early evolution of vertical vorticity in a numerically simulated idealized convective line the generation and organization of mesoscale convective vortices mcvs is a recurring theme in midlatitude and tropical meteorology during the warm season in this work a simulation of a finite length idealized convective line in a westerly shear environment is investigated in the absence of ambient vertical vorticity an asymmetry in average vertical vorticity forms rapidly at early times in the present simulation this study focuses on the formation and organization of vertical vorticity at these early simulation times previous simulations suggest that tilting of either ambient or storm generated horizontal vorticity is the primary mechanism responsible for the formation organization and maintenance of mcvs this study confirms recent work regarding the generation of vertical vorticity at early times in the simulation a lagrangian budget analysis of the vertical vorticity equation however shows that vorticity convergence becomes a comparable and at times dominant mechanism for the enhancement and long term organization of vertical vorticity early in the simulation despite differences in the initial ambient horizontal vorticity hodograph and convective available potential energy the lagrangian budget analysis in the present midlatitude case is consistent with the lagrangian budget results of a previous tropical squall line simulation the study of idealized convective lines in midlatitude environmental conditions therefore provide valuable insight into understanding vertical vorticity production in tropical squall lines and their potential relevance to tropical cyclogenesis

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

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

case studies of developing east pacific easterly waves this paper contains a study of developing east pacific easterly waves observed during the summer of 1991 with aircraft in situ and radar data and geosynchronous infrared satellite imagery the circulation and divergence profiles surface momentum and entropy fluxes as well as 700 mb and 975 mb saturated and actual equivalent potential temperatures were measured repeatedly for three disturbances that evolved into east pacific hurricanes as the disturbances develop the level of maximum updraught mass flux decreases which leads to increased convergence at low levels this process appears to be coupled to an increase in the mid level relative humidity which in turn suppresses the development of convective downdraughts comparison of the respective tendencies of convergence and surface friction to spin up and spin down a developing disturbance suggests that friction is unimportant in the early stages of development however as the surface circulation develops the two effects become comparable in magnitude if surface friction is deposited through a fairly deep layer of the troposphere the observations appear to rule out boundary layer ekman balance in these developing systems though more accurate observations of the eddy fluxes of absolute vorticity into such systems are needed to answer this question with certainty

major stages of rifting evolution in the earth s history abstract linear extensional rift and rift like structures have been generated many times during various periods of the earth s history since early times these structures have varied with time however in scale morphology formations paragenesis of tectonic features regularity of distribution and evolution i distinguish and consider five major stages of rifting they are katarchean archean early proterozoic late proterozoic paleozoic and mesozoic cenozoic linear structures of the oldest stage combine features of development and structure similar to those typical of the rift and geosynclinal zones in the later periods of the earth s history at the second stage proto rift and proto geosynclinal structures can be distinguished for the first time though differences are not distinct paleo rift zones of the third and fourth stages differ from geosynclinal belts and zones their structural and genetic evolution however is related to the development of the latter in contrast the distribution and evolution of the rift zones and belts during the fifth stage are connected mainly with the destruction of the continents and formation of the secondary oceanic basins they are complementary to the mesozoic cenozoic geosynclinal orogenic belts periods of the greatest development of rift and rift like structures in the archean riphean and mesozoic cenozoic probably correspond to the major phases of the earth s expansion which can be distinguished in its general pulsating evolution

mesoscale convective vortex formation in a weakly sheared moist neutral environment abstract idealized simulations of a diabatic rossby vortex drv in an initially moist neutral baroclinic environment are performed using the fifth generation national center for atmospheric research pennsylvania state university ncar psu mesoscale model mm5 the primary objective is to test the hypothesis that the formation and maintenance of midlatitude warm season mesoscale convective vortices mcvs are largely influenced by balanced flow dynamics associated with a vortex that interacts with weak vertical shear as a part of this objective the simulated drv is placed within the context of the bow echo and mesoscale convective vortex experiment bamex field campaign by comparing its tangential velocity radius of maximum winds cape and shear with the mcvs observed in bamex the simulations reveal two distinct scales of development at the larger scale the most rapidly growing moist baroclinic mode is excited and exponential growth of this mode occurs during the simulation embedded within the

high winds generated by bow echoes part i overview of the omaha bow echo 5 july 2003 storm during bamex abstract an analysis of a bow echo that produced damaging winds exceeding f1 in intensity on the fujita scale near omaha nebraska is shown part i of this study presents a combination of airborne doppler derived wind syntheses with a comprehensive damage survey in order to document the generation of strong winds at the surface a detailed kinematic analysis of the evolution of a quasi linear convective system into a bow shaped and subsequently a spearhead echo is shown for the first time it is hypothesized that a large cyclonic bookend vortex 70 80 km in diameter north of the bow apex enhanced the rear inflow jet and initiated the bowing process a hook shaped echo and mesovortex formed at the apex of a bowed segment of the convective line and was located to the north of the swath of strong damage rated greater than f1 in damage intensity the peak single doppler radial velocity recorded by the tail radar was 43 m s 1 in the low level outflow near the apex of the bow echo the regions of the str

the vertical structure of mesoscale convective vortices abstract simulations of two cases of developing mesoscale convective vortices mcvs are examined to determine the dynamics governing the origin and vertical structure of these features although one case evolves in strong vertical wind shear and the other evolves in modest shear the evolutions are remarkably similar in addition to the well known mesoscale convergence that spins up vorticity in the midtroposphere the generation of vorticity in the lower troposphere occurs along the convergent outflow boundary of the parent mesoscale convective system mcs lateral transport of this vorticity from the convective region back beneath the midtropospheric vorticity center is important for obtaining a deep column of cyclonic vorticity however this behavior would be only transient without a secondary phase of vorticity growth in the lower troposphere that results from a radical change in the divergence profile favoring lower tropospheric convergence following the decay of the nocturnal mcs subsequent con

case study of an intense african easterly wave abstract the life cycle of an intense african easterly wave aew over the african continent is examined using european centre for medium range weather forecasts ecmwf operational analyses meteosat satellite images and synoptic observations this system the strongest aew of 2000 can be tracked from central north africa into the eastern atlantic ocean where it is associated with the genesis of hurricane alberto synoptic analysis of the kinematic and thermodynamic fields is supplemented by analysis of potential vorticity pv allowing exploration at the role of multiple scales in the evolution of this aew the authors analysis promotes the division of the aew life cycle into three distinctive phases i initiation the aew development is preceded by a large convective event composed of several mesoscale convective systems over elevated terrain in sudan this convection provides a forcing on the baroclinically and barotropically unstable state that exists over tropical north africa ii baroclini

skolithos serratus in paleosols paleobiological paleoecological and paleobiogeographical insights abstract the ichnogenus skolithos is are recorded from continental to deep marine deposits and the simplicity of the burrows and the variety of potential burrowers make it challenging to identify a probable tracemaker and limit paleoenvironmental interpretations the paleosols of the triassic caturrita formation from southern brazil present non marine skolithos piperocks dominated by skolithos serratus with scratch marks arranged perpendicular to the axis of the tube on the inner wall of the burrow giving the burrow the shape of a screw the fossil finding provides crucial paleoenvironmental information about the texture and moisture conditions of the substrate and the producing organism the micromorphological analysis and characterization of the dominant burrows and paleosols of skolithos piperock allowed assignation to the ichnospecies skolithos serratus and attribution of this ichnotaxon to the activity of tiger beetles coleoptera carabidae cicindelidae which have morphological characters necessary to excavate a burrow with striated walls similar to a screw in response of the activity of the larva in the burrow throughout their life the burrows represent a multifunctional structure that serves simultaneously as a domicile and a hiding place from predation and feeding for the larvae pupa protection the predominance of s serratus in the skolithos piperock suggests a preference of the producers for exposed firm and predominantly sandy textured soils in little vegetated flood plains in a semiarid climate similar to modern inceptisols developed in desiccated overbank deposits of the scoyenia ichnofacies the presence of s serratus in the studied paleosols suggests that the southwest of gondwana has been a key center of diversification and dispersion of the subgenera cylindera and plectographa since the late triassic such center would include the geographic region bounded by the southern states of brazil northern argentina uruguay and eastern paraguay

the formation of a cooling induced mesovortex in the trailing stratiform region of a midlatitude squall line abstract there have been some ambiguities in recent observational studies as to whether midlevel mesovortices are induced by latent heating or cooling and develop in the descending or ascending portion of mesoscale convective systems mcs s in this study a comprehensive examination of a cooling induced mesovortex in the trailing stratiform region of a midlatitude squall line that occurred on 10 11 june 1985 during the preliminary regional experiment for storm central pre storm is presented using a 20 h high resolution simulation of the squall system this cooling induced midlevel vortex originates from the preexisting cyclonic vorticity associated with a traveling meso scale short wave the vortex is intensified in the descending rear to front rtf inflow as a result of continued sublimative melting and evaporative cooling in the stratiform region it decouples from the front to rear ftr ascending and anticyclonic flow in the upper troposphere during the formative stage the vortex tilts northw

the influence of convectively generated thermal forcing on the mesoscale circulation around squall lines abstract the dynamical processes that determine the kinematic and thermodynamic structure of the mesoscale region around 2d squall lines are examined using a series of numerical simulations the features that develop in a realistic reference simulation of a squall line with trailing stratiform precipitation are compared to the features generated by a steady thermal forcing in a dry simulation with no microphysical parameterization the thermal forcing in the dry simulation is a scaled and smoothed time average of the latent heat released and absorbed in and near the leading convective line in the reference simulation the mesoscale circulation in the dry simulation resembles the mesoscale circulation in the reference simulation and around real squall lines it includes an ascending front to rear flow a midlevel rear inflow a mesoscale up and downdraft an upper level rear to front flow ahead of the thermal forcing and an upper level cold anomaly to the rear of the thermal forcing it is also shown t

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

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

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

baroclinic transition of a long lived mesoscale convective vortex abstract the period 5 15 june 2003 during the field phase of the bow echo and mesoscale convective vortex mcv experiment bamex was noteworthy for the wide variety of mesoscale convective systems mcss that occurred of particular interest was a long lived mcv that formed in the trailing stratiform region of an mcs over west texas at 0600 utc 10 june this mcv was noteworthy for its i longevity as it can be tracked from 0600 utc 10 june to 1200 utc 14 june ii development of a surface cyclonic circulation and attendant 2 to 4 hpa sea level pressure perturbation iii ability to retrigger convection and produce widespread rains over several diurnal heating cycles and iv transition into a baroclinic surface cyclone with distinct frontal features baroclinic transition defined here as the acquisition of surface fronts occurred as the mcv interacted with a remnant cold front left behind by a predecessor extratropical cyclone over the great lakes region although the mcv developed well def

mesoscale convective vortices observed during bamex part i kinematic and thermodynamic structure abstract five cases of mesoscale convective vortices mcvs are described from observations collected during the bow echo and mcv experiment bamex over the central united states during the period from 20 may to 6 july 2003 in the present paper the kinematic and thermodynamic structure of each vortex and its environment are emphasized data consist of bamex dropsondes the national oceanic and atmospheric administration profiler network and national weather service soundings in addition weather surveillance radar 1988 doppler observations documented the signatures of nascent mcvs within nocturnal convection systems as well as the spatial pattern of convection within mcvs during the following day the vertical structure of each vortex was highly dependent on the vertical shear and the presence of upper tropospheric cyclonic vorticity anomalies in strong shear a pronounced downshear tilt of the vortex was evident but with the presence of an upper tropospheric trough the tilt was upshear in the upp

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

high winds generated by bow echoes part ii the relationship between the mesovortices and damaging straight line winds airborne radar analysis of a mesovortex that developed near the apex of a bow echo is presented the mesovortex was shown to play a critical role in determining the location of intense straight line wind damage at the surface the perturbation pressure gradient force in natural coordinates along the parcel path accelerated the horizontal winds however intense mesovortices modified the low level outflow and largely determined the locations where the strongest winds occurred regions of maximum winds are accounted for as a superposition of the vortex and the flow in which it is embedded the strongest winds occur on the side of the vortex where translation and rotation effects are in the same direction this model explains the observed tongue of high wind speeds that were confined to the periphery of the mesovortex the origin of the mesovortex is also examined similarities and differences of this bow echo event with recent modeling studies are presented

three dimensional evolution of simulated long lived squall lines abstract simulations of squall lines using nonhydrostatic convection resolving models have been limited to two dimensions or three dimensions with the assumption of along line periodicity the authors present 3d nonhydrostatic convection resolving simulations produced using an adaptive grid model where the lines are finite in length and the restriction to along line periodicity is removed the base state for the simulations is characterized by weak shallow shear and high convective available potential energy cape an environment in which longlived midlatitude mesoscale convective systems mcss are observed the simulated systems bear strong resemblance to many observed systems suggesting that large scale forcing absent in the horizontally homogeneous environment is not needed to produce many of the distinguishing features of midlatitude mcss in simulations without coriolis forcing the presence of line ends leads to mature symmetric systems characterized by a central region of strong convectio

evolution and structure of the 6 7 may 1985 mesoscale convective system and associated vortex abstract observations collected during the oklahoma kansas pre storm experiment are used to document the evolution and structure of the mesoscale convective system mcs that occurred on 6 7 may 1985 the storm began when a short squall line developed in an area of preexisting thunderstorm activity thunderstorm updrafts along the squall line lifted warm moist air with its southerly momentum to the upper troposphere a broad region of convective outflow and a meso scale updraft region with a mean vertical velocity in excess of 15 10 3 mb s 1 were created a stratiform rain area with an embedded mesovortex formed behind the squall line the vortex resided beneath the deepest upper level outflow the mesovortex altered the wind field and consequently became the principal organizational feature within the mcs a descending current from the storm s rear that depending on location extended from 1 km to the upper troposphere was intensified and focused by the vortex the descending rear inflow had a peak

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

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

the genesis of severe long lived bow echoes abstract a series of idealized simulations using a nonhydrostatic cloud model is used to investigate the genesis of bow echoes a bow shaped system of convective cells that is especially noted for producing long swaths of damaging surface winds it is hypothesized that severe long lived bow echoes represent a dynamically unique form of mesoconvective organization being produced for a restricted range of environmental conditions including a convective available potential energy cape of at least 2000 m2 s2 and vertical wind shears of at least 20 m s 1 over the lowest 2 5 5 km agl the key structural features include a 40 100 km long bow shaped segment of convective cells with a strong rear inflow jet extending to the leading edge of the bow at 2 3 km agl and cyclonic and anticyclonic eddies referred to as bookend vortices on the northern and southern flanks of the bowed segment respectively this structure characteristically develops three to four hours into the lifetime of a convective system a

an air sea interaction theory for tropical cyclones part ii evolutionary study using a nonhydrostatic axisymmetric numerical model abstract in part i of this study an analytical model for a steady state tropical cyclone is constructed on the assumption that boundary layer air parcels are conditionally neutral to displacements along the angular momentum surfaces of the hurricane vortex the reversible thermodynamics implied by this assumption allows the mature storm to be thought of as a simple carnot engine acquiring heat at the high temperature ocean surface and losing heat near the low temperature tropopause although the oceanic heat source is universally recognized as the sine qua non for the mature hurricane there is also wide acceptance of conditional instability of the second kind cisk which makes no specific reference to surface heat fluxes as the formative mechanism this ambivalence is seen in that all numerical simulation studies find it essential to have transfer from the ocean surface yet all start from a conditionally unstable atmosphere the hypothesis put forward in part i based on the steady state theory is t