the unpredictable nature of internal tides on continental shelves abstractpackets of nonlinear internal waves nliws in a small area of the mid atlantic bight were 10 times more energetic during a local neap tide than during the preceding spring tide this counterintuitive result cannot be explained if the waves are generated near the shelf break by the local barotropic tide since changes in shelfbreak stratification explain only a small fraction of the variability in barotropic to baroclinic conversion instead this study suggests that the occurrence of strong nliws was caused by the shoaling of distantly generated internal tides with amplitudes that are uncorrelated with the local spring neap cycle an extensive set of moored observations show that nliws are correlated with the internal tide but uncorrelated with barotropic tide using harmonic analysis of a 40 day record this study associates steady phase motions at the shelf break with waves generated by the local barotropic tide and variable phase motions with the shoaling of distantly generated internal tides

internal tides over abrupt topography in the southern california bight observations of diurnal waves poleward of the critical latitude 1 in the ocean a mechanism for baroclinic internal tide generation is through the interaction of barotropic tidal currents with topography velocity profiles from a bottom mounted acoustic doppler current profiler are used to characterize the tidal generation of diurnal and semidiurnal internal modes over a ridge atop an abrupt 30 bathymetric slope in the southern california bight this location is poleward of the critical latitude for diurnal frequency internal waves yet the circulation is dominated by the diurnal internal tide overall the structure of the diurnal internal tide resembles the first baroclinic mode however the mode is topographically distorted in the lower water column where it is amplified and polarized in the cross ridge direction the behavior of the diurnal response is contrasted with the nearly ideal appearance of the semidiurnal response the diurnal baroclinic mode occurs as a persistent response to tidal forcing rather than because of the diurnal sea breeze as has also been suggested as an explanation for internal diurnal tides in other areas of the southern california bight

modeling semidiurnal internal tide variability in the southern california bight abstractthe regional oceanic modeling system roms is applied in a nested configuration with realistic forcing to the southern california bight scb to analyze the variability in semidiurnal internal wave generation and propagation the scb has a complex topography with supercritical slopes that generate linear internal waves at the forcing frequency the model predicts the observed barotropic and baroclinic tides reasonably well although the observed baroclinic tides feature slightly larger amplitudes the strongest semidiurnal barotropic to baroclinic energy conversion occurs on a steep sill slope of the 1900 m deep santa cruz basin this causes a forced near resonant semidiurnal poincare wave that rotates clockwise in the basin and is of the first mode along the radial azimuthal and vertical directions the associated tidal mean depth integrated energy fluxes and isotherm oscillation amplitudes in the basin reach maximum values of about 5 kw m 1 and 100 m and are strongly modulated by the sprin

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

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

diurnal variability in currents and temperature on the continental shelf between central and southern california 1 long time series are used to describe the diurnal variability in the meteorological and astronomical tidal forcing and the temperature and current response on the continental shelf of california between port san luis and port hueneme spectral characteristics are used to attribute the response to each of the forcing mechanisms the diurnal temperature field is decomposed into two dominant vertical modes a surface enhanced mode is coherent with the meteorological forcing suggesting that it is a direct response to local heating and wind forcing the amplitude of the second mode is maximum at middepth spectra of this mode exhibit multiple peaks at frequencies corresponding to the astronomical tidal forcing the phase difference between the middepth mode and the tidally dominated sea level is not consistent across the region we conclude that this mode is a localized baroclinic response to the astronomical tidal forcing the diurnal velocity field is dominated by a clockwise component at the surface this component is coherent across the study region and it is also coherent with the diurnal wind stress suggesting that it is a direct response to the diurnal heating and wind forcing coherence with the surface enhanced temperature mode further confirms this a weaker barotropic counterclockwise component is also present in the diurnal velocity field spectra of this component exhibit multiple peaks at periods corresponding to the astronomical tidal forcing the phase difference between this component and the surface elevation varies little between the observational sites we conclude that this velocity component represents a barotropic response to astronomical forcing that is coherent over the study area

finescale vertical structure and dynamics of some dryline boundaries observed in ihop abstract several radar fine lines all with a humidity contrast were sampled in the central great plains during the 2002 international h2o project ihop this study primarily uses aircraft and airborne millimeter wave radar observations to dynamically interpret the presence and vertical structure of these fine lines as they formed within the well developed convective boundary layer in all cases the fine line represents a boundary layer convergence zone this convergence sustains a sharp contrast in humidity and usually in potential temperature across the fine line the key question addressed herein is whether at the scale examined here 10 km the airmass contrast itself in particular the horizontal density virtual potential temperature difference and resulting solenoidal circulation is responsible for the sustained convergence and the radar fine line for the 10 cases examined herein the answer is affirmative

high temperature life without photosynthesis as a model for mars discoveries in biology and developments in geochemistry over the past two decades have lead to a radical revision of concepts relating to the upper temperature at which life thrives the genetic relationships among all life on earth links between organic and inorganic compounds in geologic processes and the geochemical supply of metabolic energy it is now apparent that given a source of geochemical energy in the form of a mixture of compounds that is far from thermodynamic equilibrium microorganisms can take advantage of the energy and thrive without the need for photosynthesis as a means of primary productivity this means that life can exist in the subsurface of a planet such as mars without necessarily exhibiting a surface expression theoretical calculations quantify the geochemically provided metabolic energy available to hyperthermophilic organisms in submarine hydrothermal systems on the earth and help to explain the enormous biological productivity of these systems efforts to place these models in the context of the early earth reveal that substantial geochemical energy would have been available and that organic synthesis would have been thermodynamically favored as hydrothermal fluids mix with seawater

diurnal period internal waves near point conception california diurnal period internal waves were observed near point conception california using an array of moorings extending 120 km along the inner shelf the waves have an along shelf coherence scale of at least 50 km and appear to propagate nearly straight onshore wave amplitudes vary over time depending on thermal stratification and the amplitude of the diurnal sea breeze oscillation barotropic tides and vorticity over the mid shelf are not correlated with internal wave amplitude large amplitude internal waves with supercritical froude numbers are observed in mid summer although such waves may drive vertical mixing and cross shelf transport of passive particles there is no significant correlation between wave amplitude and invertebrate settlement in the santa barbara channel

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

gust front characteristics and the kinematics associated with interacting thunderstorm outflows abstract the morphology kinematic and thermodynamic characteristics of 30 gust fronts were examined with single and dual doppler radar and surface mesonet data collected in eastern colorado during the summers of 1982 and 1984 the majority of gust fronts examined exhibited the general shape of laboratory produced gravity currents including the elevated head body and turbulent wake region the average head depth was 1 3 km only 0 1 km above the average body depth small scale features in the vertical and horizontal vorticity fields were also observed the passage of the fronts was marked in order of event by a pressure rise wind direction and velocity change and temperature drop at the surface the average propagation speed and maximum surface wind within the outflows were 8 6 and 14 5 m s 1 respectively the average maximum temperature drop at the surface was 3 5 c and the average hydrostatic pressure rise was 0 06 kpa dual doppler analyses of colliding gust fronts revealed strong circulations a

modeling and analysis of internal tide generation and beamlike onshore propagation in the vicinity of shelfbreak canyons abstracta hydrostatic numerical model with alongshore uniform barotropic m2 tidal boundary forcing and idealized shelfbreak canyon bathymetries is used to study internal tide generation and onshore propagation a control simulation with mid atlantic bight representative bathymetry is supported by other simulations that serve to identify specific processes the canyons and adjacent slopes are transcritical in steepness with respect to m2 internal wave characteristics although the various canyons are symmetrical in structure barotropic to baroclinic energy conversion rates c are typically asymmetrical within them the resulting onshore propagating internal waves are the strongest along beams in the horizontal plane with the stronger beam in the control simulation lying on the side with higher c analysis of the simulation results suggests that the cross canyon asymmetrical c distributions are caused by multiple scattering effects on one canyon side slope because the phase variation in the spatially d

statistics of internal tide bores and internal solitary waves observed on the inner continental shelf off point sal california abstractmoored observations of temperature and current were collected on the inner continental shelf off point sal california between 9 june and 8 august 2015 the measurements consist of 10 moorings in total 4 moorings each on the 50 and 30 m isobaths covering a 10 km along shelf distance and an across shelf section of moorings on the 50 40 30 and 20 m isobaths covering a 5 km distance energetic highly variable and strongly dissipating transient wave events termed internal tide bores and internal solitary waves isws dominate the records simple models of the bore and isw space time behavior are implemented as a temperature match filter to detect events and estimate wave packet parameters as a function of time and mooring position wave derived quantities include 1 group speed and direction 2 time of arrival time duration vertical displacement amplitude and waves per day and 3 energy density energy flux and propagation loss in total over 1000 bore events and over 9000 isw events

internal tides generated on a corrugated continental slope part ii along slope barotropic forcing recent measurements in a region of continental slope characterized by ridges and valleys running up and down the slope reveal interesting high mode structure in the tidal band velocity signals with enhanced mixing above the corrugations in order to understand these observations numerical simulations of the internal tide generation in this region of topography were performed here the focus is on the response of the flow to along slope barotropic tidal forcing for small amplitude barotropic forcing internal waves are generated over the continental slope that propagate toward the ocean surface and toward shallower water when higher amplitude forcing is combined with large amplitude corrugations the flow is locally supercritical downstream of ridges and transient internal hydraulic jumps result as the flow relaxes each half tidal period these jumps are released as internal wave packets which propagate up into the thermocline the internal hydraulic jumps are a source of mixing in the valleys while the small scale shears associated with the internal waves could lead to mixing higher up the water column over the forcing range considered the response is dominated by slightly higher harmonics of the tidal forcing frequency than predicted by existing analytic theories

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

coastal water circulation patterns around the northern channel islands and point conception california abstract the northern channel islands in california host multiple marine protected areas containing kelp forest ecosystems little is known about the water circulation onshore of the 20 m isobath we use water velocity recorded at 21 sites near the 15 m isobath at the islands and mainland during 1999 2012 to describe the water circulation on time scales of days to months the mean circulation is eastward or weak at the islands but poleward along the mainland speeds 0 10 cm s 1 the subinertial frequency along shelf flow is surface intensified and reverses direction on time scales of days in summer the flow becomes more poleward throughout the region the mean cross shelf flow profiles are strikingly similar at most sites with flow speeds 1 2 cm s 1 the mean flow near bottom in the vicinity of the kelp forests is offshore the time varying two layered response to wind is stronger up to 6 cm s 1 the flushing time of the shelf onshore of the 15 m isobath is short at most 2 dy at a few sites exposed to the prevailing wind up to 60 of the velocity variance is predictable from wind measured in the santa barbara channel in the lee of point conception or at the islands however regional wind explains little of the velocity variance during weak winds the velocity at some mainland but not island sites responds to pressure gradients measured along the mainland coast these pressure gradients are associated with local wind relaxations at pt conception not with remotely generated coastal trapped waves

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

formation of mesoscale lines of pirecipitation severe squall lines in oklahoma during the spring abstract four distinct kinds of severe mesoscale convective line development are identified in oklahoma during the spring based on the analysis of an 11 year period of reflectivity data from the national severe storms laboratory s 10 cm radar in norman oklahoma the primary classes of fine formation are broken line back building broken areal and embedded areal each is described in detail along with illustrative examples comparisons are made with other observations and with numerical model simulations the former two classes of line formation have been previously documented while the latter two have not only the broken areal squall line has been realistically simulated numerically the environment for each of the types of line development was determined from data from the standard national weather service surface and upper air networks and from special rawinsonde launches it was found that broken line formation tends to occur along cold fronts in a multicell environment while back building occur

observations of the semidiurnal internal tide on the southern california slope and shelf 1 we give a detailed description of the semidiurnal band current and temperature variability observed during the internal waves on the continental margin iwaves field experiments of 1996 and 1997 off of mission beach california this variability was dominated by the internal tide and the structure of the internal tide on the slope and shelfbreak region was different from that on the narrow shelf on the slope and shelfbreak the internal tide was dominated by alongshore propagating coastal trapped waves in this region semidiurnal band currents were predominantly oriented in the alongshore direction in the lower half of the water column at a water depth h of 350 m current and temperature variability were consonant with a short wavelength 8 km bottom trapped wave propagating in the alongshore direction to the north in the upper 120 m of the water column above the depth of the shelfbreak slope and shelfbreak currents were highly coherent with a zero phase lag that is there was no phase propagation in the cross shore direction on the narrow 10 km shelf cross shore currents u were much more energetic than on the slope and had the structure of a mode one internal wave the alongshore currents v decreased monotonically from the surface to the bottom of the water column with a phase that did not change with depth the near bottom u signal propagated toward the coast during all mooring deployments faster in the summer than in the fall the near bottom u and mid column temperature relative phase was neither consistent with a purely progressive nor a purely standing mode one internal wave we conclude that the internal tide on the shelf was partially reflected

the dependence of numerically simulated convective storms on vertical wind shear and buoyancy abstract the effects of vertical wind shear and buoyancy on convective storm structure and evolution are investigated with the use of a three dimensional numerical cloud model by varying the magnitude of buoyant energy and one directional vertical shear over a wide range of environmental conditions associated with severe storms the model is able to produce a spectrum of storm types qualitatively similar to those observed in nature these include short lived single cells certain types of multicells and rotating supercells the relationship between wind shear and buoyancy is expressed in terms of a nondimensional convective parameter which delineates various regimes of storm structure and in particular suggests optimal conditions for the development of supercell type storms applications of this parameter to well documented severe storm cases agree favorably with the model results suggesting both the value of the model in studying these modes of convection as well as the value of this representation i

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

spatial patterns of convection in south florida abstract although they are a fairly consistent feature the sea breeze and lake breeze convergence lines and the associated convection over south florida during the summer may vary considerably from one day to the next daily radar maps indicate a few basic recurring patterns analyses of radiosonde data show significant differences corresponding to the different patterns in the local thermodynamic parameters most notably the mixing ratio changes in the synoptic scale wind field correspond closely to changes in the observed radar patterns and the local thermodynamic conditions explanation of the formation and development of the different patterns of convection is given in terms of the complex interaction between the regional synoptic peninsular and local scale circulations

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

near inertial motions over the continental shelf off concepcion central chile abstract the inertial response to wind forcing is studied on a continental shelf limited by two submarine canyons and near one of the biologically most important coastal areas in the chile peru upwelling system 35 57 s 37 15 s after a brief description of the tides m2 and k1 the paper focuses on the temporal and spatial variability of the near inertial band 0 045 0 055 cph which accounts for 2 6 61 5 of the total observed current variance common features of near inertial motion especially the 180 phase difference between the upper and the lowers layers and the intermittency of this motion are described for the first time for the chilean shelf outstanding aspects appear when comparing the near inertial currents in the inner shelf with those near the shelf break where the subinertial background flow changes the effective coriolis frequency generating resonance between the near inertial currents and the daily wind cycle also the amplitudes of the near inertial currents were stronger near the shelf break about 20 cm s 1 and weaker near the coast about 5 cm s 1 intermittency in the enhanced near inertial motions varied around 3 5 10 days and appears to be related to the beat period between diurnal and near inertial frequencies

local diurnal wind driven variability and upwelling in a small coastal embayment the oceanic response to high frequency local diurnal wind forcing is examined in a small coastal embayment located along an understudied stretch of the central california coast we show that local diurnal wind forcing is the dominant control on nearshore temperature variability and circulation patterns a complex empirical orthogonal function ceof analysis of velocities in san luis obispo bay reveals that the first mode ceof amplitude time series which accounts for 47 9 of the variance is significantly coherent with the local wind signal at the diurnal frequency and aligns with periods of weak and strong wind forcing the diurnal evolution of the hydrographic structure and circulation in the bay is examined using both individual events and composite day averages during the late afternoon the local wind strengthens and results in a sheared flow with near surface warm waters directed out of the bay and a compensating flow of colder waters into the bay over the bottom portion of the water column this cold water intrusion into the bay causes isotherms to shoal toward the surface and delivers subthermocline waters to shallow reaches of the bay representing a mechanism for small scale upwelling when the local winds relax the warm water mass advects back into the bay in the form of a buoyant plume front local diurnal winds are expected to play an important role in nearshore dynamics and local upwelling in other small coastal embayments with important implications for various biological and ecological processes

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

statistical location and timing of the convective lines off the mountainous coast of southeastern taiwan from long term radar observations in this study observations from the c band doppler radar on green island which is located off the southeastern coast of taiwan during 1998 2004 were analyzed to investigate the statistical characteristics of the convective lines occurring off the mountainous coast of southeastern taiwan with emphasis on their formative location and timing a total of 211 cases of the lines were identified during the study period it is shown that the lines were clearly a year round phenomenon and five cases occurred per month on average statistical analyses for all identified cases reveal that the formative area of the lines was extended substantially from nearshore regions to at least 100 km offshore with the region of the most frequent formation primarily confined to an elongated zone located 30 km off the coast along coast variations of line formation were also evident and were shown to be closely related to the nearshore terrain features the lines tended to form more frequently during the nighttime hours than the daytime hours with a formative peak between 2000 and 2200 lst minimum formation was found near noon between 1200 and 1400 lst however considerable cases still could be found during the late morning and late afternoon hours more than 70 of the lines 150 cases had a duration of less than 4 h and the mean duration for all lines was calculated to be 3 5 h in addition this study also documented statistical differences in the formative and flow characteristics between the nearshore and offshore lines which are distinguished by offshore distances of formative location that are less or greater than 40 km respectively of particular note the analyses presented strongly suggest that the physical mechanisms contributing to the initiation of the nearshore and offshore lines are fundamentally different

wind relaxation and a coastal buoyant plume north of pt conception ca observations simulations and scalings in upwelling regions wind relaxations lead to poleward propagating warm water plumes that are important to coastal ecosystems the coastal ocean response to wind relaxation around pt conception ca is simulated with a regional ocean model roms forced by realistic surface and lateral boundary conditions including tidal processes the model reproduces well the statistics of observed subtidal water column temperature and velocity at both outer and inner shelf mooring locations throughout the study a poleward propagating plume of southern california bight water that increases shelf water temperatures by 5 c is also reproduced modeled plume propagation speed spatial scales and flow structure are consistent with a theoretical scaling for coastal buoyant plumes with both surface trapped and slope controlled dynamics plume momentum balances are distinct between the offshore 30 m depth region where the plume is surface trapped and onshore of the 30 m isobath within 5 km from shore where the plume water mass extends to the bottom and is slope controlled in the onshore region bottom stress is important in the alongshore momentum equation and generates vertical vorticity that is an order of magnitude larger than the vorticity in the plume core numerical experiments without tidal forcing show that modeled surface temperatures are biased 0 5 c high potentially affecting plume propagation distance and persistence

internal tide generation and destruction by shoaling internal tides 1 internal tide generation is usually predicted from local topography surface tides and stratification however internal tides are often observed to be unrelated to local spring neap forcing appearing intermittently in 3 5 day bursts here we suggest a source of this intermittency by illustrating how remotely generated shoaling internal tides induce first order changes in local internal tide generation theory numerical simulations and observations show that pressure perturbations associated with shoaling internal tides can correlate with surface tide velocities to generate or destroy internal tides where shoaling internal tides have random phase such as on the new jersey slope time averaged internal tide generation is unaffected but instantaneous internal tide generation varies rapidly altering internal tide energy and possibly affecting nonlinear internal waves across shelf transport and mixing where shoaling internal tides are phase locked to the local surface tide such as in double ridge systems time averaged internal tide generation is affected and may result in resonance

tropical island convection in the absence of significant topography part ii nowcasting storm evolution abstract this paper examines influences on the short range prediction of organized convection under conditions of strong diurnal forcing the analyses are based on data provided by the maritime continent thunderstorm experiment which was conducted in 1995 over the tiwi islands 11 s 50 100 km north of the australian continent organized convection over the tiwi islands is often dubbed hector by residents and researchers alike the authors purpose is to utilize results from these analyses to improve convective storm nowcast systems and their associated forecast and warning products the environmental near surface wind direction is shown to be singularly influential in statistically predicting the location of convection and its time of occurrence over the tiwi islands this finding is robust despite the fact that mean wind speeds were merely 1 4 m s 1 the island boundary layer water vapor mixing ratio derived from a morning sounding and inland surface stations is shown to be correlated with measu

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

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

direct evidence of deep water intrusions onto the continental shelf via surging internal tides 1 near bottom diurnal thermocline shoaling and diurnal baroclinic currents were observed from time series data of water temperature salinity pressure and velocity collected from august 2006 to january 2007 in the nearshore zone off the huntington beach where the local inertial frequency is higher than the diurnal frequency poleward of the diurnal critical latitude during the stratified season the deep offshore cold dense water when shoaled into shallow water along the bottom was often trapped for a few hours and dissipated in the nearshore region water depth of 10 20 m during the ebb phase of the diurnal surface tide it appears that perturbations propagating onshore along the shoaled isopycnals can form an upslope surging front and an internal bolus our data allow the application of theoretical lab criteria for internal hydraulic jumps internal bolus formation and internal wave breaking and all criteria are fulfilled during a part of the tidal shoaling cycle nonlinear advection associated with the internal boluses causes higher close to 3 spectral falloff rate of near bottom temperature with frequency than the canonical garret munk spectra 2 in the range of 0 1 1 0 cph implying strong scattering of tidal energy toward smaller scales we are able to directly calculate the offshore eddy heat flux by cold water intrusion onto the shelf resulting from this process similar impacts and implications are expected for the biogeochemical quantities as well as for the role of subinertial internal waves on turbulent mixing in the immediate proximity of the generating region i e sloping bottom

a numerical study of the convection triggering and propagation associated with sea breeze circulation over hainan island based on high resolution numerical simulations the effects of sea breeze circulation sbc on associated convective initiation and propagation over hainan island are investigated the results show that the blocking of synoptic wind on the windward side of the mountains inhibits the occurrence of windward side valley breeze and sea breeze in the context of low mountains weak synoptic wind not only favors the combination of the sbc with the valley breeze circulation on the leeward side of the mountains but also makes the convergence zone between the synoptic wind and the leeward side combined circulation stay near the tops of the mountains leading to the accumulation of large quantities of water vapor taking place over the mountaintops the combined effect of enhanced water vapor and high temperatures over the mountaintops can result in the generation of much larger convective available potential energy cape than the surrounding areas the coupling of the large cape with the considerable converging ascending motion and abundant water vapor near the tops of the mountains promotes the occurrence of a strong convection band cb over the mountaintops during the cb propagation under the steering of synoptic wind the flow across the cb continuously and strongly opposes the sbc front and the fronts of the kelvin helmholtz billows behind resulting in successive and strong lifting motion as well as large quantities of water vapor and high cape near these fronts these lead to an apparent downstream wave like propagation of the cb

diurnal period wind stress and current fluctuations over the continental shelf off northern california diurnal period wind stress and current fluctuations measured over the continental shelf off northern california during the coastal ocean dynamics experiment in the summers of 1981 and 1982 are examined the diurnal currents are strongly surface intensified with amplitudes of up to 20 cm s 1 at depths of less than 35 m the diurnal currents are nonstationary and their amplitude is well correlated with the amplitude modulation of the local diurnal wind stress beneath the surface layer the diurnal current vectors rotate clockwise with ellipse semi major axes of 1 to 3 cm s 1 a mixed layer model driven with diurnal wind stress and surface heat flux produces currents similar to those observed in the upper water column the deeper currents are consistent with the combination of a freely propagating kelvin and first mode coastal trapped wave and over the inner shelf with the interior flow forced by the diurnal wind stress in the presence of a coast

an observational and modeling study of the processes leading to deep moist convection in complex terrain abstracta case study of orographic convection initiation ci that occurred along the eastern slopes of the vosges mountains in france on 6 august 2007 during the convective and orographically induced precipitation study cops is presented global positioning system gps receivers and two doppler on wheels dow mobile radars sampled the preconvective and storm environments and were respectively used to retrieve three dimensional tomographic water vapor and wind fields these retrieved data were supplemented with temperature moisture and winds from radiosondes from a site in the eastern rhine valley high resolution numerical simulations with the weather research and forecasting wrf model were used to further investigate the physical processes leading to convective precipitation this unique time varying combination of derived water vapor and winds from observations illustrated an increase in low level moisture and convergence between upslope easterlies and downslope westerlies along the eastern slo

large scale structure in wind forcing over the california current system in summer abstractthe wind that drives oceanic eastern boundary upwelling systems is highly variable in many locations the standard deviation of wind velocity on time scales of days to weeks is larger than the mean in the 1600 km long california current system ccs the spatial decorrelation scale of the wind fluctuations is 400 800 km suggesting wind fluctuations in the north and south ends of the system are not related yet there is also the suggestion in the literature of a larger scale structure in the fluctuations here empirical orthogonal function eof analysis of buoy and satellite wind velocities confirms the existence of that structure this analysis covers a larger spatial domain than previous eof studies in the ccs and to allow for propagation of the wind fluctuations includes an approach for calculating hilbert eofs from time series with gaps the large scale structure in the wind fluctuations is a quasi dipole pattern spanning the coastline from washington through california it accounts f

near surface density currents observed in the southeast pacific stratocumulus topped marine boundary layer abstractdensity currents i e cold pools or outflows beneath marine stratocumulus clouds are characterized using 30 days of ship based observations obtained during the 2008 variability of american monsoon systems vamos ocean cloud atmosphere land study regional experiment vocals rex in the southeast pacific an air density increase criterion applied to the improved meteorological imet sensor data identified 71 density current front core peak density and tail dissipating zones the similarity in speeds of the mean density current propagation speed 1 8 m s 1 and the mean cloud level advection relative to the surface layer wind 1 9 m s 1 allowed drizzle cells to deposit elongated density currents in their wakes scanning doppler lidar captured prefrontal updrafts with a mean intensity of 0 91 m s 1 and an average vertical extent of 800 m updrafts were often surmounted by low lying shelf clouds not connected to the overlying stratocumulus cloud the observed density currents were 5 10 time

tropical island convection in the absence of significant topography part i life cycle of diurnally forced convection abstract diurnally forced convection was observed over the tiwi islands north of the australian continent as part of the maritime continent thunderstorm experiment immature peninsula scale 5 15 km sea breezes were observed to initiate moist convection early each day principally through convergence that results from the confluence or collision of peninsula breeze fronts convection initiated by peninsula scale breezes usually fails to organize beyond a small cluster of cells and dissipates as a local event mature island scale 100 km breezes develop by late morning and subsequently play a pivotal role in the forcing and evolution of organized convection the initiation of mesoscale convective systems mcss is observed to be a direct consequence of breeze front collisions for only 20 of the days on which organized convection develops this is referred to as type a forcing and it occurs when normal convective development is delayed or otherwise suppressed type a forcing is nature s backup mech

radar observations of the diurnally forced offshore convective lines along the southeastern coast of taiwan this study documents offshore convective lines along the southeastern coast of taiwan a frequent but poorly understood mesoscale phenomenon that influences coastal weather during the taiwan mei yu season doppler radar and surface observations were gathered from a specially chosen period 11 15 may 1998 when the offshore convective lines were active off the southeastern coast of taiwan these observations were used to show the basic character structure and possible formative processes of offshore convective lines the synoptic environment accompanying these events was found to be relatively undisturbed and featured uniformly prevailing southerly south southeasterly winds in the boundary layer with southwesterlies westerlies aloft examination of radar data during the study period indicates that the lines generally occurred 10 30 km offshore and were characterized by an elongated narrow zone 5 10 km wide of heavy precipitation the lines were oriented roughly parallel to the coastline and generally did not move significantly the intensity of the radar reflectivity associated with the lines exhibited a marked diurnal variation and was closely related to the coastal offshore flow developing at night detailed analyses of an event on 14 15 may 1998 further show the important physical link between the offshore flow and the development of the line the offshore line was found to be located near and immediately ahead of the seaward extent of the offshore flow particularly a very narrow zone 2 km of low level heavy precipitation 40 45 dbz coincided with regions of strong updrafts and convergence where the prevailing southerly onshore flow encountered the cool offshore flow nearshore this offshore flow induced convergence given a stable thermodynamic condition in the lowest 1 km in the inflow region was a crucial low level forcing that provided lifting to trigger moist deep convection in this case the line s precipitation tilt eastward was confined primarily to the warmer inflow side rather than feeding the offshore flow to the west of the line no consistent upshear tilt of updrafts throughout the storm layer was observed which is consistent with the presence of a strong westerly shear in the line s environment both of these observations explain a relatively strong weak modification of low level onshore offshore flow by precipitation additionally a combination of surface and doppler radar observations indicates that the leading edge of the offshore flow moved seaward very slowly at 0 7 m s 1 and possessed a frontal character with notable discontinuities in near surface wind and temperature instead of pressure and dewpoint temperature

interference pattern and propagation of the m2 internal tide south of the hawaiian ridge abstract most of the m2 internal tide energy generated at the hawaiian ridge radiates away in modes 1 and 2 but direct observation of these propagating waves is complicated by the complexity of the bathymetry at the generation region and by the presence of interference patterns observations from satellite altimetry a tomographic array and the r p flip taken during the farfield program of the hawaiian ocean mixing experiment home are found to be in good agreement with the output of a high resolution primitive equation model simulating the generation and propagation of internal tides the model shows that different modes are generated with different amplitudes along complex topography multiple sources produce internal tides that sum constructively and destructively as they propagate the major generation sites can be identified using a simplified 2d idealized knife edge ridge model four line sources located on the hawaiian ridge reproduce the interference pattern of sea surface height and energy fl

numerical simulation of the interaction between the dryline and horizontal convective rolls abstract the results of high resolution simulations of an idealized dryline environment are discussed the use of a single high resolution domain combined with accurate advection numerics and minimized numerical filtering allows the explicit resolution of large horizontal convective roll hcr circulations and their daytime evolution the horizontal convective rolls are oriented in the direction of the lower planetary boundary layer pbl wind shear by midafternoon a north south oriented dryline develops near the center of the simulation domain with the pbl circulations from both sides intersecting the dryline at multiple locations west of the dryline the hcr bands evolve into open convective cell occ structures having stronger and deeper vertical circulations compared to the occs and hcrs to the east the occs and hcrs east of the dryline impact the dryline and convective cloud location by modulating the low level moisture and upslope easterly flow the interaction between occ and hcr circulations

the structure and variability of the marine atmosphere around the santa barbara channel the santa barbara channel is a region characterized by coupled interaction between the lower level atmosphere the underlying ocean and the elevated topography of the coastline the nature of these interactions and the resulting weather patterns vary between summer and winter during summer synoptic winds are largely controlled by the combined effect of the north pacific anticyclone and the thermal low located over the southwestern united states resulting in persistent northwesterly winds a well defined marine atmospheric boundary layer mabl with properties distinct from the free atmosphere above is a conspicuous feature during the summer the wind has different characteristics in each of three zones maximum winds occur in the area extending south and east from pt conception zone 1 where they initially increase as they turn to follow the coast then decrease farther east winds are usually weak in zone 2 located in the easternmost part of the channel offshore from the oxnard plain winds are also weak in zone 3 sometimes reversing to easterly at night in a narrow band located along the mainland coast summer air temperature at the surface follows the sst closely and varies significantly with location summer sea level pressure gradients are large with the lowest pressure occurring on the northeast end of the santa barbara channel diurnal variations are strongest in summer although the modulation is weakest in zone 1 the diurnal variation is parallel to the coast in all of zone 3 but the oxnard plain where it is perpendicular to the coast the height of the marine layer varies between 300 m in late afternoon and 350 m in late morning in winter synoptic conditions are driven by traveling cyclones and sometimes accompanied by fronts these are usually preceded by strong southeast winds and followed by strong northwest winds atmospheric parameters are distributed more uniformly than in summer and diurnal variations are greatly reduced sea level air temperature and pressure are more spatially uniform than in the summer spatial variations in the observed fields in the summer are consistent with a hydraulic model of the mabl as a transcritical expansion fan the summertime situation is governed by a coupled interaction between the atmosphere and the underlying water the ocean influences the density of the mabl to the extent that it behaves distinctly from the free atmosphere above resulting in strong winds polarized in the direction parallel to the coast in turn these winds provoke an upwelling response in the coastal ocean which in part determines the surface properties of the water

observations of internal tides on the oregon continental slope abstracta complex superposition of locally forced and shoaling remotely generated semidiurnal internal tides occurs on the oregon continental slope presented here are observations from a zonal line of five profiling moorings deployed across the continental slope from 500 to 3000 m a 24 h expendable current profiler xcp survey and five 15 48 h lowered adcp ladcp ctd stations the 40 day moored deployment spans three spring and two neap tides during which the proportions of the locally and remotely forced internal tides vary baroclinic signals are strong throughout spring and neap tides with 4 5 day long bursts of strong cross slope baroclinic semidiurnal velocity and vertical displacement energy fluxes exhibit complex spatial and temporal patterns throughout both tidal periods during spring tides local barotropic forcing is strongest and energy flux over the slope is predominantly offshore westward during neap tides shoaling remotely generated internal tides dominate and energy flux is pr

two dimensional convection in non constant shear a model of mid latitude squall lines numerical simulations of two dimensional deep convection are analysed using analytical models extended to include shallow downdraughts and non constant shear the cumulonimbus are initiated by low level convergence created by a finite amplitude downdraught these experiments have constant low level shear and differ only in the profile of mid and upper level winds quasi steady convenction is produced if the mid and upper level flow has small shear and the low level shear is large the surface precipitation ismaximized for no intial relative relative flow aloft if stationary this storm p o can give prodigious locilized rainfall p o is the two dimentisonal equivalent of the supercell these results are placed in context with previous two dimensional simulations attention is drawn to the similiarity with previous two dimensional simulations attention is drawn to the similarity with squall lines in central and eastern u s a storm p o is analysed by construction of time averaged fields of streamfunction vorticity teperature and height deviation the smoothness of these fields suggests a conceptual model of the storm dynamics which involves cooperation between distinct charcteristic flows an overturning updraught a jump type updraught a shallow downdraught a low level rotor and a boundary layer an idealized analytical model is described by solution of the equations for steady convection these solutions for the remote flow are derived from energy conversation mass continuity and a momentum budget and they give relationships between the non dimensional parameteres of the problem it is apparent that the convection is a high froude or low richardson number flow demanding the existence of a cross storm pressure gradient inherent in this idealized model is a vortex sheet between updraught and down draught and it is considered that the dynamical instability of this sheet is related to complexities in the numerical simulation furthermore these results show that in two dimensions both non constant shear and a shallow downdraught are necessary to maintain steady convection

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

semidiurnal baroclinic tides on the central oregon inner shelf abstractsemidiurnal velocity and density oscillations are examined over the mid and inner continental shelf near heceta bank on the oregon coast measurements from two long term observation networks with sites on and off the submarine bank reveal that both baroclinic velocities and displacements are dominated by the first mode with larger velocities on the midshelf and northern parts of the bank midshelf sites have current ellipses that are near the theoretical value for single progressive internal tidal waves compared to more linearly polarized currents over the inner shelf baroclinic current variability is not correlated to the spring neap cycle and is uncorrelated between mooring locations an idealized model of two internal waves propagating from different directions reproduces some of the observed variability in semidiurnal ellipse parameters at times the phasing between moorings along a cross shelf transect are consistent with onshelf wave propagation a characteristic also present in the out

the relationship between radar reflectivities and clouds associated with horizontal roll convection on 8 august 1982 abstract horizontal convective rolls hcrs and cloudstreets that occurred in northeastern colorado are studied using doppler radar data cloud photography and vertical soundings examination of the environment in which the hcrs form indicates a boundary layer wind speed that is much lower than those measured in previous studies evidence shows that the hcrs form in a well defined boundary layer yet the cloudstreets that develop seem to exist within a stable layer above a relationship between the radar reflectivity echoes and the cloudstreets is firmly established the echoes are aligned directly under the cloudstreets the echoes at lower levels are shown to be caused by convergence of particulate matter into updraft portions of the hcr circulation yet evidence indicates the cloud level echoes are due to backscatter from refractive index inhomogeneities at the surfaces of rising thermals examination of the echoes show that the strongest and tallest echoes are associated with cloud formation and tha

a numerical case study of convection initiation along colliding convergence boundaries in northeast colorado abstract a numerical cloud model has been used to simulate convective storm development on 17 july 1987 in northeast colorado the study involves the simulation of convergence along atmospheric boundaries and the subsequent development of convection the model was initialized using observed conditions for this case day from the convection initiation and downburst experiment cinde a two dimensional version of the clark ncar nested grid model is employed results indicate that convection in boundary line collision cases can be successfully simulated by using actual observed atmospheric data gradual deepening of the moisture layer in the convergence zone was shown to destabilize the local atmosphere leading to the initiation of deep convection on this day the modeled storm approximated the depth and intensity of the observed storms and displayed many of the features of the actual event sensitivity studies revealed that the timing and intensity of convection along boundaries is greatly affected by alter

resonant diurnal oscillations and mean alongshore flows driven by sea land breeze forcing in the coastal southern california bight abstractthis study presents observations of the cross sectional structure of resonant response to sea land breezes slbs off huntington beach hb in the southern california bight scb a resonant response to local diurnal wind stress fluctuations associated with slb forcing occurs intermittently and produces strong diurnal oscillations of flow and temperature resulting from enhanced work of the diurnal local wind on the sea surface at nighttime daytime a coherent cross sectional circulation with offshore onshore currents in the surface layer upper 15 m and onshore offshore currents in the intermediate layer around 20 m are generated with a three layered vertical structure on the outer shelf the authors find a net cross shore eddy heat flux net cooling of nearshore water during the period of strong response to slb that is a rectified mean heat flux and steeper isotherms resulting from the diurnal slb fluctuations the steepened mean isotherms are also found to be in thermal wind balance

observations and modeling of coastal internal waves driven by a diurnal sea breeze during the internal waves on the continental margin iwaves field experi ments of 1996 and 1997 off of mission beach california 32 75on we observed energetic diurnal band motions across the entire study site in water depths ranging from 15 to 500 rn and spanning a cross shore distance of 15 km the spectral peak of the currents was at the diurnal frequency av 1 cpd and was sufficiently well resolved to be clearly separated from the slightly higher local inertial frequency f 1 08 cpd these motions were surface enhanced and clockwise circularly polarized and had an upward phase propagation speed of 68 m d l suggesting that the motions were driven predominantly by the diurnal sea breeze however the downward energy upward phase propagation seems irrecon cilable with the subinertial diurnal period and moreover the intermittent diurnal current events were not obviously associated with diurnal sea breeze events we rationalize these features using a flat bottomed linear modal sum internal wave model that includes advection and refraction due to subtidal alongshore flow v z t fluctuations in v at the observing site can change the effective local coriolis parameter f vz by as much as 50 thus making the diurnal motions at different times effectively either subinertial or superinertial the model is integrated numerically for 200 days at a latitude of 32 75on under different wind and subtidal flow conditions purely diurnal winds and no v purely diurnal winds and a time independent v narrow band diurnal winds and no v and narrow band diurnal winds and subtidal time dependent v model diurnal currents forced by narrow band diurnal winds and subtidal v show complex offshore structure with realistic intermittency and spectral broadening this study suggests that continental margins in the vicinity of the 30 o latitude where av f are regions that could potentially produce energetic sea breeze driven baroclinic motions and that these motions could be regulated by the vorticity of the local subtidal currents