a long lived mesoscale convective complex part i the mountain generated component abstract using data collected during colorado state university s south park area cumulus experiment in 1977 a sequence of multi scale convective events leading to the formation of a mesoscale convective complex is described in the first phase surface based cool advection in the elevated mountain basin delayed the full transition of the morning boundary layer into a deep mixed layer until well after convective instability was reached over the adjacent ridges the second phase was earmarked by the formation of convective precipitation echoes at hot spots over the high mountain terrain two groups of cells then propagated eastward across the mountain basin forming a line of discrete cells which moved across the foothills toward the high plains the cells further intensified at the foothills high plains interface and formed a still larger north south line of thunderstorms in the third phase this north south line of thunderstorms evolved into an expanding meso scale convective cluster as it contin

observational analysis of a gust front to bore to solitary wave transition within an evolving nocturnal boundary layer abstract the evolution of a gust front to bore to solitary wave transition and comprehensive information on the evolving nocturnal boundary layer nbl associated with this change are described with analysis of radar and profiler measurements the observations were obtained on 21 june 2002 in the oklahoma panhandle during the international h2o project the evolution of this system from a strong bore initiated by a vigorous gust front to a solitary wave was observed over a 4 h period with doppler radar and surface measurements detailed information on the mature bore structure was obtained by a cluster of profiling instruments including two boundary layer wind profilers a lidar ceilometer and a microwave profiling radiometer a strong bore was initiated by an extensive gust front that perturbed an incipient nbl whose development prior to sunset was enhanced by shading from the parent mesoscale convective system at the time of bore formation the nbl was about 300 m deep and exhibited a surface t

impact of soil moisture and convectively generated waves on the initiation of a west african mesoscale convective system a mesoscale convective system mcs case study was observed over northeast mali as part of the african monsoon multidisciplinary analysis amma on 31 july 2006 observations of this case suggest that the soil moisture heterogeneity and atmospheric gravity waves emitted from a parent mcs were important trigger mechanisms for this system this study uses high resolution met office unified model metum simulations to assess the importance of the synoptic circulation land surface and gravity waves in the initiation and development of the mcs during the early afternoon shallow convection developed over a region of dry soil within a synoptic scale convergence zone which was caused by the confluence of the southerly monsoon flow with winds associated with the circulation around the saharan heat low two pronounced waves were emitted from a nearby parent storm and propagated towards the convergence zone when the second wave reached the location of the shallow convection deep convection was immediately initiated further convective cells developed later in the afternoon over dry soil many adjacent to strong soil moisture gradients these aggregated with the main storm which later developed into the case study mcs a comparison of model simulations with without the soil moisture heterogeneity and gravity waves shows that the synoptic scale circulation and convergence zones specified by the atmospheric analysis were the most important factors for the successful simulation of the mcs if the location of the initiation of the system is to be forecast accurately the land surface that is the soil moisture must be represented adequately in order to reproduce the timing of the secondary initiation of convection correctly the model must be able to capture gravity waves that are emitted by existing systems

observations of a squall line and its near environment using high frequency rawinsonde launches during vortex2 abstract rawinsonde data were collected before and during passage of a squall line in oklahoma on 15 may 2009 during the second verification of the origins of rotation in tornadoes experiment vortex2 nine soundings were released within 3 h allowing for unprecedented analysis of the squall line s internal structure and nearby environment four soundings were released in the prestorm environment and they document the following features low level cooling associated with the reduction of solar isolation by a cirrus anvil abrupt warming 1 5 k in 30 min above the boundary layer which is probably attributable to a gravity wave increases in both low level and deep layer vertical wind shear within 100 km of the squall line and evidence of ascent extending at least 75 km ahead of the squall line the next sounding was released 5 km ahead of the squall line s gust front it documented a moist absolutely unstable layer within a 2 km deep layer of ascent with vertical air velocity of approximately 6 m s 1

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

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

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

the generation and propagation of a nocturnal squall line part i observations and implications for mesoscale predictability abstract the initiation and forcing of a squall line on 26 27 may 1985 near wichita kansas is examined the squall line is secondary convection in the sense that it is preceded in the diurnal cycle by other mesoscale convective systems the squall fine develops in synoptic conditions frequently associated with convective weather in the central united states this includes moderate shear moderate to high convective available potential energy a quasi stationary dryline a low level southerly jet and an 85 kpa moist tongue the initiation of free convection is specifically attributed to a gust front that propagates into a low level jet with attendant horizontal vorticity convergence and moisture the gust front initially propagates as a gravity current and subsequently as an internal undular bore observations of gravity currents gravity waves and the collision of radar echo boundaries provide valuable clues for short period forecasting they establish the presence of potential triggering mechanism

turbulent mixing processes in atmospheric bores and solitary waves deduced from profiling systems and numerical simulation abstract families of solitary waves solitons associated with two atmospheric bores on the same day were observed by an unprecedented number of ground based and airborne profiling systems during the international h2o project ihop in addition a very high resolution numerical weather prediction model initialized with real data was used with success to simulate one of the bores and the evolving soliton the predicted wave amplitude phase speed wavelength and structure compared well to these extraordinarily detailed observations the observations suggest that during the active phase when turbulent mixing was active which was prior to bore collapse the bores and waves vigorously mixed dry air from above a nocturnal boundary layer down to the surface refractivity computed from near surface radar observations showed pronounced decreases due to sudden drying during the passage of the bores in this phase but refractivity increases appeared during the period of bore collapse during both phases the

upstream influence of numerically simulated squall line storms summary the squall line s impact on its upstream environment is examined using traditional cloud and simplieed parametrized moisture models the study was motivated by the need to explain signie cant differences between the two dynamical frameworks in both the erst environmental response to the convection consists of a rapidly propagating gravity wave characterized by deep tropospheric subsidence this gravity wave accelerates the lowlevel storm ine ow in its wake with the largest effect seen near the surface in the more sophisticated model however this wave is eventually followed by a shorter vertical wavelength feature one possessing lower tropospheric ascent this second gravity wave absent from the simplieed model runs substantially alters the upstream environment yet again the gentle low level uplift establishes the cool moist tongue ofairthat has been found to stretch well ahead of the storm insimulations between thesecond wave and the main storm updraught the accelerated ineow is shifted from the ground to the middle troposphere where it helps to push dry air into the convecting region this subsequent environmental adjustment responds to the establishment of a small yet persistent area of weak cooling during the early mature phase located in the middle troposphere at the upstream edge of the main cloud mass this cooling is the combined effect of cloud water evaporation and the ascent of subsaturated air though the cooling that excites it is of relatively small magnitude 2 k this wave s effect is dramatic and signie cant a crude ex to the moisture parametrization served to establish a qualitatively similar tongue like feature in the simplie ed model simulations bringing the results from the two dynamical frameworks more into line

effect of solidification on a propagating dike 1 magma migration through the brittle crust from depth occurs by the propagation of hydraulic fractures or dikes volcanic eruptions occur at the last stage if and when a propagating dike reaches the surface dike propagation involves complex physics because of several processes that are simultaneously occurring such as viscous flow of magma rock fracture elastic deformation of the host rock and potentially large changes of the physical properties of the magma crystallization degassing solidification etc currently the most practical way in the field or in terms of field measurements to follow the migration of magma before it reaches the surface is the analysis of the seismicity generated nevertheless a physical model that quantitatively relates the flux of magma in the dike to the seismicity is lacking we present here laboratory experiments involving propagation of a fluid filled crack such that the fluid solidifies upon contact with the cold elastic host we show that this can lead to a way of estimating the flux of the injection as a function of the surface creation rate the latter is shown to be a more reliable gauge of magma flux than the upward propagating velocity in the geologic application of a propagating dike the rate of creation of surface area may be related to the rate of release of seismic energy although this latter relation needs further work to be quantitatively reliable our new model nevertheless indicates how a new general framework can be constructed

convectively generated gravity waves and their effect on the cloud environment this study uses a two dimensional cloud resolving model to examine how convectively generated gravity waves modify the environment of an isolated convective cloud the model is initialized with an idealized sounding and the cloud is initiated by adding a locally buoyant perturbation the modeled convection generates a spectrum of gravity waves with vertical wavelengths that are harmonics of the depth of the troposphere it is shown that the first three wave modes significantly modify the cloud environment the modification of the cloud environment is quantified in terms of the convective available potential energy cape and convective inhibition cin the first two wave modes travel fastest away from the cloud and are responsible for the changes in cape whereas the third wave mode causes low level lifting and hence a reduction in cin the maximum far field perturbations in cape and cin are approximately 15 and 33 of the initial background values respectively these results agree with previous studies of more organized convection predicting the existence of a region surrounding the convective system that favors the development of new convection

environment and evolution of a cold frontal mesoscale convective system abstract observations from the oklahoma kansas preliminary regional experiment for storm central ok pre storm have been used to study the evolution and propagation characteristics of a long lived 16 h mesoscale convective system mcs that produced locally heavy 50 100 mm rainfall during 26 27 june 1985 the mcs formed in association with a synoptic scale cold front and upper level trough system mesoscale ascent contributed to an increase in convective available potential energy cape and a decrease in convective inhibition facilitating the development of deep convection during the late morning and early afternoon hours convection was present along and within an 200 km zone in advance of the cold front in advance of the main precipitation area a series of nearly parallel rainbands formed from in situ boundary layer cloud streets the development and organization of these rainbands was aided by the moderate to large cape small convective inhibition and moderate unidirectional shear at low l

structure of an atmospheric undular bore generated from colliding boundaries during cape abstract a case study of a sea breeze front originating from the east coast of florida colliding with a gust front moving toward the southeast is presented single and multi doppler radar analyses combined with serial balloon ascents suggest that the denser sea breeze flow undercut the cold pool behind the gust front and may have generated a westward propagating undular bore in addition another undular bore was generated by the collision and propagated eastward through the cape network the latter bore propagated upstream against the southeasterly flow behind the sea breeze front and was apparent as a narrow band 5 6 km wide of near zero radial velocities embedded within an overall flow that was positive as seen by the cp 4 doppler radar as the eastern bore propagated through the dual doppler lobe defined by the ncar cp 3 and cp 4 radars a detailed and unique wind synthesis revealed its three dimensional kinematic structure significant along bore variability was shown in the convergence and verti

discrete propagation in numerically simulated nocturnal squall lines abstract simulations of a typical midlatitude squall line were used to investigate a mechanism for discrete propagation defined as convective initiation ahead of an existing squall line leading to a faster propagation speed for the storm complex radar imagery often shows new cells appearing in advance of squall lines suggesting a causal relationship and prompting the search for an action at a distance mechanism to explain the phenomenon in the simulations presented the identified mechanism involves gravity waves of both low and high frequency generated in response to the latent heating which subsequently propagate out ahead of the storm the net result of the low frequency response combined with surface fluxes and radiative processes was a cooler and more moist lower troposphere establishing a shallow cloud deck extending ahead of the storm high frequency gravity waves excited in response to fluctuations in convective activity in the main storm were subsequently ducted by the storm s own upp

examination of gravity waves associated with the 13 march 2003 bow echo abstractnumerical simulations of the 13 march 2003 bow echo over oklahoma are used to evaluate bow echo development and its relationship with gravity wave generation multiple fast moving with speeds of 30 35 m s 1 gravity waves are generated in association with fluctuations in the first vertical mode of heating in the convective line the surface impacts of four such waves are observed in oklahoma mesonet data during this case observations of surface pressure surges ahead of convective lines prior to the bowing process are reproduced a slower gravity wave produced in the simulation is responsible for a prebowing pressure surge this slower gravity wave moving at approximately 11 m s 1 is generated by an increase in low level microphysical cooling associated with an increase in rear to front flow and low level downdrafts shortly before bowing the wave moves ahead of the convective line and is manifested at the surface by a positive pressure surge the pattern of low level vertical motion associated

bores observed during ihop_2002 the relationship of bores to the nocturnal environment abstractthis study documents atmospheric bores and other convergent boundaries in the southern great plains nocturnal environment during the ihop 2002 summer campaign observational evidence demonstrates that convective outflows routinely generate bores statistically resampled flow regimes derived from an adaptation of hydraulic theory agree well with observations specifically convective outflows within the observed environments are likely to produce a partially blocked flow regime which is a favorable condition for generating a bore once a bore develops the direction of movement generally follows the orientation of the bulk shear vector between the nose of the nocturnal low level jet and a height of 1 5 or 2 5 km agl this relationship is believed to be a consequence of wave trapping through the curvature of the horizontal wind with respect to height this conclusion comes after analyzing the profile of the scorer parameter overall these findings provide an impetus for future investigations ai

summary of convective storm initiation and evolution during ihop observational and modeling perspective abstract the data rich international h2o project ihop 2002 experiment is used to study convective storm initiation and subsequent evolution for all days of the experiment initiation episodes were almost evenly divided between those triggered along surface based convergence lines and elevated initiation episodes that showed no associated surface convergence the elevated episodes occurred mostly at night and the surface based episodes occurred during the afternoon and evening surface based initiations were mostly associated with synoptic fronts and gust fronts and less so with drylines and bores elevated initiations were frequently associated with observable convergent or confluent features in the rapid update cycle ruc wind analysis fields between 900 and 600 hpa the ruc10 3 h forecast of the precipitation initiation episodes were correct 44 of the time allowing a tolerance of 250 km in space and for the forecast being early by one period however the accuracy was closely tied to the scale of

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

a composite perspective on bore passages during the pecan campaign abstractatmospheric bores have been shown to have a role in the initiation and maintenance of elevated convection previous observational studies of bores have been case studies of more notable eve

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

convective episodes in the east central united states nine years of composited radar data are investigated to assess the presence of organized convective episodes in the east central united states in the eastern united states the afternoon maximum in thunderstorms is ubiquitous over land however after removing this principal diurnal peak from the radar data the presence and motion of organized convective systems becomes apparent in both temporally averaged fields and in the statistics of convective episodes identified by an objective algorithm convective echoes are diurnally maximized over the appalachian chain and are repeatedly observed to move toward the east partly as a result of this the daily maximum in storms is delayed over the piedmont and coastal plain relative to the appalachian mountains and the atlantic coast during the 9 yr studied the objective algorithm identified 2128 total convective episodes 236 yr 1 with several recurring behaviors many systems developed over the elevated terrain during the afternoon and moved eastward often to the coastline and even offshore in addition numerous systems formed to the west of the appalachian mountains and moved into and across the eastern u s study domain in particular many nocturnal convective systems from the central united states entered the western side of the study domain frequently arriving at the eastern mountains around the next day s afternoon maximum in storm frequency a fraction of such well timed systems succeeded in crossing the appalachians and continuing across the piedmont and coastal plain convective episodes were most frequent during the high instability low shear months of summer which dominate the year round statistics even so an important result is that the episodes still occurred almost exclusively in above average vertical wind shear despite the overall dominance of the diurnal cycle the data show that adequate shear in the region frequently leads to long lived convective episodes with mesoscale organization

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

geochemistry and stratigraphic correlation of basalt lavas beneath the idaho chemical processing plant idaho national engineering laboratory thirty nine samples of basaltic core were collected from wells 121 and 123 located approximately 1 8 km apart north and south of the idaho chemical processing plant at the idaho national engineering laboratory samples were collected from depths ranging from 15 to 221 m below land surface for the purpose of establishing stratigraphic correlations between these two wells elemental analyses indicate that the basalts consist of three principal chemical types two of these types are each represented by a single basalt flow in each well the third chemical type is represented by many basalt flows and includes a broad range of chemical compositions that is distinguished from the other two types basalt flows within the third type were identified by hierarchical k cluster analysis of 14 representative elements fe ca k na sc co la ce sm eu yb hf ta and th cluster analyses indicate correlations of basalt flows between wells 121 and 123 at depths of approximately 38 40 m 125 128 m 131 137 m 149 158 m and 183 198 m probable correlations also are indicated for at least seven other depth intervals basalt flows in several depth intervals do not correlate on the basis of chemical compositions thus reflecting possible flow margins in the sequence between the wells multi element chemical data provide a useful method for determining stratigraphic correlations of basalt in the upper 1 2 km of the eastern snake river plain

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

a case study on the far field properties of propagating tropospheric gravity waves abstractmesoscale gravity waves were observed by barometers deployed as part of the usarray transportable array on 29 june 2011 near two mesoscale convective systems in the great plains region of the united states simultaneously airs satellite data indicated stratospheric gravity waves propagating away from the location of active convection peak perturbation pressure values associated with waves propagating outside of regions where there was precipitation reached amplitudes close to 400 pa at the surface here the origins of the waves and their relationship to observed precipitation are investigated with a specialized model study simulations with a 4 km resolution dry numerical model reproduce the propagation characteristics and amplitudes of the observed waves with a high degree of quantitative similarity despite the absence of any boundary layer processes surface topography or moist physics in the model the model is forced with a three dimensional time dependent latent heating cooling field that

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

an observational and modeling study of an atmospheric internal bore during name 2004 abstract observations from the 2004 north american monsoon experiment name have been used to identify an atmospheric internal bore that occurred over the gulf of california goc on 31 july 2004 this bore disturbance was identified at bahia kino along the northwest coast of mexico during the late evening of 31 july it was hypothesized to have originated from the interaction of a gravity current from a large mesoscale convective system mcs which formed along the western slopes of the sierra madre occidental during the afternoon and a surface stable layer that developed from a sea breeze circulation it is suggested that the bore s energy was trapped at low levels by an elevated stable layer the vertical structure and undular nature of the bore was initially identified from 915 mhz wind profiler data at bahia kino results show a series of waves along the bore s leading edge and turbulent mixing of air from above the stable layer to the surface on the downstream face of the leading undulation the

gravity waves compensating subsidence and detrainment around cumulus clouds abstract gravity waves play an important role in the redistribution of heat and moisture in a deep convecting cloud field we explore this role in a two dimensional numerical experiment on a simple moist convecting system consisting of an isolated long lasting nonprecipitating cloud in a calm atmosphere with no surface forcing the cloud develops a horizontally averaged density variation with height which is neutrally buoyant with respect to a moist adiabatic the buoyancy difference between the cloud and the undisturbed sounding produces circulations that can be understood as spreading gravity waves which adjust the environmental buoyancy to be equal to the cloud buoyancy by compensating subsidence unlike the circulations inside clouds this adjustment takes place without turbulent mixing hence the buoyancy adjustment time t1 during which the environment comes into rough buoyant equilibrium with the clouds is much shorter than the mixing time t2 which it takes a tracer initially concentrated at s

radiometer and profiler analysis of the effects of a bore and a solitary wave on the stability of the nocturnal boundary layer abstract this study uses data from a microwave profiling radiometer mpr along with 915 mhz wind profiler doppler radar and surface data to quantify the kinematic and thermodynamic effects of two wave features an undular bore and a soliton on the nocturnal boundary layer nbl at high temporal resolution both wave features passed directly over the mpr and the wind profiler allowing for detailed analyses the effects of the wave features on the convective environment are examined and convective initiation ci associated with the wave features is discussed the undular bore was illustrated well in doppler velocity data and profiler measurements indicated that it produced four wavelengths of upward and downward motion mpr derived time height sections of potential temperature and mixing ratio showed an increase in the depth of the stable boundary layer along with a decrease in stability partially associated with mixing of the nbl the soliton produced a temporary decrease in the depth of the nbl

the life cycle of an undular bore and its interaction with a shallow intense cold front abstract the evolution of an undular bore and its associated wind shift spawned by the passage of a shallow surface cold front over the southern great plains of the united states is examined using surface and remote sensing observations along with output from a high resolution numerical model simulation observations show that a separation between the wind shift and thermodynamic properties of the front was induced by the formation of a bore over south central kansas around 0200 utc 29 november 2006 by the time the front bore complex passed through lamont oklahoma approximately 4 h later the bore had reached its maximum intensity and its associated wind shift preceded the trailing baroclinic zone by 20 min within several hours the bore decayed and a cold frontal passage characterized by a wind shift coincident with thermodynamic properties was observed at okmulgee oklahoma thus a substantial transformation in both the structural and dynamical characteristics of the bore as well as its relations

the potential role of atmospheric bores and gravity waves in the initiation and maintenance of nocturnal convection over the southern great plains abstractthis investigation explores the relationship among bores gravity waves and convection within the nocturnal environment through the utilization of measurements taken during the internation

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

structure of an internal bore and dissipating gravity current as revealed by raman lidar abstract detailed moisture observations from a ground based raman lidar and special radiosonde data of two disturbances associated with a dissipating gust front are presented a synthesis of the lidar data with conventional meteorological data in conjunction with theoretical calculations and comparison to laboratory studies leads to the conclusion that the disturbances seen in both the lidar and accompanying barograph data represent a weak gravity current and an associated undular bore the disturbances display excellent coherence over hundreds of kilometers upstream of the lidar site bore formation occurs at the leading edge of the gust front coincidentally with the rapid weakening of the gravity current analysis suggests that the bore was generated by the collapse of the gravity current into a stable nocturnal inversion layer and subsequently propagated along this wave guide at nearly twice the speed of the gravity current the raman lidar provided detailed measurements of the vertical structure o

a nonclassical cold front observed during cops 91 frontal structure and the process of severe storm initiation abstract this case study addresses the issue of gravity current and bore development at surface cold fronts and the role of these phenomena in the generation of severe frontal convection the event investigated occurred on 27 april 1991 during the cooperative oklahoma profiler studies 1991 field project the development of a bore from a gravity current like structure along a cold front the subsequent propagation of the bore ahead of the front on a low level inversion and the process of severe thunderstorm development along the front are revealed by a dense network of remote sensing and other special observations evidence for the gravity current and bore is strengthened by comparisons made between the synthesized observations and theory the bore developed after a nocturnal inversion which acted as a waveguide had become established the bore and gravity current were both evident as fine lines in the radar reflectivity displays a microscale envelope of enhanced water vapor with an embedded roll cl

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

interactions between upper and lower tropospheric gravity waves on squall line structure and maintenance abstract using a simplified thermodynamic sounding and variable vertical wind shear we investigate the role of gravity waves on the structure and propagation of a simulated two dimensional squall line based on an observed squall line environment the modeled troposphere has been divided into three distinct thermodynamic layers these consist of an absolutely stable atmospheric boundary layer abl an elevated well mixed layer and an upper tropospheric layer of intermediate stability we find the mixed layer to have a dual role it has a reduced stability and thus provides abundant buoyancy for the convective scale updrafts and it provides an ideal layer to trap meso scale 20 200 km wave energy generated in the stable layers the generated waves thus have a significant and lasting impact on the simulation we also find this thermodynamic structure to be conducive to both strong surface wind perturbations and long lived squall lines experiments that vary the vertical wind shear profile demonstrate

mesoscale surface pressure and temperature features associated with bow echoes abstract this study examines observed mesoscale surface pressure temperature and wind features of bow echoes bow echo events in the area of the oklahoma mesonet are selected for study to take advantage of high resolution surface data thirty six cases are identified using 2 km resolution radar reflectivity data over a 4 yr period 2002 05 their surface features are interrogated using the mesonet data distinct surface features usually associated with squall lines the mesohigh and cold pool are found to also accompany bow echoes a common surface pattern preceding bowing is identified prior to new bowing development the mesohigh surges ahead of the convective line while the cold pool remains centered behind it surface winds shift to a ground relative outflow pattern upon arrival of the mesohigh surge approximately 30 min later a new bowing segment forms with its apex slightly to the left with respect to the direction of system motion of the mesohigh surge the cold pool follows the convective

gregarious tropical convection abstract a beat source with a vertical profile like that of observed tropical mesoscale convective systems mcss is shown to cause through inviscid gravity wave dynamics upward displacement at low levels in a mesoscale region surrounding the heating typical values are 10 30 area contraction at the surface everywhere within 270 km of the heating 6 h after it starts as a result conditions near an existing mcs but beyond the area of mcs outflow become more favorable for the development of additional convection this theory predicts that cloud clusters should be gregarious infrared satellite imagery confirms that almost half of the cold cloudiness observed in a month over the oceanic warm pool region was contributed by just 14 objectively defined multiday supercluters

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

the formation of internal bores in the atmosphere a laboratory model summary recently several atmospheric observations have been interpreted as internal undular bores or internal solitary waves evolving from internal bores that propagate along low level temperature inversions it has been speculated that such disturbances are generated by some type of gravity current such as cold fronts sea breeze fronts and thunderstorm outflows interacting with an existing temperature inversion in this paper we describe a systematic laboratory study in a water channel of internal bores and their generation by the movement of gravity currents through a two layer model of the atmosphere we compare the results of our laboratory experiments with previous theories and numerical simulations and with several detailed atmospheric observations of internal bores at different stages of development