remote trigger of deep convection by cold outflow over the taiwan strait in the mei yu season a modeling study of the 8 june 2007 case abstractin this study the heavy rainfall event over central taiwan during the mei yu season on 8 june 2007 is investigated with an emphasis on the triggering mechanism for the deep convection that produced the rain observations indicate that there existed two lines of forcing with convection prior to the rain one over the northern taiwan strait along the mei yu front and the other over the southern taiwan strait yet the convection in question developed over the central strait between these two lines in an unstable environment with strong westerly vertical wind shear this motivated the authors to carry out the present study the cloud resolving storm simulation cress of nagoya university was used and the event was reproduced at a horizontal grid size of 2 km including the initiation of new convection over the central strait at the correct location and time the model results suggest a crucial role played by the series of active persistent and propagating storms in the southern strait along the

a wave cisk model of squall lines abstract the wave cisk model of raymond incorporating lag effects in the updraft and downdraft is implemented as an initial value problem in physical space examples of both midlatitude and tropical squall lines are successfully simulated diagnosis of the model shows that condensational heating in the updraft is the primary driving mechanism of a mature squall line with evaporative cooling and convective momentum transfer playing subsidiary roles however an instability involving the displacement of boundary layer air by downdrafts apparently plays an important role in squall line initiation a weakness of the model is its inability to predict the direction of squall line propagation relative to the low level wind shear this is traced to the insensitivity of the convective parameterization to midlevel entrainment however unlike strict two dimensional squall lint models the parameterization allows cross stream mass transfer to occur in the context of overall slab symmetry such transfer is dynamical

the life cycle of thunderstorm gust fronts as viewed with doppler radar and rawinsonde data abstract this paper presents the time dependent analysis of the thunderstorm gust front with the use of project nimrod data rhi cross sections of reflectivity and doppler velocity are constructed to determine the entire vertical structure the life cycle of the gust front is divided into four stages 1 the formative stage 2 the early mature stage 3 the late mature stage and 4 the dissipation stage a new finding is a horizontal roll detected in the reflectivity pattern resulting from airflow that is deflected upward by the ground while carrying some of the smaller precipitation ahead of the main echo core of the squall line this feature is called a precipitation roll as determined from rawinsonde data the cold air behind the gust front accounts for the observed surface pressure rise calculations confirm that the collision of two fluids produce a nonhydrostatic pressure at the leading edge of the outflow the equation governing the propagation speed of a density current accurately predicts t

an atmospheric solitary gust observed with a doppler radar a tall tower and a surface network abstract doppler radar and a 444 m tall instrumented tower provide a detailed view of the kinematic and thermodynamic structure of a solitary gust a study of the data fields and comparison with theoretical and laboratory work leads to the conclusion that the gust is an internal solitary wave of permanent form launched by a thunderstorm outflow onto an inversion layer formed by the passage of an earlier storm comparisons with results from fluid experiments and numerical models are made and the similarities are striking both observations show turbulent breakdown at the rear of the wave the ease with which solitary waves can be generated in experiments gives reason to believe that these nonlinear waves might be of considerable interest in the context of geophysical fluid dynamics

evaluation of infrasound signals from the shuttle atlantis using a large seismic network inclement weather in florida forced the space shuttle atlantis to land at edwards air force base in southern california on june 22 2007 passing near three infrasound stations and several hundred seismic stations in northern mexico southern california and nevada the high signal to noise ratio broad receiver coverage and atlantis positional information allow for the testing of infrasound propagation modeling capabilities through the atmosphere to regional distances shadow zones and arrival times are predicted by tracing rays that are launched at right angles to the conical shock front surrounding the shuttle through a standard climatological model as well as a global ground to space model the predictions and observations compare favorably over much of the study area for both atmospheric specifications to the east of the shuttle trajectory there were no detections beyond the primary acoustic carpet infrasound energy was detected hundreds of kilometers to the west and northwest nw of the shuttle trajectory consistent with the predictions of ducting due to the westward summer time stratospheric jet both atmospheric models predict alternating regions of high and low ensonifications to the nw however infrasound energy was detected tens of kilometers beyond the predicted zones of ensonification possibly due to uncertainties in stratospheric wind speeds

observations of mesocale wave disturbances during the genesis of atlantic lows experiment abstract the portable automated mesonet pam data obtained during the genesis of atlantic lows fxperiment gale are used to document mesoscale wave activity during the 3 day period from 4 to 6 february 1986 from the surface pressure analyses four cases of wave activity are identified with wavelengths of 200 400 km phase speeds of 20 40 m s 1 and trough to crest pressure amplitudes of 0 5 3 5 mb precipitation was associated with the waves in two of the four cases detailed analyses of the horizontal structure show that the waves do not have the pressure wind relationship expected from linear gravity wave theory the wind vectors are oriented from high to low pressure with a maximum amplitude between the high and low pressure areas low level inversions were present in three of the four cases in the raw without a low level inversion the amplitude rapidly decreased as the wave moved towards the east in the case which lasted for the longest time period at least 8 h and had the largest pressure amp

shear parallel moist convection over the tropical ocean a case study from 18 february 1993 toga coare abstract this paper describes a newly observed form of shear parallel rainbands that were observed on 18 february 1993 in tropical ocean global atmosphere coupled ocean atmosphere response experiment using the ncar eldora airborne doppler radar interesting features of these rainbands included their rapidly changing and highly cellular nature their complicated and layered kinematic structure and the effects of the rainbands on the tropical environment in their lower levels the rainbands consisted of east west elongated clusters of small convective cells aligned with the z 0 5 km shear vector strong low level convergence inflow from the north and enhanced westerly winds extended from the surface up to 5 km much of this air was vented out of the storm at midlevels exiting to the north in the 0 c stable layer at z 5 7 km this midlevel outflow fed an area of widespread stratiform precipitation lying to the north of the rainband the cold pool outflow emanating from this area of precipitation 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 mesoscale circulations within extratropical cyclones over the north atlantic ocean during erica abstract pseudo dual doppler analyses of two mesoscale circulations 20 40 km in horizontal dimensions that formed along a warm front within a rapidly deepening extratropical cyclone over the ocean are presented the circulations were analyzed using airborne doppler radar during erica experiment on rapidly intensifying cyclones over the atlantic iop intensive observing period 4 and are believed to be a type of frontal instability that has not been addressed in past theoretical studies of frontal waves and cyclones these features may be the shallow circulations that have been documented to play a role in cyclogenesis when they become coupled with an upper level baroclinic wave the present case is compared and contrasted with the only other well analyzed event during erica iop 5 a retrieval of the perturbation pressure and buoyancy fields using the kinematic wind fields is performed in order to facilitate the interpretation of the dynamic structure of these vortices in addition a set of equations

on assessing local conditional symmetric instability from atmospheric soundings abstract the standard parcel method of assessing the susceptibility of the atmosphere to moist convection using tephigrams is extended to account for the centrifugal as well as the gravitational potential energy of the displaced air parcel this leads to a measure of the stability of the moist baroclinic atmosphere to finite slantwise reversible displacements of a two dimensional air parcel such a measure differs from previously derived measures of conditional symmetric instability which have considered only infinitesimal displacements in saturated atmospheres it is demonstrated that the combined gravitational and centrifugal potential of a two dimensional air parcel or tube can be assessed by displacing the tube slantwise along a surface of constant angular momentum and that this combined potential energy can be estimated using a single atmospheric sounding several examples of the application of this technique are presented in the context of a case study of apparent slantwise convection the result

the relationship of surface pressure features to the precipitation and airflow structure of an intense midlatitude squall line abstract observations from the oklahoma kansas preliminary regional experiment for storm central ok pre storm have been used to document the surface pressure features accompanying an intense midlatitude squall line with trailing stratiform precipitation three well known features are observed a pre squall mesolow a squall mesohigh and a wake low particular attention is given to the wake low its life cycle and association with the trailing stratiform portion of the squall line during the formative stage the pressure field to the rear of the squall line mesohigh is relatively flat with only weak stratiform precipitation present as the squall line enters the developing to mature stages a pronounced wake low appears at the back edge of the surface stratiform precipitation area the squall line at this time is characterized by a strong rear inflow jet descending from the upper troposphere as far as 500 km behind the leading convective line to the lower troposphere just behind the line the trailin

travelling waves and bores in the lower atmosphere the morning glory and related phenomena abstract observations of solitary wave and travelling bore like disturbances in the lower atmosphere are reviewed together with relevant theoretical laboratory and numerical studies concerning the structure propagation and genesis of such disturbances primary emphasis is given to a discussion of the morning glory phenomenon in northern australia the example par excellence of these types of disturbance and the best documented observationally to date observations of related phenomena elsewhere are reviewed briefly while such occurrences appear to be less frequent in any single location than in the southern gulf of carpentaria region of northern australia reported occurrences are widespread and there is mounting evidence that such disturbances are more common than is generally supposed the evidence suggests that whenever a suitable wave guide exists for the propagation of disturbances the latter can be generated as the natural response of quite general forcing mechanisms examples being the collision of two sea breezes from opposite directions on a peninsula the interaction between a thunderstorm outflow and a sea breeze front or simply the transformation of a thunderstorm or squall line outflow as it moves into a low level stable layer because of the large vertical displacements they produce the larger amplitude disturbances typically with surface pressure jumps of 1 mb or more must be considered as potential triggers for deep convection if the atmosphere is sufficiently conditionally unstable and the large low altitude wind shears associated with them present a serious hazard to low flying aircraft

derecho and mcs development evolution and multiscale interactions during 3 5 july 2003 abstract from 3 to 5 july 2003 during the bow echo and mesoscale convective vortex experiment bamex multiple mesoscale convective systems mcss 1 and 2 and derechos derechos an as a bw and be progressed across a preferred upper midwest corridor the derechos evolved in a favorable synoptic scale environment however the environmental details associated with each derecho such as the characteristics of the initial surface boundary the formation position relative to the upper level jet stream the presence of an upper level mesoscale disturbance and the cape shear environment varied from derecho to derecho the mcss and derechos composed three distinct convective episodes multiple mesoscale interactions between the mcss and derechos and the environment altered the character and longevity of these episodes the first convective episode consisted of derecho a which formed from merging derechos an and as northern and southern systems respectively the 200 hpa deep cold pool associated with d

surface pressure and precipitation life cycle characteristics of pre storm mesoscale convective systems abstract extensive observations of the may june 1985 oklahoma kansas preliminary regional experiment for storm central ok pre storm are used to examine the life cycle characteristics of 16 mesoscale convective systems mcss the primary focus is on the surface pressure flow and precipitation structures of the mess it is found that despite the wide variety of initial precipitation structures of the mcss reputable patterns developed in 75 of the cases during their mature to dissipating stages the precipitation structure at this later stage of the life cycle can be described as asymmetric following the definition of houze et al due to the variety of directions of movement the systems are examined in a motion relative quadrant perspective one axis is along the direction of system motion and the other perpendicular to it crossing at the center of the convective line the asymmetry is characterized by 1 a leading convective line containing relatively weak cells on the northern end and a trailing

a new look at the super outbreak of tornadoes on 3 4 april 1974 abstract the outbreak of tornadoes from the mississippi river to just east of the appalachian mountains on 2 5 april 1974 is analyzed using conventional techniques and the pennsylvania state university national center for atmospheric research fifth generation mesoscale model mm5 the mm5 was run for 48 h using the ncep ncar reanalysis dataset for initial conditions it is suggested that the first damaging squall line within the storm of 2 5 april 1974 herein referred to as the super outbreak storm was initiated by updrafts associated with an undular bore the bore resulted from the forward advance of a pacific cold front into a stable air mass the second major squall line within the super outbreak storm which produced the strongest and most numerous tornadoes was directly connected with the lifting associated with a cold front aloft this second squall line was located along the farthest forward protrusion of a pacific cold front as it occluded with a lee trough dryline an important factor in the

observations simulations and analysis of nonstationary trapped lee waves abstract although considerable understanding of mountain waves has been gained with the aid of the steady state assumption it is clear that mountain waves evolve over time group velocity arguments indicate that this evolution can occur in less than 1 h this study uses observations of trapped lee waves to measure the rate at which their horizontal wavelengths change including a detailed analysis of two events in which such changes are clearly documented in one case doppler lidar observations show a steady increase in horizontal wavelength of 6 h 1 over 4 h and clearly illustrates the relationship between the wave clouds and wave motions in a second case visible satellite imagery reveals an increase in wavelength of 14 h 1 which is related to temporal changes in vertical air motions measured by wind profilers within the wave field hourly vertical profiles of wind and virtual temperature measured by radio acoustic sounding systems rass and wind profilers reveal important changes in the wave env

a case study of the interaction of a mesoscale gravity wave with a mesoscale convective system abstractthis study documents the high amplitude mesoscale gravity wave mgw event of 7 march 2008 in which two mgws strongly impacted the sensible weather over a large portion of the southeast united states these mgws exhibited starkly contrasting character despite propagating within similar environments the primary i e long lived mgw was manifest by a solitary wave of depression associated with rapid sinking motion and adiabatic warming while the secondary short lived mgw was manifest by a solitary wave of elevation mgwel dominated by rising motion and moist adiabatic cooling genesis of the primary mgw occurred as a strong cold front arrived at the foot of mexico s high terrain and perturbed the appreciable overriding flow the resulting gravity wave became ducted in the presence of a low level frontal stable layer and caused surface pressure falls up to 4 hpa the mgw later amplified as it became coupled with a stratiform precipitation system which led to its evolution into an intense

crosshole imaging in anisotropic media seismologists are becoming increasingly aware of the ubiquity of anisotropy albeit mostly weak this is partly due to field observations and partly to the results of measurements in the laboratory furthermore it has been known for a long time that layering of distinct isotropic media at subwavelength scales can cause apparent anisotropy if unaccounted for this anisotropy can result in distortion of tomographic images to the point of affecting their interpretation c h chapman and r g pratt in traveltime tomography in anisotropic media theory geophysical journal international 1992 show how anisotropy may most generally be included in a 2 d tomographic inversion resulting in a requirement for five distinct parameter fields

mesoscale gravity waves and their environment in the central united states during storm fest abstract in an effort to better understand mesoscale gravity waves in winter storms in the central united states their frequency of occurrence wave characteristics the general conditions under which they occur and their effects upon the weather mesoscale surface and rawinsonde data as well as radar and satellite imagery collected during the storm scale operational and research meteorology fronts and experimental system test are analyzed in addition factors affecting the ability of objective surface map analysis to properly represent the waves are investigated thirteen coherent pressure pulse events with amplitudes of 0 2 4 0 mb and periods of 1 6 h were identified in the surface pressure data during the 6 weeks of the project involving 34 of the total hours investigated a variety of wave types occurred including wavelets wave trains and singular waves the three largest amplitude events were analyzed in detail using autospectral analysis and a barnes time to space conversion objective analysis

origin evolution and finescale structure of the st valentine s day mesoscale gravity wave observed during storm fest part i origin and evolution abstract on 14 15 february 1992 a long lived mesoscale gravity wave was observed over the storm scale operational and research meteorology fronts experiment systems test observational network a precipitation band formed and intensified as the wave moved across kansas and missouri the disturbance was tracked for 14 h surface dual doppler radar and wind profiler analyses as well as isentropic analyses derived from a special rawinsonde network are used to examine the origin and evolution of this wave the wave originated at the leading edge of a dry air mass associated with downslope flow in the lee of the rockies the earliest surface pressure signatures of wave motion began as a dry air mass associated with the downslope flow ascended a warm front east of a lee cyclone a weak rainband developed simultaneously with the wave at the leading edge of the dry air mass the mesoscale gravity wave and convection remained tied to the leading edge of the advancing dry air mass during the first 8 10 h of

a mesoscale gravity wave event observed during ccope iii wave environment and probable source mechanisms abstract synoptic and special mesoscale observations taken during the cooperative convective precipitation experiment ccope are used to describe the multiscale environment of a gravity wave event understand the wave environment interactions that led to the development of severe thunderstorms and asses possible wave generation mechanisms the storms formed sequentially as a packet of gravity waves propagated across a stationary thunderstorm outflow boundary convection developed most rapidly in that part of the mesonetwork in which existed the combination of relatively high parcel buoyant energy weak restraining inversion strong storm downdraft potential and substantial vertical wind shear associated with a mesoscale jet streak synoptic scale analysis reveals that the waves were excited north of a stationary front and within the right exit region of the jet streak as it approached a stationary ridge in the 300 mb height field strong indications of unbalanced flow were diagnosed within the gravit

analysis of gravity waves generated at the top of a drainage flow abstract drainage or katabatic flows are common mesoscale circulations established as a result of differential radiative cooling of near surface air masses in sloping terrain the initial irruption of these flows with sudden shifts in wind speed and direction may result in vertical displacements of air parcels from their equilibrium position which prove to be a common source of internal gravity waves this paper illustrates this mechanism and describes the main features of the oscillations following the study of observational data gathered throughout one night during the stable atmospheric boundary layer experiment in spain 2006 sables2006 field campaign pressure differences measured by microbarometers set at different levels of a tower help to interpret the evolution of other atmospheric variables provide a detailed picture of the irruption of a drainage current and reveal the formation of gravity waves at its top the main parameters of the waves are derived from wavelet cross correlation of p

potential coordinate mislocations in crosshole tomography results from the grimsel test site switzerland tomographic techniques based on borehole to borehole and tunnel to borehole traveltime data are now being employed in a wide range of studies associated with the exploration and exploitation of hydrocarbons and metallic minerals the disposal of chemical and radioactive waste diverse civil engineering projects and archaeology a fundamental assumption of currently employed tomographic inversion strategies is that the coordinates of the boreholes and tunnels containing the seismic sources and receivers are accurately known by inverting both synthetic and observed traveltime data we demonstrate that relatively minor coordinate errors 1 2 in the deeper parts of long boreholes 100 m may produce artifacts in the tomographic images that are comparable in extent and amplitude to true velocity anomalies to address this problem we introduce the coupled inverse method commonly used in earthquake studies as a means to determine simultaneously borehole coordinate adjustments and an estimate of the tomog

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

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

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

boundary layer oscillations from thunderstorms at sydney airport abstract analyses of wind velocity and air pressure data acquired by a set of low level anemometers at sydney airport australia indicate the passage of a set of three remarkably smooth atmospheric boundary layer oscillations that traveled ahead of a thunderstorm on 27 december 1991 the oscillations were probably generated by a nearby thunderstorm outflow propagating into a stably stratified atmospheric layer it is likely that the phenomenon was initiated by the degenerating of an outflow gravity current into a family of amplitude ordered solitary waves although reasonable agreement can be obtained on the propagation speed using a linear theory the weakness of the trapping mechanism for this solution and an overestimation of the weakly nonlinear wave half width leads to a conclusion that the waves fully nonlinear

geostatistical traveltime tomography in elliptically anisotropic media in geological materials anisotropy may arise due to different mechanisms and can be found at different scales neglecting anisotropy in traveltime tomographic reconstruction leads to artefacts that can obscure important subsurface features in this paper a geostatistical tomography algorithm to invert cross hole traveltime data in elliptically anisotropic media is presented the advantages of geostatistical tomography are that the solution is regularized by the covariance of the model parameters that known model parameters can be used as constraints and fitted exactly or within a prescribed variance and that stochastic simulations can be performed to appraise the variability of the solution space the benefits of the algorithm to image anisotropic media are illustrated by two examples using synthetic georadar data and real seismic data the first example confirms suspected electromagnetic anisotropy in the vadose zone caused by relatively rapid water content variations with respect to wavelength at georadar frequencies the second presents how sonic log data can be used to constrain the inversion of cross well seismic data and how geostatistical simulations can be used to infer parameter uncertainty results of both examples show that considering anisotropy yields a better fit to the data at high ray angles and reduces reconstruction artefacts

evidence of very large amplitude solitary waves in the atmosphere atmospheric solitary waves are gravity waves that retain their integrity over long periods because of a near balance between nonlinearity and dispersion they have been observed on various scales in many regions of the world1 3 but we present here detailed measurements of solitary waves with amplitudes comparable to the scale height of the lower troposphere two such waves were generated downstream of intense mid tropospheric pressure troughs over the central united states they propagated over 1 000km several times their wavelength with no appreciable change in structure within a waveguide formed by surface inversion and a middle tropospheric critical level fluctuations in surface pressure associated with the two waves exceeded 6 mbar and 10 mbar the waves caused banded patterns of precipitation and significantly influenced other meteorological phenomena the restoration of balance between pressure driven air flow and the coriolis force geostrophic adjustment seems to have a prominent role in the formation of these solitary waves

origin evolution and finescale structure of the st valentine s day mesoscale gravity wave observed during storm fest part ii finescale structure abstract this paper presents observations of the finescale three dimensional kinematic and thermodynamic structure of a long lived mesoscale gravity wave that occurred on 14 15 february 1992 during the storm scale operational and research meteorology fronts experiment systems test storm fest in part i of this series of papers it was shown that the wave was generated just behind the leading edge of an advancing dry air mass that originated as a foehnlike downslope flow over the rocky mountains of southern colorado and new mexico surface pressure signatures of wave motion began as the dry air mass ascended a warm front east of a lee cyclone and a rainband developed along its leading edge the wave and rainband intensified remaining near the leading edge of the dry air mass as the dry air mass advanced northeastward over the warm frontal inversion after 7 h of evolution the leading edge of the dry air mass passed over the dual doppler network in northeast kansas it was at this point in the evolution

reconstructing sea level pressure variability via a feature tracking approach abstractthe aim of this paper is to quantify the contribution of synoptic transients to the full spectrum of space time variability of sea level pressure slp in middle latitudes in previous work by the authors it was shown that tracking cyclones and anticyclones in an idealized atmospheric model allows one to reconstruct a surprisingly large fraction of the model s variability including not only synoptic components but also its large scale low frequency component motivated by this result the authors performed tracking of cyclones and anticyclones and estimated cyclone and anticyclone size and geometry characteristics in the observed slp field using the 1948 2008 ncep ncar reanalysis dataset the reconstructed synoptic field was then produced via superimposing radially symmetrized eddies moving along their actual observed trajectories it was found that similar to earlier results for an idealized model the synoptic reconstruction so obtained accounts for a major fraction of the full observed slp v

validation of a thermodynamic retrieval technique by application to a simulated squall line with trailing stratiform precipitation abstract a thermodynamic retrieval technique which uses the equation of motion in conjunction with the thermodynamic equation is validated in a two dimensional numerical model simulation of a squall line with a trailing stratiform region model wind and reflectivity output are used as input to the retrieval the availability of model thermodynamic output allows us to examine the performance of the retrieval the computational technique involved is found to be valid when the retrieval is applied to the time averaged model wind fields reasonably accurate results are obtained for the stratiform region but errors arise for the convective region because of the neglect of eddy correlations of the temporally fluctuating wind components application of the retrieval to instantaneous model wind fields demonstrates that very high lime resolution is needed in the wind data about 2 min to obtain reliable results where time changes are large and nonlinear

a study of acoustic propagation from a large bolide in the atmosphere with a dense seismic network 1 a large meteor entered the atmosphere above northeastern oregon on 19 february 2008 at 530 pst several hundreds of broadband seismic stations in the u s pacific northwest recorded acoustic to seismic coupled signals from this event the travel times of the first arriving energy are consistent with a terminal explosion source model suggesting that the large size of the explosion masked any signals associated with a continuous line source along its supersonic trajectory several infrasound arrays in north america also recorded this event both the seismic and infrasound data have been used to locate the explosion in 3 d space and time climatological atmospheric velocity models predict that infrasound signals from sources that occur at mid northern latitudes in winter are usually ducted to the east due to eastward zonal winds in this paper we analyze travel time picks and use 3 d ray tracing to generate synthetic travel times based on various atmospheric models to show that the seismic network data instead reveal a predominant westward propagation direction a sudden stratospheric warming event that reversed the zonal wind flow explains this westward propagation the seismic data illuminate in unprecedented spatial detail the range and azimuthal definition of shadow zones out to a range of 500 km suggesting that dense seismic networks can be used to study infrasound propagation at spatial resolutions that exceed that which can be done with only a handful of globally distributed infrasound arrays

a study of mesoscale convective bands behind cold fronts part i mesoscale organization this paper reports observations made over the north atlantic of a system of convective cloud bands found within the cold air behind an occluded front the observations were made from an instrumented aircraft which additionally released a pattern of dropsondes measuring temperature relative humidity and wind as functions of pressure these data are analysed to establish some of the mesoscale cloud scale and microphysical properties of the system here in part i the mesoscale structure is described and compared with the predictions of various theoretical models the convective cloud structure emerges as a consequence of the mesoscale organization but appears to play only a minor role in its creation and maintenance one of the theoretical models considered conditional symmetric instability provides a piausible explanation of the mesoscale observations

deep tropospheric gravity waves created by leeside cold fronts abstract the water vapor channel of the geostationary operational environmental satellite goes 8 reveals narrow 30 km wide elongated 500 1000 km bands that propagate southward on the eastern side of the rocky mountains from colorado to texas two events in which surface and wind profiler observations show that these bands are associated with leeside cold fronts are documented in detail and several other cases are summarized the wind profilers observe vertical motions exceeding 1 m s 1 in narrow plumes at the leading edge of the fronts in broader zones in the upper troposphere and in the lower stratosphere these cause vertical displacements of up to 1 km and are responsible for the signature in water vapor images the bands occur when the rocky mountains block either arctic leeside cold fronts coming from the north or northeast or pacific cold fronts coming from the northwest the blocking changes the frontal orientation and disrupts geostrophic thermal wind balance near the terrain modified fron

central and eastern u s surface pressure variations derived from the usarray network abstractlarge magnitude pressure signatures associated with a wide range of atmospheric phenomena e g mesoscale gravity waves convective complexes tropical disturbances and synoptic storm systems are examined using a unique set of surface pressure sensors deployed as part of the national science foundation earthscope usarray transportable array as part of the usarray project approximately 400 seismic stations were deployed in a pseudogrid fashion across a portion of the united states for 1 2 yr then retrieved and redeployed farther east surface pressure observations at a sampling frequency of 1 hz were examined during the period 1 january 2010 28 february 2014 when the seismic array was transitioning from the central to eastern continental united states surface pressure time series at over 900 locations were bandpass filtered to examine pressure perturbations on three temporal scales meso 10 min 4 h subsynoptic 4 30 h and synoptic 30 h 5 days scales case studies of strong pressure pe

the relevance of conditional symmetric instability to the prediction of mesoscale frontal rainbands this paper examines the theory of conditional symmetric instability bennetts and hoskins 1979 and considers its relevance to meso scale frontal rainbands the theoretical growth rate of the instability is evaluated from synoptic scale data obtained from a numerical forecast model and compared with observations of the horizontal structure of rainfall observed by radar one case study is presented in detail and a further 44 cases summarized rainbands were observed on 80 of the occasions on which they were predicted

detection of gravity waves across the usarray a case study abstract barometers deployed as part of the usarray transportable array ta recorded large 300 pa peak to peak gravity waves or gust fronts that originated near a severe tornadic storm system in the southern united states on april 27 2011 we present a new method in which the ta is divided into a large number of elemental sub arrays each 3 element sub array triad is sufficiently closely spaced so that the long period gravity wave signal is coherent but large enough to provide a robust estimate of the signal s direction and speed the results from each triad are combined to follow the progress of gravity waves as they propagate across the ta over 2 days in late april 2011 we observe a large high amplitude gravity wave spanning a region over 200 000 km2 progressing to the nnw away from the tornadic storm region we also observe gravity waves with lower amplitudes and smaller spatial extent along the gulf coast propagating southward away from the storm region this study demonstrates the functionality of the usarray pressure sensors for analyzing gravity wave dynamics over periods greater than 40 min and across a wide region in principle the method could be applied to study other long period wave phenomena recorded by any dense large scale network and is not limited to gravity waves

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

review of wave turbulence interactions in the stable atmospheric boundary layer flow in a stably stratified environment is characterized by anisotropic and intermittent turbulence and wavelike motions of varying amplitudes and periods understanding turbulence intermittency and wave turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans the stable atmospheric boundary layer sabl commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces or even daytime over snow and ice surfaces and when warm air is advected over cold surfaces intermittent turbulence intensification in the sabl impacts human activities and weather variability yet it cannot be generated in state of the art numerical forecast models this failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random turbulence generation in a stably stratified flow in which wave turbulence interaction is a potential mechanism for turbulence intermittency a workshop on wave turbulence interactions in the sabl addressed the current understanding and challenges of wave turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent turbulence from the perspectives of theory observations and numerical parameterization there have been a number of reviews on waves and a few on turbulence in stably stratified flows but not much on wave turbulence interactions this review focuses on the nocturnal sabl however the discussions here on intermittent turbulence and wave turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general

a comparative study of large amplitude gravity wave events abstract two large amplitude gravity waves were observed over the midwestern united states on 5 and 14 january 1989 during the university of illinois winter precipitation program on both days an extensive amount of data was recorded including data from two radars and a radiosonde facility the waves originated near missouri registered pressure fluctuations as large as 10 mb and produced distinct precipitation bands along their updraft regions the waves were long lived and maintained their identity over 1000 km a distance several times their wave lengths the synoptic features at the surface were dissimilar a deep cyclone was present on 5 january while a leeside trough was present on 14 january however the middle and upper tropospheric flow patterns were similar in both cases the axis of a trough was immediately upstream of the gravity wave genesis area and a jet streak had just propagated through the base of the trough toward a downstream ridge soundings taken near the gravity waves were re

sources of mesoscale variability of gravity waves part i topographic excitation abstract aircraft measurements of winds and temperatures collected during the gasp program are used to study the effects of topography as a source of mesoscale variability variances of fluctuations at the mesoscale over rough terrain are enhanced up to nearly two orders of magnitude compared to nonsource regions in some cases and are frequently enhanced by an order of magnitude the implications of these episodic enhancements of variances for the vertical transports of energy and momentum are considered in the framework of gravity wave theory the observed flight data are used to estimate the momentum flux u w on several flight segments results show that the flux is generally negative with mean value 0 26 m2 s 2 and with magnitudes ranging up to 1 5 m2 s 2 spectral analysis shows that the largest contributions to the net flux come from horizontal scales of 25 x 60 km finally the observed momentum fluxes are used to infer the anisotropy factor of gravity waves over rough terrain which is foun

mechanics of a strong subsynoptic gravity wave deduced from satellite and surface observations abstract the three dimensional structure and implied dynamics of a strong tropospheric gravity wave event am studied it is shown that satellite and continuous surface observations reveal the subsynoptic nature of this wave of depression to an extent impossible with conventional data the observations and theory suggest that the gravity wave originated in the upper troposphere near a jet streak was quasi hydrostatic and hence relatively nondispersive and long lived the behavior of the wave at upper tropospheric levels is revealed by sequences of visible and infrared goesynchronous satellite imagery quantitative estimates of cloud top temperatures and winds suggest strong subsidence new 300 mb with an isentropic depression as large as 900 m the upper level depression and the surface disturbance propagate coherently with a speed of 32 m s 1 indicating that they are part of the same internal gravity wave the vertical tilt with height is opposite to the propagation direction and thus is consistent with

a variational multiple doppler radar three dimensional wind synthesis method and its impacts on thermodynamic retrieval abstract a multiple doppler radar synthesis method is developed to recover the three dimensional wind field in this method the solutions are obtained by variationally adjusting the winds to satisfy a series of constraints in weak formats among them the primary ones are multiple radar radial velocity observations the anelastic continuity equation the vertical vorticity equation the background wind and spatial smoothness terms the retrieved wind products are at two time levels and can be readily applied to deduce the information about the pressure and temperature through the use of the thermodynamic retrieval algorithm in which the temporal derivatives of the wind fields are required experiments using model simulated data are conducted from which two major findings are obtained first the wind field along and near the radar baseline can still be recovered this is a major advantage over the traditional approach therefore the proposed method is capable of providing uninterrupted observations o

initiation of a solitary wave family in the demise of a nocturnal thunderstorm density current abstract this paper describes the characteristics and evolving nature of a vigorous thunderstorm density current very early in the morning of 9 may 1981 in oklahoma because the ambient lower atmosphere was stratified interesting interactions between the outflow current and the ambient environment resulted the leading portion of the current was modulated by at least three gravity wavelike perturbations of horizontal spacing 12 km which initially coexisted with it however as the current evolved it initiated an undular borelike disturbance which propagated ahead into the stable boundary layer carrying cold outflow air in large amplitude rolls eventually the wave family left the decelerating outflow air in its wake this borelike disturbance resembles the australian morning glory phenomenon and appears to represent an early stage in the development of a solitary wave family the observations resemble other reported morning glories and solitary waves as well their laboratory and numerically simulated

observations of vertical velocity over illinois by the flatland radar a new vhf clear air doppler radar has been constructed in very flat terrain near urbana illinois this radar called the flatland radar as presently configured measures a profile of the vertical component of the wind velocity every 2 5 minutes it is found that typical time variances of vertical velocity over this very flat terrain are similar to the small variances observed during quiet periods near mountains the observed absence of extended periods of large variance supports the hypothesis that the active periods observed near mountains are mainly due to orographic effects the absence of such effects at flatland should facilitate the study of other meteorological processes for example in the case study presented here it is suggested that the vertical motions associated with large scale baroclinic storms are measurable by the flatland radar

numerical simulation of the large amplitude mesoscale gravity wave event of 15 december 1987 in the central united states abstract an observational study employing spectral methods is first made to establish a background for a modeling effort of the mesoscale gravity wave event of 15 december 1987 the waves are found to have wavelengths of 100 160 km phase speeds of approximately 30 m s 1 and lifetimes of over 6 h conditions for their maintenance are evaluated indicating the presence of a wave duct and a supportive role for wave cisk convection shearing instability and geostrophic adjustment are all implicated as possible source mechanisms for the observed waves the case is then simulated with the pennsylvania state university national center for atmospheric research mm4 mesoscale forecast model with the following primary objectives i to test the model s ability to simulate a mesoscale gravity wave event ii to examine in detail the environments of mesoscale gravity wave development and iii to investigate the mechanisms of mesoscale gravity wave generation and maintenance the full physics control experim

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

band formation in a new england winter storm abstract this case study addresses mechanisms of band formation in a new england winter storm the structure of the bands and their environment are documented with synoptic observations radar data and analyses of instrumented aircraft flights through the bands we postulate that processes on three scales are responsible for the bands observed that the bands are probably a manifestation of mesoscale symmetric instability and that potential energy for the instability is generated by synoptic scale differential lapse rate advection and converted to kinetic energy by symmetric overturning frontogenetical forcing results in an intermediate or subsynoptic scale region of ascent which brings the atmosphere to saturation and initiates the release of potential energy

a study of a mesoscale solitary wave in the atmosphere originating near a region of deep convection abstract an analysis of a mesoscale wave which occurred over the eastern united states on 6 march 1969 is presented its origin is attributed to the perturbation of a midtropospheric inversion by a squall line after the wave formed it propagated in the direction of the mid and upper level tropospheric flow and expanded as an arc with the center located near the region of convective activity the wave travelled from western tennessee and kentucky over a distance of more than 1000 kilometers to nova scotia with a mean speed of 55 m s 1 the event was quite obvious on surface barographs throughout this region pressure traces showed an obvious v shaped pressure drop of 3 to 6 mb over much of the wave path the wave persisted for about 9 hours with little change in character the synoptic situation is analysed and compared with similar atmospheric conditions in other studies the generation mechanism of an internal gravity wave of depression is investigated by a simple model it is found that wave of depre

tracking mesoscale pressure perturbations using the usarray transportable array abstractmesoscale convective phenomena induce pressure perturbations that can alter the strength and magnitude of surface winds precipitation and other sensible weather which in some cases can inflict injuries and damage to property this work extends prior research to identify and characterize mesoscale pressure features using a unique resource of 1 hz pressure observations available from the usarray transportable array ta seismic field campaign a two dimensional variational technique is used to obtain 5 km surface pressure analysis grids every 5 min from 1 march to 31 august 2011 from the ta observations and gridded surface pressure from the real time mesoscale analysis over a swath of the central united states bandpass filtering and feature tracking algorithms are employed to isolate identify and assess prominent mesoscale pressure perturbations and their properties two case studies the first involving mesoscale convective systems and the second using a solitary gravity wave are analyzed u

the cold front of 15 april 1994 over the central united states part i observations abstract detailed observations of the interactions of a cold front and a dryline over the central united states that led to dramatic undulations in the boundary layer including an undular bore are investigated using high resolution water vapor mixing ratio profiles measured by raman lidars the lidar derived water vapor mixing ratio profiles revealed the complex interaction between a dryline and a cold frontal system an elevated well mixed and deep midtropospheric layer as well as a sharp transition between 5 and 6 km altitude to a drier region aloft was observed the moisture oscillations due to the undular bore and the mixing of the prefrontal air mass with the cold air at the frontal surface are all well depicted the enhanced precipitable water vapor and roll clouds the undulations associated with the bore the strong vertical circulation and mixing that led to the increase in the depth of the low level moist layer and the subsequent lifting of this moist layer by the cold frontal surface

the lagrangian parcel dynamics of moist symmetric instability abstract a simple model describing the slantwise ascent of a two dimensional horizontal air tube subject to moist symmetric instability is developed under the assumptions that the froude number is small and that mixing is absent it is shown that in general the horizontal velocities attained by the tube are comparable to those of the mean flow and that vertical velocities of up to a few meters per second are possible the tube ascends slantwise in such a way that its buoyancy remains nearly zero unless the environment is my very nearly moist adiabatic in which case ascent at an angle of 45 to the vertical is preferred results of the analysis support the contentions of bennetts and hoskins and emanual that moist symmetric instability is the cause of some mesoscale rainbands in a companion paper it is demonstrated that the stability of the moist baroclinic atmosphere to two dimensional slantwise displacements of arbitrary magnitude can be approximately assessed by reversibly lifting parcel along sur

near monochromatic ducted gravity waves associated with a convective system close to the pyrenees near monochromatic gravity waves gws associated with a mesoscale convective system mcs were detected during the boundary layer late afternoon and sunset turbulence bllast field campaign in lannemezan france on 21 june 2011 these gws are analyzed using available instrumental data e g an array of microbarometers a microwave system humidity and temperature profiler hatpro and an ultra high frequency uhf wind profiler pressure oscillations of up to 0 5 hpa were recorded after a pronounced pressure drop of 1 4 hpa identified as the mcs weak low wavelet analysis and evaluated wave parameters confirm the occurrence of such gws period 9 min horizontal wavelength 7 km which propagated from southwest to northeast i e in the same direction of propagation as the mcs observational evidence suggests the downdraughts associated with the rear inflow jet at the weak low zone of the mcs as the most likely generator mechanism of the gws however the complex orography and proximity of the pyrenees to the field campaign could also play an important role wave propagation was possible through the ducting mechanism favoured by the existence of a critical level in a wind sheared environment around 2000 m above ground level wave like motions related to the passage of the gws were also observed in other atmospheric parameters close to the surface and within the lower troposphere the effects of gws on the surface fluxes have also been analyzed through multi resolution flux decomposition mrfd methods

the mysteries of mammatus clouds observations and formation mechanisms mammatus clouds are an intriguing enigma of atmospheric fluid dynamics and cloud physics most commonly observed on the underside of cumulonimbus anvils mammatus also occur on the underside of cirrus cirrocumulus altocumulus altostratus and stratocumulus as well as in contrails from jet aircraft and pyrocumulus ash clouds from volcanic eruptions despite their aesthetic appearance mammatus have been the subject of few quantitative research studies observations of mammatus have been obtained largely through serendipitous opportunities with a single observing system e g aircraft penetrations visual observations lidar radar or tangential observations from field programs with other objectives theories describing mammatus remain untested as adequate measurements for validation do not exist because of the small distance scales and short time scales of mammatus modeling studies of mammatus are virtually nonexistent as a result relatively little is known about the environment formation mechanisms properties microphysics and dynamics of mammatus this paper presents a review of mammatus clouds that addresses these mysteries previous observations of mammatus and proposed formation mechanisms are discussed these hypothesized mechanisms are anvil subsidence subcloud evaporation sublimation melting hydrometeor fallout cloud base detrainment instability radiative effects gravity waves kelvin helmholtz instability rayleigh taylor instability and rayleigh benard like convection other issues addressed in this paper include whether mammatus are composed of ice or liquid water hydrometeors why mammatus are smooth what controls the temporal and spatial scales and organization of individual mammatus lobes and what are the properties of volcanic ash clouds that produce mammatus the similarities and differences between mammatus virga stalactites and reticular clouds are also discussed finally because much still remains to be learned research opportunities are described for using mammatus as a window into the microphysical turbulent and dynamical processes occurring on the underside of clouds

mesoscale structure in the megalopolitan snowstorm of 11 12 february 1983 part iii a large amplitude gravity wave abstract a large amplitude singular gravity wave is studied through the analysis of hourly observations radar and satellite data and observations of cloud to ground lightning flashes the wave activity was initiated just ahead of and to the left of the track of the major atlantic coast cyclone of 11 12 february 1983 the initial wave of depression was followed by a wave of elevation and finally a wake depression pressure amplitudes were several millibars the system propagated northeastward at 15 m s 1 accelerating to more than 25 m s 1 against increasing northeasterly flow in the lower troposphere surface northeasterlies increased and became gusty with the approach of the first pressure falls reaching a maximum at the pressure trough then abruptly weakening and backing as strong pressure increases were observed strong fluctuations in column total condensation rate and radar reflectivity occurred with the passage of the wave clustered lightning activity accompanied wave passage principally near

structure and evolution of the 22 february 1993 toga coare squall line aircraft observations of precipitation circulation and surface energy fluxes abstract this study documents the precipitation and kinematic structure of a mature eastward propagating oceanic squall line system observed by instrumented aircraft during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare doppler radar and low level in situ observations are used to show the evolution of the convection from an initially linear nnw sse oriented convective line to a highly bow shaped structure with an embedded low to midlevel counterclockwise rotating vortex on its northern flank in addition to previously documented features of squall lines such as highly upshear tilted convection on its leading edge a channel of strong front to rear flow that ascended with height over a rear inflow that descended toward the convective line and a pronounced low level cold pool apparently fed from convective and mesoscale downdrafts from the convective line rearward the observations of this system showed distinct multiple maxima in updraft strength with

mesoscale dynamics in the palm sunday tornado outbreak abstract radar and satellite imagery suggest that strong mesoscale forcing occurred in the palm sunday tornado outbreak on 27 march 1994 parallel lines of severe thunderstorms within each of three mesoscale convective systems developed just ahead of a cold front in mississippi and alabama on this date analyses of routine meteorological observations barograph data and forecasts from the eta and ngm models and a mesoscale research model mass are used to examine the relative roles of large scale dynamics and mesoscale processes in triggering and organizing the mesoscale convection quasigeostrophic forcing was absent in the outbreak region likewise a thermally direct circulation system transverse to the upper level jet that was present to the northwest of the outbreak region was decoupled from the strong low level ascent occurring in northern alabama and mississippi at the time of the outbreak strong ageostrophic frontogenesis in the presence of conditional symmetric instability csi was the chief

a study of cyclone mesoscale structure with emphasis on a large amplitude inertia gravity wave abstract an analysis is presented of prominent mesoscale structure in a moderately intense cyclone with emphasis on a long lived large amplitude inertia gravity wave igw that moved through the northeastern united states on 4 january 1994 available national weather service wsr 88d doppler radar and wind profiler observations are employed to illustrate the rich time dependent three dimensional structure of the igw as the igw amplified peak crest to trough pressure falls exceeded 13 hpa 30 min 1 it also accelerated away from the cyclone reaching a peak forward speed of 35 40 m s 1 across eastern new england the igw was one of three prominent mesoscale features associated with the cyclone the others being a weak offshore precursor warm frontal wave and an onshore band of heavy snow snow bomb in which peak hourly snowfalls of 10 15 cm were observed none of these three prominent mesoscale features were well forecast by existing operational prediction models particularly with regard to preci

a case study of gravity waves convective storms interaction 9 may 1979 abstract an analysis is presented of a series of severe storms which occurred in the north central united states on 9 may 1979 and whose spatial distribution and movement correlate well with observed gravity waves two gravity wave trains of 2 1 3 mb amplitude 2 5 3 3 h period and 240 265 km horizontal wavelength were isolated through power spectra analysis and cross correlation techniques applied to national weather service barograph traces the wave trains propagated in the 200 direction which coincided with the jet axis with a phase velocity of 20 30 m s 1c and within a 300 km wide band the storms were identified on enhanced infrared goes satellite pictures with the help of radar summaries these convective systems initially developed in nebraska and propagated north northeast at 25 m s 1 revealing wave like characteristics with a separation of 300 400 km the convective systems were closely linked to the observed wave trains with cell intensity height and associated rainfall maximized at the wa

wavelet analysis and the governing dynamics of a large amplitude mesoscale gravity wave event along the east coast of the united states detailed diagnostic analyses are performed upon a mesoscale numerical simulation of a well observed gravity wave event that occurred on 4 january 1994 along the east coast of the united states the value of using wavelet analysis to investigate the evolving gravity wave structure and of using potential vorticity pv inversion to study the nature of the flow imbalance in the wave generation region is demonstrated the cross stream lagrangian rossby number the residual in the nonlinear balance equation and the unbalanced geopotential height field obtained from pv inversion are each evaluated for their usefulness in diagnosing the flow imbalance all of these fields showed clear evidence of strong imbalance associated with a middle to upper tropospheric jet streak and tropopause fold upstream of the large amplitude gravity wave several hours before the wave became apparent at the surface analysis indicates that a train of gravity waves was continuously generated by geostrophic adjustment in the exit region of the unbalanced upper level jet streak as it approached the inflection axis in the height field immediately downstream of the maximum imbalance associated with the tropopause fold a split front in the middle troposphere characterized by the advance of the dry conveyor belt above the warm front was overtaken by one of these propagating waves during this merger process a resonant interaction resulted which promoted the rapid amplification and scale contraction of both the incipient wave nonlinear wave development and the split front frontogenesis the gravity wave and front aloft became inseparable following this merger the situation became even more complex within a few hours as the vertical motion enhanced by this front wave interaction acted upon a saturated potentially unstable layer to produce elevated moist convection an analysis of the temporal changes in the vertical profile of wave energy flux suggests that moist convective downdraughts efficiently transported the wave energy from the midlevels downward beneath the warm front surface where the wave became ducted however pure ducting was not sufficient for maintaining and amplifying the waves rather wave cisk conditional instability of the second kind was crucial this complex sequence of nonlinear interactions produced a long lived large amplitude gravity wave that created hazardous winter weather and disrupted society over a broad and highly populated area although gravity waves with similar appearance to this large amplitude wave of depression occasionally have been seen in other strong cyclogenesis cases involving a jet streak ahead of the upper level trough axis it is unknown whether other such events share this same sequence of interactions

accounting for velocity anisotropy in seismic traveltime tomography a case study from the investigation of the foundations of a byzantine monumental building we estimate velocity anisotropy factors from seismic traveltime tomographic data and apply a correction for anisotropy in the inversion procedure to test possible improvements on the traveltime fit and the quality of the resulting tomographic images we applied the anisotropy correction on a traveltime data set obtained from the investigation of the foundation structure of a monumental building a byzantine church from the 11th century ad in athens greece vertical transverse isotropy is represented by one axis of symmetry and one anisotropy magnitude for the entire tomographic inversion grid we choose the vertical direction for the symmetry axis by analysing the available data set and taking into account information on the character of the foundations of the church from the literature and past excavations the anisotropy magnitude is determined by testing a series of values of anisotropy and examining their effect on the tomographic inversion results the best traveltime fit and image quality are obtained with an anisotropy value vmax vmin of 1 6 restricted to the high velocity structures in the subsurface we believe that this anisotropy value which is significantly higher than the usual values reported for near surface geological material is related to the fabric of the church foundations due to the shape of the individual stone blocks and the layout of the stonework inversion results obtained with the correction for anisotropy indicate that both the traveltime fit and the image quality are improved providing an enhanced reconstruction of the velocity field especially for the high velocity features based on this enhanced and more reliable reconstruction of velocity distribution an improved image of the subsurface material character was made possible in particular the pattern and state of the church foundations and possible weak ground material areas were revealed more clearly this improved subsurface knowledge may assist in a better design of restoration measures for monumental buildings such as byzantine churches

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

a 4 yr climatology of pressure disturbances using a barometer network in central illinois this paper presents a climatology of coherent disturbances detected during 1991 95 by a network of barometers with a diameter of about 50 km located in a very flat terrain centered on the flatland atmospheric observatory in east central illinois an automatic wavelet based adaptive filter is used to extract the waveforms of all disturbance events with amplitudes larger than a frequency dependent threshold the extracted events cover characteristic temporal scales from about 30 min to 6 h that is the range that includes mesoscale disturbances that affect the weather and the forecasts the analysis resulted in two classes of events one class called coherent events or ces consists of disturbances that propagated coherently through the barograph network and for which the phase propagation velocity dominant period and horizontal wavelength could be estimated with good accuracy the propagation directions of 97 of the ces were between 08 and 1808 i e had an eastward component and the speeds of 96 were between 10 and 50 ms 21 with a mode at 25 30 m s21 the other class called incoherent events or ies consists of disturbances that had significant amplitudes but that did not propagate coherently across the network so that the propagation velocity could not be estimated this class consists of localized disturbances and wave packets with short periods and or wavelengths or with pressure signatures that were too different at the network stations the extracted events are attributed to gravity waves wave packets gravity currents pressure jumps solitary waves bores etc the rate of occurrence of events had a strong seasonal dependence with a maximum in fall and winter and a minimum in summer the ces occurred about 20 21 of the total time in fall and winter and 12 in summer while all events occurred 34 in both fall and winter and 23 in summer the seasonal dependence of events confirms the strong relation of these disturbances to the baroclinicity of the atmosphere concurrent vertical velocity fluctuations observed by the 50 mhz radar at the flatland atmospheric observatory showed that many of the large amplitude events extended up to at least 7 km the highest altitude reliably observed by the radar

diagnosis of hydrometeor profiles from area mean vertical velocity data a simple one dimensional microphysical retrieval model is developed for estimating vertical profiles of liquid and frozen hydrometeor mixing ratios from observed vertical profiles of area mean vertical velocity in regions of convective and or stratiform precipitation the mean vertical velocity profiles can be obtained from doppler radar single and dual or other means the one dimensional results are shown to be in good agreement with two dimensional microphysical fields from a previous study sensitivity tests are performed

origin evolution and finescale structure of the st valentine s day mesoscale gravity wave observed during storm fest part iii gravity wave genesis and the role of evaporation abstract on 14 february 1992 a long lived moderate amplitude mesoscale gravity wave formed in kansas during the storm scale operational and research meteorology fronts experiment systems test storm fest wave formation was evident in correlated surface pressure and wind fields the wave of depression accompanied by a weak rainband tracked across the state a wealth of data was collected on the mature wave as it passed over the storm fest dual doppler domain however the mechanism of genesis remained difficult to ascertain since wave formation occurred in a region of less comprehensive observations the genesis of the storm fest gravity wave is successfully simulated using the fifth generation pennsylvania state university national center for atmospheric research penn state ncar mesoscale model mm5 which was run at 6 km grid spacing in the innermost domain the lee cyclone movement dry airmass development and gravity wave formation over kansas were successfully captured by the model results

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

frontogenesis in the presence of small stability to slantwise convection abstract it is often observed that despite the existence of near neutrality to slantwise convection rainbands and snowbands can persist for long periods with narrow intense updrafts producing large quantities of precipitation in many cases this is probably due to the presence of active frontogenesis which as shown here maintains such structures in order to investigate this process we use two dimensional semigeostrophic theory to solve the deformation forced frontogenesis problem for a circumstance in which the stability to moist slantwise convection is small but positive in this case numerical simulation is necessary to determine the evolution of the front several previous studies have described the role of diabatic forcing in modifying the cross frontal circulation by use of the sawyer eliassen equation in particular analytic solutions of that equation for the case of small moist symmetric stability show that a narrow updraft should occur ahead of the maximum geostrophic frontogenesis numeri

a study of infrasound propagation using dense seismic network recordings of surface explosions abstract we use dense seismic network recordings of accurately located surface explosions in northern utah to shed light on the propagation of infrasound through the stratosphere the data clearly show propagation of infrasound downwind from the source as expected the data also clearly show the penetration of infrasound into geometric shadow zones near the source and the spread of infrasound to a distance of 800 km from the source the spread of infrasound both toward and away from the source is not predicted by applying either ray theory or the full wave finite difference technique to smooth ground to space g2s models the mismatch between synthetics and data suggest a missing component in these models possibly a small scale gravity wave structure comparison of the network recordings of approximately 1500 infrasound signals with travel time predictions based on rays shows no significant average bias in the travel times on average recorded signals arrived 1 s earlier than predictions travel time residuals are normally distributed about the mean with a standard deviation of 15 s the small bias of the travel time predictions indicates that despite the fact that small scale structure is averaged out of commonly used g2s models the large scale structure of the atmosphere is accurately represented the scatter of travel time residuals is suggestive of small scale structure missing from the models that we used to make the predictions but firm conclusions would require a more in depth study

observations of a mesoscale ducted gravity wave abstract this paper reports coordinated observations of a mesoscale gravity wave made during the fronts 84 field experiment conducted in southwestern france in the summer of 1984 the observations were unique in the sense that all relevant wave characteristics including its detailed vertical structure could be directly ascertained and shown to be mutually consistent the wave was observed to be ducted the static stability structure of the atmosphere was favorable for the existence of such a duct a critical level where the phase velocity of the wave matches the wave parallel background wind speed was present in or just above a layer of low static stability that capped a stabler layer at a still lower level the observed vertical structure was that of a standing wave with the top of the stable lower layer corresponding roughly to an antinode and one half the vertical wavelength below the critical level the wave was observed when there was extensive activity associated with two line of deep convection

an observation of banded convective development in the presence of weak symmetric stability abstract satellite imagery dramatically portrays a mesoscale organization of deep convection over the south central united states on 5 june 1986 free convection was expected over the region the rapid development and organization of the convection simultaneously across a broad area suggests the presence of a mesoscale instability analysis of satellite and conventional data suggests that a layer of weak symmetric stability modified the atmosphere s response to free convective instability contributing to the highly organized banded structure observed

a case study of an unusually intense atmospheric gravity wave abstract a remarkable long lived large amplitude gravity wave in the carolinas and virginia on 27 february 1984 is investigated by means of a subsynoptic scale case study the wave was characterized by a minor wave of elevation followed by a sharp wave of depression with a period of 2 3 h a horizontal wavelength of 100 150 km and surface pressure perturbation amplitudes of 3 14 mb the wave propagated toward the east southeast at 1 5 m s 1 accelerating to more than 20 m s 1 after it crossed the atlantic coast wave passage was accompanied by gusty surface easterly winds reaching 30 m s 1 and an abrupt termination of precipitation with the rapid surface pressure fall the synoptic criteria identified by uccellini and koch as common to many cases of large amplitude gravity waves were present in this case gravity waves were first detected across western tennessee and northern mississippi in a wake depression region to the rear of an advancing squall line an amplifying wave emerged out of the wave packet

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

solitary waves in the lower atmosphere solitary waves are of intense interest in the physical and mathematical sciences1 these nonlinear waves often seem to have a primary role in the asymptotic description of propagating disturbances in inland lakes and coastal waters2 4 in the thermocline of the open sea5 and in the lower atmosphere6 7 we present here new acoustic sounder observations of complex tropospheric solitary wave disturbances at tennant creek in the arid interior of australia fig 1 a description and interpretation of a new type of visible wave phenomena over northern australia which appear as thin propagating cumulus cloud lines and a discussion of observations at burketown on the gulf of carpentaria of a new class of low altitude propagating solitary wave roll clouds which originate to the south these observations when correlated with observations at tennant creek indicate that solitary wave generating disturbances in the form of internal bores8 9 propagate over large distances

the synoptic setting and possible energy sources for mesoscale wave disturbances abstract thirteen case studies of mesoscale wave disturbances characterized by either a singular wave of depression or wave packets with periods of 1 4 h horizontal wavelengths of 50 500 km and surface pressure perturbation amplitudes of 0 2 7 0 mb are reviewed to isolate common synoptic features for these cases and to shed light on possible energy sources for the waves a strong thermal inversion in the lower troposphere north of a frontal boundary and a jet streak propagating toward a ridge axis in the upper troposphere are commonly observed in all the cases in general the area of wave activity is bounded by the jet axis to the west or northwest a surface front to the southeast an inflection axis between the trough and ridge axes to the southwest and the ridge axis to the northeast the conditions specified by lindzen and tung as being necessary to form a wave duct which include the existence of the lower tropospheric inversion seem to be met in many of these cases this suggests that a du

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