analysis of a heavy rainfall event during tamex abstract a heavy rainfall event during the taiwan area mesoscale experiment intensive observing period 13 has been studied using upper air surface mesonet and dual doppler radar data the heavy rainfall 231 mm day 1 occurred over northwestern taiwan with the maximum rainfall along the northwestern coast and was caused by a long lived convective rainband in the prefrontal atmosphere it occurred in an upper level divergence region and along the axis of the maximum equivalent potential temperature at the 850 hpa level as a mei yu front advanced southeastward the postfrontal cold air in the lowest levels was retarded by the hilly terrain along the southeastern china coast as a result a low level wind shift line associated with a pressure trough at the 850 hpa level moved over the taiwan strait before the arrival of the surface front the westerly flow behind the trough interacted with a barrier jet along the northwestern coast of taiwan the barrier jet is caused by the interaction between the pref

a diabatically driven mesoscale vortex in the lee of the tibetan plateau abstract an analysis of a diabatically driven and long lived midtropospheric vortex in the lee of the tibetan plateau during 24 27 june 1987 is presented the large scale conditions were characterized by the westward expansion of the 500 mb western pacific subtropical high and the amplification of a trough in the lee of the plateau embedded within the lee trough three mesoscale convective systems mcss developed a vortex emerged following the dissipation of one mcs with its strongest circulation located in the 400 500 mb layer low level warm advection and surface sensible and latent heating contributed to the convective initiation weak wind and weak ambient vorticity conditions inside the lee trough provided a favorable environment for these mcss and the vortex to develop and evolve the organized vortex circulation featured a coherent core of cyclonic vorticity extending from near the surface to 300 mb with virtually no vertical tilt the air in the vicinity of the vortex was very moist and the

warm core vortex amplification over land abstract a convectively generated mesoscale vortex that was instrumental in initiating and organizing five successive mesoscale convective systems over a period of three days is documented two of these convective systems were especially intense and resulted in widespread heavy rain with localized flooding based upon radar and satellite data the detectable size of the vortex became much larger following the strong convective developments nearly tripling its initial diameter over its three day life cycle during nighttime when convection typically intensified within the vortex movement of the system tended to slow following dissipation of the convection in the morning the daytime movement accelerated cross sections of potential vorticity taken through the vortex center clearly show a maximum at midlevels and a well defined minimum directly above the vortex and the potential vorticity maximum were essentially colocated and the system was nearly axisymmetric in the vertical over the three day life

mesoscale analyses of the sichuan flood catastrophe 11 15 july 1981 abstract during the period 11 15 july 1981 heavy rainfall occurred over the sichuan basin in china resulting in severe floods that took a large toll in human life and property damage synoptic analyses indicate that early in this period the southerly monsoon flow was particularly strong near the basin because of a favorable positioning of the pacific subtropical high and the indian monsoon depression the passage of a deep midlatitude trough from the lake baikal region brought colder drier air from siberia into southwest china the siberian air stream met the monsoon current over the eastern plateau and the sichuan basin creating a region of large scale low level convergence mesoscale analyses show that the flood was directly related to the extreme development of a long lived mesoscale vortex called south sw vortex by chinese meteorologists over the basin as it merged with another mesoscale vortex generated over the tibetan plateau mesoscale heat and moisture budgets suggest that the latent hea

a numerical study of the genesis of extratropical convective mesovortices part i evolution and dynamics abstract the purpose of this study is to understand the genesis of extratropical convective mesovortices and the large scale environmental features that influence the vortex formation a hypothesis is proposed that mesovortices form in the stratiform rain regions of mesoscale convective systems mcss due to the reduction of static stability that reduces the effective local rossby radius in such regions a conceptual model of the mesoscale convective cyclogenesis is introduced which describes the three stages of the mesovortex formation a modified version of the pennsylvania state university national center for atmospheric research three dimensional hydrostatic mesoscale model is used to simulate mesovortex genesis in analytically generated pre mcs large scale environments the model simultaneously incorporates parameterized convection and a grid resolvable convective scheme containing the effects of hydrostatic water loading condensation evaporation freezing melting and sublimation a control si

tropical cyclone formations in the south china sea associated with the mei yu front abstract this study examines the 119 tropical cyclone tc formations in the south china sea scs during 1972 2002 and in particular the 20 in may and june eleven of these storms are associated with the weak baroclinic environment of a mei yu front while the remaining nine are nonfrontal seven of the 11 initial disturbances originated over land and have a highly similar evolution comparison of the frontal and nonfrontal formation shows that a nonfrontal formation usually occurs at a lower latitude is more barotropic develops faster and possibly intensifies into a stronger tc six nonformation cases in the scs are also identified that have similar low level disturbances near the western end of a mei yu front but did not develop further in the nonformation cases both the northeasterlies north of the front and the monsoonal southwesterlies are intermittent and weaker in magnitude so that the vorticity in the northern scs does not spin up to tropical depression intensity because of the influence o

a diagnostic case study of mei yu frontogenesis and development of wavelike frontal disturbances in the subtropical environment abstract during 6 7 june 2003 a mei yu front over southern china with active mesoscale convective systems mcss along it and to its south intensified rapidly in 24 h to possess a strong cyclonic circulation with relative vorticity centers reaching 1 7 10 4 s 1 and a low level jet llj of 22 5 m s 1 at 850 hpa moreover both the mass and wind fields and convection developed a wavelike structure at meso scale along the front using mainly gridded analyses from the european centre for medium range weather forecasts ecmwf the present study documented the evolution of this case and diagnosed the mechanisms responsible for its rapid intensification and the development of mesoscale disturbances using methods including the piecewise potential vorticity pv inversion results indicate that this mei yu front was characterized by strong horizontal shear and moderate temperature gradient and its development was not baroclinic in nature the initiation of a wavelike structure along the frontal shear zon

radar analysis of a tamex frontal system abstract during the taiwan area mesoscale experiment tamex three doppler radars complemented enhanced surface and upper air observations the focus of the experiment was to better understand the interaction of the terrain with precipitation systems in the production of the important heavy rainfall the intensive operational period iop number 8 extended from 1400 ist local standard time 7 june 1987 until 0800 lst 9 june 1987 during this time a mesoscale convective system mcs formed in the straits of taiwan and moved inland it was interrogated by many observing instruments including three doppler radars over a 6 h period during this time the front moved through the radar network the front was shallow and the precipitation widespread both ahead of and behind the front the front was only 1 6 km deep over a distance of 100 km using velocity azimuth display vad data a portion of the frontogenetic function was computed during the times the front was in the vicinity of the radar the increas

diagnosed characteristics of precipitation systems over taiwan during the may june 1987 tamex abstract characteristics of mei yu precipitating cloud systems over taiwan during the may june 1987 taiwan area mesoscale experiment tamex have been studied using sounding surface precipitation and radar data vertical motion has been computed over the island at 6 h intervals from 13 may to 15 june using a modification of the kinematic method that takes into account the mountainous lower boundary within a four station sounding polygon two primary characteristics of the precipitation have been found first the major rainfall event were linked to the passage of midlatitude disturbances and typically consisted of both deep convective and stratiform components deep convection was primarily prefrontal or frontal while the stratiform precipitation was postfrontal presumably in association with overrunning and orographic lifting second there was a pronounced diurnal variability in the rainfall vertical motion heating q1 and moistening q2 profiles have been used to define the character of the pr

a subtropical oceanic mesoscale convective vortex observed during sowmex timrex abstractthis study examines a subtropical oceanic mesoscale convective vortex mcv that occurred from 1800 utc 4 june to 1200 utc 6 june 2008 during intensive observing period iop 6 of the southwest monsoon experiment sowmex and the terrain influenced monsoon rainfall experiment timrex a dissipating mesoscale convective system reorganized within a nearly barotropic vorticity strip which formed as a southwesterly low level jet developed to the south of subsiding easterly flow over the southern taiwan strait a cyclonic circulation was revealed on the northern edge of the mesoscale rainband with a horizontal scale of 200 km an inner subvortex on a scale of 25 30 km with maximum shear vorticity of 3 10 3 s 1 was embedded in the stronger convection the vortex relative southerly flow helped create local potential instability favorable for downshear convection enhancement strong low level convergence suggests that stretching occurred within the mcv higher e air associated with significant pot

u pb geochronology of late neoarchean tonalites in the flin flon belt trans hudson orogen surprise at surface the flin flon volcanic belt of the trans hudson orogen in northern manitoba comprises magmatic rocks 1 88 1 90 ga generated in an intra oceanic arc and identified as one of the best examples of juvenile paleoproterozoic crust in the flin flon athapapuskow lake area the belt consists of a series of fault bounded blocks each having distinct stratigraphic and magmatic affinities juxtaposed to form an accretionary collage two tonalitic bodies within the northeast arm shear zone a major deformation corridor separating two of the most important blocks in the area have been dated by the u pb zircon method at and these results indicate the presence of fragments of late neoarchean crust within the flin flon belt possibly related to ca 2 5 ga granitic bodies found in terranes beyond the western limit of the belt the presence of ca 2 5 ga tonalites within the flin flon belt herein reported for the first time has major implications for basement involvement in the early tectonic evolution of the f

mesoscale convective vortices observed during bamex part ii influences on secondary deep convection abstract observations from the bow echo and mesoscale convective vortex mcv experiment are used to examine the role of the five mesoscale convective vortices described in part i on heavy precipitation during the daytime heating cycle persistent widespread stratiform rain without deep convection occurs for two strong mcvs in conditionally stable environments with strong vertical shear two other mcvs in moderate to strong vertical shear have localized redevelopment of deep convection termed secondary convection on their downshear side where conditional instability exists the strongest of the five mcvs occurs in weak vertical shear and has widespread secondary convection which is most intense on its conditionally unstable southeast periphery the two mcvs with only localized secondary convection have well defined mesoscale vertical motion couplets with downshear ascent and upshear descent above the planetary boundary layer pbl although the amplitude is significantly greater the kinematically der

the development mechanism for tibetan plateau warm vortices abstract the low level cyclonic vortices which form over the tibetan plateau in the summer monsoon season are major rain producing systems and have the potential to trigger cyclogenesis on the lee side when they move off the plateau two cases of the plateau vortices which occurred in july 1979 are studied the characteristics of the vertical structure in their developing stage and the circulation condition favorable for the eastward movement in the mature stage are diagnosed and presented by use of fgge iiib datasets numerical simulations with real data were performed using the gfdl limited area mesoscale simulation model results suggest that the latent heating is an essential driving force for the development of the vortices studied here the analysis of a continuous cisk model with a basic state resembling that actually observed over the summer plateau shows that the predicted unstable mode has a preferred scale growth rate and vertical structure all of which are qualitatively comparable to observ

midlevel cyclonic vortices generated by mesoseale convective systems abstract despite the large number of convective systems that occur over the central united states every year there are typically only a few well defined midlevel vortices apparent in satellite imagery after the overlying anvil debris from some convective complexes has dissipated or advected away a climatology of mesoscale convectively generated vortex mcv events for 1981 1988 is presented and the synoptic setting in which the circulation becomes apparent is discussed proximity sounding data from numerous cases are used to examine features of the kinematic and thermodynamic setting of mcvs at various lifelycle stages defined by satellite imagery features ofthe large scale environment that appear conducive to the formation and longevity of mcvs include weak flow weak vertical shear weak background relative vorticity and intense horizontal and vertical moisture gradients the rapid mesovortex generation observed can be explained by the stretching term of the vorticity equation most mcvs emerge fro

the development of an intense east asian summer monsoon disturbance with strong vertical coupling abstract the east asian summer monsoon mei yu disturbance of 17 25 june 1992 was the most intense 850 hpa low center of such systems during a 7 yr period due to the moisture fluxes associated with the southwesterlies from the warm tropical oceans diabatic heating has generally been considered the main energy source of these heavy precipitation disturbances as they propagate eastward from the eastern flank of the tibetan plateau across southeastern china and move into the east china sea in this study piecewise potential vorticity inversion is used to analyze the physical mechanisms of this intense case particularly the possible roles of midlatitude baroclinic processes in its development and evolution the development of the low level vortex involved the coupling with two upper level disturbances one at 500 hpa that also originated from the eastern flank of the tibetan plateau and another at 300 hpa both disturbances appeared later than and upstream of the low level vortex faster eastward movemen

study of a heavy rain vortex formed over the eastern flank of the tibetan plateau abstract a case of the heavy rain vortex which occurred during the period 14 15 july 1979 is studied using a limited area mesoscale numerical model this is a representative example of a group of warm southwest vortices that often form over the eastern flank of the tibetan plateau after the onset of the summer indian monsoon some common features of the dynamic structures exhibited both by the simulation and by observations are discussed the developing vortex is noticeably detached from the polar frontal zone a 180 phase shift exists between the upper and lower layer vorticity fields in the boundary layer a pronounced northward transport of mass and moisture is connected with an intense upward motion near and to the east of the 700 mb vortex center whole the southward cold advection is insignificant the vortex originated and rapidly developed in a stagnation region on the lee side of the plateau the presence of the stagnation region not only removes local dynamical energy sources from the environm

formative stage of a long lived mesoscale vortex observed by airborne doppler radar abstract the formative stage of a long lived mesoscale cyclonic vortex was captured by the noaa p 3 aircraft as it investigated a developing mesoscale convective system mcs near the southeastern coast of taiwan on 16 june 1987 during the taiwan area mesoscale experiment the supporting environment of the mesovortex was characterized by an exceptionally moist atmosphere and moderate ambient vertical shear through a deep layer from the near surface to 6 km with much weaker shear and winds aloft in addition a pronounced low level mesoscale shear convergence zone which resulted from the interaction of southeasterly flow with northeasterly flow confined to the near coast region existed in the vicinity of the observed mesovortex composite three dimensional wind fields derived via pseudo dual doppler synthesis show the vortex had a horizontal diameter expanding from 40 km to 70 km in the lower to midtroposphere respectively and exhibited considerable tilt through this layer contrary to previously d

reconstructing the exhumation history of the lesser himalaya nw india from a multitechnique provenance study of the foreland basin siwalik group 1 this research presents the first multitechnique provenance study of the siwalik group in the himalayan foreland basin in india using the jawalamukhi section magnetostratigraphically dated at 13 5 ma combined with provenance data from a dharamsala formation sedimentary section 21 13 ma located close by it forms the longest temporally continuous record of himalayan erosion in the indian foreland basin sandstone petrography and heavy mineral analysis conglomerate clast composition ar ar dating of detrital white micas and sm nd analyses on siltstones conglomerate matrix and conglomerate clasts was undertaken to determine 1 shifts in source region through time and 2 changes in detrital lag times related to exhumation rates in the hinterland together interpreted in the light of thrusting events we interpret the data to show a slow down in exhumation rate of the higher himalaya by 16 17 ma after which time the locus of thrusting propagated south of the main central thrust and erosion of the low grade haimanta formation to the south became significant the nonmetamorphosed inner lesser himalaya breached its haimanta cover by 9 ma with the metamorphosed inner lesser himalaya lesser himalayan crystalline series exhuming to surface by 6 ma this event caused sufficient disruption to established drainage patterns that all higher himalayan material was diverted from this location at this time

rear inflow in squall lines with trailing stratiform precipitation abstract the relative airflow and accompanying precipitation structure of squall lines trailed by mesoscale regions of stratiform rain are examined with emphasis on the occurrence of rear inflow i e the intrusion of environmental air into these storms across the trailing precipitation boundary three cases from kansas and oklahoma provide examples of strong rear inflow which crosses the back edge of the stratiform precipitation area at relative speeds exceeding 10 m s 1 the vertical profiles of relative flow at the trailing precipitation boundary of these three systems were remarkably similar with the rear inflow confined to a jet like layer centered at about 550 mb doppler radar data for two of these cases showed that the rear inflow jet occupied a continuous channel extending from middle levels at the back edge of the stratiform region to lower levels of the leading convective region where it merged with outflow from convective downdrafts to bolster the leading gust front strong front to rea

influence of balanced motions on heavy precipitation within a long lived convectively generated vortex abstract the forcing of heavy precipitation within a long lived convectively generated mesoscale vortex mcv is investigated with the aid of diagnoses from rapid update cycle gridded analyses organized convection within the mcv followed a distinct diurnal cycle which featured organized mesoscale convective systems mcss that matured overnight near the mcv center on successive days the mcv was typically most intense in the middle troposphere but intensified within the lower troposphere during the episodes of organized nocturnal convection the lower tropospheric vertical shear was an important organizing factor in mcs development and sustenance in the sense that its interaction with the cold temperature anomaly beneath the mcv center determined where balanced lower tropospheric ascent occurred from trajectory analyses we estimate that balanced ascent accounted for approximately half of the total vertical displacement of the thermodynamically unstable air that eventually composed elevated saturated

cloud resolving simulations of mesoscale vortex intensification and its effect on a serial mesoscale convective system abstract the authors performed numerical simulations of the 27 28 may 1998 mesoscale convective vortex mcv and mesoscale convective system mcs to understand how the mcv modulated the convection and how the convection intensified the vortex the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 was used initialized with the analysis from the rapid update cycle version 2 ruc 2 and nested to achieve 1 5 km grid spacing covering the mcs the model successfully simulated a north south convective band that formed near the center of the mcv in the early evening the simulation then correctly reoriented the convection along a roughly east west line in response to northward transport of warm conditionally unstable air within the nocturnal low level jet balanced vertical motion was found to contribute substantially to mesoscale lifting and thermodynamic destabilization which localized the convection horizontal transport of moist uns