dryline on 19 june 2002 during ihop part i airborne doppler and leandre ii analyses of the thin line structure and convection initiation the evolution and finescale structure of a dryline that initiated a line of thunderstorms is presented both the along line variability and mean vertical structure were examined using data collected by an airborne doppler radar and a water vapor differential absorption lidar dial the initiation of convection appeared to result from the diurnally induced easterly flow in the maritime air east of the dryline that typically develops late in the day this flow increased the low level convergence and allowed rising parcels of air to reach the level of free convection the along line variability was largely attributed to numerous misocyclones distorting the thin line of radar reflectivity by advecting dry moist air across the dryline south north of the misocyclone the misocyclones also influenced the location of the updrafts with most of the peak values positioned north of the circulations as a result these updrafts were fortuitously positioned in regions of high mixing ratio where the first convective cells initiated

relationship between a weakening cold front misocyclones and cloud development on 10 june 2002 during ihop abstract the finescale structure and evolution of a cold front in the presence of small scale circulations are examined using overdetermined dual doppler syntheses of mobile radar data along with thermodynamic data and cloud imagery collected on 10 june 2002 during the international h2o project ihop linear clear air reflectivity maxima and open cellular convection intersect the cold front causing spatial variations in convergence along the front small scale vertical vorticity maxima misocyclones often are coincident with these intersections and are associated with vertical velocity maxima throughout the deployment trajectory analyses indicate that parcels entering the frontal circulation travel predominately in the along front direction during the first hour of the deployment upward motion is nearly continuous along the front consequently parcels remain in regions of upward motion as they move along the front and many eventually ascend to cloud base in response a line of cumulus clouds dev

the evolution of an oklahoma dryline part i a meso and subsynoptic scale analysis abstract a study is made of the 8 june 1974 oklahoma dryline and tornado outbreak case using data synthesis 1 to fit existing concepts on dryline structure and behavior to this case and 2 to identify processes contributing to moisture convergence along the dryline the dryline undergoes a major transformation in structure from sloped to slopeless during the day as implied from mesoscale 10 100 km and subsynoptic scale 100 1000 km analysis of virtual potential temperature fields mesoscale examination of dryline movement reveals the presence of wavelike perturbations which propagate along the dryline irregardless of its slope and contribute more to its eastward progression than does the downward slope of the terrain all but one of 22 tornadoes reported in oklahoma on this date were associated with thunderstorms that formed within a subsynoptic moisture convergence region at the dryline in central oklahoma results indicate a downward transport of southwesterly momentum through a well develope

the triple point on 24 may 2002 during ihop part i airborne doppler and lase analyses of the frontal boundaries and convection initiation an analysis of the initiation of deep convection near the triple point between a cold front and dryline is presented high spatial resolution doppler wind syntheses combined with vertical cross sections of mixing ratio q and aerosol scattering ratio retrieved from a lidar flying over the triple point provide an unprecedented view of the initiation process the doppler wind synthesis revealed variability along the dryline similar to the precipitation core gap structure documented for oceanic cold fronts vertical cross sections through the dryline suggest a density current like structure with the hot and dry air being forced up and over the moist air double thin lines associated with moisture gradients were also resolved the vertical profile of retrieved q approximately perpendicular to the dryline showed a pronounced jump in the depth of the moisture layer across the triple point analyses of dropsonde data show the existence of virtual potential temperature v gradients across the cold front and the dryline although the vertical velocity was strong at the triple point deep convection initiated 50 km to the east the location where convection first developed was characterized by a prominent aerosol and moisture plume reduced static stability and the largest potential instability an internal gravity wave may have provided the lift to initiate convection

airborne pseudo dual doppler analysis of a dryline outflow boundary intersection abstract on 3 june 1995 as part of the verification of the origins of rotation in tornadoes experiment vortex the electra doppler radar eldora onboard the national center for atmospheric research ncar electra aircraft made possible a high resolution examination of clear air motions in the texas panhandle in and around the intersection of the dryline and a surface baroclinic boundary a location commonly referred to as the triple point the eldora observations as well as conclusions drawn from analyses of these data are presented and discussed a transverse secondary circulation associated with the dryline is visualized through analyses of the eldora data typical values of rising and sinking air are found to be 2 m s 1 and 2 3 m s 1 respectively these vertical velocities are approximately the same as those indicated by in situ data collected onboard the electra because the maximum in rising motion is found at the western edge of the dewpoint gradient and because the low level relative airfl

boundary layer thermodynamics of a high plains severe storm abstract a new analysis method based on air parcel saturation point is used to intercompare data sampled by different systems aircraft rawinsondes and a surface mesonet during the passage of one severe storm in the 1981 cooperative convective precipitation experiment the low level thermodynamic structure simplifies into two distinct branches on a thermodynamic diagram the lower tropospheric environment ahead of the severe storm has a characteristic mixing line structure while the storm low level outflow has a distinct evaporation line structure

a review of cold fronts with prefrontal troughs and wind shifts the conceptual model of a classical surface based cold front consists of a sharp temperature decrease coincident with a pressure trough and a distinct wind shift at the surface many cold fronts however do not conform to this model time series at a single surface station may possess a pressure trough and wind shift in the warm air preceding the cold front hereafter called a prefrontal trough and prefrontal wind shift respectively although many authors have recognized these prefrontal features previously a review of the responsible mechanisms has not been performed to date this paper presents such a review ten disparate mechanisms with different frontal structures have been identified from the previous literature these mechanisms include those external to the front i e those not directly associated with the cold front itself synoptic scale forcing interaction with lee troughs drylines interaction with fronts in the mid and upper troposphere and frontogenesis associated with inhomogeneities in the prefrontal air mechanisms internal to the front i e those directly associated with the structure and dynamics of the front include the following surface friction frontogenesis acting on alongfront temperature gradients moist processes descent of air ascent of air at the front and generation of prefrontal bores gravity waves given the gaps in our knowledge of the structure evolution and dynamics of surface cold fronts this paper closes with an admonition for improving the links between theory observations and modeling to advance understanding and develop better conceptual models of cold fronts with the goal of improving both scientific understanding and operational forecasting

thermodynamic variability within the convective boundary layer due to horizontal convective rolls abstract data from the convection and precipitation electrification cape experiment conducted during the summer of 1991 are used to examine and quantify the horizontal variability of temperature and moisture within the convective boundary layer cbl potential temperature variations were only about 0 5 k while variations in water vapor mixing ratio values of 1 5 2 5 g kg 1 were observed throughout the cbl using radar aircraft and sounding data it is shown that horizontal convective rolls are the likely cause of these variabilities the enhanced moisture occurred within the roll updraft regions thus rolls were transporting moist air from the surface upward the observed cloud base heights obtained from cloud photogrammetry were produced from the highest moisture values within the roll updraft regions since the roll ascending branches contained moisture values that were most representative of the observed cloud base heights it is likely that measurements from within the roll updrafts would prov

a lagrangian objective analysis technique for assimilating in situ observations with multiple radar derived airflow abstract a new lagrangian analysis technique is developed to assimilate in situ boundary layer measurements using multi doppler derived wind fields providing output fields of water vapor mixing ratio potential temperature and virtual potential temperature from which the lifting condensation level lcl and relative humidity rh fields are derived the lagrangian analysis employs a continuity principle to bidirectionally distribute observed values of conservative variables with the 3d evolving boundary layer airflow followed by temporal and spatial interpolation to an analysis grid cloud is inferred at any grid point whose height z zlcl or equivalently where rh 100 lagrangian analysis of the cumulus field is placed in the context of gridded analyses of visible satellite imagery and photogrammetric cloud base area analyses brief illustrative examples of boundary layer morphology derived with the lagrangian analysis are presented based on data collected during the international h2o project iho

finescale vertical structure of a cold front as revealed by an airborne doppler radar abstract in the afternoon of 24 may 2002 a well defined and frontogenetic cold front moved through the texas panhandle detailed observations from a series of platforms were collected near the triple point between this cold front and a dryline boundary this paper primarily uses reflectivity and doppler velocity data from an airborne 95 ghz radar as well as flight level thermodynamic data to describe the vertical structure of the cold front as it intersected with the dryline the prefrontal convective boundary layer was weakly capped weakly sheared and about 2 5 times deeper than the cold frontal density current the radar data depict the cold front as a fine example of an atmospheric density current at unprecedented detail 40 m the echo structure and dual doppler inferred airflow in the vertical plane reveal typical features such as a nose a head a rear inflow current and a broad current of rising prefrontal air that feeds the accelerating front to rear current over the head the 2d cross fro

kinematic and moisture characteristics of a nonprecipitating cold front observed during ihop part i across front structures abstract a wide array of ground based and airborne instrumentation is used to examine the kinematic and moisture characteristics of a nonprecipitating cold front observed in west central kansas on 10 june 2002 during the international h2o project ihop this study the first of two parts is focused on describing structures in the across front dimension coarsely resolved observations from the operational network and dropsondes deployed over a 200 km distance centered on the front are combined with higher resolution observations from in situ sensors doppler radars a microwave radiometer and a differential absorption lidar that were collected across a 40 km swath that straddled a 100 km segment of the front the northeast southwest oriented cold front moved toward the southeast at 8 10 m s 1 during the morning hours but its motion slowed to less than 1 m s 1 in the afternoon in the early afternoon the cold front separated cool air with a northerly component flow of 2 4 m s 1 from a 10 km wide ban

analysis of convergence boundaries observed during ihop_2002 abstract an analysis of six convergence boundaries observed during the international h2o project ihop 2002 is presented the detailed kinematic and thermodynamic structure of these boundaries was examined using data collected by an airborne doppler radar and a series of dropsondes released by a jet flying at 500 mb the former and latter platforms were able to resolve the meso and meso scale circulations respectively convection initiated on three of the days while no storms developed in the regions targeted by the mobile platforms on the other days referred to as null cases the airborne radar resolved the finescale structure of four drylines a cold front and an outflow boundary on the six days horizontal profiles through radar detected thin lines revealed bell shaped distributions and there appeared to be a seasonal dependence of the peak values of radar reflectivity the echo profiles through the fine line in may were in general greater than those plotted for the june cases there was

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

sulfate mineralogy of fumaroles in the salton sea geothermal field imperial county california abstract the salton trough lies in the transition between the san andreas fault and oblique spreading centers and transform faults in the gulf of california the salton sea geothermal field is the northernmost expression of those spreading centers in 2007 two ammonia emitting fumarole fields that had been submerged beneath the salton sea were exposed for the first time in nearly 50 years as the sea level continued to drop these fields have developed a number of boiling pools mud pots gryphons and a unique suite of ammonium sulfate minerals these have been studied over time with long wave infrared remote sensing coupled with ground truth surveys backed by laboratory analyses of the minerals many vents lie at the center of concentric rings of mineralization with systematic occurrence of different minerals from center to edge three semi concentric zones fumarole transition and evaporite have been defined with respect to ammonia emitting vents and bubbling pools the scale of these zones range from several meters localized around individual vents to that of the fumarole fields as a whole the fumarole zone is closest to the vents and locally contains cavernous sulfur crystals and significant deposits of gypsum mascagnite boussingaultite and other ammonium sulfates the transition zone comprises a dark brown surficial band of inconspicuous sodium nitrate underlain by anhydrite bassanite that is thought to have formed by ammonia oxidizing microbes interacting with the ammonium sulfates of the outer fumarole zone the evaporite zone is the outermost and contains blodite thenardite and glauberite which are typical of the sulfates associated with the shoreline of the salton sea remote sensing has shown that the mineral zones have remained relatively stable from 2013 to 2017 with minor variations depending on rainfall temperature and levels of agricultural runoff

the role of boundary layer convergence zones and horizontal rolls in the initiation of thunderstorms a case study abstract the initiation of thunderstorms is examined through a combined observational and modeling case study the study is based on doppler radar aircraft mesonet balloon sounding and profiler and photographic data from the convection initiation and downburst experiment cinde conducted near denver colorado the study examines the initiation of a line of thunderstorms that developed along a preexisting quasi stationary boundary layer convergence line on 17 july 1987 the storms were triggered at the intersection of the convergence line with horizontal rolls where enhanced updrafts were present the primary effect of the convergence line was to deepen the moist layer locally and provide a region potentially favorable to deep convection the critical factor governing the time of storm development was apparently related to the attainment of a balance between horizontal vorticity in the opposing flows on either side of the convergence line the effect was to cause the updrafts in the convergence line

observations of the finescale structure of a dryline during vortex 95 abstract the three dimensional finescale structure of a dryline observed over the texas panhandle during the verification of the origins in tornadoes experiment vortex on 6 may 1995 is presented high resolution observations documenting dryline evolution were collected from midafternoon while it moved slowly eastward until late afternoon as it retrogressed back to the west dryline variability in the horizontal along line direction was revealed by airborne doppler radar observations from the national center for atmospheric research electra doppler radar and ground based measurements from the nearby wsr 88d at amarillo texas this variability was created as the dryline interacted with horizontal convective rolls forming west of the dryline the rolls intersected the dryline at periodic locations creating radar reflectivity and vertical velocity maxima more importantly clouds initiated at these intersection points additional dryline variability was generated through the interaction of the low level fl

initiation of convective storms at radar observed boundary layer convergence lines abstract the origin of 653 convective storms occurring over a 5000 km2 area immediately east of the colorado rocky mountains from 18 may to 15 august 1984 was examined seventy nine percent of the 418 storms that initiated within the study area occurred in close proximity to radar observed boundary layer convergence lines this percentage increased to 95 when only the more intense storms 60 dbze were considered colliding convergence lines initiated new storms or intensified existing storms in 71 of the cases a new storm took a median time of 24 min to grow to 30 dbz following line collision the convergence lines ranged in length between ten and several hundred kilometers both radar and mesonet stations indicated that the primary convergence was concentrated in a zone 0 5 to 5 km in width these lines were characterized on doppler radar as thin lines of enhanced reflectivity between 0 and 20 dbze and as a line of strong radial or azimuthal gradient in doppler velocity these lines were observed ev

observations of convection initiation failure from the 12 june 2002 ihop deployment abstract observations of the development of cumulus convection which reached depths of several kilometers but failed to develop into sustained precipitating cumulonimbus clouds an event the authors term convection initiation failure are presented from the 12 june 2002 international h2o project ihop case the investigation relies heavily on remote and in situ data obtained by mobile truck borne doppler radars mobile mesonets mobile soundings and stereo cloud photogrammetry data collection was focused in northwestern oklahoma near the intersection of an outflow boundary and dryline thunderstorms developed along the dryline during the late afternoon approximately 40 km east of the domain intensively observed by the ground based observing systems farther west within the region of dense observations analyzed herein cumulus congestus clouds formed along an outflow boundary multiple doppler wind syntheses revealed that the boundary layer vertical velocity field was dominated by thermals rather t

a modeling study of the dryline abstract results of a modeling study of the 24 may 1989 dryline are presented a nonhydrostatic two dimensional version of the colorado state university regional atmospheric modeling system csu rams is used to deduce the impact of east west variability of soil moisture and vegetation on convective boundary layer evolution and dryline formation the effects of the initial moisture and wind fields and the impact of the coriolis force on the model results are also examined model output is compared with special airborne and sounding observations of the 24 may dryline several findings of an earlier observational study of the 24 may dryline are supported in the present study the modeled drylines are broadly comparable to the observed dryline with respect to the following properties 1 width 10 km 2 strong horizontal moisture and virtual potential temperature gradients 4 g kg 1 10 km and 2 k 10 km 3 strong horizontal convergence updraft w e shear of n s wind component 8 10 4 s 1 1 m s 1 10 m

the triple point on 24 may 2002 during ihop part ii ground radar and in situ boundary layer analysis of cumulus development and convection initiation abstract cumulus formation and convection initiation are examined near a cold front dryline triple point intersection on 24 may 2002 during the international h2o project ihop a new lagrangian objective analysis technique assimilates in situ measurements using time dependent doppler derived 3d wind fields providing output 3d fields of water vapor mixing ratio virtual potential temperature and lifted condensation level lcl and water saturated i e cloud volumes on a subdomain of the radar analysis grid the radar and lagrangian analyses reveal the presence of along wind i e longitudinal and cross wind i e transverse roll circulations in the boundary layer bl a remarkable finding of the evolving radar analyses is the apparent persistence of both transverse rolls and individual updraft vertical vorticity and reflectivity cores for periods of up to 30 min or more while moving approximately with the local bl wind satellite cloud images and single camera ground photogrammetry imply tha

the frontal hydraulic head a micro α scale 1 km triggering mechanism for mesoconvective weather systems abstract measurements from the noaa boulder atmospheric observatory bao 300 m tower the national center for atmospheric research ncar sabreliner aircraft and the noaa goes 5 satellite give evidence for the cross front scale collapse of nonprecipitating surface cold frontal zones to horizontal distances of 1 km or less the leading edges of these frosts possess the characteristic structure of density current flows an elevated hydraulic head followed by a turbulent wake vertical motions at the frontal heads exceed 5 m s 1 at 300 m agl the ascent at the frontal head may act as a 1 km scale triggering mechanism for the release of potential instability and the formation of intense squall line mesoconvection

the impact of spatial variations of low level stability on the life cycle of a simulated supercell storm abstract this study reports on the dynamical evolution of simulated long lived right moving supercell storms in a high cape strongly sheared mesoscale environment which initiate in a weakly capped region and subsequently move into a cold boundary layer bl and inversion region before dissipating the storm simulations realistically approximate the main morphological features and evolution of the 22 may 1981 binger oklahoma supercell storm by employing time varying inflow lateral boundary conditions for the storm relative moving grid which in turn are prescribed from a parent fixed steady state mesoscale analysis to approximate the observed inversion region to the east of the dryline on that day a series of full life cycle storm simulations have been performed in which the magnitude of boundary layer coldness and the convective inhibition are varied to examine the ability of the storm to regenerate and sustain its main updraft as it moves into environments with increasing convective stability the

observations of the sea breeze front during cape part ii dual doppler and aircraft analysis abstract the three dimensional kinematic structures of offshore and onshore flow sea breeze fronts observed during the cape experiment are shown using high resolution dual doppler and aircraft data the fronts interact with horizontal convective rolls hcrs that develop within the convective boundary layer nearly perpendicular intersections between the hcrs and sea breeze front were observed during the offshore flow case close to the front the hcr axes were tilted upward and lifted by the frontal updrafts consequently a deeper updraft was created at the intersection points providing additional impetus for cloud development furthermore clouds forming at periodic intervals along the ncrs intensified as they propagated over the front during the onshore flow case the hcr orientation was nearly parallel to the front extended sections of the front merged with the hcrs this process strengthened the front and is explained as the merger of like sign vortices associated with both the front and hcrs

erratum to magnesium sulphate salts on monuments in saxony germany regional geological and environmental causes a record of mortar and salt analyses from the last 20 years on various monuments in saxony demonstrates the close relation between the occurrence of magnesium sulphate salts and the use of dolomitic lime mortars in a regional frame the regional distribution scheme of dolomitic lime in historic mortars depends on the geological setting of the territory i e the natural occurrence of dolomite deposits sulphation of these mortars with the formation of magnesium sulphate and gypsum is mainly due to environmental pollution as can be shown by sulphur stable isotope analyses exposure of the sulphated mortar surfaces to rain leads to the preferential dissolution and advective transport of the novel formed magnesium sulphate salts which effloresce or subfloresce on the mortar surface or can be accumulated in the structure of adjoining porous building materials like natural stones these processes may cause severe damages in mortars by the weakening of the binder and in porous stones by salt crystallisation of phases like epsomite and hexahydrite

mobile sounding observations of a tornadic storm near the dryline the canadian texas storm of 7 may 1986 abstract on 7 may 1986 thunderstorms formed during the afternoon near a dryline in the texas panhandle under weak synoptic scale forcing five tornadoes and large hail were produced by one storm near canadian texas the focus of the paper is the analysis of soundings obtained by a storm intercept crew a sounding launched into the wall cloud of the storm just after the fourth tornado indicated a nearly pseudomoist adiabatic lapse rate a temperature excess of 10 c over the environment at 500 mb and an updraft speed of almost 50 m s 1 near 6 km agl in reasonable agreement with parcel theory

an observational study of the dryline abstract this study presents analyses of data collected in the vicinity of a cloud free dryline that occurred in western oklahoma on 24 may 1989 observations reveal sharp contrasts across the quasi stationary north south dryline during midafternoon of greatest significance is a pronounced gradient of virtual potential temperature although horizontal convergence and vorticity also maximize at the dryline the environment of the 24 may dryline is dominated by vertical mixing that maintains a convective boundary layer cbl on both sides of the dryline the dryline resembles a mixing zone containing varying proportions of hot dry air to the west side and warm moist air from the lowest 200 m within 10 km to the east of the dryline the mixing zone slopes eastward from the surface dryline location then becomes a quasi horizontal elevated moist layer above the cbl east of the dryline saturation point analysis indicates that the mixing zone is characterized by a single mixing line structure defined by

finescale radar observations of the 22 may 2002 dryline during the international h2o project ihop abstract the dryline has long been associated with the development of severe thunderstorms in the southern plains during the spring and early summer months the propagation and structure of the dryline are closely tied to surface processes that are neither well understood nor well resolved with current observational capabilities as a result there are often large errors in forecasts of dryline position and structure improvements in radar technology have allowed for better observations of the dryline in recent years here very finescale radar observations taken with the university of massachusetts amherst umass mobile w band radar during an international h2o project ihop double dryline event on 22 may 2002 in the oklahoma panhandle are presented the observations are placed in the context of the dryline secondary circulation which describes flow in a plane normal to the dryline the narrow half power beamwidth of the antenna on the w band 0 18 permitted the measurements of channels of upward 8

convective initiation at the dryline a modeling study abstract a nonhydrostatic three dimensional version of the colorado state university regional atmospheric modeling system csu rams is used to deduce the processes responsible for the formation of drylines and the subsequent initiation of deep moist dryline convection a range of cumuliform cloud types are explicitly simulated along drylines on 15 16 and 26 may 1991 in accordance with observations in the simulations narrow convergence bands along the dryline provide the lift to initiate deep moist convection the thermally direct secondary convective boundary layer cbl circulations along the dryline are frontogenetic and solenoidally forced maximum updrafts reach 5 m s 1 and the bands are 3 9 km wide and 10 100 km or more in length the updrafts penetrate and are decelerated by the overlying stable air above the cbl reaching depths of about 2000 m in the cases studied moisture convergence along the mesoscale updraft bands destabilizes the local sounding to deep convection while simultaneously

a comparison of the finescale structures of a prefrontal wind shift line and a strong cold front in the southern plains of the united states abstractthe objectives of this study are to determine the finescale characteristics of the wind and temperature fields associated with a prefrontal wind shift line and to contrast them with those associated with a strong cold front data from a mobile polarimetric x band doppler radar and from a surveillance s band radar temperature profiles retrieved from a thermodynamic sounder and surface observations from the oklahoma mesonet are used to analyze a prefrontal wind shift line in oklahoma on 11 november 2013 data from the same mobile radar and the oklahoma mesonet are used to identify the finescale characteristics of the wind field associated with a strong surface cold front in oklahoma on 9 april 2013 it is shown that the prefrontal wind shift line has a kinematic and thermodynamic structure similar to that of an intrusion elevated density current while the cold front has a kinematic structure similar to that of a classic density current other characteristics of the prefrontal wind shift line

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

frontal and radar refractivity analyses of the dryline on 11 june 2002 during ihop an analysis of a dryline that did not initiate convection during the observational period is presented the dryline was the weakest kinematic boundary observed during the international h2o project ihop but was associated with a large moisture gradient detailed dual doppler wind syntheses from an airborne doppler radar were combined with radar refractivity measurements providing a rare opportunity to examine both the kinematic and moisture characteristics of this boundary the radar thin line denotes the approximate kinematic position of the dryline and was quasi linear on this day in contrast the moisture pattern across the dryline was more complex than was suggested by the characteristics of the thin line prominent in the horizontal plots was the presence of narrow few kilometers wide channels of moisture extending 15 20 km into the dry air mass past studies have suggested that echo thin lines observed in the clear air can be used as a proxy for delineating the moisture contrast across the dryline in contrast the moisture extrusions were present even though the thin line was quasi linear and were located in weak echo regions along the thin line it is hypothesized that transverse rolls developed at an angle to the boundary layer winds and intersected the dryline the kinematic airflow associated with these rolls could have protected the moist tongues from the eroding effect of the dry flow west of the dryline the moisture extrusions appear to diminish with time as they mix with the surrounding dry air

a case study of severe storm development along a dryline within a synoptically active environment part ii multiple boundaries and convective initiation abstract a dryline that occurred on 16 may 1991 within a synoptically active environment is examined in detail using research aircraft radar surface satellite and upper air observations the work focuses on multiple boundaries in the dryline environment and initiation of tornadic storms in two along line areas aircraft measurements in the boundary layer reveal that both the east west extent of moisture gradients and the number of regions containing large moisture gradients vary in the along dryline direction aircraft penetrations of thinlines observed in clear air return from radar reveal that all thinlines are associated with convergence and a moisture gradient and that more distinct thinlines are associated with stronger convergence however significant moisture gradients are not always associated with either thinlines or convergent signatures convective clouds on this day formed at the dryline rather than significantly east of the dryline the three thunderstorm cells that occurred in east cen

convective initiation on 19 june 2002 during ihop high resolution simulations and analysis of the mesoscale structures and convection initiation 1 the 19 june 2002 convective initiation ci case from the international h2o project ihop is simulated using the arps at 1 km grid spacing it involves three distinct ci groups ci a ci b and ci c associated with a cold front dryline system initial condition at 1800 utc 19 june 2002 was created using the arps 3dvar including standard as well as special observations the simulation captured the three groups of cis rather well with small timing and spatial errors ci a is most typical of dryline initiation vertical cross sections through the initiation locations show typical dryline structures with an upward moisture bulge forced by lifting along the dryline convergence for ci b the model predicted mesoscale structures agree with special ihop aircraft dropsonde observations closely strong low level convergence from opposing cold front and dryline circulations produces deep symmetric upwelling of moist air and the convection is initiated at the crest of the moisture bulge ci c is more typical of frontal convection where deep convection is first initiated at the front edge of the cold air for ci b and ci c north south moisture bands that have dryline characteristics and can be considered multiple drylines and contain enhanced vertical motion and upward moisture bulges intercept the dryline and cold front respectively providing the most favored locations on the dryline or cold front for initiation furthermore the air parcels feeding the initial cells at ci b and ci c have trajectories along the moisture bands and have already experienced uplifting when they reach the dryline and cold front locations

impact of a front dryline merger on convection initiation near a mountain ridge in beijing abstracta case study is presented of convection initiation ci resulting from the merger of a cold front with a dryline in southwestern beijing china on the afternoon of 11 june 2011 this process is analyzed with s band doppler radar data surface automatic weather station data and mesoscale numerical simulation results the formation of this dryline is analogous to that on the great plains of the united states and it is conducive to ci with mesoscale updrafts generated from the baroclinic frontogenesis and with favorable instability immediately on the moist side prior to the front dryline merger as the cold front approached the observed boundary layer convergence line or the simulated meso scale secondary dryline ci occurred ahead of the cold front with little contribution from frontogenetic baroclinity of the dryline the cold front then merged with the dryline and the baroclinity of the dryline was enhanced by the associated convergence to a degree comparable to that caused by frontogene