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

seasonal upper shelf circulation along the central western gulf of mexico a preferential upcoast flow reinforced by the recurrent arrival of loop current eddies

the numerical simulation of non supercell tornadogenesis part i initiation and evolution of pretornadic misocyclone circulations along a dry outflow boundary abstract high resolution three dimensional simulations are used to study misocyclone initiation and development along the leading edge of an outflow boundary model conditions were designed such that this development could be simulated independent of moist processes the outflow boundary is allowed to propagate into a region of southerly low level flow which results in a vertical vortex sheet along the outflow s leading edge lobe and cleft instabilities follow and provide perturbations for the subsequent development of horizontal shearing instabilities these growing instabilities are the inaugural circulations of leading edge misocyclones with wavelengths ranging from 1 6 to 3 2 km the structure of these modeled misocyclones compares favorably to observed pretornadic misocyclones along outflow boundaries in northeast colorado vortex sheet dynamics are observed to exert substantial control over the structure of the evolving outflow leading edge the vertical vortex sheet passes through discrete evoluti

a severe frontal rainband part ii tornado parent vortex circulation abstract by means of multiple doppler radar analysis part i established the stormwide hydrodynamic structure as an intense gravity current which advances on a prefrontal low level jet part ii examines the initiation and evolution of a tornado parent vortex circulation in the context of stormwide vorticity production tilting of the prefrontal inflow below the low level jet axis accounts for production of observed vorticity 10 2 s 1 at the surface front the two dimensional flow pattern is modified by the development of an inflectional instability with a wavelength of 13 km breaking or roll up of this instability occurs on a time scale of roughly 500 s and results in small scale vortices along the surface front one such vortex is examined in detail this vortex is the parent circulation of a small tornado the parent vortex structure is determined to be quite similar to those observed in summertime deep convection this suggests a generality to the findings concerning parent vortex initiation and

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

three dimensional kinematic and microphysical evolution of florida cumulonimbus part i spatial distribution of updrafts downdrafts and precipitation abstract this paper is the first in a three part study that examines the kinematic and microphysical evolution of florida cumulonimbus and focuses on the convective to stratiform transition of the storm this first paper lays the groundwork for the subsequent papers by defining the problem under study delineating the setting for the storm and describing the spatial distribution of updrafts downdrafts and precipitation high resolution radar data of a typical line of storms associated with the florida sea breeze is the centerpiece of this study the high resolution data reveal details of the internal structure of the squall line that were beyond the resolution of previous squall line studies radar reflectivity filled in between cells at upper levels as the storm evolved reflectivity values were only weakly associated with updraft and downdraft magnitude the updrafts and downdrafts in the storm tended to be irregular in their three dimensional shape and less than 5 km in horizontal extent at any giv

a primitive equation ocean circulation model using a general vertical coordinate transformation 1 description and testing of the model the ocean general circulation model of the geophysical fluid dynamics laboratory has been modified to accommodate a generalized vertical coordinate transformation the model with a slightly modified transformation z h is applied to three simple test cases a clear improvement of barotropic and baroclinic topographic rossby waves has been achieved compared with the z coordinate model a somewhat more typical time independent problem for the overflow of dense water masses over a zonal ridge exhibits the potential benefits as well as the flaws of the new model vertically integrated mass transport is very sensitive to changes in bottom slope in regions where planetary and topographic are of comparable magnitudes this translates into large errors in the z model due to the crude approximation to the actual topography the deep flow in the z model does not follow the bottom exactly horizontal overshoots of dense water lead to convective mixing on the southern side of the ridge this can be a serious problem for modeling more realistic overflow situations with the z model increased diapycnal diffusion has been identified as the most serious problem with the terrain following coordinate system for this specific application

the initiation and organization of convective cells atop a cold air outflow boundary abstract on 13 july 1986 a cold air outflow from thunderstorms over illinois and missouri propagated through the mist microburst and severe thunderstorm network over northern alabama the study of this outflow is important since the gust front was solely responsible for the initiation of numerous convective cells previous studies have documented the initiation of convection due to colliding gust fronts in addition there was a pronounced mesoscale organization of the cells atop the outflow boundary this was most likely due to a combination of kelvin helmholtz k h and internal gravity ig wave activity in contrast to previous cases the k h wave crests were oriented nearly perpendicular to the gust front within the analysis area the resulting intersections between the circulations associated with the k h waves and the gust front produced favorable locations for the initiation of convection subsequently the convective cells remained along the updraft side of the k h wave circulations as they pro

circulation over the continental shelf of the western and southwestern gulf of mexico 1 the circulation over the continental shelf break of the western and southwestern gulf of mexico is inferred from the analysis of drifter trajectories and 12 19 months of continuous current measurements at seven different locations the interpretation of the data is backed up by satellite altimetry coastal sea level from tide gauges and wind model outputs in accordance with previous numerical results subinertial surface currents are driven by the wind along the shelves of the states of tamaulipas and veracruz northern wind regimes would force southward currents whereas southern wind regimes would force northward currents at the surface but southward near the bottom through a process involving ekman drift and geostrophic balance our results show however that alongshore current variations are not correlated with the wind over the western campeche bank in addition we identify other sources of current forcing the transient eddies that collapse along the continental shelf can force strong alongshore currents and overwhelm the influence of established wind regimes their erratic occurrence is likely to be a major factor of interannual variability of the alongshore currents also we point out the existence of coastally trapped waves generated by the wind in the northern shelf of tamaulipas and propagating down to the western campeche bank the period of these waves ranges between 6 and 10 days with phase speeds in the 4 m s range

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

observations of the sea breeze front during cape part i single doppler satellite and cloud photogrammetry analysis abstract an analysis of two sea breeze events on 6 august an onshore flow event and 12 august an offshore flow event 1991 is presented using single doppler observations satellite images and cloud pictures collected during the convection and precipitation electrification cape experiment documentation of the alongfrontal variability at the leading edge of the sea breeze circulation is presented for the first time the horizontal structure of the front was strongly modulated by the near perpendicular intersections of horizontal convective rolls developing in the ambient air out ahead of the sea breeze on 12 august these intersection points also appeared to be preferred locations for cloud development along the front horizontal convective rolls were also documented on 6 august however their orientation was nearly parallel to the sea breeze front as a result extended sections of these rolls appeared to have merged with the front as it propagated inland rather than having distinct intersection po

a nested grid model of the oregon coastal transition zone simulations and comparisons with observations during the 2001 upwelling season 1 the oregon coastal transition zone octz extends several hundred kilometers offshore where shelf flows interact with the northern california current a primitive equation numerical ocean model is used to study the upwelling circulation in this region from 1 may to 1 november 2001 this octz model obtains initial and boundary conditions from a larger scale model of the california current system and forcing from a regional atmospheric model product the model results are compared with extensive in situ and remotely sensed data and the model is found to provide a realistic representation of flows both over the shelf and in the broader octz simulation of coastal sea level and shelf currents over the complex topography of the central oregon coast is improved quantitatively relative to previous regional models a particularly significant qualitative improvement is realistic representation of coastal jet separation and eddy formation offshore of cape blanco three dimensional lagrangian analysis of water parcel displacement shows that the surface waters inshore of the separated jet are upwelled from near the bottom along the shelf as far north as 45 5 n a large eddy which incorporates some of this upwelled water and carries it farther westward forms offshore in the late summer ensemble simulations show a distinction between the strongly deterministic response to wind forcing over the shelf and the more unstable less predictable jet separation and offshore eddy formation processes in the region near cape blanco

how does the el nino generated coastal current propagate past the mendocino escarpment during an el nino an internal coastal kelvin wave bore propagates poleward along the west coast of north america leaving behind a steady anomalous coastal jet a nonlinear two layer plane shallow water model is used to determine the amplitude change of the steady coastal current over an escarpment as the el nino generated warm coastal current passes the mendocino escarpment off northern california its amplitude is marginally enhanced in contrast for a cold coastal current the amplitude will be reduced north of the mendocino escarpment when the kelvin wave bore travels over a depth increase the amplitude change is predicted to be much larger than over a depth decrease as in the case of the mendocino escarpment this model is also applicable to bottom water flowing equatorward along a western boundary in this case much larger amplitude changes are found

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

numerical study of horizontal shear instability waves along narrow cold frontal rainbands abstractthe effects of variations in low level ambient vertical shear and horizontal shear on the alongfront variability of narrow cold frontal rainbands ncfrs that propagate into neutral and slightly unstable environments are investigated through a series of idealized cloud resolving simulations in cases initialized with slightly unstable sounding and weak ambient cross frontal vertical shears core gap structures of precipitation along ncfrs occur that are associated with wavelike disturbances that derive their kinetic energy mainly from the mean local vertical shear and buoyancy however over a wide range of environmental conditions core gap structures of precipitation occur because of the development of a horizontal shear instability hsi wave along the ncfrs the growth rate and amplitude of the hsi wave decrease significantly as the vertical shear of the ambient cross front wind is reduced these decreases are a consequence of the enhancement of the low level local vertical shear immediately beh

misocyclone characteristics along florida gust fronts during cape multiple doppler radar and rawinsonde data are used to examine misocyclone characteristics along gust fronts observed during the convection and precipitation electrification cape project in florida the objective of this study is to investigate the observational representativeness of previous numerical simulations of misocyclones by employing a consistent analysis strategy to 11 gust fronts observed in the same region the investigation focuses on the intensity range of misocyclones and their organization along gust fronts the relationship between misocyclone intensity and horizontal wind shear vertical wind shear and static stability and the relationship between misocyclones and convection initiation the intensity of misocyclones as indicated by the maximum values of vertical vorticity varied from 2 8 10 3 to 13 9 10 3 s 1 although all but one case exhibited values less than 6 4 10 3 s 1 organized misocyclone patterns were only found along small segments of gust fronts within those segments misocyclones were spaced between 3 and 7 km results show that the intensity of misocyclones was most closely related to the strength of horizontal wind shear across the gust front the relationship between misocyclone intensity and vertical wind shear and static stability was not as clear although convection was initiated along the gust front in 7 of the 11 cases those regions were not collocated with or in close proximity to misocyclones

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

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

application of wavelet transform in the study of coastal trapped waves off the west coast of south america 1 wavelet transform and cross wavelet transform were applied for analyzing long time series of sea level and alongshore wind stress to identify intraseasonal variability off western south america and the relations with remote and local forcings hydrographic data were used to estimate properties of coastal trapped waves with a theoretical model for el nino years we found the existence of intraseasonal oscillations with periods 20 90 days between 2s and 27s at the peak of 91 92 and 97 98 el ninos we found perturbations in the northern region probably associated with remotely forced internal kelvin waves with periods 6 11 days and phase velocities 160 260 km day between 12s and 15s during two el nino events our calculations show perturbations which appear to be barotropic shelf waves propagating southward with velocities between 110 and 150 km day and periods between 30 and 50 days

a primitive equation ocean circulation model using a general vertical coordinate transformation 2 application to an overflow problem the version of the ocean general circulation model of the geophysical fluid dynamics laboratory with a generalized vertical coordinate transformation introduced in part 1 is used to study the overflow of a zonal ridge in a coarse resolution grid typical for climate applications the configuration roughly resembles the greenland scotland ridge with respect to scale latitude and height of the ridge reasonable qualitative agreement with observed conditions over the iceland faroe section has been achieved especially when a deeper passage was included at the eastern end of the idealized model ridge upwelling of deep water occurs at the eastern boundary where friction and more importantly diapycnal diffusion accomplish the necessary changes in potential vorticity the overflow consists of intermediate water when the renewal time for the deep water is made much larger than that for intermediate water the meridional mass transport is most sensitive to geometric factors like the height of the ridge frictional and diapycnal processes are crucial for the potential vorticity conversion at the ridge and have a strong effect on the water mass distribution bottom friction increases the near bottom flow across f h lines resulting in a large amount of northern basin deep water south of the ridge this effect can be represented only when the frictional bottom boundary layer is adequately resolved by the numerical grid

characterizing thunderstorm gust fronts near complex terrain abstractfire safety aviation wind energy and structural engineering operations are impacted by thunderstorm outflow boundaries or gust fronts gfs particularly when they occur in mountainous te

an observational study of atmospheric bore formation from colliding density currents abstract observations from east central florida during the convection and precipitation electrification cape experiment are used to investigate the factors that influence atmospheric bore formation from colliding density currents ten cases involving the collision of a gust front with a sea breeze front are analyzed with doppler radar and sounding and surface mesonet data the gust fronts in these collisions were generally deeper denser and faster propagating than their sea breeze front counterparts seven of the 10 cases produced dual boundaries that moved away from each other in a relative sense after the collision post collision boundaries moving in the same direction and oriented similarly to the pre collision gust front occurred in all 10 cases they transported mass in the manner of a density current in six cases while the others behaved more like bores or bore density current hybrids as they were characterized by little or no mass transport similarity of gust front and sea breeze front prop

influence of the synoptic scale flow on sea breezes observed during cape abstract mean sea breeze characteristics were determined by analyzing a number of sea breeze events during offshore parallel and onshore flow regimes during the convection and precipitation electrification experiment cape it was observed that offshore flow cases exhibited the widest and relatively strongest radar detected thin lines the thin line reflectivity values steadily increased during the day in contrast a thin line was detected only during late afternoon on parallel flow days while no easily identifiable thin line was observed during onshore flow days the gradients of temperature and moisture as measured by a surface meteorological station during sea breeze passage were strongest and weakest during offshore and onshore flow days respectively in addition the moisture and temperature gradients across the leading edge of the sea breeze steadily increased during the day and were strongest during late afternoon using dual doppler techniques the detailed kinematic structure of the sea

dynamics of a thunderstorm outflow abstract the kinematic and thermodynamic structures of a thunderstorm outflow are examined by means of dual doppler radar analysis mesonet lower and sounding data the data were collected in the denver colorado area during june 1984 the dual doppler analysis shows that the cold outflow is ducted beneath the pbl inversion along the gust front there is a narrow quasi two dimensional updraft kelvin helmholtz instability khi developed along the top of the gust front head near the surface front and propagated backwards dissipating in the wake of the head region an isothermal layer aloft appears to have limited billow amplification to the quasi neutral layer below the gust front s leading edge had numerous inflections which are believed to result from barotrophic instabilities small vortices develop at some of the inflection points detailed analysis of one such circulation shows evidence of the formation of two enhanced updrafts separated by an occlusion downdraft these observations are the firs

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

wind driven coastal trapped waves off southern tamaulipas and northern veracruz western gulf of mexico during winter 2012 2013 four months of observations from a near coastal mooring deployed off southern tamaulipas northern veracruz coast western gulf of mexico during winter 2012 2013 provide velocity and pressure series in a coastal region where apparently no in situ measurements have been formally reported the observations show numerous events of intense alongshore velocities with magnitudes typically exceeding 30 cm s 1 related to intensified winds associated with cold fronts invading the western gulf during fall winter via coastal trapped motions coming from northern locations these motions can be explained by a time dependent coastal trapped wave ctw mode using a phase speed 4 m s 1 which is consistent with analyses of correlation lag of historical sea level data ctw dynamic modes and sensitivity to such a phase speed the ctw time dependent mode reproduces most of the variability of the sea level and hence the alongshore barotropic velocity observed at the mooring and it can also be used to estimate the contribution of remote regions to the variance observed at the central portion of the western gulf the mooring s location more than half of that variance is generated in the southernmost coast of texas and northernmost coast of tamaulipas and 40 is generated in the central and southern portions of tamaulipas coast thus the method described in this paper is useful not only to explain the near coastal flow variability but it also presents the potential predictability of intensified flow events in the western gulf of mexico

gap filling mobile radar observations of a snow squall in the san luis valley abstracton 24 january 2017 a convective snow squall developed in the san luis valley of colorado this squall produced rapidly varying winds at san luis valley airport in alamosa with gusts up to 12 m s 1 and an associated visibility drop to 1 4 km from unlimited in less than 10 minutes this snow squall was largely undetected by the operational wsr 88d radar network due to the sangre de cristo range of the rocky mountains lying between the valley and the nearest wsr 88d radar in pueblo colorado this study presents observations of the snow squall from the x band noaa x pol radar which was deployed in the san luis valley during the event these observations document the squall developing from individual convective cells and growing upscale into a linear squall with peak radial velocities of 15 m s 1 the environment conducive to the development of this snow squall is examined using data from the high resolution rapid refresh model which shows an environment unstable to ascending surface based parcel

vertical velocity and vertical heat flux observed within loop current eddies in the central gulf of mexico abstract sixteen months of observations from a surface to bottom mooring in the central gulf of mexico show that acoustic doppler current profilers adcps are useful for directly measuring the vertical velocity within mesoscale anticyclonic eddies such as those shed from the loop current and combining simultaneous temperature measurements vertical heat flux can also be estimated as a covariance of both variables there is evidence of significant and coherent signals of vertical velocity 2 3 mm s 1 and vertical heat temperature transport 10 3 c m s 1 during the presence of three anticyclones a simple analysis shows downward flow near the eddies centers above 350 m and essentially upward flow in the peripheries but below 700 m depth the pattern is indeed the opposite however further study is necessary to determine the eddies interior structures the observations also suggest the existence of a vertical convergence of heat somewhere around 600 m depth and estimations of adiabatic heat flux

on stratified flow over a ridge intersecting coastlines abstract the adjustment between two interconnecting basins of stratified fluid resulting from the formation of a pool of dense water in one is investigated with an 18 level numerical general circulation model cycm it is found that basic features of the adjustment i e i the generation of low frequency coastally trapped kelvin waves which carry information about the alongshore pressure gradient created by the denser water toward the dividing ridge ii the subsequent generation of barotropic double kelvin waves by the jebar joint effect of baroclinicity and relief effect which propagate infinitely rapidly along the ridge setting up an anticyclonic gyre iii the generation of further coastally trapped kelvin waves at the opposite coast due to an alongshore pressure gradient created by upwelling at the ridge edge associated with the closure of the barotropic gym iv the generation of a coastally confined cyclonic gyre at the opposite ridge by the jebar effect and viscous and diffusive

the cape canaveral sea and river breezes kinematic structure and convective initiation abstract this study examines complex flow patterns associated with the cape canaveral sea breeze and sea breeze front using dual doppler radar sounding and surface data collected on 26 july 1991 during the convection and precipitation electrification experiment this case focuses on a the structure of the sea breeze an associated trailing convergence line river induced convergence zones and thunderstorm outflow boundaries and b the development of convection where these features interacted variations in the direction of the sea breeze in the vicinity of irregular coastlines such as cape canaveral can lead to persistent zones of convergence within the sea breeze air the findings show that these zones of convergence in turn can locally increase the depth of the sea breeze air and create circulations at the top of the sea breeze which can support the development of convection the observational study is the first to document the development and evolution of the trailing convergence line over

seasonal cycles of currents temperatures winds and sea level over the northeast pacific continental shelf 35 n to 48 n seasonal cycles of coastal wind stress adjusted sea level asl shelf currents and water temperatures off the west coast of north america 35 n to 48 n are estimated by fitting annual and semiannual harmonics to data from 1981 1983 longer records 9 34 years of monthly asl indicate that these two harmonics adequately represent the long term monthly average seasonal cycle and that the current measurement period is long enough to estimate the seasonal cycles we characterize the differences between fall winter and spring summer as follows for fall winter monthly mean winds north of 35 n are northward for 3 6 months longer in the north than in the south south of 35 n the mean winds are near zero or weakly southward monthly mean alongshore currents are northward over midshelf and shelf break at all locations sampled at depths of 35 m and deeper and are associated with high coastal sea levels and relatively warm water temperatures for spring summer monthly mean wind stresses are southward at all latitudes for 3 6 months longer in the south than in the north sea levels are low and water temperatures are relatively cool monthly mean currents at 35 m depth over the shelf are southward for 1 6 months longer at the shelf break than over midshelf and longer in the north than in the south while the deeper currents are less southward or northward the magnitudes of the seasonal cycles of all variables are maximum between approximately 38 n and 43 n generally decreasing slightly to the north and greatly to the south at each location the seasonal cycle of the alongshore current from 35 m depth at midshelf leads the sea level slightly and both lead the wind stress and temperatures by 1 2 months the seasonal cycles of all variables show a south to north progression south leads north by 1 2 months at 48 n annual mean currents at 50 m depth over the shelf break oppose the annual mean wind northward wind and southward current similarly at 35 n annual mean currents at 35 m depth over both midshelf and shelf break are opposed to the annual mean wind southward wind and northward current from 35 n to 43 n both summer and winter regimes are dominated by strongly fluctuating currents

thunderstorm initiation organization and lifetime associated with florida boundary layer convergence lines abstract the initiation organization and longevity of thunderstorms associated with boundary layer convergence lines in the cape canaveral florida vicinity are examined using data from the convection and precipitation electrification cape experiment the project was conducted during july and august 1991 under low vertical wind shear situations this observational study is based on doppler radar mesonet balloon sounding and satellite data the primary convergence lines studied were the east coast sea breeze front ecsbf and a frequently occurring gust front from the west termed the west coast front wcf that originates with storms initiated by the west coast sea breeze front significantly fewer storms were associated with the ecsbf in comparison to the wcf this was because the convergence with the ecsbf was shallower and weaker and the updrafts were shallow and tilted the environmental winds were generally westerly near the top of the ecsbf and at storm steering level as a result the low le

the effect of bottom friction on low frequency coastal trapped waves abstract an approximate technique is presented for including the effect of turbulent bottom friction in the forced first order wave equation governing long generalized coastal trapped waves the resulting governing equations include both damping and a cross shelf and vertical phase shift a set of examples shows that damping of free waves decreases as the static stability increases consistent with the inhibition of vertical motions by stratification

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

the numerical simulation of nonsupercell tornadogenesis part ii evolution of a family of tornadoes along a weak outflow boundary abstract nonsupercell tornadogenesis along a weak outflow boundary has been simulated using a three dimensional moist convective cloud model thermodynamic conditions similar to those observed for nonsupercell tornado nst events of the high plains were utilized in the model initialization as the ensemble system of storm outflow boundary and leading edge vortices evolve six distinct life cycle stages for the development and decay of nsts are documented that span a period of about 35 min consistent with the results of part i of this numerical study vortex sheet dynamics exert considerable control over the outflow leading edge the progression of pretornadic life cycle stages serves to concentrate vertical vorticity effectively along the outflow boundary in discrete misocyclone circulations aligned in a 3 km wavelength pattern the organization of larger scale misocyclones and ultimate intensification to initial tornadic intensity occurs coincident with the rapid development of deep convection overhe

the ventilation of the deep gulf of mexico abstract recent measurements over the sill in the yucatan channel indicate that the deepest flows between the caribbean sea and the gulf of mexico those that take place below the sill level at the florida straits have zero mean net mass transport but carry significant amounts of heat and oxygen the heat flux associated with the mean exchange exports approximately 150 gw from the deep gulf toward the caribbean and may be related to the formation of the yucatan undercurrent the eddy heat transfer is also significantly different from zero and exports on average an additional 60 gw this eddy transfer is attributable mostly to events that last from a few days to about 1 5 months during which colder water from deeper levels in the caribbean beneath 2000 m flows over the sill within a bottom boundary layer close to 200 m thick the colder water is also very rich in oxygen and the deep exchange sustains the near bottom oxygen maximum in the gulf of mexico whence that cold water must slide down the north

analysis of a dryline during ihop implications for convection initiation abstract a detailed analysis of a dryline that formed on 22 may 2002 during the international h2o project ihop is presented the dryline was classified as a null case since air parcels lifted over the convergence boundary were unable to reach the level of free convection preventing thunderstorms from forming a secondary dryline associated with a distinct moisture discontinuity developed to the west of the primary dryline the primary dryline exhibited substantial along frontal variability owing to the presence of misocyclones this nonlinear pattern resembled the precipitation core gap structure associated with cold fronts during one of the analysis times although the misocyclones were positioned within the gap regions radar refractivity has been recently shown to accurately retrieve the low level moisture fields within the convective boundary layer however its use in forecasting the initiation of convection has been restricted to qualitative interpretations this study introduces the total derivati

seasonal circulation on the western shelf of the gulf of mexico using a high resolution numerical model 1 the seasonal circulation on the western shelf of the gulf of mexico is studied using a high resolution numerical simulation historical hydrographic data sea level data and satellite images three regions are distinguished the tamaulipas veracruz tave shelf the louisiana texas latex shelf and the western campeche bank on the tave shelf there is a swift reversal of the along shelf current downcoast from september to march and upcoast from may to august when there is upwelling due to offshore ekman transport circulation on the western campeche bank is upcoast throughout the year the latex shelf has a cyclonic circulation except during summer months when the flow is eastward during spring summer the upcoast current on the tave shelf reaches the southern texas shelf where it encounters a downcoast coastal current favoring offshore transports in the fall winter the downcoast current reaches the southern bay of campeche where it meets an opposing along shelf current generating seasonal offshore transports during fall and winter cool low salinity water from the mississippi and atchafalaya rivers is advected westward along the latex shelf onto the tave shelf developing along shelf fronts and temperature inversions commonly observed over the outer shelf and shelf break the main forcing over the western shelf of the gulf is the along coast wind stress component the existence of the cross shelf transports in the confluence regions is supported by chlorophyll a data up to 80 of the seasonal sea level variability is explained by the along shelf currents and the low frequency variability of the atmospheric sea level pressure

tornadoes and downbursts in the context of generalized planetary scales abstract in order to cover a wide range of horizontal dimensions of airflow the author proposes a series of five scales maso meso miso to be read as my so moso and muso arranged in the order of the vowels a e 1 o u the dimensions decrease by two orders of magnitude per scale beginning with the planet s equator length chosen to be the maximum dimension of masoscale for each planet mesoscale highs and lows were described on the basis of mesoanalyses while sub mesoscale disturbances were depicted by cataloging over 20 000 photographs of wind effects taken from low flying aircraft during the past 15 years various motion thus classified into these scales led to a conclusion that extreme winds induced by thunderstorms are associated with misoscale and mososcale airflow spawned by the parent mesoscale disturbances

non supercell tornadoes abstract analyses of tornadoes that are not associated with supercells are presented the database for this study was collected during cinde convention initiation and downburst experiment a field project operated during the summer of 1987 in colorado a total of 27 visual vortices were studied they appeared to form as shear instabilities along radar detected convergence lines the circulations initiated at low levels generally in the absence of precipitation echo subsequently as these vortices propagated along the convergence line they appeared to strengthen to tornadic intensity when they became colocated with the updraft of a rapidly developing storm it is hypothesized that vortex stretching is responsible for intensifying the initial rotation although these tornadoes were weaker than those accompanied by strong midlevel mesocyclones estimates of their strength suggest damage capability as high as f2 the implications for operational radars to detect these types of phenomena were identified the

kinematic observations of misocyclones along boundaries during ihop during the international h2o project mobile radars collected high resolution data of several 0 5 2 kmwide vertically oriented vortices or misocyclones along at least five mesoscale airmass boundaries this study analyzes the properties of the misocyclones in three of these datasets 3 10 and 19 june 2002 to verify findings from finescale numerical models and other past observations of misocyclones and to further the understanding of the role that they play in the initiation of deep moist convection and nonsupercell tornadoes misocyclones inflect or disjoint the swath of low level convergence along each boundary to varying degrees depending on the size of their circulations when several relatively large misocyclones are next to each other the shape of low level convergence along each boundary is arranged into a staircase pattern mergers of misocyclones are an important process in the evolution of the vorticity field as a population of small vortices consolidates into a smaller number of larger ones additionally merging misocyclones may affect the mixing of thermodynamic fields in their vicinity when the merger axis is perpendicular to the boundary misocyclones interact with linear and cellular structures in the planetary boundary layers pbls of the air masses adjacent to each boundary cyclonic low level vertical vorticity generated by both types of structures makes contact with each boundary and sometimes is incorporated into preexisting misocyclones intersections of either type of pbl structure with the boundary result in strengthened pockets of low level convergence and typically strengthened misocyclones

a comparison of long coastal trapped wave theory with observations off peru abstract the agreement between coastal trapped wave theory and observation is studied for the case of observations made off peru during the 1977 cuea joint ii experiment wave properties are calculated using a numerical model with realistic horizontally uniform stratification and realistic bottom topography these properties are then explored as a function of the ratio of the first internal rossby radius of deformation to the shelf slope width the agreement of observed and calculated first mode free wave phase speeds 230 cm s 1 is excellent while modal structures agree more poorly a forced wave calculation using observed winds and currents as input is used to hindcast alongshore currents and sea level in the frequency band where smith 1978 observed free coastal trapped waves during 1977 the model suggests that most of the observed sea level and alongshore velocity fluctuations in the 5 10 day period band are due to free waves originating equatorward of 5 deg s while winds between 5 deg s and

convection initiation associated with a sea breeze front a gust front and their collision abstract the initiation of convection associated with a sea breeze front a gust front and their collision is analyzed using data collected in east central florida during the convection and precipitation electrification project in conjunction with satellite surface and rawinsonde information dual doppler radar derived winds are used to determine the three dimensional kinematic factors critical to storm development the gust front which emanated from storms on the western half of the peninsula propagated more rapidly and was deeper than the sea breeze front which originated from the east coast and was characterized by a distinctly scalloped appearance convection associated with the sea breeze front appeared to develop preferentially at the vertices of this scalloped pattern where there were enhanced regions of convergence and upward motion on the gust front a helmholtz shearing instability produced an organized configuration of convergence and updraft maxima along its length however these were

coefficients for sea surface wind stress heat flux and wind profiles as a function of wind speed and temperature surface layer coefficients for wind profiles wind stress and heat flux in typical open sea conditions are briefly reviewed businger dyer flux gradient relationships and a charnock wind stress formula fit the empirical data and are dimensionally consistent these have been solved by an iterative method and the results are presented in a tabular form suitable for climatological calculations from marine wind and temperature data

application of remote wind forced coastal trapped wave theory to the oregon and washington coasts abstract the theory of coastal trapped waves generated by remote wind forcing clarke is used to calculate coastal subsurface pressure ssp and longshore velocity along the oregon and washington coasts for three two month periods summer of 1972 summer of 1978 and winter of 1977 the response in ssp and longshore velocity is assumed to be dominated by the mode one wave in every case coherence squared between observed and modeled ssp is significant at the 95 level over the entire low frequency band 0 2 cpd with an average phase difference less than 30 greater than 80 of the variance in coastal ssp is accounted for by the mode one coastal trapped wave ctw the ssp response off washington and oregon during summer is primarily 35 of the variance a result of wind forcing between san francisco and cape mendocino california wind stress in this region during summer is significantly larger than that off oregon and washington at low frequencies so that the ctw generated off california propagate

large scale sea level response to atmospheric forcing along the west coast of north america summer 1973 abstract along the west coast of north america the response of sea level to fluctuations in alongshore wind stress at large alongshore scales 1000 km accounted for a substantial faction of the total sea level variance during summer 1973 space time contour plots of sea level and alongshore stress show that the response of sea level to poleward propagating wind stress events was generally stronger than the response to equatorward propagating events atmospheric forcing was most effective in two regions along the coast with relatively strong forcing and response along northern california and oregon and somewhat weaker forcing and response along northern baja california the forced fluctuations in sea level propagated poleward away from these forcing regions causing local sea level to be most correlated with alongshore wind stress earlier in time and at a distant equatorward 1ocation along the southern and central california coast fluctuation in sea level were partly forced along northern baja cali