reanalyses based on observations for the 1973 95 period as well as the output from a 100 yr integration of a general circulation model gcm with a rhomboidal truncation at 30 wavenumbers and 14 vertical levels an identical set of diagnostic tools including progressive retrogressive variance analysis crossspectra and complex empirical orthogonal functions eofs are applied to the reanalysis and gcm datasets for 300 mb height these diagnoses all indicate that the wtp are most prominent during the cold season in the high latitude zone extending westward from northwestern canada to northeastern siberia with a typical period of 22 days outstanding episodes are identified on the basis of the temporal coefficients of the leading complex eof composite charts of the anomalous 300 mb height sea level pressure and 850 mb temperature fields at various phases of these events are constructed the typical circulation changes accompanying the passage of the wtp are similar to those associated with well known regional weather phenomena such as amplified pressure ridges over alaska cold air outbreaks over western north america and east asia and heavy snowfall over the pacific northwest the occurrence of the wtp over the north pacific is also characterized by notable changes in the spatial distribution and intensity of synoptic scale activity the contributions of relative vorticity advection planetary vorticity advection the b effect and horizontal divergence to the vorticity tendency in various phases of the composite wave at 300 500 and 850 mb are investigated in the mid and upper troposphere the vorticity dynamics of the wtp is similar to that of free external rossby waves with the b effect which leads to westward propagation being the dominant term whereas the eastward advection of relative vorticity is less important due to the weak mean zonal flow in the alaska siberia sector most of the essential characteristics of the observed wtp deduced from the ncep ncar reanalyses are well reproduced by the gcm the realism with which this phenomenon can be simulated in a model environment offers considerable promise for using the gcm as a tool for studying the impact of wtp on intraseasonal atmospheric variability in extended model experiments and for assessing the dependence of the locality and activity level of the wtp on various states of the ambient circulation

midlatitude westward propagating disturbances preceding intraseasonal oscillations of convection over the subtropical western north pacific during summer 1 we start with an analysis of the abruptly enhanced convection over the subtropical western north pacific wnp around late july the so called convection jump and indicate that intraseasonal oscillations isos play a dominant role in this feature then we analyze the extratropical circulation anomalies in association with the convection isos over the subtropical wnp which are more common than the convection jump and thus provide a greater sample size it is found that prior to convection iso peaks a well defined wave train of alternating cyclonic and anticyclonic perturbations appears and propagates westward in the upper troposphere over the midlatitude north pacific and bends southward to the subtropical wnp the present results imply that midlatitude circulation anomalies in the north pacific may affect intraseasonal variability of climate in the subtropical wnp and east asia during summer

mesoscale interactions in tropical cyclone genesis with the multitude of cloud clusters over tropical oceans it has been perplexing that so few develop into tropical cyclones the authors postulate that a major obstacle has been the complexity of scale interactions particularly those on the mesoscale which have only recently been observable while there are well known climatological requirements these are by no means sufficient a major reason for this rarity is the essentially stochastic nature of the mesoscale interactions that precede and contribute to cyclone development observations exist for only a few forming cases in these the moist convection in the preformation environment is organized into mesoscale convective systems each of which have associated mesoscale potential vortices in the midlevels interactions between these systems may lead to merger growth to the surface and development of both the nascent eye and inner rainbands of a tropical cyclone the process is essentially stochastic but the degree of stochasticity can be reduced by the continued interaction of the mesoscale systems or by environmental influences for example a monsoon trough provides a region of reduced deformation radius which substantially improves the efficiency of mesoscale vortex interactions and the amplitude of the merged vortices further a strong monsoon trough provides a vertical wind shear that enables long lived midlevel mesoscale vortices that are able to maintain or even redevelop the associated convective system the authors develop this hypothesis by use of a detailed case study of the formation of tropical cyclone oliver observed during toga coare 1993 in this case two dominant mesoscale vortices interacted with a monsoon trough to separately produce a nascent eye and a major rainband the eye developed on the edge of the major convective system and the associated atmospheric warming was provided almost entirely by moist processes in the upper atmosphere and by a combination of latent heating and adiabatic subsidence in the lower and middle atmosphere the importance of mesoscale interactions is illustrated further by brief reference to the development of two typhoons in the western north pacific

centrifuge model testing of a loess landslide induced by rising groundwater in northwest china abstract considerable artificial irrigation in the heifangtai area has caused the continued rise of groundwater levels which has resulted in several large scale landslides in the loess platform area considering the no 13 landslide of jiaojia in the heifangtai area as a geological archetype a series of centrifuge tests was conducted to study the deformation and failure characteristics of the slope due to the continuous rise in the groundwater level meanwhile the pore water pressure earth pressure deformation and evolution characteristics of the slope were monitored and recorded in real time furthermore isotropically consolidated undrained triaxial testing icu was conducted to investigate the static liquefaction of loess specimens which was related to the slope instability the centrifuge test results showed that a series of parallel and steep tension cracks at the top of the slope were present before the landslide which was caused by the rising groundwater the icu experimental results showed that as the pore water pressure increased strong strain softening and static liquefaction of saturated loess soils were found which was related to the sudden destruction of the slope

global and regional diurnal variations of organized convection abstract an automated objective classification procedure the convection classification and automated tracking system ccats is used to analyze the mean life cycles of organized convection in the global tropics and midlatitudes 40 n 40 s five years 1989 93 of infrared satellite imagery are examined for the pacific and atlantic basins and one year april 1988 march 1989 is studied for the indian basin two main classes of organized convection lifetime of 6 h or more are tracked mct and ccc mct represent a combined dataset of tropical cyclones and mesoscale convective complexes mcc convective cloud clusters ccc meet the same cold cloud top temperature time and size criteria used to distinguish mcc but fail to sustain the same high degree of symmetry for at least 6 h that is ccc represent more elongated systems such as squall lines the frequency of ccc exceeds that of mct by a factor of 30 over both land and sea mct and ccc are each stratified to into 12 continental and oceanic regio

structure and mechanisms of the southern hemisphere summertime subtropical anticyclones abstract the three dimensional structure and dynamics of the climatological mean summertime subtropical anticyclones in the southern hemisphere sh are investigated as in the northern hemisphere nh each of the surface subtropical anticyclones over the south pacific south atlantic and south indian oceans is accompanied by a meridional vorticity dipole aloft exhibiting barotropic and baroclinic structures in its poleward and equatorward portions respectively in a manner that is dynamically consistent with the observed midtropospheric subsidence their dynamics are also similar to their nh counterpart it is demonstrated through the numerical experiments presented here that each of the sh surface anticyclones observed over the relatively cool eastern oceans can be reproduced as a response to a local near surface cooling heating couplet the cooling is mainly due to radiative cooling associated with low level maritime clouds and the heating to the east is due to sensible heat flux over the dry hea

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

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

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

gravitational deformation mechanisms of slate slopes revealed by model tests and discrete element analysis abstract this study investigated the factors influencing the gravitational deformation of slate slopes prior to sliding failure including the slope angle foliation angle and material deterioration to simulate these phenomena physical model tests were performed in the laboratory under simplified environmental conditions subsequently the discrete element method was employed in simulations to elucidate the deformation behavior exhibited by slate slopes under the long term influence of gravity and material deterioration the physical model tests revealed two types of gravitational deformation of slate slopes the first type is flexural toppling which was observed in obsequent slopes with high angle foliation the second type is fold extrusion near the slope toe this was exhibited by consequent slopes with low angle foliation and is attributable to gravitation and deterioration caused by wetness the results of the physical model test were used to verify the results of the discrete element simulation the simulated deforming patterns were in strong agreement with the actual deformation at various slope angles regarding the factors influencing slope deformation the simulation showed that the fold in consequent slopes became sharper and the folding area increased as the foliation angle increased moreover the folding area rose as the slope angle increased in obsequent slopes higher slope and foliation angles induced more substantial flexural toppling deformation

diagnoses of an eddy resolving atlantic ocean model simulation in the vicinity of the gulf stream part ii eddy potential enstrophy and eddy potential vorticity fluxes abstract output of an eddy resolving model of the north atlantic is diagnosed in the vicinity of the gulf stream gs using quasigeostrophic potential vorticity qgpv quasigeostrophic potential enstrophy qgpe and modified divergent eddy potential vorticity flux v hq d a tongue or an elongated island of large mean qgpv along the model gs in the top 1000 m is associated with predominantly downgradient v hq d suggesting that the horizontal eddy fluxes are balancing a sink of eddy qgpe in most of the tongue or island by converting the mean qgpe into eddy qgpe some large upgradient v hq d is observed to the north of the center of the tongue or island however suggesting that some of the eddy fluxes in the northern half of the tongue or island of high qgpv are balancing a source of eddy qgpe there by converting eddy qgpe into the mean qgpe at the intermediate levels of the model under the gs eddy qgpe is small and the role of eddies appears to be mixed they are forcing the mean to some

modeling rock joint behavior using a rough joint model abstract this study proposed a rough joint model to simulate the strength and deformability of rock joint under various loadings the proposed model adopted the barton model to consider the roughness effect of joint to implement the rough joint model in dem software three calculation modifications are performed afterward the proposed model was verified by comparing to theoretical model the comparisons showed that the proposed model is versatile in simulating the shear displacement normal closure and shear dilation of joint moreover this study investigated the influence of particle size on the applicability of rough joint model and the results indicate that particle sizes have no significant influence on shear behavior which indicates the rough joint model is suitable for different scale simulations finally the proposed model was applied on the simulation of jointed rock mass the simulation was compared with the experimental data of artificial jointed rock mass the simulation results reveal that the proposed model reasonably reflects the varying strength and elastic modulus of rock mass under different joint orientations

the structure dynamics and tropospheric signature of the polar annular mode 1 intraseasonal variability in the stratospheric polar vortex is intrinsically linked to concomitant tropospheric variability via the annular modes the primary mode the northern annular mode nam represents variability in the polar vortex strength while the second mode the lesser studied polar annular mode pam represents variability in the latitudinal position of the polar vortex the current study examines the structural evolution zonal mean dynamical forcing and tropospheric impact of discrete pam episodes occurring during boreal winter the analysis identifies large amplitude positive and negative pam events occurring in the absence of nam or sudden stratospheric warming events composite time evolution analyses are performed for both positive and negative pam events the onset of positive negative pam events is preceded by a weak and broad acceleration deceleration within the stratospheric polar vortex at midlatitudes during pam onset the canonical pam structure in zonal mean zonal wind develops over a 5 day period in association with robust stratosphere troposphere coupling zonal wind changes occurring during onset are induced by anomalous wave driving associated with low frequency rossby wave activity after pam onset the zonal wind anomaly features at high latitudes quickly weaken while those in the subtropics and midlatitudes persist for a period of 2 3 weeks during this time pam events provide a statistically significant impact upon the tropospheric circulation with large scale perturbations in a surface air temperature over north america and eurasia and b the structure and amplitude of the primary storm tracks

investigation of rainfall induced failure processes and characteristics of cataclinal and anaclinal slopes using physical models in this study two types of small scale physical modeling tests have considered the impact of the infiltration of rainfall and groundwater level in order to investigate the processes involved in rock slope deformation and failure the study conducted the physical tests under controlled conditions of groundwater level with rock block shape for two rock slope types cataclinal and anaclinal slopes observations obtained during each stage of deformation and failure were used to explain how gravity deformation varies with groundwater conditions on cataclinal and anaclinal slopes and infer how rainfall and groundwater influence slope failure our results indicate that groundwater level is a crucial factor in the deformation failure of slopes the failure mechanisms of cataclinal slopes differ considerably from those of anaclinal slopes the infiltration of surface water and groundwater can have a significant influence on rock layer deformation and the speed of failure different shapes of rock block have two toppling types of rock slope the spherical rock model relatively close to flexural toppling type and the triangular rock model relatively similar to block flexural toppling type respectively details of the failure characteristics of cataclinal and anaclinal slope models are discussed in this paper

a striking example of the atmosphere s leading traveling pattern abstract conventional and complex empirical orthogonal function eof techniques show that for at least four months during the fall and winter of 1979 80 a large amplitude large scale traveling flow anomaly existed in the troposphere and stratosphere this feature evolved in a cyclic manner exhibiting an average period of about 23 days its phase propagation was toward the west while its amplitude was concentrated in a broad envelope centered over canada the phenomenon was equivalent barotropic in the troposphere and increased in amplitude with altitude it represented about 25 of the variance of geopotential heights in the troposphere and stratosphere for the months of november through march the meridional and zonal structure of the zonal wavenumber one component of the traveling anomaly is similar to that of the theoretical 16 day wave however it is distinct from that theoretical mode in that its period is longer and in the troposphere zonal wave two makes a large contribution to its structur

on the origin of planetary scale extratropical winter circulation regimes abstract sectorial and planetary scale winter circulation regimes are studied and the relationship between them is investigated in order to find how much the simultaneous occurrence of sectorial regimes contributes to the occurrence of hemispheric regimes the strategy is based on the multivariate gaussian mixture model the number of components in the model is estimated using two approaches the first one is based on arguments from order statistics of the mixture proportions and the second uses a more severe test based on reproducibility the procedure is applied next to the 500 hpa height field over the north pacific the north atlantic and the northern hemisphere using the empirical orthogonal function state space two highly significant regimes are found in each case namely the pacific north america pattern pna north atlantic oscillation nao for the hemisphere pna for the pacific sector and nao for the atlantic sector the sectorial regimes reflect mainly blocking and no blocking flows t

seasonality and interannual variability of the westerly jet in the tibetan plateau region abstract in this study 40 yr ecmwf re analysis era 40 data are used for the description of the seasonal cycle and the interannual variability of the westerly jet in the tibetan plateau region to complement results based on the analysis of monthly mean horizontal wind speeds an occurrence based jet climatology is constructed by identifying the locations of the jet axes at 6 hourly intervals throughout 1958 2001 thus a dataset describing the highly transient and localized features of jet variability is obtained during winter and summer the westerly jet is located respectively to the south and north of the tibetan plateau during the spring and autumn seasons there are jet transitions from south to north and vice versa the median dates for these transitions are 28 april and 12 october the spring transition is associated with large interannual variations while the fall transition occurs more reliably within a 3 week period the strength of the jet exhibits a peculiar seasonal cycle during northw

centrifuge model test on the retrogressive landslide subjected to reservoir water level fluctuation abstract geological disasters have occurred frequently in the three gorges reservoir area therefore the stability and failure mode research on riverside landslides has become increasingly important taking the toe of liangshuijing landslide as a case study and combining the geological conditions of the three gorges reservoir area a centrifuge slope model is constructed in addition the fluctuation of the water level is simulated in the centrifuge model test based on the digital photography laser displacement sensors lds pore pressure transducers ppt and earth pressure sensors e multi physical data are obtained finally numerical simulation is carried out to analyze the stability and deformation characteristics of the slope model the results indicate that 1 at the water level rise stage the model is dominated by the vertical displacement and the horizontal displacement is much larger than the vertical displacement at the drainage stage 2 cracks first appear at the toe of the slope and extend to the middle and rear of the model gradually then deformation occurs in the middle platform of the slope 3 at the water level rise stage the factor of safety increases rapidly when the reservoir water level remains stable the stability of the slope decreases slowly and at the drainage stage the factor of safety decreases first and then increases 4 there is a significant positive linear correlation between the decline rate of the safety factor and the drainage rate over a certain test range and the stability of the landslides on the reservoir banks would become worse gradually during the long term cyclic operation of the three gorges reservoir

impacts of mountain plains solenoid on diurnal variations of rainfalls along the mei yu front over the east china plains abstractconvection permitting numerical experiments using the weather research and forecasting wrf model are performed to examine the impact of a thermally driven mountain plains solenoid mps on the diurnal variations of precipitation and mesoscale convective vortices along the mei yu front over the east china plains during 1 10 july 2007 the focus of the analyses is a 10 day simulation that used the 10 day average of the global analysis at 0000 utc as the initial condition and the 10 day averages every 6 h as lateral boundary conditions with diurnal variations only despite differences in the rainfall intensity and location this idealized experiment successfully simulated the observed diurnal variation and eastward propagation of rainfall and mesoscale convective vortices along the mei yu front it was found that the upward branch of the mps along with the attendant nocturnal low level jet is primarily responsible for the midnight to early morning rainfall enhancement along the mei yu front th

life cycle variations of mesoscale convective systems over the americas abstract using goes 7 isccp b3 satellite data for 1987 88 the authors studied the evolution of the morphological and radiative properties of clouds over the life cycles of deep convective systems cs over the americas at both tropical and middle latitudes a deep convective cloud system is identified by adjacent satellite image pixels with infrared brightness temperatures tir 245 k 28 c that at some time contain embedded convective clusters that are defined by pixel values of tir 218 k 55 c the first part of the analysis computes parameters for each convective system that describe the system areal size number of convective clusters fractional convective area average and maximum size of the convective clusters shape eccentricity and orientation mean tir variance of tir tir gradient and the mean variance and gradient of collocated visible reflectances when available the second part of the analysis searches a 5 5 region centered on each convective system but in the subsequent

dependency of the north pacific winter storm tracks on the zonal distribution of mjo convection 1 we investigate the effects of the tropical madden julian oscillation mjo convection on the zonal location and intensity of storm activity during the boreal cool season nov 1 to feb 28 120 days over the pacific ocean as tropical convection shifts eastward from the eastern indian ocean to the western north pacific mjo induced local hadley circulation leads to an eastward displacement of extratropical rossby wave source rws consequently this influence leads to an eastward shift of the peak area of the storm track the storm track is strongest with the mjo convection over the eastern indian ocean phase 3 and it experiences the suppression when mjo convection is located over the maritime continents phase 4 and it increases again when the mjo propagates to the western pacific phase 5 after which it weakens again phase 6 the intensity of the storm track particularly over the western north pacific 120 e 180 is determined by the integrated effects of three factors the midlatitude convective forcing mcf the jet stream and rws these factors are associated with the locations of mjo convections it is estimated that mjo induced suppression accounts for only 2 5 of the total observed midwinter suppression mws however the pattern generated by the mjo is remarkably similar to the observed meridional displacement of north pacific storm track associated with sub seasonal variation we conclude that the spatial distribution of mjo affects the variation of the pacific storm track but is not a cause of the mws

the structure and evolution of cold surges east of the rocky mountains abstract northerly surges of cold air often move southward along the eastern side of the rockies from southern canada into mexico the strongest surges which generally develop in midwinter are associated with temperature decreases and pressure rises of 20 30 c and 15 30 mb respectively within 24 h surges are usually accompanied by a meridionally elongated pressure ridge and strong low level ageostrophic winds that parallel the terrain the width of the pressure ridging is approximately 1000 km over the southern plains but decreases to only a few hundred kilometers when the surge enters mexico this paper provides a detailed description of a northerly surge to the east of the rocky mountains that occurred on 12 14 november 1986 using both observational and model data the structural evolution of the surge is analyzed in addition the dynamics of the event is explored by diagnosing the momentum thermodynamic energy and vorticity equations to determine the typical synoptic scale evolution of these

a numerical study of a mesoscale convective system during toga coare part ii organization in part i the authors presented a successful numerical simulation of the life cycle of a warm pool mesoscale convective system mcs that occurred on 15 december 1992 during the tropical ocean global atmosphere coupled ocean atmosphere response experiment in this study the simulation results of part i are diagnosed to investigate the organization of the mcs and the convective onsets that occurred during the growing and mature stages of the mcs during the life cycle of the mcs four convective onsets occur in the presence of large scale ascent convective available potential energy cape and surface potential temperature drop off sptd it is found that the first convective onset is caused by the existence of upward motion cape and sptd in the model initial conditions the second convective onset is regulated by the favorable occurrence of sptd the third and fourth convective onsets arise from the development of upward motion associated with the westward propagation of the quasi 2day wave the four mesoscale precipitation features clustered together to form the mcs in response to the evolution of the vertical motion field the organization of the mcs is characterized by the presence of a midtropospheric mesovortex situated near the position of the first convective onset analysis of the relative vorticity rv budget indicates that the mesovortex originates and intensifies largely from vortex stretching induced by deep convective heating a decrease in rv above below the mesovortex arises because of the combined effects of the tilting and horizontal advection terms the tilting stretching and solenoidal terms our results suggest that the mesovortex played little role in the subsequent onsets i e second third and fourth and that other warm pool mcss occurring near the transequatorial flow are likely to be associated with mesovortices

a climatology of midlatitude mesoscale convective vortices in the rapid update cycle abstract climatological characteristics of mesoscale convective vortices mcvs occurring in the state of oklahoma during the late spring and summer of four years are investigated the mcv cases are selected based on vortex detection by an objective algorithm operating on analyses from the rapid update cycle ruc model consistent with a previous study true mcvs represent only about 20 of the mesoscale relative vorticity maxima detected by the algorithm the mcvs have a broad range of radii and intensities and their longevities range between 1 and 54 h their median radius is about 200 km and their median midlevel relative vorticity is 1 2 10 4 s 1 there appears to be no significant relationship between mcv longevity and intensity similar to past estimates approximately 40 of the mcvs generate secondary convection within their circulations the mean synoptic scale mcv environment is determined by the use of a ruc based composite analysis at four different stages in the mcv life cycle defined b

long term gravitational deformation of rocks by mass rock creep abstract subsurface rocks beneath slopes are deformed to various degrees in various ways by mass rock creep mrc when they are subjected to a gravitationally unstable state for a long period mrc forms folds faults and numerous kinds of fractures such deformation is one of the main factors for deteriorating rock masses on slopes and also precursors of many landslides mrc deformations which have often been ascribed to tectonic origins can be distinguished from tectonic ones by their deformational features landforms and relationships between slope morphology and subsurface structures mrc folds are flexural slip folds that have the following mesoscopic to microscopic characteristics their axial surfaces are not smooth but are jagged and many visible openings or open fractures develop in association with the folds the jagged axial surfaces become smoother at depth and openings decrease in width with increasing overburden at the deformation site macroscopic types of mrc folds change according to the relationship between foliations and slopes buckling folds form in consequent slopes drag folds form in a deeper part of obsequent slopes and bending folds form in slopes with steep dipping foliations consequent or obsequent by downslope bowing of foliations shear fractures and tension fractures are the main deformational structures formed by mrc in massive rocks among shear fractures those of listric origin are remarkable tension fractures in general occur either in networks dividing rocks into fragments that slip and rotate irregularly in relation to each other or in parallel arrays of steeply dipping fractures an mrc fault has a shear zone consisting of a pulverized zone with gouge and a phyllitic or brecciated zone in a densely foliated rock the phyllitic zone is formed by microscopic slip along foliations in a sparsely foliated rock the brecciated zone is formed by random crushing except for the faults made through the shear fractures in massive rocks landforms due to mrc are gentle slopes bounded by horseshoe knicklines upslope convex slopes ridge top depressions multiple ridges uphill facing scarps and ridge crossing depressions

the morphology of northern hemisphere blocking abstract the morphology of regional blocking in the northern hemisphere is discussed using the 40 yr ecmwf re analysis era 40 dataset and a measure of blocking based on the reversal at storm track latitudes of meridional contrasts on a potential vorticity pv surface representative of the tropopause the focus is on cyclonic and anticyclonic rossby wave breaking that is inherent to the blocking development and the extent to which this is determined by the climatological jet position and the ambient shears more generally the importance of the climatological planetary scale is discussed the approach is mainly through composite behavior but informed by consideration of many individual events a diversity of behavior is found with longitude in both winter and summer and there is a striking reversal of the sense of the wave breaking between the two seasons that is generally consistent with the difference in the jet locations preferred behaviors are found in various regions and seasons and retrogre

revisiting nigawa landslide of the 1995 kobe earthquake a simplified pseudo static limit equilibrium approach is used to analyse a full scale slope failure that occurred during the 1995 kobe earthquake the slope is 28 m high having a gentle angle of 26 5 and has a factor of safety as high as 2 43 in the absence of an earthquake in addition to a factor of safety the critical failure surface obtained from pseudo static analysis is compared with that of the actual failure surface contradictory to some design codes that use only a horizontal seismic coefficient this study finds that a rational analysis must take into consideration both horizontal and vertical seismic accelerations the analysis including vertical acceleration may give a shallower or deeper failure surface than cases where vertical acceleration is ignored an analysis combining horizontal and upward accelerations results in a deeper failure surface than when only downward or no vertical acceleration is considered the effects of soil properties on the slope stability are also investigated

deformation characteristics of slate slopes associated with morphology and creep abstract this study investigated the deformation characteristics of consequent slate slopes in the region between cuifeng and wuling in taiwan onsite surveys terrain analysis and udec numerical models were used to describe the characteristics of gravity driven deformation under various conditions and identify the process of slate deformation as well as potential failure mechanisms our results demonstrate that valley erosion and slope toe soaking mechanisms play key roles in the deformation of slate and accelerate the weakening of slate material comparisons of material strength of rock and foliation the location of erosion gullies and the inclination of the foliation indicate that a reduction in the strength of rock material and foliation expanded the range of slate deformation the inclination of foliation is the most important factor in the deformation of slate and the location of erosion gullies has relatively little influence slate deformation was shown to begin in the tension zone at the cliff top wherein the slope body slips along the highly inclined foliation contributing to shear failure or composite failure near the eroded zone of weakness the phenomenon of foliation opening was widespread within the area of deformation enabling surface water and groundwater to seep in thereby accelerating failure in the slate deformation zone

characteristics of mesoscale convective systems over china and its vicinity using geostationary satellite fy2 abstractthis study investigates mesoscale convective systems mcss over china and its vicinity during the boreal warm season may august from 2005 to 2012 based on data from the geostationary satellite fengyun 2 fy2 series the authors classified and analyzed the quasi circular and elongated mcss on both large and small scales including mesoscale convective complexes mccs persistent elongated convective systems pecss meso circular convective systems m ccss meso elongated convective system m ecss and two additional types named small meso circular convective systems sm ccss and small meso elongated convective systems sm ecss results show that nearly 80 of the 8696 mcss identified in this study fall into the elongated categories overall mcss occur mainly at three zonal bands with average latitudes around 20 30 and 50 n the frequency of mcss occurrences is maximized at the zonal band around 20 n and decreases with increase in latitude during the eight warm seasons the p

simultaneous atlantic pacific blocking and the northern annular mode a synoptic situation termed high latitude blocking hlb is shown to occur frequently in both the atlantic and pacific sectors and to result in flow anomalies very similar to those associated with the negative phase of the northern annular mode nam in the respective sector there is a weak but significant link between the occurrence of hlb in the two sectors with atlantic hlb tending to lead pacific hlb by 1 3 days this link arises from rare events in which both sectors are almost simultaneously affected by a large scale wave breaking event which distorts the polar trough over northern canada in several cases the tropospheric wave breaking occurs in tandem with a large scale disturbance of the stratospheric polar vortex there is therefore a physical link between the atlantic and pacific sectors but analysis suggests that this does not contribute to determining the pattern of the nam as conventionally defined from monthly mean data however an alternative version of the nam derived directly from daily data does appear to reflect this physical link these conflicting results highlight the sensitivity of the nam to the period over which data are averaged copyright c 2008 royal meteorological society

characteristics of a deep seated flexural toppling fracture and its relations with downcutting by the lancang river a case study on a steeply dipping layered rock slope southwest china abstract a deep seated flexural toppling fracture situated on the left bank of the lancang river southwest china was used as a case study of the fracture mechanism and relations with the rapid and continuous downcutting of the lancang river the toppling fracture body has a maximum horizontal distance to the slope surface exceeding 150 m and a volume of approximately 6 106 m3 based on surface and adit surveys the toppled rock mass was divided into three zones highly toppled moderately toppled and weakly toppled zones the formation of the deep seated toppling failure in the steeply dipping layered rock mass was the result of the intense unloading of rock mass caused by the continuous and rapid downcutting of the lancang river the intense unloading caused the rock mass to be relaxed and cataclastic and formed a deep stress relaxation zone in rock mass on both banks the toppling failure of the steeply dipping layered rock mass occurred in the stress relaxation zone under the action of gravity and developed inwards and downwards to the lower parts of the slope with the river further downcutting the horizontal distance to the slope surface of highly toppled and moderately toppled rock mass was limited by the boundary of strongly unloaded rock mass

observed changes in baroclinic wave activity during the life cycles of low frequency circulation anomalies abstract anomalous baroclinic wave activity during the onset and decay of blocking patterns in the northern hemisphere winter is investigated based upon a 30 year record of 500 mb height and sea level pressure a slowly varying envelope function is defined at each gridpoint in order to represent the modulation of the amplitude of baroclinic wave activity by the low frequency circulation anomalies related to blocking the envelope function fields and the low frequency circulation fields are composited relative to the onset and decay times of four persistent dipole patterns in low frequency circulation anomalies located downstream of the climatological mean stormtracks one polarity of the anomaly patterns corresponds to dipole or modon like blocking patterns over the eastern oceans and the other to strong zonal flow patterns each of the eight composites is comprised of more than 50 persistent blocking or zonal flow episodes the most striking common feature observed during the onset of blocking over th

surface cyclogenesis from convectively driven amplification of midlevel mesoscale convective vortices mesoscale convective vortices mcvs are midtropospheric warm core cyclonic circulations that often develop in the stratiform region of mesoscale convective systems typically divergent anticyclonically circulating mesoscale cold anomalies appear both above and below the mcv the upper level cold anomaly is usually found near the tropopause while the low level anomaly is surface based and exhibits locally higher pressure one aspect of mcvs that has received much attention recently is the role that they may play in tropical cyclogenesis of special interest is how an mcv amplifies when deep convection redevelops within the borders of its midlevel cyclonic circulation and how the amplified mcv transforms the divergent surface based cold pool with anomalously high surface pressure into a convergent cyclonic circulation with anomalously low pressure the pennsylvania state university national center for atmospheric research fifth generation mesoscale model is used to simulate an mcv that was instrumental in initiating within the borders of the midlevel vortex s circulation several successive cycles of convective development and decay over a 2 day period after each cycle of convection both the horizontal size of the cyclonic circulation and the magnitude of the potential vorticity associated with the vortex were observed to increase the simulation reproduces the development and evolution of the mcv and associated convective cycles mesoscale features responsible for the initiation of convection within the circulation of the vortex and the impact of this convection on the structure and evolution of the vortex are investigated a conceptual model is presented to explain how convective redevelopment within the mcv causes low level heights to fall and cyclonic vorticity to grow downward to the surface applying this conceptual model to a tropical marine environment is also considered

low frequency variability in a simplified atmospheric global circulation model storm track induced spatial resonance the interaction between two storm tracks is analysed by using idealized experiments with a simplified global circulation model a zonal distance of 180 between the storm tracks drives a retrograde travelling zonal wave number two wave with an amplitude modulation of about 50 days the stream function tendency equation demonstrates that the amplitude modulation is excited in the storm track regions by the high frequency periods between two and eight days eddy forcing spatial resonance of a retrograde propagating zonal wave number two rossby wave and high frequency eddy forcing are proposed as the amplifying mechanisms while friction and self interaction between the low frequency eddies ensure damping sensitivity experiments indicate that the pronounced modulation of 50 days vanishes with decreasing zonal distance between the storm tracks thereby enhancing the intensity and duration of blocking events

analysis of a small vigorous mesoscale convective system in a low shear environment part i formation radar echo structure and lightning behavior the evolution of a small vigorous mesoscale convective system mcs over northern alabama is described using doppler radar goes satellite surface mesonet lightning and sounding data the mcs formed near noon in a relatively unstable environment having weak synoptic forcing and weak shear the initiation of separate lines and clusters of deep convection occurred in regions exhibiting cumulus cloud streets horizontal variations in stratocumulus cloud cover and variations in inferred soil moisture mcs growth via merger of storms within clusters and lines and among the clusters was accomplished largely through intersection of storm scale and mesoscale outflow boundaries the mcs maximum anvil area 60 000 km2 at 220 k and lifetime 8 h were about 50 that of the typical great plains mesoscale convective complex mcc despite its smaller size this mcs displayed many aspects that typify the mostly nocturnal great plains mcs the precipitation output was highly variable due to the transient nature of the intense convective elements many of which produced microbursts the radar measurements documented the formation of a stratiform region along the trailing side of an intense convective line this stratiform region formed as decaying convective cores coalesced rather than through advection of precipitation particles directly from the convective region combined goes ir imagery and radar reflectivity analyses within the stratiform region show a sinking anvil cloud top in the presence of increases in the vertical radar reflectivity gradient within the cloud during the maturation of the stratiform region during its intense developing stages the mcs generated a peak cloud to ground cg flash rate of 2400 h 21 comparable to rates produced by larger mccs early on positive cg flashes were most prevalent around intense convective core regions exhibiting strong divergence at anvil level during the latter stages the emergence of positive cg was coincident with the formation of a prominent radar bright band within the stratiform region thus a bipole was established but its length was quite short at approximately 50 km 25 50 of the distance documented in other mcss

an updated analysis of northern hemisphere submonthly retrograde waves abstractthis study performs an updated analysis of northern hemisphere retrograde disturbances that were first identified by classical observational studies as one of the dominating coherent struct

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

mesoscale convective complexes in the western pacific region abstract a climatological study of mesoscale convective complexes mccs during 1983 1985 over the western pacific region wpr using full disc enhanced infrared satellite imagery from the japanese geostationary meteorological satellite is presented the results indicate that mccs are common in the wpr and display many of the same characteristics as those found in the americas the systems are nocturnal and tend to form over or in the immediate vicinity of land cold cloud shields in the americas last for about 10 h while wpr shields last about 11 h the cold cloud shield size distribution is similar to that of the americas with most systems exhibiting areas between 2 105 and 3 105 km2 seasonal distributions of wpr systems are also similar to that in the americas specifically the frequency of midlatitude systems peaks in late spring and early summer while low latitude mccs are distributed uniformly throughout the warm season as with western systems wpr mccs occur in preferred zones climatolog

centrifuge model simulations of rainfall induced slope instability abstractthis study focused on landslides resulting from heavy precipitation such as rainfall from hurricanes a series of centrifuge model simulations were performed with reference to a landslide that occurred during typhoon nabi in japan in 2005 the procedures of simulation on the slope using a sand clay soil mixture were illustrated the rainfall event was simulated by applying precipitation in increments to the slope surface until it exceeded that of the field measurements the instability was examined using an infinite slope analysis and the mechanism of rainfall induced failure was discussed for this particular study the results showed that incremental rainfall of less than 200 mm led to local failures whereas total accumulation of 400 mm resulted in a global slope failure a reduction in apparent cohesion in the soil combined with an increase in pore pressure because of infiltration was responsible for the slope instability during rainfall

storm track organization and variability in a simplified atmospheric global circulation model a storm track is simulated in a coarse resolution multilevel primitive equation model with linear surface friction and heating terms a restoration temperature distribution consisting of a dipole embedded in a zonally symmetric profile forces the model to simulate the surface heating three simulations each with a different dipole orientation are performed to test the sensitivity of storm track organization to the external forcing field the climatological time mean circulation and the transient disturbances of the reference simulation agree well with observations of northern hemisphere wintertime storm tracks local energetics show that baroclinic instability is responsible for the enhanced eddy kinetic energy downstream of the jet and the downstream end of the storm track results from the barotropic conversions of eddy kinetic energy to the time mean flow low frequency fluctuations with a period of about 50 days associated with a retrograding large scale wave pattern are identified by a complex empirical orthogonal function analysis of the vertically averaged stream function a composite life cycle of the low frequency variability reveals the growth and decay of a blocking anticyclone downstream of the storm track a cyclogenesis initiated by an eastward propagating wave train is observed a few days before the amplitude of the low frequency anomaly attains its peak the net forcing of the high frequency eddies contributes to the growth and decay of the blocking anticyclone the results suggest that the occurrence of the blocking like event is part of the storm track dynamics

a climatology of warm season cloud patterns over east asia based on gms infrared brightness temperature observations abstract in the present study hourly infrared ir brightness temperatures observed by the geostationary meteorological satellite gms over the region 20 40 n 95 145 e in may august 1998 2001 are used to compile a climatology of warm season cloud precipitation episodes over east asia with a goal to better understand the characteristics of warm season convection and the behavior of these episodes results are compared with those obtained in north america using radar derived data the convection in east asia similar to that in north america is shown to also exhibit coherent patterns and characteristics of propagating events in the longitude time hovmoller space with a preferred phase speed of 10 25 m s 1 considerably faster than warm season synoptic scale waves near the eastern edge of the tibetan plateau convection was most active with a strong diurnal signal peaking in late afternoon or early evening then propagating eastward the zonal span and duration of episodes could reach 3000 km and

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

evaluating the stability of anti dip slate slope using an innovative failure criterion for foliation abstract toppling failure is one main failure types of anti dip slate slopes and is strongly affected by the mechanical properties of foliation this study conducted a series of pull off tests and direct shear tests on slate foliation to obtain its failure envelope and an innovative failure criterion was accordingly proposed the proposed failure criterion exhibits a nonlinear trend in the low normal stress range considers both tensile and shear strengths and has three material parameters tensile strength t 0 and parameters and are related to the slope variation of the failure criterion to investigate the effectiveness of the proposed failure criterion on the evaluation of slope stability it is implemented in a discrete element code udec and a simulation was carried out to evaluate the deformation and failure pattern of an anti dip slate slope the results of the udec analysis demonstrate that the simulated failure pattern and deformation characteristics agree with that of an actual anti dip slate slope the proposed failure criterion of foliation and the mohr coulomb criterion are further compared in slope stability analysis the proposed failure envelope accurately reflects the tensile strength and shear strength under low normal stress but the mohr coulomb criterion apparently overestimates the strength in this stress range therefore the proposed criterion is more effective than the existing criteria in predicting the toppling failure of slate slopes

a general rule for synoptic eddy feedback onto low frequency flow in this study scale interaction between synoptic eddies and low frequency flow is investigated it is demonstrated here that there is a general rule the left hand rule that describes synoptic eddy feedback onto low frequency flow the rule is that low frequency anomalies systematically stir and deform the transient eddies in such a way that the irrotational eddy vorticity fluxes are directed preferentially about 90 toward the left hand side of the low frequency flow thus this eddy feedback plays a positive role in maintaining and prolonging low frequency flow under the stormy atmosphere similarly we show that the irrotational eddy temperature and moisture fluxes are also directed preferentially about 90 toward the left hand side of the low frequency flow in the northern hemisphere the eddy temperature fluxes and their vertical structure play a positive role in reinforcing the low frequency flow in the low levels the moisture fluxes play a role in enhancing low frequency flow by providing eddy induced moisture convergence and divergence

earthquake response of reinforced segmental retaining walls backfilled with substantial percentage of fines abstractthis paper reports on the seismic performance of three geosynthetic reinforced segmental retaining wall systems backfilled with a silty sand mixture using a shaking table excited by 1995 kobe earthquake loadings the preparation of the backfill mixture and its properties the tested wall configurations the reinforcement layouts and instrumentations and the observed wall performance are described visual observations and test results indicate that walls having 0 4 m vertical reinforcement spacing backfilled with soil containing a large percentage of fines performed better than those having good quality sandy soil under otherwise identical conditions vertical spacing of 0 8 m with removal of interlocking facing blocks in one of the walls did not lead to global collapse under repeated applications of the kobe earthquake loadings only localized shear failure behind the top block layer was observed as the top facing blocks tended to topple the good performance was attributable to apparent cohes

the role of synoptic waves in the formation and maintenance of the western hemisphere circulation pattern abstractprevious studies have demonstrated that the nao the leading mode of atmospheric low frequency variability over the north atlantic could be linked to northeast pacific climate variability via the downstream propagation of synoptic waves in those studies the nao and the northeast pacific climate variability are considered as two separate modes that explain the variance over the north atlantic sector and the east pacific north american sector respectively a newly identified low frequency atmospheric regime the western hemisphere wh circulation pattern provides a unique example of a mode of variability that accounts for variance over the whole north atlantic north american north pacific sector the role of synoptic waves in the formation and maintenance of the wh pattern is investigated using the ecmwf reanalysis datasets persistent wh events are characterized by the propagation of quasi stationary rossby waves across the north pacific north american north atlantic regions and by associated s

the effects of orography on midlatitude northern hemisphere dry climates abstract the role of mountains in maintaining extensive midlatitude arid regions in the northern hemisphere was investigated using simulations from the gfdl global climate model with and without orography in the integration with mountains dry climates were simulated over central asia and the interior of north america in good agreement with the observed climate in contrast moist climates were simulated in the same regions in the integration without mountains during all season but summer large amplitude stationary waves occur in response to the tibetan plateau and rocky mountains the midlatitude dry regions are located upstream of the troughs of these waves where general subsidence and relatively infrequent storm development occur and precipitation is thus inhibited in summer this mechanism contributes to the dryness of interior north america as a stationary wave trough remains east of the rockies but is not effective in eurasia due to seasonal changes in the atmospheric circulation the dryness

measuring the in situ deformation of retaining walls by the digital image correlation method in this study the digital image correlation dic method was used to monitor the full field deformation of a retaining wall two retaining walls located in mountainous areas of taiwan were investigated the first fushan slope was characterized by substantial long term deformation and the second bulao slope was located beneath an expressway and was severely damaged by typhoon morakot this paper first describes the preparation procedures for in situ applications of the dic method various environmental factors such as fog rain light direction and spot mark clarity affected measurement precision and consequently produced monitoring images that were unsuitable for further analysis the dic analysis results clearly indicate the deformation pattern of the retaining walls the proposed method is accurate and effective for performing long term monitoring of retaining walls and the results can be used to accurately predict the tendency location and quantity of retaining wall displacement therefore the proposed dic method can be implemented to prevent disasters caused by landslide

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

centrifuge modeling of slope instability this paper demonstrates the use of a centrifuge modeling technique in studying slope instability the slope models were prepared from sand and sand mixed with 15 and 30 fines by weight compacted at optimum water content the validity of the modeling technique was confirmed using slope models of different heights inclinations and soil types the soil behavior was studied under triaxial and plane strain conditions and the extended mohr coulomb failure criterion was found relevant for expressing the strength of unsaturated compacted soil based on the angle of internal friction and apparent cohesion the bishop s circular mechanism together with the extended mohr coulomb failure criterion was able to simulate the slope failure reasonably well the rainfall of different intensities was then induced on the 60 stable slopes of sand with 15 fines it was found that the failure of slope under rainfall may be interpreted as a reduction in apparent cohesion the centrifuge tests also allowed the rainfall intensity duration threshold curve local curve to be generated for the test slopes and the accumulated rainfall corresponded well to some of the reported field observations

dynamical feedbacks and the persistence of the nao the persistence of the north atlantic oscillation nao is studied using observations of the threedimensional vorticity budget in the atlantic sector analysis of the relative vorticity tendency equation shows that convergence of eddy vorticity flux in the upper troposphere counteracts the effect of anomalous largescale divergence at the upper level at low levels the convergence associated with this large scale vertical circulation cell maintains the relative vorticity anomaly against frictional drag the eddy vorticity flux convergence thus acts to sustain the vorticity anomaly associated with the nao against drag and increases the persistence of the nao vorticity anomaly the adiabatic cooling associated with the rising motion in the vorticity maximum sustains the thermal structure of the nao anomaly enhancing the baroclinicity and thus eddy generation this constitutes a positive eddy feedback that helps maintain the nao the positive eddy feedback occurs only in the midlatitude region and is strongest during the negative phase of the nao when the atlantic jet is displaced toward the equator with a high pressure anomaly to the north and a low pressure anomaly to the south the stronger feedback demonstrated during the negative phase is consistent with the greater persistence observed for this phase of the nao the positive feedback appears to be associated with anomalous northward eddy propagation away from the jet

water isotopic variability in response to mesoscale convective system over the tropical ocean 1 in tropical regions the empirical negative relationship between the isotopic content of precipitation and rainfall amount known as the amount effect has been used as a rationale for paleohydroclimate reconstruction from isotope records however there is still no comprehensive physical explanation for this empirical effect here we reconsider the well known amount effect using newly available isotope data for both surface water vapor and precipitation obtained from shipboard observations in this study we hypothesized that stratiform rainfall associated with mesoscale convective systems mcss is a key process in reducing tropical water isotopic concentrations and tested this hypothesis with an idealized mcs model our conceptual model reasonably accounted for several observed features and indicated that isotopic reductions in tropical oceanic regions reflect a precipitating system s change relatively high isotope ratios corresponded to disorganized convection on the other hand mcss were characterized by lower isotope ratios with increasing stratiform area in addition the amplitude of this isotopic depletion was related to the scale of the precipitation system the lowest isotopic ratios were observed during the passage of large scale disturbances corresponding to the madden julian oscillation convective envelope in which mcss are embedded this means that the frequent appearance of mcss results in further decreases in the isotopic ratio of surface vapor and precipitation from this we conclude that the amount effect can be interpreted as the development of a precipitation system from an isolated convection cell into a large scale system containing several mcss and that past large scale convective activity can be reconstructed from isotope records

anatomy of synoptic eddy nao interaction through eddy structure decomposition abstracta method of eddy structure decomposition is proposed to detect how low frequency flow associated with the north atlantic oscillation nao organizes systematically synoptic eddy se activity to generate in phase and upstream feedbacks in this method a statistical eddy streamfunction ses field defined by the three point covariance of synoptic scale streamfunction is introduced to characterize spatiotemporal se flow structures the ses field is decomposed into basic and anomalous parts to represent the climatological se flow structure and its departure these two parts are used to calculate the basic and anomalous eddy velocity eddy vorticity and thus eddy vorticity flux fields in order to elucidate those two se feedbacks onto the nao this method is validated by the fact that the observed anomalous eddy vorticity flux field can be reproduced well by two linear terms the basic eddy velocity field multiplied by anomalous eddy vorticity field and the anomalous eddy velocity field multiplied

organized convective systems in the tropical western pacific as a process in general circulation models a toga coare case study we examine the large scale effects of organized convective systems in the tropical western pacific observed during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare in a case study approach we examine realizations of a supercluster associated with the onset of the december 1992 westerly wind burst in the t213 operational medium range weather forecasting model of the european centre for medium range weather forecasts ecmwf we idealize a supercluster as a hierarchy of three interacting scales namely organized cumulonimbus c 1 mesoscale convective systems c 2 and the supercluster component c 3 it is shown that the ecmwf model represents this hierarchy as a c 3 like surrogate whose influence dominates the effect of parametrized convection this causes over prediction of the model tendencies which in the case of zonal momentum is explained in elementary terms the structure of the resolved scale momentum flux is explained by moncrieff s 1992 archetypal theory of organized convection which has been verified against observations and cloud resolving model data sets the parametrization of subgrid scale convective momentum flux in the ecmwf model based on a momentum mixing concept produces subgrid scale tendencies that are physically different from transports associated with cumulonimbus convection in a shear flow we outline a strategy for parametrizing the momentum flux by the c 1 component based on the archetypal model the c 2 component which is part resolved and part parametrized is at odds with the assumptions of scale separation underpinning parametrization it is argued that this component should be represented as part of the prognostic treatment of convectively generated cirrus finally we suggest cloud resolving modelling studies to further quantify the structure and large scale impact of superclusters in a westerly wind burst environment ranging from idealized models to models having data assimilation capability

the global population of mesoscale convective complexes a global set of 714 mesoscale convective complexes is compiled and some of the common properties of the convective systems are identified and examined from a global perspective the data set includes date of occurrence time of first storms initiation maximum extent termination duration cold cloud shield areas and tracks from initiation to termination it is found that the typical convective complex is nocturnal generates a cold cloud shield area of approximately 350 000 km2 and persists for about 10 h the largest systems and most persistent systems tend to occur near the summer solstices for the globe about 400 systems occur each year primarily over land areas most systems develop in favoured zones although some activity occurs over every continent except antarctica and all major oceans the concentration of activity into favoured zones indicates that there must be special dynamic and or thermodynamic conditions necessary for convection to organize into convective complexes activity is strongly tied to the solar day and shifts from 35 s in early january to about 50 n during the boreal summer and back to 35 s by december within the northern hemisphere there is a pronounced poleward migration as the jet stream shifts northward relatively little migration occurs in the ocean dominated southern hemisphere where the subtropical jet remains quasi stationary over the convective complex regions the nocturnal life cycles copious rainfall large cloud shields and great frequency of mesoscale convective complexes suggest that they may be significant contributors to the global hydrologic cycle and earth system energy budget

deep seated rockslide avalanches preceded by mass rock creep of sedimentary rocks in the akaishi mountains central japan abstract seven large rockslide avalanches of sedimentary rocks are known in japan almost all of these major landslides were preceded by gravitational deformation of rocks mass rock creep mrc as inferred from geologic and geomorphic investigations of five rockslide avalanches in the akaishi mountains the mrc that preceded the rockslide avalanches in the akaishi mountains was characterized by a slow but steady downslope bowing of steeply dipping foliations which accompanied intensive deformation and fragmentation of the rock mass by shearing along foliations this deformation and fragmentation of the rock mass provides a basic cause for the occurrence of rockslide avalanches which occur when a creeping rock mass has lost its support from the lower part of a slope by stream erosion this type of mrc continues for a long time after a part of the creeping area has slid and results in longterm generation of debris by the landslide sear of the rockslide avalanche

mesoscale convective systems 1 mesoscale convective systems mcss have regions of both convective and stratiform precipitation and they develop mesoscale circulations as they mature the upward motion takes the form of a deep layer ascent drawn into the mcs in response to the latent heating and cooling in the convective region the ascending layer overturns as it rises but overall retains a coherent layer structure a middle level layer of inflow enters the stratiform region of the mcs from a direction determined by the large scale flow and descends in response to diabatic cooling at middle to low levels a middle level mesoscale convective vortex mcv develops in the stratiform region prolongs the mcs and may contribute to tropical cyclone development the propagation of an mcs may have a discrete component but may further be influenced by waves and disturbances generated both in response to the mcs and external to the mcs waves of a larger scale may affect the propagation velocity by phase locking with the mcs in a cooperative mode the horizontal scale of an mcs may be limited either by a balance between the formation rate of convective precipitation and dissipation of stratiform precipitation or by the rossby radius of the mcv the vertical redistribution of momentum by an mcs depends on the size of the stratiform region while the net vertical profile of heating of the large scale environment depends on the amount of stratiform rain regional variability of the stratiform rain from mcss affects the large scale circulation s response to mcs heating

left hand rule for synoptic eddy feedback on low frequency flow 1 in this study scale interaction between synoptic eddies and low frequency flow is investigated the synoptic eddy feedback is a key process in sustaining the low frequency flow we show clear evidence using ncep reanalysis data that there is a general underlying rule the left hand rule governing the synoptic eddy feedback onto low frequency flow this rule states that eddy vorticity fluxes are directed preferentially about 90 degrees toward their left hand side so that they converge into cyclonic flow and diverge from anticyclonic flow therefore the eddy vorticity flux plays a positive role in reinforcing low frequency flow citation kug j s and f f jin 2009 left hand rule for synoptic eddy feedback on low frequency flow geophys res lett 36 l05709 doi 10 1029 2008gl036435

influence of the east asian winter monsoon on the storm track activity over the north pacific 1 we investigate the relationship between the east asian winter monsoon eawm and synoptic eddy activity over the north pacific ocean it is well known that the subtropical pacific jet becomes stronger during strong monsoon periods than during weak monsoons the storm track is generally expected to be active when the eawm is strong owing to the enhanced subtropical jet contrary to this expectation synoptic eddy activity is significantly reduced in strong eawm years and conversely significantly increased during weak years in addition we found that eawm induced lower level cooling brings about the reverse relationship a stronger jet but with weaker storm activities it is suggested that the local baroclinicity induced by the eawm modulates the variation of both the jet and north pacific storm track simultaneously in the interannual time scale because major lower level cooling is located in the western parts of both the subtropical jet and the storm track in longitudes and between the two central axes in latitudes it induces the opposite sign of anomalous local baroclinicity at the two active regions and causes this reverse relationship the wave seeding from east asia to the north pacific storm track is weakened owing to the anomalous lower level cooling in the northwestern pacific which also results in reduction of eddy generation and storm track activities

an observational study of large scale atmospheric rossby waves during fgge abstract analyzed global data from the european centre for medium range weather forecasts for the fgge year are projected onto hough functions at each synoptic time and the time series filtered to retain all westward propagating components on time scales less than seasonal the evolution of hough mode phase agrees closely with rossby wave theory whenever the amplitudes are not small the evolution of the wave amplitude is described as irregular vacillation the first three zonal and meridional wavenumbers are studied the total rossby wave field can be as large as 130 m and can potentially explain a significant part of observed persistent anomalies

variability of warm season cloud episodes over east asia based on gms infrared brightness temperature observations abstract the present study has used the geostationary meteorological satellite gms ir brightness temperature observations to investigate the regional and intraseasonal variability of east asian warm season cloud precipitation episodes in distance time space due to land sea contrast and latitudinal effects the data period was may august 1998 2001 and harmonic analysis was employed as the major tool for analysis the full domain of study 20 40 n 95 145 e was divided into northern and southern zones and into eastern and western sectors and statistics of episodes in each subregion were derived and compared for latitudinal effects episodes were found to be significantly larger in span and duration in northern 30 40 n than in southern 20 30 n zones in the northern zone the propagation characteristics were also stronger and remain evident even in midsummer while episodes south of 30 n reversed in direction and traveled westward in july and august for land sea contrast the may august tra

evaluating failure mechanisms of dip slope using a multiscale investigation and discrete element modelling abstract this study proposed an in depth multiscale analysis procedure to identify the dip slope area and assess dip slope stability and influencing area the proposed analysis procedure comprised five stages 1 identifying the potential area of a dip slope 2 analyzing the possible failure types of the dip slope 3 evaluating slope activity 4 analyzing dip slope stability under the influence of possible triggering factors and 5 assessment of the deformation and deposition area to validate the proposed procedure the chaochouhu region of taiwan was analyzed as a dip slope case in stages 1 to 3 the scale of the utilized map and the precision of associated data were evaluated to identify the potential area of a dip slope the possible failure types and the activity of each slope unit in stages 4 and 5 the processes of deformation and sliding in a high activity slope unit were simulated using the discrete element method the numerical model was first verified using in situ monitoring data obtained from inclinometers subsequently the model was used to predict the slope behavior under conditions of wetting deterioration of geomaterial the multiscale analysis revealed comprehensive information regarding the dip slope the application of the proposed approach would be useful to civil engineers for evaluating dip slope stability as well as to relevant authorities for planning hazard mitigation strategies

dynamical feedbacks of the southern annular mode in winter and summer abstract the persistence of the southern annular mode sam is studied during austral winter june september and summer december march using observations of the three dimensional vorticity budget analysis of the relative vorticity tendency equation shows that convergence of eddy vorticity flux in the upper troposphere coupled with a secondary circulation constitutes a positive eddy feedback that acts to sustain the vorticity anomaly associated with the jet shift against drag the feedback exhibits a strong seasonality with summer months revealing a positive feedback through much of the hemisphere and winter months showing a positive feedback over the indian ocean but not over the western pacific results suggest that the lack of wintertime feedback over the western pacific is due to the weakness of the eddy driven midlatitude jet in that region

retrograding wintertime low frequency disturbances over the north pacific ocean abstract retrograding westward moving features over the middle and high latitudes of the northern hemisphere during winter are examined in observations and data from a gcm simulation using complex principal component analysis the first eigenvector of the low frequency middle troposphere geopotential height over the north pacific has a zonal scale of 120 160 deg longitude and a dipole like meridional structure with maximum amplitude over the gulf of alaska and the bering sea these disturbances propagate westward and go through a life cycle of growth and decay over a period of about three weeks the temporal evolution of the energy and its conversions during the life cycle of the simulated pacific disturbances are composited using the time dependent coefficient of the principal component analysis as an index for their occurrence the composite energy cycle indicates that the kinetic and available potential energy of these disturbances grow and decay together both baroclinic and barotropic conversion

the average behavior of large scale westward traveling disturbances evident in the northern hemisphere geopotential heights abstract the average structure of westward traveling disturbances that contribute to relative maxima found in space time spectra from 13 32 days at northern latitudes is determined for each season a compositing method used employs a minimum of space and time filtering in order to avoid biasing the results the average latitudinal structure is global in that it is discernible in the southern hemisphere during december february and september november it is primarily confined to northern latitudes during march august in all seasons the disturbance is out of phase between northern high latitudes and subtropical and tropical latitudes the longitudinal structure is primarily zonal wavenumber 1 in all seasons further work is suggested to confirm the structures determined here and to learn if they reflect the superposition of a number of occasionally excited rossby normal modes

assessing the role of precursor cyclones on the formation of extreme greenland blocking episodes and their impact on summer melting across the greenland ice sheet a 30 year climatology of north atlantic cyclones from 1979 to 2008 is examined within the context of extreme greenland blocking and accelerated surface melting across the greenland ice sheet gris a distinct class of north atlantic cyclones known as precursor cyclones was identified as any extratropical cyclones originating to the west of greenland blocks prior to the peak of blocking intensity composite map analysis reveals that precursor cyclones contributed to a significant intensification of extreme greenland blocking episodes gbes through the process of upper level wave amplification across all seasons most extreme gbes are associated with multiple precursor cyclones prior to peaking in intensity and a majority of these cyclones have continental rather than oceanic origins over both the western and eastern sectors of greenland daily meltwater production simulated by the modele atmospherique regional regional climate model is greater during extreme gbes accompanied by precursor cyclones compared to extreme gbes lacking a precursor cyclone based on an analysis of air parcel trajectories and north atlantic sst anomalies enhanced surface melting during the summer particularly over southern and western greenland is strongly linked to the combination of vigorous adiabatic warming generated by subsiding air within the blocking anticyclones and warm air advection supplied by the precursor cyclones with the increased frequency of extreme gbes accompanied by precursor cyclones observed during a strong positive phase of the atlantic multidecadal oscillation recent long term increases in gris surface melting can be partially attributed to the interaction of these atmospheric and oceanic processes

the structure and energetics of midlatitude disturbances accompanying cold air outbreaks over east asia abstract the onset dates for 11 individual cold air outbreaks over the east asian seaboard during the winter monsoon experiment 1 december 1978 28 february 1979 are used for constructing composite synoptic charts the three dimensional structure and energetics of disturbances with time males shorter than 5 days are distinguished from the corresponding properties of more slowly varying fluctuations by using time filtering techniques it is seen that the high frequency disturbances accompanying the cold surges experience systematic structural changes as they migrate along a well defined storm track from east asia to the gulf of alaska the typical life cycle of such extratropical storms is characterized by a barolinic growth phase coinciding with the polar outbreaks and a decay phase in which barotropic processes play an active role the propagation of low frequency fluctuations is oriented toward lower latitudes with new vorticity centers developing downstream and equatorward of the primary disturbanc

mesoscale convective complexes over southern africa abstractthe maximum spatial correlation technique mascotte is an objective and automated method developed to simultaneously determine both the structural properties and evolution tracking of cloud shields of convective systems originally designed to monitor systems over the amazon region this method has now been adapted for subtropical southern africa in this paper a detailed climatology of 70 mesoscale convective complexes mccs that occurred during the austral summer months over southern africa during the 1998 2006 period are presented most mccs are clustered along the eastern regions of southern africa adjacent to the warm waters of the mozambique channel and agulhas current a few infrequent systems are found to be developing in namibia and botswana the systems are found to predominantly occur during the months of november february with maximum activity occurring in november and december the transition from a more midlatitude dominated circulation to a tropical circulation over the regio

a climatology of mesoscale convective systems over europe using satellite infrared imagery ii characteristics of european mesoscale convective systems an automated method for mesoscale convective system mcs identification and tracking described in part i is applied in order to derive a sound european mcs database using meteosat infrared channel ir10 8 images centred over europe the western mediterranean and north africa the database covers five warm seasons from april to september for the years 1993 to 1997 and includes more than 6000 mcss reaching at least an area of 10 000 km2 first results of the derived climatology of european mcss are presented they mainly address the mcs geographical location general mcs characteristics maximum extent eccentricity duration and the diurnal cycle of the mcs mcss are shown to be mainly continental but some mcs triggering is observed during the second half of august and september over the western mediterranean sea furthermore mcs triggering is strongly correlated with orography and local maxima of mcs triggering are observed near all mountain ranges regions near the alps which favour mcs triggering are described in detail the monthly distributions of occurrence of warm season european mcss are also presented distributions of maximum extent eccentricity direction of propagation life duration and triggering and dissipation times are also derived on average a theoretical typical european mcs moves to the east north east triggers near 3 p m local solar time lst lasts around 5 5 hours and dissipates near 9 p m lst it typically has an eccentricity at the time of maximum extent of 0 53 the diurnal cycle is also studied and proved to be in phase with the diurnal radiative heating except for around 20 of the mcss a detailed analysis of the maximum extent distribution shows that it can be fitted by a log normal distribution which leads to an average value of the mcs maximum extent of around 9000 km2 this approximation is statistically meaningful and it is independent of the choice to study only mcss reaching at least 10 000 km2 finally a section of this article is devoted to indirect verifications of the discrimination method see part i for the whole geographical domain copyright 2002 royal meteorological society

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

centrifuge modeling of failure behaviors of sandy slope caused by gravity rainfall and base shaking abstract this study focused on slope stability behaviors under different conditions including gravity rainfall and earthquake the slope models were prepared by mixing sand 80 and clay kaolinite 20 and compacting at optimum water content under the gravitational condition the model tests were performed with three different directions of a gravel layer embedded into the slope during the test the artificial acceleration was gradually increased until slope failure occurred to observe the slope behaviors under rainfall and earthquake the results indicated that the direction of the gravel layer affected the distribution of water content additionally it was found that the inclination angle was a key factor influencing slope stability rainfall intensity played an important role in infiltration water with regard to the failure wedge among the three conditions examined the earthquake condition generated the most significant effect on slope stability herein for evaluating the stability of slopes the bishop s method incorporating an inclination angle of a gravel layer and apparent cohesion is introduced

model simulation and projection of european heat waves in present day and future climates abstractthe synoptic behavior of present day heat waves hw over europe is studied using the gfdl high resolution atmospheric model hiram with 50 km grid spacing three regions of enhanced and coherent temperature variability are identified over western russia eastern europe and western europe the simulated hw characteristics are compared with those derived from climate forecast system reanalysis products composite charts for outstanding hw episodes resemble well known recurrent circulation types the hw region is overlain by a prominent upper level anticyclone which blocks the passage of synoptic scale transients the altered eddy vorticity transports in turn reinforce the anticyclone the anticyclone is part of a planetary scale wave train the successive downstream development of this wave train is indicative of rossby wave dispersion additional runs of hiram are conducted for the time slices of 2026 35 and 2086 95 in the climate scenario corresponding to representative concentration pathway

evolution and dynamics of summertime blocking over the far east and the associated surface okhotsk high time evolution and dynamics of an upper level blocking ridge over the far east and the associated surface high over the sea of okhotsk that give rise to abnormal summertime coolness over eastern japan are investigated through a composite analysis applied to distinct surface high events the formation mechanism and vertical structure of the blocking differ fundamentally between may and july attributable to seasonal changes in the jet structure storm track activity over the far east and the land sea thermal contrast within the okhotsk region in may forcing from migratory eddies is strong enough for precursory anticyclonic anomalies retrograding slowly over the north pacific to develop into a blocking ridge the ridge remains equivalent barotropic under the weak land sea thermal contrast in the okhotsk region in contrast the eddy forcing is no longer the primary factor for the blocking formation in july in the presence of the weakened and split westerlies rather the propagation of a stationary rossby wave packet that has emanated from precursory anticyclonic anomalies over northern europe stagnates over the far east and the subsequent local breaking of the packet leads to the blocking formation in a particular case in july 1993 a wave packet involved in blocking formation could be traced back as far upstream as the east coast of north america over the two previous weeks acting on the strong thermal contrast in july between the cool sea surface and a warm land mass to the west the anomalous surface easterlies induced by the blocking ridge can build up a cold surface anticyclone through cold advection rendering the blocking anomalies distinctly baroclinic copyright 2004 royal meteorological society

the kinematics of a midlatitude continental mesoscale convective system and its mesoscale vortex the authors present a unique scale discriminating study of the environment relative circulations within a mesoscale convective system mcs and mesoscale convective vortex mcv the mcs a leading convective line and trailing stratiform region that became asymmetric passed through the national oceanic and atmospheric administration noaa profiler network npn in kansas and oklahoma on 1 august 1996 the mcv appeared in the mcs s stratiform region just prior to the system s mature stage and grew to a depth of over 12 km as the mcs dissipated the mcv did not apparently survive to the next day a spatial bandpass filter was used to divide observed wind into a component that was predominantly synoptic background wind and a component that was predominantly a mesoscale perturbation on that background wind a mesoscale updraft mesoscale downdraft and divergent outflows in the lower and upper troposphere were evident after the synoptic background wind was removed so these four circulations were internal and fundamental to the mcs the mesoscale perturbation in wind in the middle troposphere extended farther behind the mcs than ahead of it consistent with analytic studies and numerical simulations of gravity waves generated by heat sources characteristic of mcss with leading convective lines and trailing stratiform regions deepening of the mcv appeared to be reflected in the vertical wind shear at the vortex s center as the mcv strengthened the mesoscale shear through its lower part decreased perhaps as wind became more vortical at increasing altitudes mesoscale and synoptic vertical shears were of similar magnitude so an average of environmental soundings outside an mcs probably does not accurately represent the shear that affects an mcv this suggests the need to reevaluate how the kinematical settings of mcvs are diagnosed

evaluating triggering and causative factors of landslides in lawnon river basin taiwan this study evaluates triggering and causative factors of landslides by comparing their occurrence in the lawnon river basin prior to and after rainfall and earthquake events over a five year period 2005 2009 the landslide ratio in the study area was low less than 4 before 2007 and significantly increased in the wake of typhoon morakot in 2009 the high accumulation of rainfall was the major triggering factor in addition the major seismic activity of march 4 2008 also contributed to landslide occurrence the combined influence of rainfall and the earthquake is evaluated based on multi variable regression analysis though no significant co seismic landslides were found after the march 4 2008 earthquake its influence on slope stability has been observed from the apparent growth of landslide ratio in the four rainfall events following the quake causative factors include the higher landslide ratios occurring in sedimentary rock zones especially sandstone formations with intercalations of shale and dip slopes which are demonstrably prone to plane failures

the large scale environments of the global populations of mesoscale convective complexes abstract the mean genesis environment was constructed for each of five mesoscale convective complex mcc population centers around the world africa australia china south america and the united states it is found that the environments are very similar and exhibit many of the same dynamic and thermodynamic structures that are present with systems in the united states in particular mccs initiate within prominent baroclinic zones characterized by locally large values of lower tropospheric vertical wind shear and convective available potential energy cape typically a low level jet of air with low static stability high equivalent potential temperature oriented nearly perpendicular to the baroclinic zone intrudes into the genesis region and is forced to ascend over a relatively shallow surface based layer of relatively cool air pronounced warm advection accompanied by strong lower tropospheric veering overlays the surface based cool layer a local maximum in absolute humidity and a local minimu