modeling study of turbulent mixing over the continental shelf comparison of turbulent closure schemes limitation is imposed during upwelling favorable winds the majority of turbulent mixing occurs in the top and the bottom boundary layers and in the vicinity of the vertically and horizontally sheared coastal jet turbulent mixing in the coastal jet is primarily driven by shear production the near surface flow on the inner shelf becomes convectively unstable as wind stress forces the upwelled water to flow offshore in the surface layer during downwelling favorable winds the strongest mixing occurs in the vicinity of the downwelling front the largest turbulent kinetic energy and dissipation are found near the bottom of the front turbulence in the bottom boundary layer offshore of the front is concentrated between recirculation cells which are generated as a result of symmetric instabilities in the boundary layer flow index terms 4219 oceanography general continental shelf processes 4568 oceanography physical turbulence diffusion and mixing processes 4255 oceanography general numerical modeling 4279 oceanography general upwelling and convergences

structure of a midtropospheric vortex induced by a mesoscale convective system on 9 june 1988 a mesoscale 200 km diameter convectively generated vortex mcv passed through the colorado wind profiling network the generating convective system which was too small to meet maddox s mesoscale convective complex criteria developed beneath a high amplitude mid and upper level ridge axis profiler winds obtained within the stratiform region of the convective system and near the center of the ensuing mcv form the basis of this study with the addition of satellite including rapid scan images and conventional and doppler radar data this vortex was well observed over its entire life cycle the slowly moving vortex was observed by the flagler 50 mhz profiler for more than 16 h for a portion of this period the circulation was quasi steady hence the spatial structure of the vortex was depicted by timeto space conversion of the profiler data the results show a strong coherent circulation with maximum tangential speeds greater than 16 m s21 at 6 km above mean sea level msl and at radii of 50 70 km corresponding relative vorticity was more than three times as large as the local coriolis parameter the long duration and the apparent dominance of vorticity over divergence suggest that the flow in the vortex was in a quasi balanced state hence the temperature perturbation necessary to support the tangential velocity distribution was computed assuming gradient balance in the radial direction the resulting estimated temperature structure showed a warm core with a magnitude of 2 38c at 7 3 km msl and a cold core below 6 3 km msl the associated potential vorticity pv structure at the vortex center consisted of a lens of high pv with a maximum at 6 3 km msl and relative minima above and below this height

global correlation of the early cambrian of south australia shelly fauna of the dailyatia odyssei zone a lack of well resolved biostratigraphic data has prevented robust regional and global correlation of lower cambrian successions from south australia a new early cambrian biostratigraphy based on data derived from 21 measured stratigraphic sections and drill cores 11 described herein reveals the abundance and diversity of shelly fauna from the arrowie basin and the value of early cambrian small shelly fossils ssf for biostratigraphic studies here we examine shelly fauna associated with the youngest of three recently established biozones the dailyatia odyssei taxon range zone hereafter d odyssei zone and their correlative potential the d odyssei zone features a diverse suite of tommotiids organophosphatic brachiopods bradoriid arthropods molluscs and phosphatic problematica this fauna permits strong correlation often at species level with other major early cambrian terranes particularly antarctica south china and laurentia and suggest a cambrian series 2 stages 3 4 age for the d odyssei zone bradoriids have proven to be useful biostratigraphic tools four new species and three new genera are described herein acutobalteus sinuosus gen et sp nov eozhexiella adnyamathanha gen et sp nov manawarra jonesi gen et sp nov and mongolitubulus descensus sp nov the description of eohadrotreta sp cf zhenbaensis represents the first occurrence of the acrotretoid brachiopod eohadrotreta from australia

numerical simulations of the postsunrise reorganization of a nocturnal mesoscale convective system during 13 june ihop_2002 abstracta convection permitting numerical model is used to simulate the postsunrise reorganization of a nocturnal mesoscale convective system mcs observed over western and central oklahoma on 13 june 2002 during the international h2o ihop 2002 field experiment the mcs reorganization consists of a transition from northwest southeast oriented convective rainbands near sunrise to a single northeast southwest ne sw oriented convective rainband with trailing stratiform precipitation later in the morning results indicate the importance of environmental preconditioning on mcs reorganization in particular the development of the ne sw rainband that redefines the mcs organization is facilitated by a similarly oriented zone of antecedent mesoscale upward motion which increases the depth of large water vapor mixing ratios this allows convective updrafts to be fed primarily by moist and conditionally unstable air from 1 to 2 5 km agl in the ne sw oriented rainband which lacks a surface cold pool during its

first report of the early cambrian stem group brachiopod mickwitzia from east gondwana abstract the first mickwitziid brachiopod mickwitzia sp from east gondwana is described from the lower cambrian ajax limestone mt scott range in south australia the shells are fragmentary but preserve sufficient details of morphology and micro structure to allow positive identification to genus the morphology of the dorsal valve apex and the extended cones on the internal surface indicate a close affinity with mickwitzia muralensis walcott 1913 from the early cambrian of british columbia but scarcity of material precludes detailed comparison this find extends the known range of the pivotal stem group brachiopod mickwitzia to east gondwana

early cambrian palaeogeography and the probable iberia siberia connection abstract the end of the proterozoic beginning of the cambrian is marked by some of the most dramatic events in the history of earth the fall of the ediacaran biota followed by the cambrian explosion of skeletonised bilaterians a pronounced shift in oceanic and atmospheric chemistry and rapid climatic change from snowball earth to greenhouse conditions all happened within a rather geologically short period of time these events took place against a background of the rearrangement of the prevailing supercontinent some authors view this as a sequence of individual supercontinents such as mesoproterozoic midgardia neoproterozoic rodinia and early cambrian pannotia assembled in the mesoproterozoic this supercontinent appears to have existed through the neoproterozoic into the early cambrian with periodic changes in configuration the final rearrangement took place during the precambrian cambrian transition with the cadomian and related phases of the pan african orogeny the distribution of early cambrian molluscs and other small shelly fossils ssf across all continents indicates a close geographic proximity of all major cratonic basins that is consistent with the continued existence of the supercontinent at that time subsequently rodinia experienced breakup that led to the amalgamation of gondwana separation of laurentia baltica siberia and some small terranes and the emergence of oceanic basins between them spreading oceanic basins caused a gradual geographic isolation of the faunal assemblages that were united during the vendian early cambrian

continental shelf baroclinic instability part ii oscillating wind forcing abstractcontinental shelf baroclinic instability energized by fluctuating alongshore winds is treated using idealized primitive equation numerical model experiments a spatially uniform alongshore wind sinusoidal in time alternately drives upwelling and downwelling and so creates highly variable but slowly increasing available potential energy for all of the 30 model runs conducted with a wide range of parameters varying coriolis parameter initial stratification bottom friction forcing period wind strength and bottom slope a baroclinic instability and subsequent eddy field develop model results and scalings show that the eddy kinetic energy increases with wind amplitude forcing period stratification and bottom slope the dominant alongshore length scale of the eddy field is essentially an internal rossby radius of deformation the resulting depth averaged alongshore flow field is dominated by the large scale periodic wind forcing while the cross shelf flow field is dominated by the edd

topographic rectification of tidal currents abstract the rectification of oscillatory tidal currents on the sloping sides of a low submarine bank is discussed using the moment method this method has been previously used in shear dispersion studies where it is used to analyze the advection diffusion equation in the present problem it is applied to the barotropic potential vorticity equation linearized about an oscillatory spatially uniform tidal velocity to apply the method it is necessary to assume that the topography produces only a small change in depth the method economically provides the most important qualitative properties e g transport location and width of the time averaged current these results are obtained without making an harmonic truncation they can then be used to assess the accuracy of the harmonic truncation approximation used by other authors it is shown that harmonic truncation correctly predicts the transport and location of the rectified current when the bank is low however if the width of the bank is much less tha

multiscale convective overturning in mesoscale convective systems reconciling observations simulations and theory abstract an analysis of how parameterized convection interacts with hydrostatic explicitly resolved precipitation processes to represent multiscale convective overturning in a mesoscale resolution numerical simulation is presented critically important ingredients of the successful simulation are identified and the degree to which simulations are consistent with observations and theoretical considerations is examined of particular concern is how convective parameterization routines reconcile the deep moist absolutely unstable structures that form in mesoscale convective systems it is found that these structures arise primarily from resolvable scale vertical motion and that the model responds to these structures not only by maintaining parameterized convection but also by developing a hydrostatic manifestation of convective overturning on its smallest resolvable horizontal scales the strongest and most distinctive mesoscale perturbations develop in regions where the mesoscale contribution to convectiv

structural characteristics of convective systems over south america related to cold frontal incursions abstract international satellite cloud climatology project isccp dx and microwave sensor data collected by the tropical rainfall measuring mission trmm are used to identify and describe structural characteristics of convective systems css over continental south america sa related to cold frontal incursions in a 3 yr period an austral wet season climatology for cs events of the three most important types of front tropical convection interaction is built by applying latitude time diagrams and a cloud tracking method to dx data type 1 is characterized by the penetration of a cold front over subtropical sa that interacts with convection and moves with it into lower tropical latitudes type 2 refers to amazon convection and its enhancement in a quasi stationary northwest southeast oriented band extending from the amazon to subtropical sa along with the passage of a cold front in the subtropics and characterizes the synoptic formation of the south atlantic convergence zone a quasi stationary cold fro

environment and early evolution of the 8 may 2009 derecho producing convective system abstractthis study documents the complex environment and early evolution of the remarkable derecho that traversed portions of the central united states on 8 may 2009 central to this study is the comparison of the 8 may 2009 derecho environment to that of other mesoscale convective systems mcss that occurred in the central united states during a similar time of year synoptic scale forcing was weak and thermodynamic instability was limited during the development of the initial convection but several mesoscale features of the environment appeared to contribute to initiation and upscale growth including a mountain wave a midlevel jet streak a weak midlevel vorticity maximum a denver cyclone and a region of upper tropospheric inertial instability the subsequent mcs developed in an environment with an unusually strong and deep low level jet llj which transported exceptionally high amounts of low level moisture northward very rapidly destabilized the lower troposphere and enhanced frontogenetica

surface cooling winds and eddies over the continental shelf abstractmodels show that surface cooling over a sloping continental shelf should give rise to baroclinic instability and thus tend toward gravitationally stable density stratification less is known about how alongshore winds affect this process so the role of surface momentum input is treated here by means of a sequence of idealized primitive equation numerical model calculations the effects of cooling rate wind amplitude and direction bottom slope bottom friction and rotation rate are all considered all model runs lead to instability and an eddy field while instability is not strongly affected by upwelling favorable alongshore winds wind driven downwelling substantially reduces eddy kinetic energy largely because the downwelling circulation plays a similar role to baroclinic instability by flattening isotherms and so reducing available potential energy not surprisingly cross shelf winds appear to have little effect analysis of the model runs leads to quantitative relations for the wind eff

a new lower cambrian shelly fossil biostratigraphy for south australia abstract definition of early cambrian chronostratigraphic boundaries is problematic with many subdivisions still awaiting ratification integrated multi proxy data from well resolved regional scale schemes are ultimately the key to resolving broader issues of global correlation within the cambrian in australia early cambrian biostratigraphy has been based predominantly on trilobites phosphatic shelly fauna have great potential as biostratigraphic tools especially in pre trilobitic strata because they are widespread and readily preserved but they have remained underutilised here we demonstrate their value in a new biostratigraphic scheme for the early cambrian of south australia using a diverse shelly fauna including tommotiids brachiopods molluscs and bradoriids biostratigraphic data are derived from ten measured stratigraphic sections across the arrowie basin targeting hawker group carbonates including the wilkawillina wirrapowie and ajax limestones and the mernmerna formation the stratigraphic ranges of shelly fossils are predictable and repeatable across the arrowie basin allowing three discrete shelly biozones to be identified spanning terreneuvian stage 2 to series 2 stages 3 4 the kulparina rostrata zone new and part of the overlying micrina etheridgei zone new are pre trilobitic predominantly terreneuvian the cambrian series 2 stage 3 dailyatia odyssei zone new features a very diverse shelly fauna and will be described in detail in a separate publication these zones provide robust means to correlate terreneuvian series 2 successions in neighbouring coeval basins in australia particularly the stansbury basin wider correlation is possible throughout east gondwana and especially with south china

the unusual early morning tornado in ciudad acuna coahuila mexico on 25 may 2015 abstractthis study analyzes the synoptic and mesoscale conditions present during initiation and intensification of the supercell thunderstorm that produced a tornado in ciudad acuna a community located in the state of coahuila mexico 10 km southwest of the u s border early morning convective activity first detected by radar at 0628 utc 25 may 2015 developed into an intense and well defined supercell thunderstorm that produced a tornado between approximately 1045 and 1130 utc hourly analyses from the rapid refresh model indicated an upslope component to surface flow in the region of convection initiation over the serranias del burro sdb along the storm s trajectory dewpoint temperatures increased from 15 to 22 c convective available potential energy increased from 1500 to near 4000 j kg 1 and convective inhibition changed from 150 j kg 1 at the time of convection initiation to near zero in ciudad acuna simulations from the weather research and forecasting model confirmed the sensitivity o

a 20 year climatology of nocturnal convection initiation over the central and southern great plains during the warm season abstracta nocturnal maximum in rainfall and thunderstorm activity over the central great plains has been widely documented but the mechanisms for the development of thunderstorms over that region at night are still not well understood elevated convection above a surface frontal boundary is one explanation but this study shows that many thunderstorms form at night without the presence of an elevated frontal inversion or nearby surface boundary this study documents convection initiation ci events at night over the central great plains from 1996 to 2015 during the months of april july storm characteristics such as storm type linear system orientation initiation time and location and others were documented once all of the cases were documented surface data were examined to locate any nearby surface boundaries the event s initiation location relative to these boundaries if a boundary existed was documented two main initiation locations relative to a surface boundary were identified on a surface

interactions between a developing mesoscale convective system and its environment part ii numerical simulation the 19 july 1993 mesoscale convective system mcs discussed in part i was simulated using the regional atmospheric modeling system rams the model was initialized with variable physiographic and atmospheric data with the goal of reproducing the convective system and its four dimensional environment four telescopically nested moving grids allowed for horizontal grid spacings down to 1 67 km on the cloud resolving grid comparisons with the analysis show that the propagation evolution and structure of this mcs were well simulated the simulation is used to further investigate the interactions between this mcs and its surrounding environment in part i the doppler derived winds indicated that upshear westward propagating gravity waves left uppertropospheric front to rear and midtropospheric rear to front flow perturbations in their wake a similar flow structure developed in the simulated mcs and unlike the doppler results the low frequency waves that produced it were resolved in the data in the simulation much of the convectively generated temperature and momentum perturbations propagated westward with the waves leaving a warm wake in the clear air trailing the system although the gravity waves traveled rearward the perturbation flow in their wake was not strong enough to reverse the upper tropospheric storm relative winds thus most of the anvil condensate advected ahead of the convective line as the mcs encountered the low level jet the midtropospheric upward mass flux increased but gravity wave motions became less detectable the upper tropospheric anvil pushed westward into the strong flow as the system expanded into a characteristically oval shape temperature and momentum perturbations propagated rearward along with the anvil in a disturbance that resembled an advective outflow unlike the gravity waves this disturbance became almost stationary with respect to the ground and it retained its continuity through the rest of the simulation vertical cross sections indicate that a large slab of convectively processed air had detrained into the upper troposphere prior to this event much of the warm temperature anomalies generated within the convective towers either remained in the updrafts or propagated outward with the gravity waves early on individual updrafts were relatively erect and although condensate did detrain eastward in the forward anvil the temperature anomalies did not propagate with it in contrast convective updrafts associated with the expanding oval anvil disturbance were more continuous and they tilted strongly westward with height

evolution of a quasi linear convective system sampled by phased array radar abstracton 2 april 2010 a quasi linear convective system qlcs moved eastward through oklahoma during the early morning hours wind damage in rush springs oklahoma approached enhanced fujita ef1 scale intensity and was likely associated with a mesovortex along the leading edge of the qlcs the evolution of the qlcs as it produced its first bow echo was captured by the national weather radar testbed phased array radar nwrt par in norman oklahoma the nwrt par is an s band radar with an electronically steered beam allowing for rapid volumetric updates 1 min and user defined scanning strategies the rapid temporal updates and dense vertical sampling of the par created a detailed depiction of the damaging wind mechanisms associated with the qlcs key features sampled by the par include microbursts an intensifying midlevel jet and rotation associated with the mesovortex in this work par data are analyzed and compared to data from nearby operational radars highlighting the advantages of using

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

nocturnal convective cloud formation under clear sky conditions at the eastern andes of south ecuador 1 the formation of nocturnal convective clouds at the eastern andes of south ecuador and the adjacent peruvian amazon basin was investigated in a numerical model study their formation is expected to be an interactive procedure of nocturnal downslope flows in the andean terrain which forms a concave drainage system in the target area satellite imagery were used for both the identification of a sample case with a nocturnal cold cloud appearance and for the verification of the simulated results the cloud patterns were distinguished on the basis of ir temperatures a comparison of the data demonstrated the occurrence of a cold cloud shield in the target area although the modeled cluster is significantly smaller further analysis of the development of the convective cells confirmed the assumed underlying processes a strong current in the lower atmosphere presumably a drainage flow was recognizable in association with strong moisture convergence using a cross section through the cluster their presence was confirmed on the basis of their characteristic features and the surface energy fluxes as the driving force for thermally induced downslope flows

continental shelf baroclinic instability part i relaxation from upwelling or downwelling abstractthere exists a good deal of indirect evidence from several locations around the world that there is a substantial eddy field over continental shelves these eddies appear to have typical swirl velocities of a few centimeters per second and have horizontal scales of perhaps 5 10 km these eddies are weak compared to typical wind driven alongshore flows but often seem to dominate middepth cross shelf flows the idea that motivates the present contribution is that the alongshore wind stress ultimately energizes these eddies by means of baroclinic instabilities even in cases where obvious intense fronts do not exist the proposed sequence is that alongshore winds over a stratified ocean cause upwelling or downwelling and the resulting horizontal density gradients are strong enough to fuel baroclinic instabilities of the requisite energy levels this idea is explored here by means of a sequence of idealized primitive equation numerical model studies each driven by a modest nearly steady alongs

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

orogenic convection in subtropical south america as seen by the trmm satellite abstractextreme orogenic convective storms in southeastern south america are divided into three categories storms with deep convective cores storms with wide convective cores and storms containing broad stratiform regions data from the tropical rainfall measuring mission satellite s precipitation radar show that storms with wide convective cores are the most frequent tending to originate near the sierra de cordoba range downslope flow at upper levels caps a nocturnally enhanced low level jet thus preventing convection from breaking out until the jet hits a steep slope of terrain such as the sierra de cordoba mountains or andean foothills so that the moist low level air is lifted enough to release the instability and overcome the cap this capping and triggering is similar to the way intense convection is released near the northwestern himalayas however the intense storms with wide convective cores over southeastern south america are unlike their himalayan counterparts in that they exhibit leadi

test of a convective wake parameterization in the single column version of ccm3 abstract a convective wake parameterization incorporated into the single column scm version of the ncar community climate model ccm3 is tested using observational data from 12 squall line cases to determine whether it can successfully reproduce convectively driven wakes in a global climate model the key spatial thermodynamic and kinematic properties of the modeled versus the observed wakes are examined as these features determine the effects of the wakes on surface fluxes and the initiation of convection effects that should be simulated correctly in general circulation models if deep convection and the resulting earth atmosphere energy exchanges are to be adequately represented results from these simulations indicate that while the scm convective wake scheme combination generally produced long lasting squall wake systems the wakes were often too shallow too warm and too moist these differences occurred despite the ability of ccm3 s standard cumulus parameterization to provide the wake scheme

mesoscale vertical motions near nocturnal convection initiation in pecan abstractradiosonde measurements from the plains elevated convection at night pecan 2015 field campaign are used to diagnose mesoscale vertical motions near nocturnal convection initiation ci these ci events occur in distinctly different environments including ones with 1 strong forcing for ascent associated with a synoptic cold front and midtropospheric short wave 2 nocturnal low level jets interacting with weaker quasi stationary fronts or 3 the absence of a surface front or boundary altogether radiosonde derived vertical motion profiles in each of these ci environments are characterized by low to midtropospheric ascent the representativeness of these vertical motion profiles is supported by distributions of corresponding mesoscale averages from model produced 0 6 h ensemble forecasts thermodynamic data from radiosondes are then analyzed along with selected model ensemble members to elucidate the role of the vertical motions on subsequent ci in a case with strong forcing for mesoscale asce

neoproterozoic to early cambrian small shelly fossil assemblages and a revised biostratigraphic correlation of the yangtze platform china abstract small shelly fossils ssfs occur widely on the yangtze platform and have great potential for biostratigraphic subdivision of pre trilobitic early cambrian strata based on the ssf record of the shallow water realm five biozones can be recognized for the meishucunian stage in ascending order the biozones are anabarites trisulcatus protohertzina anabarica assemblage zone paragloborilus subglobosus purella squamulosa assemblage zone watsonella crosbyi assemblage zone formerly heraultipegma yunnanensis zone poorly fossiliferous interzone sinosachites flabelliformis tannuolina zhangwentangi assemblage zone in addition one ssf biozone is recognized for the overlying qiongzhusian stage pelagiella subangulata taxon range zone the formerly used siphogonuchites triangularis paragloborilus subglobosus zone and heraultipegma yunnanensis zone are discussed and redefined approximately 80 species of ssfs were screened for their spatial and temporal distribution on the yangtze platform variations in lithofacies and biofacies can be recognized throughout the yangtze platform extending over an area of 2000 900 km in a deeper water shelf setting the first zone is represented by the protohertzina anabarica kaiyangites novilis assemblage zone while younger zones are not recognized in the southern region at the northern platform margin the qiongzhusian is represented by the ninella tarimensis cambroclavus fangxianensis assemblage zone and the rhombocorniculum cancellatum taxon range zone the southeastern shaanxi western hubei region followed a slightly different lithological and faunal development than the rest of yangtze platform indicating a stronger similarity with parts of east gondwana some taxa such as w crosbyi p subangulata r cancellatum microdictyon effusum a trisulcatus protohertzina unguliformis and p anabarica occur nearly worldwide and support an international correlation of early cambrian sequences between the yangtze platform and smaller west gondwanan blocks siberia newfoundland and australia the six investigated zones of the yangtze platform comprise an interval spanning the early nemakit daldynian to the late atdabanian early botoman stage on the siberian platform palaeobiogeographic analysis revealed a strong taxic similarity between the yangtze platform and the tarim platform a smaller number of species are shared with other west gondwanan platform fragments such as india and iran palaeobiogeographic results do not support the previously reported position of the south china block between australia and siberia during the early cambrian

longshore coherence of currents on the southern california shelf during the summer abstract observations of horizontal currents and temperature made along a mid shelf isobath during the summer on the southern california shelf are used to determine longshore coherent length scales the observations are characterized by weak atmospheric forcing and strong density stratification of the water column for periods longer than a day coherent longshore length scales of currents are around 25 km while coherent length scales of temperature were longer than the instrumental array 57 5 km for periods ranging from a day to an hour near surface motions were dominated by diurnal fluctuations which were coherent over lengths of 5 km whereas near bottom motions dominated by semidiurnal fluctuations showed evidence of a signal propagating up coast at phase speeds of order 1 m s 1 the observed scales of motion in different frequency bands are used to estimate the dispersive properties of the shelf motions the dispersion coefficient is found to vary with scale as the current variance associated

ambient conditions associated with the maintenance and decay of quasi linear convective systems crossing the northeastern u s coast abstractquasi linear convective systems qlcss crossing the atlantic coastline over the northeastern united states were classified into three categories based on their evolution upon encountering the coast composite analyses show that convective lines that decay near the atlantic coast or slowly decay over the coastal waters are associated with 900 800 hpa frontogenesis with greater ambient 0 3 km vertical wind shear for the slowly decaying lines systems that maintain their intensity over the coastal ocean are associated with 900 hpa warm air advection but with little low level frontogenetical forcing neither sea surface temperature nor ambient instability was a clear delimiter between the three evolutions sustaining convective lines have the strongest environmental 0 3 km shear of the three types and this shear increases as these systems approach the coast in contrast the low level shear decreases as decaying and slowly decaying convective lines move toward the atlantic coastline there was als

long lived mesoconvective vortices and their environment part ii induced thermodynamic destabilization in idealized simulations abstract idealized numerical simulations are used to quantify the effect of quasi balanced lifting arising from the interaction of the ambient vertical shear with midtropospheric cyclonic vortices mcvs generated by mesoscale convective systems on thermodynamic destabilization over a range of ambient vertical shear strengths and vortex characteristics observed in part i maximum upward displacements occur beneath the midtropospheric potential vorticity anomaly near the radius of maximum tangential vortex winds the location of the region of upward displacements relative to the ambient vertical shear vector depends on the relative strength of the vortex tangential flow and the ambient vertical shear and ranges from downshear for vortices of moderate strength in strong ambient vertical shear to 90 to the left of downshear for strong vortices in weak ambient vertical shear although significant upward displacements occur most rapidly with small vortices in strong ambient vertical shear maximum upward di

potential vorticity generation by west african squall lines abstractthe west african summer monsoon features multiple complex interactions between african easterly waves aews moist convection variable land surface properties dust aerosols and the diu

rainfall occurrence in the u s warm season the diurnal cycle the diurnal occurrence of warm season rainfall over the u s mainland is examined particularly in light of forcings at multiple scales the analysis is based on a radar dataset of 12 seasons duration covering the u s mainland from the continental divide eastward the dataset resolves 2 km features at 15 min intervals thus providing a detailed view of both large and regional scale diurnal patterns as well as the statistics of events underlying these patterns the results confirm recent findings with respect to the role of propagating rainfall systems and the high frequency at which these are excited by sensible heating over elevated terrain between the rockies and the appalachians 60 of midsummer rainfall occurs in this manner most rainfall in the central united states is nocturnal and may be attributed to the following three main forcings 1 the passage of eastward propagating rainfall systems with origins near the continental divide at 105 w 2 a nocturnal reversal of the mountain plains solenoid which is associated with widespread ascent over the plains and 3 the transport of energetic air and moisture convergence by the great plains low level jet other features of interest include effects of the appalachians semidiurnal signals of regional significance and the impact of breezes along the gulf of mexico a modest effort was put forth to discern signals associated with el nino and the southern oscillation while tendencies in precipitation patterns are observed the record is too short to draw conclusions of general significance

multiscale evolution of a derecho producing mesoscale convective system abstract in this paper the authors address one type of severe weather strong straight line winds the case of a mesoscale convective system that developed in eastern colorado on 12 13 may 1985 was studied the system formed in the afternoon was active until early morning and caused strong winds during the night a multiscale nonhydrostatic full physics simulation was performed to formulate a conceptual model of the main airflow branches of the system and to gain understanding of the physical processes involved in the strong wind generation in this storm four telescopically nested grids covering from the synoptic scale down to cloud scale circulations were used a lagrangian model was employed to follow trajectories of parcels that took part in the updraft and downdraft and balances of forces were computed along the trajectories the strong nocturnal winds were caused by downdrafts reaching the surface and by a dynamically forced horizontal pressure gradient force the most important branch of the do

wave disturbances and their role in the maintenance structure and evolution of a mesoscale convection system abstractthis study investigates a nocturnal mesoscale convective system mcs observed during the plains elevated convection at night pecan field campaign a series of wavelike features were obse

serial upstream propagating mesoscale convective system events over southeastern south america abstract serial mesoscale convective system mcs events with lifetimes over 18 h and up to nearly 70 h are routinely observed over southeastern south america from infrared satellite imagery during the spring and summer these events begin over the southern la plata river basin with individual convective systems generally moving eastward with the cloud layer mean wind however an important and common subset of these serial mcs events shows individual mcss moving to the east or southeast yet the region of convective development as a whole shifts upstream to the north or northwest analyses of the composite mean environments from 10 of these upstream propagating serial mcs events using ncep ncar reanalysis data events indicates that the synoptic conditions resemble those found in mesoscale convective complex environments over the united states the serial mcs events form within an environment of strong low level warm advection and strong moisture advection between the surface and 700 hpa from the amazon

large scale meteorological conditions associated with midlatitude mesoscale convective complexes abstract objective analyses of composited meteorological conditions attending ten mesoscale couvective complexes mcc reveal a number of distinctive characteristics and important interactions with the large scale environment the systems appear to be linked to eastward progression of a weak middle tropospheric short wave trough initial thunderstorms develop within a region of mesoscale convergence and lifting that is apparently forced primarily by low level warm advection the mcc system acquires mesoscale organization while it moves eastward ahead of the short wave trough diabatic heating eventually produces a system that is warm core in the middle troposphere and cold core in upper levels the mature mcc exhibits many similarities to tropical convective systems although it occurs within a considerably different large scale setting inflow within the lower half of the troposphere feeds convection within a region characterized by significant net upward mass flux and widespread precipitation thickne

simulation of a progressive derecho using composite initial conditions abstract this study focuses on the progressive derecho a widespread convectively induced windstorm produced by a mesoscale convective system that often occurs within a relatively benign synoptic scale environment sounding data from 12 progressive derechos which occurred in weakly forced large scale environments are composited in order to examine important large scale features in the preconvective environment this analysis captures many features that are common in warm season derecho environments such as an upper level wind maximum a relatively dry midtroposphere and low level warm advection initial and boundary conditions for the pennsylvania state university national center for atmospheric research fifth generation mesoscale model mm5 are created using this analysis a three dimensional horizontally nonhomogeneous explicitly resolved simulation of a progressive derecho is produced and compared to previous more idealized simulations of similar convective systems that have been used to expla

finite amplitude evolution of instabilities associated with the coastal upwelling front abstract a primitive equation model is used to study the finite amplitude evolution of instabilities associated with the coastal upwelling front simulations of increasing complexity are examined that represent idealizations of summer conditions off the oregon coast including cases with steady and with time variable wind in a domain with alongshore uniform bathymetry and with time variable wind in a domain with realistic oregon coast bathymetry the numerical results indicate that the fastest growing mode in this system has approximately an 8 10 km alongshore wavelength but that once the disturbances grow to finite amplitude the predominant alongfront scale increases rapidly because of nonlinear effects separation of the total kinetic energy into contributions from the alongshore average flow and perturbation about that average shows that the initial growth of the perturbation kinetic energy is due to potential energy conversion but transfer of energy from the kinetic energy of the alongshore average

balanced and unbalanced circulations in a primitive equation simulation of a midlatitude mcc part i the numerical simulation abstract a midlatitude mesoscale convective complex mcc which occurred over the central united states on 23 24 june 1985 was simulated using the regional atmospheric modeling system rams the multiply nested grid simulation agreed reasonably well with surface upper air and satellite observations and ground based radar plots the simulated mcc had a typical structure consisting of a leading line of vigorous convection and a trailing region of less intense stratiform rainfall several other characteristic mcc circulations were also simulated a divergent cold pool in the lower troposphere midlevel convergence coupled with a relatively cool descending rear inflow jet and relatively warm updraft structure and a cold divergent anticyclone in the tropopause region early in the mcc simulation a mesoscale convectively induced vortex mcv formed on the eastern edge of the convective line while frequently associated with mccs and other mesoscale convective systems mcss mcvs are more typically repo

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

submesoscale baroclinic instability in the bottom boundary layer abstractweakly stratified layers over sloping topography can support a submesoscale baroclinic instability mode a bottom boundary layer counterpart to surface mixed layer instabilities the instab

simulation of a serial upstream propagating mesoscale convective system event over southeastern south america using composite initial conditions abstract serial upstream propagating mesoscale convective system mcs events over southeastern south america are important contributors to the local hydrologic cycle as they can provide roughly half of the total monthly summer precipitation however the mechanisms of upstream propagation for these events have not been explored to remedy this situation a numerical simulation of the composite environmental conditions from 10 observed serial mcs events is conducted results indicate that the 3 day simulation from the composite yields a reasonable evolution of the large scale environment and produces a large region of organized convection in the warm sector over an extended period as seen in observations upstream propagation of the convective region is produced and is tied initially to the development and evolution of untrapped internal gravity waves however as convective downdrafts develop and begin to merge and form a surface cold pool in the simulation the cold pool and its interaction with the env

mesoscale ascent in nocturnal low level jets abstracta theory for gentle but persistent mesoscale ascent in the lower troposphere is developed in which the vertical motion arises as an inertia gravity wave response to the sudden decrease of t

convection initiation caused by heterogeneous low level jets over the great plains abstractobservations from three nights of the plains elevated convection at night pecan field campaign were used in conjunction with rapid refresh model forecasts to find the cause of north south

the response of simulated nocturnal convective systems to a developing low level jet some recent numerical experiments have examined the dynamics of initially surface based squall lines that encounter an increasingly stable boundary layer akin to what occurs with the onset of nocturnal cooling the present study builds on that work by investigating the added effect of a developing nocturnal low level jet llj on the convective scale dynamics of a simulated squall line the characteristics of the simulated llj atop a simulated stable boundary layer are based on past climatological studies of the llj in the central united states a variety of jet orientations are tested and sensitivities to jet height and the presence of lowlevel cooling are explored the primary impacts of adding the llj are that it alters the wind shear in the layers just above and below the jet and that it alters the magnitude of the storm relative inflow in the jet layer the changes to wind shear have an attendant impact on low level lifting in keeping with current theories for gust front lifting in squall lines the changes to the system relative inflow in turn impact total upward mass flux and precipitation output both are sensitive to the squall line relative orientation of the llj the variations in updraft intensity and system relative inflow are modulated by the progression of the lowlevel cooling which mimics the development of a nocturnal boundary layer while the system remains surfacebased the below jet shear has the largest impact on lifting whereas the above jet shear begins to play a larger role as the system becomes elevated similarly as the system becomes elevated larger changes to systemrelative inflow are observed because of the layer of potentially buoyant inflowing parcels becoming confined to the layer of the llj

interactions between a developing mesoscale convective system and its environment part i observational analysis this paper is the first in a two part series in which the interactions between a growing mesoscale convective system mcs and its surrounding environment are investigated the system studied here developed in northeastern colorado on 19 july 1993 and propagated into kansas as a long lived nocturnal mcs high resolution dual doppler and surface mesonet data collected from this system are discussed in part i while the results of a numerical simulation are discussed in part ii the observations show that organized mesoscale surface pressure and flow features appeared very early in the lifetime of this system long before the development of any trailing stratiform precipitation most of the stratiform anvil advected ahead of the convective line in the strong upper tropospheric westerlies in accordance with this most of the mid and upper tropospheric storm relative flow behind the line remained westerly or rear to front despite the westerlies the strongest flow perturbations with respect to the ambient winds developed to the rear of the line the structure of these perturbations was similar to the upper tropospheric front to rear and midtropospheric rear to front flows typically found in more mature leading line trailing stratiform systems the presence of these perturbations on the upwind side of the convective line indicates that gravity wave propagation was primarily responsible for their development

observations of elevated convection initiation leading to a surface based squall line during 13 june ihop_2002 abstract the evolution of a mesoscale convective system mcs observed during the international h2o project that took place on the great plains of the united states is described the mcs formed at night in a frontal zone with four initiation episodes occurring between approximately 0000 and 0400 local time radar radiosonde and surface data together show that at least three of the initiation episodes were elevated occurring from moist conditionally unstable layers located above the boundary layer which had been stabilized by previous mcss initiation occurred in northwest southeast oriented lines where a southerly nocturnal low level jet terminated generating elevated convergence one initiation episode was observed using the s band dual polarization doppler radar s pol and occurred at the intersection of this convergence zone with a propagating wave calculations of the scorer parameter were consistent with wave trapping downdrafts from the developing convection generated both waves and bores w

first occurrence of a new ocruranus like helcionelloid mollusc from the lower cambrian of east gondwana a new cap shaped mollusc emargimantus angulatus gen et sp nov is described from the arrowie basin of south australia the new species is closely comparable to mollusc species from south china and north east greenland previously described under the generic name ocruranus liu a genus recently reinterpreted as a multiplated possibly polyplacophoran mollusc emargimantus is interpreted as a univalved helcionelloid mollusc and differs from ocruranus in both morphology and function e angulatus represents the first discovery of ocruranus like helcionelloids in the lower cambrian of eastern gondwana and demonstrates that these molluscs had a global distribution during the early cambrian

synoptic conditions associated with propagating and nonpropagating cloud rainfall episodes during the warm season over the east asian continent abstractusing european centre for medium range weather forecasts ecmwf analyses this study identifies common synoptic flow patterns associated with propagating long lived and nonpropagating short lived precipitation cloud episodes in the warm season over east asia 25 40 n 95 125 e among 123 initial cases during may july 1997 2003 86 were classified into three categories propagating cases with strong and weak forcing and nonpropagating ones with strong inhibition consisting of 10 types based on their 500 hpa flow patterns for each type composites at various levels when episodes moved across 100 105 110 115 and 120 e were made and discussed to elucidate the influence of synoptic conditions for propagating episodes with strong 500 hpa forcing 46 cases four types were identified in their composites favorable positive vorticity advection forcing from an approaching trough short wave exists aloft and concurrent development of southwest vortex and front wind shift line at low lev

an integrated view of the 1987 australian monsoon and its mesoscale convective systems i horizontal structure this observational study is organized around three issues the forcing of the monsoon flow by embedded deep convection the thermodynamic conditions that support the convection and the structures of the mesoscale convective systems mcss that constitute much of the deep convection the monsoon convective cloudiness occurred predominantly offshore over the earth s warmest waters week long periods of widespread deep convection caused cycles of monsoon spin up culminating in tropical cyclone formation momentum transports by the convection also created smaller scale vortex pairs in the upper troposphere sounding data suggest that the convection was modulated by low level processes not by large scale deep forced ascent triggering by mesoscale boundary layer cold pool boundaries and coastlines determined specifically where convection occurred while several positive feedbacks acted to keep regional thermodynamic conditions favourable hence monsoon convection once initiated persisted as self exciting superclusters composed at any instant of many distinct mcss the observed mcss all contained areas of deep convection and stratiform precipitation areas stratiform precipitation usually evolved in place from convective cells although precipitation also occasionally fell from overhanging anvils created by upper level shear the mcss within similar synoptic wind environments tended to have similar mesoscale structures this fact reflects the effects illustrated herein of environmental winds upon the relative motions of cold pools which trigger new convective cells and stratiform precipitation areas which evolve from old convective cells

organizational modes of midlatitude mesoscale convective systems this paper discusses common modes of mesoscale convective organization using 2 km national composite reflectivity data the authors investigated linear mesoscale convective systems mcss that occurred in the central united states during may 1996 and may 1997 based upon the radar observed characteristics of 88 linear mcss the authors propose a new taxonomy comprising convective lines with trailing ts leading ls and parallel ps stratiform precipitation while the ts archetype was found to be the dominant mode of linear mcs organization the ls and ps archetypes composed nearly 40 of the studied population in this paper the authors document the characteristics of each linear mcs class and use operational surface and upper air data to describe their different environments in particular wind profiler data reveal that the stratiform precipitation arrangement associated with each class was roughly consistent with the advection of hydrometeors implied by the mean middle and upper tropospheric storm relative winds which were significantly different among the three mcs modes case study examples are presented for both the ls and ps classes which have received relatively little attention to this point as well the authors give a general overview of the synoptic scale meteorology accompanying linear mcss in this study which was generally similar to that observed by previous investigators

simulations of an observed elevated mesoscale convective system over southern england during csip iop 3 simulations of an elevated mesoscale convective system mcs observed over southern england during the convective storm initiation project csip provide the first detailed modelling study of a case of elevated convection occurring in the uk the study shows that many factors can influence the maintenance of elevated deep convection from large scale flow through to surface heating processes and diabatic cooling within the convective system it is also shown that interactions and feedback mechanisms between a stable layer and the storm can act to maintain deep convection the simulation successfully reproduced an elevated mcs above a low level stable undercurrent with a wave in the undercurrent linked to a rear inflow jet rij convection was fed from an elevated 840 hpa source layer with cape of about 350 j kg 1 the undercurrent in the simulation was approximately 1 km deep about half that observed unlike the observed mcs a transition from elevated to surface based convection occurred in the simulation due to the combined effects of a pre existing large scale e gradient advection and surface heating causing the system to encounter increasingly unstable low level air and a shallower stable layer that was more susceptible to penetration by downdraughts the transition to surface based convection was accompanied by the development of cold pool outflow and an increase in system velocity from about 6 to 10 m s 1 diabatic cooling from microphysical processes in the simulation enhanced the undercurrent and strengthened the rij this strengthened the wave in the undercurrent and led to more extensive convection the existence of a positive feedback process between the convection rij and stable layer is discussed uncertainty in the synoptic scale generating errors in the undercurrent is shown to be a major source of error for convective scale forecasts

views on applying rkw theory an illustration using the 8 may 2009 derecho producing convective system abstractthis work presents an analysis of the vertical wind shear during the early stages of the remarkable 8 may 2009 central u s derecho producing convective system comments on applying rotunno klemp weisman rkw theory to mesoscale convective systems mcss of this type also are provided during the formative stages of the mcs the near surface based shear vectors ahead of the leading convective line varied with time location and depth but the line normal component of the shear in any layer below 3 km ahead of where the strong bow echo developed was relatively small 6 9 m s 1 concurrently the midlevel 3 6 km line normal shear component had magnitudes mostly 10 m s 1 throughout in a previous companion paper it was hypothesized that an unusually strong and expansive low level jet led to dramatic changes in instability shear and forced ascent over mesoscale areas these mesoscale effects may have overwhelmed the interactions between the cold pool and low level shear that modulate system st

formation of long lived summertime mesoscale vortices over central east china semi idealized simulations based on a 14 year vortex statistic abstractregions around dabie mountain dbm in the yangtze river basin yrb are the source of a mesoscale vortex the dabie vortex dbv based on a 14 yr statistical study 11 long lived heavy rain producing dbvs were composited for convection permitting semi idealized simulations a control simulation initialized 12 h before the composite vortex formation successfully reproduced a dbv with all the salient characteristics of the 11 events sensitivity experiments were designed to understand the impacts of large scale environmental conditions regional topography and latent heating on dbv formation the main results were as follows i supposition of a 500 hpa shortwave trough with an east west oriented lower level transversal trough around the dbm is crucial for the formation of vortices a nocturnal lower level jet on the southern side of the transversal trough accelerates dbv formation by enhancing convergence triggering sustaining convection and producing cyclonic vorticity ii during the si

a satellite based climatology of central and southeastern u s mesoscale convective systems abstracta satellite based climatology is presented of 9607 mesoscale convective systems mcss that occurred over the central and southeastern united states from 1996 2017 this climatology is cons

satellite and radar survey of mesoscale convective system development abstract an investigation of several hundred mesoscale convective systems mcss during the warm seasons april august of 1996 98 is presented circular and elongated mcss on both the large and small scales were classified and analyzed in this study using satellite and radar data the satellite classification scheme used for this study includes two previously defined categories and two new categories mesoscale convective complexes mccs persistent elongated convective systems pecss meso circular convective systems m ccss and meso elongated convective systems m ecss around two thirds of the mcss in the study fell into the larger satellite defined categories mccs and pecss these larger systems produced more severe weather generated much more precipitation and reached a peak frequency earlier in the convective season than the smaller meso systems overall pecss were found to be the dominant satellite defined mcs as they were the largest most common most severe and most prolific

coastal upwelling in the california current system abstract coastal upwelling in the california current system has been the subject of large scale studies off california and baja california and of small scale studies off oregon recent studies of the winds along the entire coast from 25 n to 50 n indicate that there are significant along shore variations in the strength of coastal upwelling which are reflected in the observed temperature distribution active upwelling appears to be restricted to a narrow coastal band about 10 25 km wide along the entire coast but the region influenced by coastal upwelling may be much wider intensive observations of the upwelling zone during summer off oregon show the presence of a southward coastal jet at the surface a mean vertical shear a poleward undercurrent along the bottom and persistently sloping isopycnals over the continental shelf most of the upwelling there occurs during relatively short periods several days long of upwelling favorable winds during the upwelling season off oregon the offshore ekman transport is carried by the surface ekman layer and the onshore return flow occurs through a quasi geostrophic interior it is not known whether the structure and dynamics observed off oregon are typical of the upwelling zone along the entire coast though some of the same features have been observed off baja california current and future research will eventually show whether the oregon results are also applicable in the region of persistently strong upwelling favorable winds off northern california and in the region of complex bathymetry off central and southern california

subseasonal variations in warm season moisture transport and precipitation over the central and eastern united states abstract subseasonal variations in warm season may august precipitation over the central and eastern united states are shown to be strongly linked to variations in the moisture entering the continent from the gulf of mexico within a longitudinally confined channel referred to here as the texas corridor or tc these variations reflect the development of low level southerly wind maxima or jets on a number of different timescales in association with distinct subcontinental and larger scale phenomena on the diurnal timescale the tc moisture flux variations are tied to the development of the great plains low level jet the composite nighttime anomalies are characterized by a strong southerly moisture flux covering northeast mexico and the southern great plains and enhanced boundary layer convergence and precipitation over much of the upper great plains the strongest jets tend to be associated with an anomalous surface low over the great plains reflecting a predilection for periods when midlatitude

response of simulated squall lines to low level cooling abstract organized convection has long been recognized to have a nocturnal maximum over the central united states the present study uses idealized numerical simulations to investigate the mechanisms for the maintenance propagation and evolution of nocturnal like convective systems as a litmus test for the basic governing dynamics the experiments use horizontally homogeneous initial conditions i e they include neither fronts nor low level jet streams the simulated storms are allowed to mature as surface based convective systems before the boundary layer is cooled in this case it is then surprisingly difficult to cut the mature convective systems off from their source of near surface inflow parcels even when 10 k of the low level cooling has been applied the preexisting system cold pool is sufficient to lift boundary layer parcels to their levels of free convection the present results suggest that many of the nocturnal convective systems that were previously thought to be elevated may actually

the importance of lateral variability on exchange across the inner shelf south of martha s vineyard ma this study examines the spatial variability of transport within the inner shelf south of martha s vineyard massachusetts its time and space dependence and its importance to the total volume exchanged between the nearshore and the coastal ocean the exchange of water across the inner shelf is often considered to be driven primarily by wind forcing yet the effects of small scale o 1 10 km variability on the total exchange have not been well quantified using a combination of high resolution hf radar based surface currents and a dense array of moorings to document the lateral variability of across shelf exchange the cumulative wind driven across shelf transport over the summer stratified period was less than the volume of the inner shelf onshore of the 25 m isobath along shelf variations in the wind driven exchange were as large as the spatial mean of the wind driven exchange a spatially varying time averaged circulation caused by tidal rectification resulted in across shelf exchange larger in magnitude than and independent of the integrated wind forced exchange coherent submesoscale eddies also occurred frequently within the domain due to flow topography effects onshore and horizontal density gradients offshore generally with lifespans shorter than 10 h diameters smaller than 6 km and vertical depths shallower than 10 m the across shelf volume transport due to eddies estimated by seeding particles within the surface current fields was more than half the wind driven depth dependent exchange thus accounting for the potential coherent along shelf variability present over the inner shelf can significantly increase estimates of the across shelf transfer of water masses and particles

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

clarifying the baroclinic contribution to the great plains low level jet frequency maximum abstractthe frequency and intensity of the great plains nocturnal low level jet llj are enhanced by baroclinicity over the sloped terrain of the region a classical description of baroclinic indu

the structure evolution and dynamics of a nocturnal convective system simulated using the wrf arw model abstractprevious studies have documented a nocturnal maximum in thunderstorm frequency during the summer across the central united states forecast skill for these systems remains relatively low and the explanation for this nocturnal maximum is still an area of active debate this study utilized the wrf arw model to simulate a nocturnal mesoscale convective system that occurred over the southern great plains on 3 4 june 2013 a low level jet transported a narrow corridor of air above the nocturnal boundary layer with convective instability that exceeded what was observed in the daytime boundary layer the storm was elevated and associated with bores that assisted in the maintenance of the system three dimensional variations in the system s structure were found along the cold pool which were examined using convective system dynamics and wave theory shallow lifting occurred on the southern flank of the storm conversely the southeastern flank had deep lifting with favorable integrated vertical shear ov

convection permitting simulations of the environment supporting widespread turbulence within the upper level outflow of a mesoscale convective system abstract widespread moderate turbulence was recorded on three specially equipped commercial airline flights over northern kansas near the northern edge of the extensive cirrus anvil of a nocturnal mesoscale convective system mcs on 17 june 2005 a noteworthy aspect of the turbulence was its location several hundred kilometers from the active deep convection i e large reflectivity regions of the mcs herein the mcs life cycle and the turbulence environment in its upper level outflow are studied using rapid update cycle ruc analyses and cloud permitting simulations with the weather research and forecast model wrf it is demonstrated that strong vertical shear beneath the mcs outflow jet is critical to providing an environment that could support dynamic e g shearing type instabilities conducive to turbulence comparison of a control simulation to one in which the temperature tendency due to latent heating was eliminated indicates that strong vertical shear and corresponding reductions in the l

mesoscale convective systems over southeastern south america and their relationship with the south american low level jet abstract prior studies have shown that the low level jet is a recurrent characteristic of the environment during the initiation and mature stages of mesoscale convective systems mcss over the great plains of the united states the south american low level jet sallj over southeastern south america sesa has an analogous role advecting heat and moisture from the amazon basin southward into the central plains of southeastern south america generating ideal environmental conditions for convection initiation and growth into mcss this research has two purposes one is to describe the characteristics of a 3 yr mcs sample in south america south of the equator and its related geographical distribution of convection frequency the other is to advance the knowledge of the evolution of favorable environmental conditions for the development of large mcss specifically those that mature under sallj conditions high horizontal and temporal resolution satellite images are used to detect mcss in the area for the

the operculum and mode of life of the lower cambrian hyolith cupitheca from south australia and north china the operculum of the problematic tubular fossil cupitheca holocyclata bengtson in bengtson et al 1990 is described for the first time based on collections from south australia and north china the phosphatized sub circular operculum exhibits well defined cardinal processes and a narrow cardinal shield unequivocally demonstrating that cupitheca is a hyolith probably an orthothecid c holocyclata has an almost global distribution in cambrian stages 3 4 the apical structure of the operculum is an elevated disc shaped platform with a concave base and a marginal rim that could represent the scar of a specialized larval attachment structure perhaps anchoring the larval hyolith to a sediment grain algae or other benthic substrate cupitheca probably had a pelagic larval stage and settled on the seafloor by attachment of the apical disc to suitable substrates before developing a free living benthic adult lifestyle this contrasting mode of life compared to other hyolith genera suggests that the group had already evolved a range of distinct lifestyles in the cambrian providing significant clues into their ecology and distribution

a modeling study of eulerian and lagrangian aspects of shelf circulation off duck north carolina the effects of wind forced upwelling and downwelling on the continental shelf off duck north carolina are studied through experiments with a two dimensional numerical primitive equation model moored and shipboard measurements obtained during august november 1994 as part of the coastal ocean processes coop inner shelf study iss are used for model data comparisons the model is initialized with realistic stratification and forced with observed wind and heat flux data both strongly stratified and weakly stratified conditions found during august and october respectively are studied august is characterized by fluctuating alongshelf wind direction and october is dominated by downwelling favorable winds the across shelf momentum balance is primarily geostrophic on the continental shelf the alongshelf momentum balance is mainly between the coriolis force and vertical diffusion with additional contributions from the local acceleration and nonlinear advection terms the model solutions are utilized to acquire detailed information on the time and space dependent variability of the across shelf circulation and transport and to investigate the dependence of this circulation on the seasonal change in stratification when the stratification breaks down as in october the across shelf transport is reduced significantly in comparison with the theoretical ekman transport for large wind stress values the paths of individual model water parcels are traced using two methods calculation of lagrangian trajectories and time evolution of three lagrangian label fields the august period produces complex lagrangian dynamics because of the switching between upwelling and downwelling winds the october period illustrates a mean downwelling response that advects parcels across and along the shelf and vertically

mechanisms supporting long lived episodes of propagating nocturnal convection within a 7 day wrf model simulation abstract a large domain explicit convection simulation is used to investigate the life cycle of nocturnal convection for a one week period of successive zonally propagating heavy precipitation episodes occurring over the central united states similar to climatological studies of phase coherent warm season convection the longest lived precipitation episodes initiate during the late afternoon over the western great plains 105 100 w reach their greatest intensity at night over the central great plains 100 95 w and typically weaken around or slightly after sunrise over the midwest 95 85 w the longest lived episodes exhibit average zonal phase speeds of 20 m s 1 consistent with radar observations during the period composite analysis of the life cycle of five long lived nocturnal precipitation episodes indicates that convection both develops and then propagates eastward along an east west oriented lower tropospheric frontal zone an elevated 2 km deep layer of high e air helps sustain convect

a 1d theoretical analysis of northerly low level jets over the great plains abstractthe forcing of northerly low level jets over the eastward sloped terrain of the u s great plains was studied using a one dimensional 1d nonstationary analytical model based on the boussinesq approximated equations of motion and thermal energy for northerly low level jets the forcing from diurnal changes in surface heating of the sloped terrain holton mechanism is out of phase with the nocturnal inertial oscillation resulting from the cessation of turbulent mixing at sunset blackadar mechanism which results in weaker northerly nocturnal low level jets when compared to southerly nocturnal low levels jets with the same magnitude background pressure gradient forcing because of the blackadar and holton mechanisms acting out of phase nocturnal northerly low level jets cannot solely explain the northerly low level jet maximum over the great plains found in climatological studies it is shown that negative buoyancy values over the eastward sloped terrain enhance the low level northerly geostro

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

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

objective categorization of heavy rain producing mcs synoptic types by rotated principal component analysis abstractin this research rotated principal component analysis was applied to the atmospheric fields associated with a large sample of heavy rain producing mesoscale convective systems mcss cluster analysis in the subspace defined by the leading two resulting principal components revealed two subtypes with distinct synoptic and mesoscale characteristics which are referred to as warm season type and synoptic type events respectively subsequent composite analysis showed that both subtypes typically occurred on the cool side of a quasi stationary low level frontal boundary within a region of locally maximized low level convergence and warm advection synoptic type events which tended to exhibit greater horizontal extent than warm season type events typically occurred downstream of a progressive upper level trough along a low level potential temperature gradient with the warmest air to the south and southeast warm season type events on the other hand occurred within the right entrance region of

environmental distinctions between cellular and slabular convective lines abstract the organizational mode of quasi linear convective systems often falls within a spectrum of modes described by a line of discrete cells on one end cellular and an unbroken two dimensional swath of ascent on the other slabular convective events exhibiting distinctly cellular or slabular characteristics over the continental united states were compiled and composite soundings of the respective inflow environments were constructed the most notable difference between the environments of slabs and cells occurred in the wind profiles lines organized as slabs existed in much stronger low level line relative inflow and stronger low level shear a compressible model with high resolution x 500 m was used to investigate the effects of varying environmental conditions on the nature of the convective overturning the numerical results show that highly cellular convective lines are favored when the environmental conditions and initiation procedure allow the convectively generated cold pools to

seven doppler radar and in situ analysis of the 25 26 june 2015 kansas mcs during pecan abstractthis case study analyzes a nocturnal mesoscale convective system mcs that was observed on 25 26 june 2015 in northeastern kansas during the plains elevated convection at night pecan pro

is midlatitude convection an active or a passive player in producing global circulation patterns abstract the ability of persistent midlatitude convective regions to influence hemispheric circulation patterns during the northern hemisphere summer is investigated global rainfall data over a 15 yr period indicate anomalously large july total rainfalls occurred over mesoscale sized midlatitude regions of north america and or southeast asia during the years of 1987 1991 1992 and 1993 the anomalous 200 hpa vorticity patterns for these same years are suggestive of rossby wave trains emanating from the regions of anomalous rainfall in the midlatitudes results from an analysis of an 11 yr mean monthly 200 hpa july wind field indicate that in the climatological mean rossby waveguides are present that could assist in developing a large scale response from mesoscale sized regions of persistent convection in the midlatitudes this hypothesis is tested using a barotropic model linearized about the 200 hpa july time mean flow and forced by the observed divergence anomalies the model results are in qualit

mesoscale circulation growth under conditions of weak inertial instability abstract the hypothesis that inertial instability plays a role in the upscale development of mesoscale convective systems mcss is explored by sampling environments that supported the growth of mcss in the preliminary regional experiment for storm stormscale operational and research meteorology pre storm network with high quality special soundings secondary circulations that occurred in the presence of inertial instabilities were analyzed and documented using rawinsonde data with high spatial and temporal resolution from the pre storm field program additional examples of mcs environments were examined using data from the mesoscale analysis and prediction system results show strong divergence and cross stream accelerations occurred at upper tropospheric levels where inertial instabilities were present these accelerations were not uniform over the domain but were focused in the regions of instability also the analyses of these data showed that regions of inertial instability may be more commonpla

vortex structure and evolution within bow echoes part i single doppler and damage analysis of the 29 june 1998 derecho abstract single doppler radar along with damage observations are examined to investigate the structural evolution of vortices observed within the 29 june 1998 derecho event that propagated through southeastern iowa into central and eastern illinois a total of 13 meso scale vortices observed primarily at low levels 0 3 km agl along the leading edge of the convective system were detected by the weather surveillance radar 1988 doppler wsr 88d radars at davenport iowa and lincoln illinois all but one of the vortices formed after the system evolved into a bow echo ten of the vortices formed north of the apex while three formed south of the apex seven of the vortices produced tornadoes that created f0 f1 surface damage none of the vortices exhibited appreciable upscale growth careful analysis of the radar data suggests that it may be possible to discern between the tornadic and nontornadic vortices the tornadic vortices tended to be stronger longer lived and deeper than their nontornadic count

effects of quasi stationary large scale anomalies on some mesoscale features associated with the 1993 flood a regional model simulation we investigate the effect of quasi stationary large scale anomalies on mesoscale factors contributing to the 1993 u s midwest flood by performing 30 day simulations with a mesoscale model the contributions of anomalous mesoscale features to the flood were quantified by contrasting model integrations forced by initial and lateral boundary conditions with and without large scale anomalous stationary waves that are believed to have been responsible for the flood supplementing previous investigations the present study finds the following 1 the large scale anomalies produced environmental conditions that favored a generation of mcc like systems rather than individual convective cells or squall lines that would have produced less precipitation over large areas ambient conditions favoring mesoscale convective complex mcc include an intensified east west orientation of quasistationary fronts weaker upper tropospheric inertial stability and a strong low level jet llj 2 the anomalous ageostrophic wind component to the far south of the flood region texas area and geostrophic wind component over the flood region bridged together to form an extended moisture conveyer that sustained the long lasting 1993 flood

observations and simulation of elevated nocturnal convection initiation on 24 june 2015 during pecan abstractthe environment of elevated nocturnal deep convection initiation ci on 24 june 2015 is investigated using radiosonde data from the plains elevated convection at night pecan field experi

a unified theory for the great plains nocturnal low level jet abstracta theory is presented for the great plains low level jet in which the jet emerges in the sloping atmospheric boundary layer as the nocturnal phase of an oscillation arising from diurnal variations in turbulent diffusivity blackadar mechanism and surface buoyancy holton mechanism the governing equations are the equations of motion mass conservation and thermal energy for a stably stratified fluid in the boussinesq approximation attention is restricted to remote far above slope geostrophic winds that blow along the terrain isoheights southerly for the great plains diurnally periodic solutions are obtained analytically with diffusivities that vary as piecewise constant functions of time and slope buoyancies that vary as piecewise linear functions of time the solution is controlled by 11 parameters slope angle coriolis parameter free atmosphere brunt vaisala frequency free atmosphere geostrophic wind radiative damping parameter day and night diffusivities maximum and minimum surfa

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