island wakes in deep and shallow water observations of island wakes from the continental shelf have been used by various authors to suggest that the reynolds number is not an appropriate parameter for wake behaviour in shallow water it is shown here that wake behaviour both in deep and shallow water is well described by the reynolds number if it is derived correctly by taking into account frictional effects in horizontal as well as vertical boundary layers

coastal southerlies and alongshore surges of the west coast of north america evidence of mesoscale topographically trapped response to synoptic forcing abstract one of the most important warm season weather phenomena of the west coast of north america is the temporal transition from northerly to southerly flow within a few hundred kilometers offshore from the coastal mountains such wind shifts are often accompanied by cooler temperatures higher pressure and a change from nearly cloud free to low overcast conditions the more vigorous coastal transitions termed alongshore surges are characterized by an abrupt change in wind direction a sudden increase in wind speed to 15 m s 1 or more a precipitous temperature drop exceeding 10 c and a sharp rise in sea level pressure this paper presents two detailed case studies of topographically trapped coastal southerlies the strong surge event of 15 17 may 1985 and the far weaker case of 3 7 may 1982 it is shown that coastal southerlies and alongshore surges are controlled by the alongshore pressure gradients created by the synoptic scale flow at low levels and within approximately one rossby radius of th

local atmospheric forcing during the coastal ocean dynamics experiment 1 a description of the marine boundary layer and atmospheric conditions over a northern california upwelling region as part of the coastal ocean dynamics experiment code meteorological instruments were deployed on buoys and at coastal stations and instrumented aircraft flights and coastal soundings were made to study the three dimensional structure of the marine boundary layer over the continental shelf off northern california during the 1981 and 1982 upwelling seasons these measurements show that after the atmospheric spring transition the airflow in the marine layer is dominated by the north pacific high and the surface wind field over the shelf is characterized by periods of strong 7 15 m s upwelling favorable alongshelf winds lasting for up to 30 days interrupted by shorter periods of much weaker winds directed either equatorward or poleward these periods of weak or reversed winds typically last several days and are called wind relaxations even though they are primarily associated with coastally trapped perturbations of the marine layer along the central and northern california coast and not with a large scale weakening of the north pacific high the atmospheric boundary layer measurements made in code suggest a simple conceptual model which can explain much of the physiology or structure of the marine layer and associated surface wind field during periods of persistent upwelling favorable winds during these periods which represent the quasi steady state regime during the upwelling season the inversion base of the marine layer drops eastward toward the coast until it intersects the coastal mountain range at a height of several hundred meters and the associated thermal wind produces an alongshelf wind jet which has a maximum speed just below the inversion base turbulent mixing tends to homogenize any stratification in the marine layer beneath the jet and couple the jet to the ocean surface producing strong upwelling favorable winds over the shelf day night heating cooling over the narrow coastal strip beneath the marine layer generates a weak cross coast secondary circulation which causes the core of the alongshelf jet to drop in elevation and shift onshore this diurnal change in the marine layer structure explains both the daytime acceleration of the surface winds observed over and near the coast and its offshore decay and the associated offshore increase in the subdiurnal alongshelf wind thus the quasi steady component of the wind stress has a significant curl over the inner shelf during periods of active upwelling this mean summer atmospheric boundary layer regime is occasionally interrupted by synoptic and or mesoscale events or anomalous conditions analysis of the code observations suggests five types of events two primarily synoptic scale conditions which lead to stronger than normal upwelling favorable winds over the shelf and three primarily mesoscale events which lead to wind relaxation about half of the wind relaxation events observed in 1981 and 1982 are believed to be associated with either coastal trapped gravity currents or internal kelvin waves which propagate north ward in the marine layer along the central and northern california coastal mountain range

effects of wind stress and wind stress curl variability on coastal upwelling abstract aircraft measurements during the winter 1989 shelf mixed layer experiment smile and summer 1982 coastal ocean dynamics experiment code were used to characterize the spatial variation of the low level wind and wind stress over the northern california shelf the curl of the wind stress was calculated from directly measured turbulent stress components the accuracy of the computed curl was estimated to be adequate to map the spatial structure wintertime measurements showed a concentration of large positive curl over 1 pa 100 km 1 west of point arena regardless of wind direction due to the effects of the coastal topography on the wind fields results from summertime measurements showed a similar local maximum of positive curl west of point arena larger curl values over 3 5 pa 100 km 1 however were observed across a hydraulic jump propagating from stewarts point for highly supercritical marine boundary layer flow a two layer vertically integrated numerical model of coastal upwellin

diagnoses of vertical transport in a three dimensional finite element model of the tidal circulation around an island a three dimensional finite element model is used to investigate the formation of shallow water eddies in the wake of rattray island great barrier reef australia field measurements and visual observations show that stable eddies develop in the lee of the island at rising and falling tides the water turbidity downstream of the island suggests the existence of strong upwelling that would be responsible for carrying bed sediments tip to the sea surface we first propose to look at the upwelling velocity and then use the theory of the age to diagnose vertical transport the water age is defined as the time elapsed since particles of water left the sea bottom where the age is prescribed to be zero two versions of this diagnosis are considered although the model predicts upwelling within the eddies it is not sufficiently intense to account for vertical transport throughout the water column during the life span of the eddies as mesh resolution increases this upwelling does not intensify however strong upwelling is then resolved off the island s tips which is confirmed by the results obtained with the age this study also shows that the finite element method together with unstructured meshes performs well for representing three dimensional flow past ail island c 2006 elsevier ltd all rights reserved

island wakes and headland eddies a comparison between remotely sensed data and laboratory experiments island wakes and headland eddies in coastal waters are identified from spaceborne and airborne remotely sensed imagery in the visible wavelengths the imagery were obtained for the bristol and english channels united kingdom which are characterized by high tidal currents and levels of turbidity suspended matter in the surface waters is used as a passive tracer for the flow features scaling parameters e g the reynolds ekman and rossby numbers obtained from the depth averaged equation of motion are presented based upon information on oceanographic conditions at the times of the overpasses the parameters are compared then with data obtained from laboratory model investigations presented by other experimenters in the published literature the remotely sensed data demonstrate that in coastal waters with nonuniform obstacles and bathymetry for a given ekman number the flow regimes occur at a lower rossby number than might be expected from laboratory experiments in the absence of a method for the accurate determination of the horizontal eddy viscosity hence the reynolds number it is concluded that an island wake parameter wolanski et al 1984a should be adopted to describe such features in coastal waters

in situ measurements of spring neap variations to unsteady island wake development in the firth of forth scotland field data and a numerical model have been used to investigate the von karman vortex street generated by a 50 m wide island in the firth of forth for which the characteristics differ between flood and ebb during the flood water depth in the lee of the island is shallow hence little vertical structure develops in the velocity due to bottom induced mixing in contrast the ebbing water depth is deeper in the lee of the island allowing vertical structure to develop in the velocity field however the ebb wake is complicated by the presence of a lateral flow due to a bathymetric restriction the effect of this lateral flow is to inhibit development of the ebb wake during spring tide conditions whereas the effect is minimal during neap lower freestream velocity conditions this change in wake development was clearly visible in the in situ horizontal and vertical velocity fields while the observed flood wake varied considerably between neap and spring the characteristics of the ebb wake were similar for neap and spring because of this overbank flow the overbank flow has an important role in determining the varying magnitude of the vorticity of eddies generated either side of the island

observed dynamics of coastal flow at cape mendocino during coastal waves 1996 abstract airborne in situ and remote meteorological measurements from around cape mendocino california sampled during the coastal waves 1996 field program are analyzed for three different days 7 12 and 26 june 1996 two days conformed to typical summertime conditions with a strong northerly downcoast flow while the wind on the third day was weaker on the first 2 days the flow was supercritical in the sense that the froude number was larger than unity and these 2 days feature expansion fans in the lee of the cape on the third day no such phenomenon was observed all 3 days had a strong thermal wind caused by the marine inversion sloping down toward the coast on the first 2 days the flow aloft was westerly or northerly so that the thermal wind added to the background flow results in a strong jet on the third day the flow aloft was southerly and consequently even with the added thermal wind the northerly flow in the marine layer was too weak to be supercritical the main difference between t

island wakes in deep water abstract density stratification and planetary rotation distinguish three dimensional island wakes significantly from a classical fluid dynamical flow around an obstacle a numerical model is used to study the formation and evolution of flow around an idealized island in deep water i e with vertical island sides and surface intensified stratification and upstream flow focusing on wake instability coherent vortex formation and mesoscale and submesoscale eddy activity in a baseline experiment with strong vorticity generation at the island three types of instability are evident centrifugal barotropic and baroclinic sensitivities are shown to three nondimensional parameters the reynolds number re rossby number ro and burger number bu the dependence on re is similar to the classical wake in its transition to turbulence but in contrast the island wake contains coherent eddies no matter how large the re value when re is large enough the shear layer at the island is so narrow that the ver

observations of large wind shear above the marine boundary layer near point buchon california abstractparticularly strong winds along the coast of southern california on 24 may 2012 were measured by the wyoming king air research aircraft during the precision atmospheric marine boundary layer experiment preamble the fast flow is bounded laterally by the coastal topography and vertically by a pronounced temperature inversion separating the cool moist air in the marine boundary layer mbl from the warm dry air aloft many studies have investigated the response of this two layer flow to changes in the coastline by invoking hydraulic theory which explains the essential characteristics including changes in mbl depth and the attendant wind processes occurring just above the mbl are important to the low level thermodynamic and kinematic structure observations on this day demonstrate how the large shear above the mbl can impact the lower atmosphere a typical two layer system was observed north of point buchon which was supercritical around point buchon the depth of the mbl decreased and wind i

objective maps of near surface flow states near point conception california abstract objective streamfunction and velocity potential maps of three commonly observed flow states near point conception california are derived from moored current meter and drifter observations the states are defined using current meter data drifter data are sorted by flow state and averaged within spatial bins to resolve their spatial structures spatial correlations of drifter data show the along shelf and cross shelf decorrelation distances are approximately 45 and 25 km respectively this information is used to make the objective streamfunction and velocity potential maps the total velocity is represented as the sum of the rotational nondivergent streamfunction component and the irrotational divergent velocity potential component the velocity derived from the streamfunction is much stronger than that derived from the velocity potential the streamfunction is sufficiently well resolved to make meaningful vorticity maps the velocity potential indicates a source term in the western santa bar

evolution of an oceanic anticyclone in the lee of madeira island in situ and remote sensing survey island wakes are areas of a strong eddy activity influencing the availability and transport of organic matter in the ocean which in turn impact biological productivity despite this eddy formation in the lee of north atlantic tropical islands is scarcely documented except for the canary islands moreover the occurrence of anticyclones leeward of madeira has seldom been detected during the summer of 2011 a multiplatform approach combining satellite data with in situ measurements was used to study an anticyclonic eddy generated in the lee of the madeira island the main objective was to confirm recent numerical evidence suggesting that orographically perturbed winds can induce anticyclonic eddies leeward of madeira particularly during summer months the high resolution sampling of the eddy s interior shows a strong downwelling of 100 m of the isopycnal layer below the mixed layer typical of intrathermocline eddies the 25 km radius of this anticyclonic structure exceeds the local deformation radius by a factor of 2 the vortex rossby number remained moderate ro 0 26 even if the relative core vorticity reached a finite value f 0 7 the occurrence of strong trade winds 10 15 m s 1 prior to the detection of the first surface eddy signatures july 2011 concurrent with opposite flowing geostrophic currents shows that the orographic wind forcing is the main mechanism for generating this mesoscale long lived eddy after leaving the shelter of the island the eddy traveled northwesterly following a perpendicular net ekman transport pathway at a speed of 5 km d for at least 2 months an interaction with a cyclonic partner generated in the area helped precipitate the northward trajectory this study presents the first clear evidence of a wind induced mesoscale anticyclone in the lee of madeira

coastally trapped wind reversals along the united states west coast during the warm season part i climatology and temporal evolution abstract the northerly winds that predominate along the u s west coast during april september are interrupted periodically by abrupt reversals to southerly flow the climatology and composite temporal evolution of these reversals from point conception to the canadian border are documented using hourly data from moored coastal buoys and coastal marine automated network stations for the period 1981 91 the reversals are divided into two categories coastally trapped reversals in which the southerly flow is highly ageostrophic and restricted to the coastal zone and synoptic reversals which are associated with landfalling troughs or fronts coastally trapped events occur on average about 1 5 times per month along the central and northern california coast about twice a month near the california oregon border and about once a month near the oregon washington border the ratio of coastally trapped reversals to synoptic reversals is higher during july september and lower during april june particularly in t

the horizontal momentum balance in the marine atmospheric boundary layer during code 2 abstract the horizontal momentum balance in the marine atmospheric boundary layer during the coastal ocean dynamics experiment code is analyzed using meteorological data from an array of surface moorings previous studies have indicated the presence of orographically generated mesoscale features that are induced by strong southward flow around point arena the present analysis demonstrates that during periods of strong southward flow the cross shore momentum equation is dominated by a balance between the ageostrophic acceleration associated with the flow curvature around point arena and the cross shore pressure gradient while the along shore momentum equation is dominated by a balance between vertical stress divergence and alongshore pressure gradient these balances are consistent with results from a shallow water model of the marine layer the calculations provide evidence for orographic modification of the horizontal structure of the boundary layer under a broader range of southward flow conditio

the nonnormality of coastal ocean flows around obstacles and their response to stochastic forcing abstract the effect of stochastic variability upon the wake downstream of a real headland is investigated from observations taken at bass point australia three sources of stochastic forcing are identified and quantified these being variability in the wind stress in the flow incident on the headland and that generated in the flow by complex reef topography at the headland s tip these sources of stochastic forcing are found to induce a significant degree of unsteadiness in a nonlinear numerical model of flow around bass point that in the absence of stochastic forcing simulates steady recirculating flow the observed stochastic variability of the flow incident on the headland is found to be larger than is necessary to support unsteadiness in the simulated straining zone the dynamics of the perturbation growth observed in the model are understood by applying the techniques of generalized stability theory to the associated tangent linear model tlm the eigenmodes of the tlm confirm that the system

islands as eddy transformation and generation hotspots cabo verde case study abstract deep ocean islands have long been associated with the generation of oceanic eddies in their wakes however their interaction with incoming eddies has seldom been considered this study focuses on the characterization of background and locally generated mesoscale eddies in the cabo verde archipelago between 2003 and 2014 special attention is given to the interaction of incoming eddies with the bathymetry of the islands along with their impacts on the local generation of eddies island induced wind shear effects are also considered in addition some examples of the biological response to background and locally generated eddies are discussed this is achieved by combining remote sensing satellite observations for wind sea surface height and chlorophyll a chla surface concentrations the results show that the interaction between incoming background eddies and the archipelago is a recurrent phenomenon which results in eddy deflection splitting merging intensification and termination sorted by highest to lowest number of occurrences local island induced disturbances are also significant mainly due to atmospheric effects such processes result in the generation of island induced eddies and in wind mediated eddy intensification and confinement more often observed in the leeward group nonetheless it is strongly suggested that many of the locally generated eddies are a direct product or by product of the interaction of background eddies with the islands with respect to the biological realm a locally generated cyclonic eddy is observed to originate a pronounced phytoplankton bloom in the vicinity of the tallest island nonetheless background eddies generated off the african coast are often associated with enhanced chla concentrations when they intersect the archipelago such observations challenge the idea that local biological productivity in deep oceanic islands is exclusively driven by island induced mechanisms

transport variability across the korea tsushima strait and the tsushima island wake abstract transport variations are calculated across the korea tsushima strait using continuous current measurements made between may 1999 and march 2000 twelve bottom mounted acoustic doppler current profilers provide velocity profiles along two sections one section south line at the strait entrance southwest upstream of tsushima island and the other section north line at the strait exit northeast downstream of tsushima island transport variations across the strait are large particularly in the lee of tsushima island where a countercurrent commonly exists the tsushima current transport averaging 2 65 sverdrups sv 1 sv 10 6 m 3 s 1 is split into two cores by tsushima island which divides the strait into eastern and western channels transport in the western channel is 23 higher than in the eastern channel over the measurement period some seasonality in transport variability is observed for both the western and eastern channels transports are largest in fall and smallest during winter the single velocity core observed upstream of tsushima island is estimated to split directly behind tsushima island over an aperture of about 31 km along the south line a wake zone that averages 40 km in width is observed downstream of tsushima island and appears to follow island wake zone dynamics reynolds numbers can range from 22 to 90 in the wake zone and eddy shedding can occur throughout the year

transcritical flows in the coastal marine atmospheric boundary layer abstract numerical solutions of shallow water flow in a variable width channel are computed to model the summertime marine atmospheric boundary layer off the u s west coast using an idealization of the coastline in the vicinity of point arena california as an example several steady state base flows are presented that are hydraulically transcritical these flows are strongly nonlinear weakly rotational and are forced by constant pressure gradients and damped by nonlinear bottom drag at the sea surface the transcritical base flows are supercritical in the vicinity of bends in the coastline but are subcritical to the north upstream and to the south downstream where the coastline is straight within the supercritical region orographic bends in the coastline produce expansion fans and compression jumps the same structures found in globally supercritical flows when the imposed pressure gradient forcing is increased the resulting base flow has a supercritical to subcritical transitional jump that

stable isotopic studies of mafic sills and proterozoic metasedimentary rocks located beneath the duluth complex minnesota abstract thin 3 20 m picritic to noritic sills are found in the proterozoic metasedimentary footwall rocks of the duluth complex minnesota the sills were emplaced prior to the major intrusions that comprise the duluth complex and underwent contact metamorphism along with the country rocks oxygen hydrogen and sulfur isotopic compositions of the sills indicate a varied history of isotopic exchange between minerals melts and hydrothermal fluids in the high temperature environment below the major plutonic bodies of the midcontinent rift system the pre duluth complex sills exhibit a range in 18o values from 4 9 to 14 8 with values between 6 and 7 generally found in sill interiors high 18o values near sill contacts with high 18o metasedimentary rocks of the pelitic virginia formation or biwabik iron formation coupled with a smooth sigmoidal isotopic profile centered at the contact suggest that oxygen diffusion was an important exchange mechanism the elevated 18o values near the center of the thickest sills are thought to reflect the emplacement of isotopically contaminated basaltic magma dehydration reactions in the pelitic rocks of the contact aureole liberated high 18o fluids that enhanced subsolidus diffusive exchange advective displacement of the diffusion profiles toward the sill interior is less than 40 cm and suggests that layer parallel flow dominated in the dehydration of the contact aureole elevated but uniform 18o values 9 7 to 10 5 in thinner sills suggests that oxygen diffusivity was increased relative to country rocks due to enhanced porosity perhaps related to extensive development of microcracks although d values of the pelitic country rocks record a history of dehydration systematic variations of d 64 to 143 and h2o 0 15 to 5 40 wt content are not found in the sills 18o values of coexisting plagioclase and pyroxene from the sills indicate a close approach to isotopic equilibrium and are consistent with a diffusion dominant exchange process at temperatures near 500 c results of diffusion modelling suggest a duration of isotopic exchange that may have extended from tens of thousands of years to 1 4 ma depending on local controls of porosity and permeability as well as rates of fluid production in the contact aureole localized areas of 18o and d depletion in the sills values as low as 4 9 and 143 respectively denote exchange with meteoric water after interaction with the high 18o metamorphic fluids in the contact aureole although all of the elevated 18o samples in the contact environment may have suffered 18o depletion most exchange with meteoric water appears to be spatially localized and is thought to reflect highly channelized fracture controlled fluid flow sulfur isotopic values of the sills are variable 2 7 to 11 2 and indicative of an evolution involving pre emplacement contamination of basaltic magma and sub solidus exchange with an h2s bearing metamorphic fluid sulfur contents exceed 3 0 wt only within troctolitic to melatroctolitic sills and 34s values of 7 8 to 8 3 are strongly suggestive of pre emplacement contamination by sulfur derived from a proterozoic sedimentary unit high 18o and 34s rocks particularly at sill margins are consistent with either hydrothermal precipitation of fine grained sulfide minerals or isotopic exchange between magmatic sulfides and an h2s bearing metamorphic fluid

ducted coastal ridging over s e australia the intense and rapidly established coastal ridging which is a regular occurrence over south eastern australia during the warm seasons is investigated using a detailed case study and mesoscale numerical model simulations we suggest that the ridge is initiated by a forced kelvin type edge wave which forms on the south western edge of the great dividing range and is ducted in an anticlockwise sense around the coast the ridge is then stabilized by inertial modification and decays over a synoptic time scale of a few days our results apply to similar phenomena in other parts of the world notably southern africa and south america

diurnal cycle of supercritical along coast flows abstract in this study a three dimensional hydrostatic mesoscale model is used to address the transient behavior of supercritical along coast flow a control experiment and several sensitivity tests are performed in order to investigate the diurnal cycle of flow characteristics an idealized representation of the northern california terrain is used and the model results are interpreted within the reduced gravity shallow water concept in two preceding studies by the authors this theory appeared to be violated since the flow accelerated along the coastline upstream of the change in coastline orientation even though the flow was supercritical here it is shown that the criticality of the flow for typical summertime conditions along the california coast actually varies diurnally the gradual acceleration of the flow along the upstream coastline is established during a subcritical phase of the simulation thus the shallow water concept is not violated because the along coast jet is primarily driven by

life cycle of a linear coastal trapped disturbance abstract a recent climatology of observed coastal trapped disturbances in the marine atmospheric boundary layer along the united states west coast motivates the detailed examination for a specific form of imposed forcing of a linear shallow water boundary layer model the model is forced by a time dependent pressure field imposed at a fixed level above the boundary layer that is an idealized representation of the climatological synoptic evolution a low pressure center translates westward across the coastal boundary corresponding to the observed offshore extension of a continental thermal trough the alongshore structure of the model disturbance is characterized by enhanced northerly flow a depressed marine layer and low surface pressure to the north and southerly flow a raised marine layer and high surface pressure to the south initially the marine layer thickness along the coast responds predominantly to convergence of the ageostrophic cross shore flow driven by the imposed cross shore press

detection of monsoonal phytoplankton blooms in luzon strait with modis data abstract the luzon strait experiences a seasonal surge of phytoplankton based on ocean color data to examine the timing and position of the bloom daily modis chlorophyll data 2002 2005 were acquired and analyzed supporting data such as modis sst and nlw bands quikscat wind data river discharge and bathymetry were also used and processed in order to investigate the possible driving forces behind the bloom occurrence results show that chlorophyll concentration in the luzon strait dramatically increases during ne monsoon reaching to approximately 2 0 mg m 3 highest chlorophyll concentration is observed near the western slope of the luzon strait the monsoonal bloom in the luzon strait is likely due to upwelling and can be possibly associated with the interaction of the northward flowing luzon coastal current with the westward intrusion of kuroshio during ne monsoon the positive wind stress curl also contributes to this occurrence the influence of cagayan river is only limited within few kilometers from the river mouth

synoptic forcing of coastal trapped disturbances in the marine atmospheric boundary layer abstract motivated by recent observations along the west coast of the united states the authors investigate the generation and propagation of coastal trapped disturbances in the marine atmospheric boundary layer analytic solutions are obtained in a linear shallow water reduced gravity model of the flow subject to forcing by upper level pressure disturbances and dissipation in the form of wind stress at the sea surface it is found that unless the mean alongshore flow is to the south with speeds larger than the gravity wave phase speed a northward propagating coastal trapped response develops the superposition of cross shore propagating forcing and the northward propagating response in marine layer thickness can give rise to surface pressure ridges at the coast with both narrow and broad cross shore extent wind reversals associated with the disturbance lead the change in surface pressure at the coast the magnitude of the response increases for weaker inversion strength greater undisturbed marine l

the dynamics of coastally trapped mesoscale ridges in the lower atmosphere abstract the dynamics of coastally trapped ridges that propagate in the marine layers of western north america and southeastern australia is examined a nonlinear semigeostrophic theory shows that the coastal ridges develop initially as an alongshore intrusion of denser marine air that is driven by the synoptic scale pressure gradient nonlinear kelvin waves evolve with the intruding flow on a slower time scale governed by the dynamic parameters if dispersive effects balance the nonlinearities then these waves evolve into solitary form otherwise the nonlinear waves steepen so that the leading edge of the ridge eventually propagates as a shock the theory is applied to two ridging events in california and one in southeastern australia in each case good agreement is found between theory and observations of the evolution times and propagation speeds of the coastal ridges the theory also explains the observed behavior of the events at prominent convex bends and gaps in the coastal topography

mesoscale simulation of supercritical subcritical and transcritical flow along coastal topography abstract a mesoscale atmospheric model is used to address the characteristics of stratified flow bounded by a side wall along a varying coastline initial froude number values are varied through alteration of marine inversion strength permitting examination of supercritical subcritical and transcritical flow regimes encountering several coastal configurations consistent with shallow water models sharp drops in boundary layer depth and flow acceleration occur in flow rounding convex bends however significant flow response occurs in the stratified layer aloft which is unexplained by conventional shallow water theory the strongest flow acceleration occurs in the transcritical case while regardless of inversion strength the deformation of the isentropes aloft shows general structural similarity advection of horizontal momentum is an important component of the horizontal force balance a simulation having several coastline bends exhibits a detached oblique hydraulic jump upwind of a concave bend t

the dynamics of northwest summer winds over the santa barbara channel a mesoscale model is used to examine the dynamics of northwest flow over the santa barbara channel region three cases are considered each characterized by typical summertime synoptic conditions but with differences in pressure gradient strength and marine boundary layer depth mbl the first case examines a relatively deep mbl and strong pressure gradient case 2 is characterized by a more shallow mbl and weaker pressure gradient and case 3 represents a transition from a deep mbl to shallow conditions in all cases simulated surface winds show reasonable agreement with observations over most of the model domain with the exception of regions near abrupt terrain changes results from the model indicate that the flow with a deep mbl 400 m and strong pressure gradient case 1 is supercritical causing regions of acceleration and expansion in the lee of point conception when the mbl is shallow 150 m case 2 a transcritical flow scenario exists with subcritical flow upstream from point conception and a supercritical flow region over the santa barbara channel and downstream from the channel islands flow over the channel is strongly affected by diurnal heating in shallow mbl cases reversing direction in step with a land breeze circulation induced by nighttime cooling the land breeze forces an internal wave disturbance that propagates westward across the channel eliminating the supercritical flow region in the lee of point conception conditions with a deep mbl 400 m produce less variability in the surface winds except for the region sheltered by the santa ynez mountains an expansion fan is still evident in this case but it is produced by the interaction of the flow with higher terrain north and east of the channel the low hills on point conception and the channel islands do not have a large blocking effect on the surface flow when the mbl is deep analysis of the momentum budget supports the conclusion that the boundary layer behaves like a transcritical hydraulic flow when the mbl is shallow except for the open ocean region the coriolis term is minor in comparison with the pressure and advection terms diurnal heating effects are evident in the nearshore pressure term which varies from offshore during the late evening to onshore in the afternoon these effects are most significant when the mbl is shallow and can augment the hydraulically forced pressure pattern causing a stronger expansion fan in the late afternoon and a collapse of the expansion fan during the early morning

coastal jet adjustment near point conception california with opposing wind in the bight abstracttypical spring and summer conditions offshore of california consist of strong northerly low level wind contained within the cool well mixed marine boundary layer mbl that is separated from the warm and dry free troposphere by a sharp temperature inversion this system is often represented by two layers constrained by a lateral boundary aircraft measurements near point conception california on 3 june 2012 during the precision atmospheric mbl experiment preamble captured small scale features associated with northerly flow approaching the point with the added complexity of encountering opposing wind in the santa barbara channel an extremely sharp cloud edge extends south southwest of point conception and the flight strategy consisted of a spoke pattern to map the features across the cloud edge lidar and in situ measurements reveal a nearly vertical jump in the mbl from 500 to 100 m close to the coast and a sharp edge at least 70 km away from the coast in this case it is hypothesized that

generation of coastal lows by synoptic scale waves a model is presented in which eastward propagating synoptic waves interact with a meridional escarpment it is shown that under suitable conditions trapped waves are produced at the escarpment the dominant wave being poleward propagating this model is intended to represent the generation of coastally trapped disturbances like those found in southern africa

island wakes in shallow coastal waters rattray island northeast australia is 1 5 km long 300 m wide and lies in well mixed water approximately 25 m deep its long axis is inclined at about 60 into the direction of the dominant semidiurnal tidal current the length of the wake in the lee of the island as documented by aerial photographs and satellite imagery appears to equal that of the wake behind a flat plate in a two dimensional flow at a reynolds number of about 10 however current metering drogues measurements and temperature mapping indicate internal wake velocities much greater than would be consistent with such a simple low reynolds number model further estimates of the turbulent eddy coefficient suggest an effective reynolds number more in the vicinity of 103 to reconcile these observational differences and to explain the observed upwelling in the core of the wake an ekman pumping model is proposed it is postulated that the ekman benthic boundary layer driven by rotation in the wake allows the vertical vorticity introduced into the water at the tip of the island at the point of separation to be negated by the vorticity of opposite sign introduced at the bottom further it is shown that a large fraction of the kinetic energy of the upstream flow facing the island is used to drive the wake eddies leading to the conclusions that the trapping of water in the lee of islands greatly increases head losses on continental shelves with numerous islands coral reefs and rock outcrops

a nonhydrostatic mesoscale simulation of the 10 11 june 1994 coastally trapped wind reversal abstract during the summer months the california coast is under the influence of persistent northwesterly flow several times each summer this regime is disrupted by coastally trapped wind reversals ctwr in which the northwesterly flow is replaced by southerlies in a narrow zone along the coast controversy exists as to the physical mechanisms responsible for initiation and maintenance of ctwrs while it is clear that coastal terrain is important in creating the trapped response the precise role played by terrain is unclear in the present study these issues are investigated using a nonhydrostatic mesoscale model to simulate the 10 11 june 1994 ctwr event the results show that the model successfully reproduces many of the observed features of this event including anomalous vertical structure involving the relatively shallow boundary layer with a warm nearly neutral layer above the northward propagation of southerly flow in advance of a tongue of coastal stratus fog and a substantial reduction i

kuroshio induced wake in the lee of green island off taiwan 1 the wake of green island was investigated in the alongshore flowing kuroshio east of taiwan where current speeds range from 1 to 1 5 ms 1 vertical profiling with shipboard lowered acoustic doppler current profiler and conductivity temperature depth profiler revealed sizable anomalies in flow and water characteristics in the lee of green island two different stages of wake evolution were observed from two shipboard surveys in the first stage a recirculation developed leeward of the island followed by a wavy wave like tail that resembled a weak vortex street in the second stage a cold eddy probably originating from the leeward side of the island showed up 14 km downstream of the island the wake water was colder saltier higher in chlorophyll a concentration and produced isopycnal doming up to 60 m in the recirculation area the relative vorticity either positive or negative was 10 times of planetary vorticity and the horizontal divergence or convergence was o 10 4 s 1 on average flow divergence and convergence in the wake were expected to form upwelling and downwelling zones producing a vertical circulation that vertically displaces isotherms high inverse richardson number produced by strong vertical shear of horizontal currents was associated with intense overturning events in the wake high vertical shear of horizontal currents drove the mixing the dissipation rate of turbulent kinetic energy in the overturn regions is o 10 7 10 5 w kg 1 the corresponding eddy diffusivity is o 10 3 10 1 m2 s 1 the wake water properties are vertically diffused via upwelling and turbulence and can be delivered downstream through eddy shedding or advection the extent of downstream influence remains to be investigated

orographically trapped coastal wind events in the pacific northwest and their oceanic response three ageostrophic orographically trapped wind events in the coastal zone of the pacific northwest are examined time series of wind speed wind direction air temperature sea level pressure ocean currents and ocean temperature are utilized to establish the general features of these events and to characterize the oceanic response it is suggested that these atmospheric events are highly nonlinear bores or gravity currents rather than quasi linear kelvin waves observed oceanic responses include a drop in sea surface temperature sst of 1 3 c offshore to approximately 150 km approximately the atmospheric rossby radius and a rise in sst of similar magnitude within 15 km of the shore a set of reduced gravity fully nonlinear single layer models is utilized to investigate the dynamics of the atmospheric features and their oceanic response and a possible air sea interaction the models reproduce several of the first order features of the air and sea phenomena such as the development of the atmospheric front and the wake of near inertial waves in the ocean

observations and analysis of the 10 11 june 1994 coastally trapped disturbance abstract a coastally trapped disturbance ctd characterized by southerly flow at the surface on 10 11 june 1994 was observed from the california bight to bodega bay during a field experiment along the california coast north south approximates the coast parallel direction data from a special observational network of wind profilers radio acoustic sounding systems special surface data balloon ascents and a research aircraft were used with satellite and synoptic data to explore both the ctd structure and the regional scale changes before the event the disruption of the climatological northerly flow along the central california coast which preconditioned the area for the development of a ctd began with the eastward movement of a surface high into washington and oregon and the amplification of a thermal low in northern california as with most ctds in the region this occurred over the 2 3 days preceding the ctd s initiation these large scale changes caused westward advection of warm continental

tidal flow separation at protruding beach nourishments in recent years the application of large scale beach nourishments has been discussed with the sand motor in the netherlands as the first real world example such protruding beach nourishments have an impact on tidal currents potentially leading to tidal flow separation and the generation of tidal eddies of length scales larger than the nourishment itself the present study examines the characteristics of the tidal flow field around protruding beach nourishments under varying nourishment geometry and tidal conditions based on extensive field observations and numerical flow simulations observations of the flow field around the sand motor obtained with a ship mounted current profiler and a set of fixed current profilers show that a tidal eddy develops along the northern edge of the mega nourishment every flood period the eddy is generated around peak tidal flow and gradually gains size and strength growing much larger than the cross shore dimension of the coastline perturbation based on a 3 week measurement period it is shown that the intensity of the eddy modulates with the spring neap tidal cycle depth averaged tidal currents around coastline perturbations are simulated and compared to the field observations the occurrence and behavior of tidal eddies is derived for a large set of simulations with varying nourishment size and shape results show that several different types of behavior exist characterized by different combinations of the nourishment aspect ratio the size of the nourishment relative to the tidal excursion length and the influence of bed friction

synoptic scale forcing of coastal lows forced double kelvin waves in the atmosphere gill 1977 has interpreted the coastal lows of southern africa as atmospheric coastal kelvin waves the lows are trapped horizontally next to the steep slopes of the great central plateau by coriolis forces and vertically by a low level inversion this hypothesis is tested and extended using two linear models a barotropic primitive equation analysis on an equatorial beta plane models the generation of these waves an impermeable eastern boundary is included to reflect the blocking of the low level flow below the coastal inversion by the orography results of the linear analysis suggest that the formation of the coastal lows may be explained in terms of the scattering of eastward propagating synoptic scale disturbances at the meridional boundary the boundary response is structurally similar to a kelvin wave at the frequencies of interest no zonally propagating rossby waves are excited further in contrast to the case of a western boundary the equatorial response is negligible a two layer f plane model enables the dynamics of the layer of fluid below the interior inversion to be incorporated at the period of the synoptic forcing six days the boundary response is a maximum along the escarpment and decays exponentially from it the e folding distance is slightly less than the appropriate rossby radius of deformation these results together with observations suggest that the coastal low and its companion low over the interior may be interpreted as forced internal double kelvin waves the possible application of these results to foehn chinook winds and lee cyclogenesis is mentioned

supercritical flow interaction within the cape blanco cape mendocino orographic complex abstract supercritical flow interaction occurring in the marine boundary layer between closely spaced coastal capes is investigated with a mesoscale numerical prediction model as an extension of previous work the u s navy s coupled ocean atmosphere mesoscale prediction system coamps is used to perform idealized model simulations with marine layers of varying upstream froude number to elucidate the different flow responses for a single convex bend the impact upon the supercritical flow of introducing a series of closely spaced coastal bends is then investigated the expansion fan is significantly reduced in magnitude and size by the formation of a compression wave at a blocking concave bend approximately 150 km downstream building upon the idealized marine layer response real data forecasts are then examined for several time periods of supercritical flow interaction between cape blanco oregon and cape mendocino california observations from the coastal waves 1996 cw96 field program were colle

flow separation and vertical motions in a tidal flow interacting with a shallow water island this paper reports on the case study of rattray island great barrier reef northeast australia lying perpendicular to tidal flow in shallow waters at ebb and flood attached stable eddies develop in the wake where swirls of turbidity suggest that sediment laden waters are brought to the surface as a result of vertical transport both eddy and tip upwellings are encountered in the tidal flow around rattray island but there is currently no clear cut answer as to which secondary flow generates upwelling with the largest intensity this paper addresses this specific issue through idealized and realistic high resolution numerical experiments the analysis is supported by physical arguments based on the theory of flow separation given rattray s geometry and surrounding bathymetry the mechanism of flow separation in shallow waters helps explain the asymmetry in size of the eddies and their intensity the results of idealized numerical experiments also suggest that eddy and tip upwellings may be of similar intensity at rattray island

the marine layer off northern california an example of supercritical channel flow abstract during the spring and summer northerly winds driven by the north pacific high pressure system are prevalent over the northern california continental shelf only interrupted for periods of a few days when weak or southerly winds occur in the course of the coastal ocean dynamics experiment code fixed station and observations were made to describe the temporal and spatial structure of the lower atmosphere and their relation to the strong upwelling of coastal waters in a region extending up to 40 km offshore and 100 km along the coast these observations suggest that atmospheric conditions during the spring and summer usually fall into one of three categories the surface wind can be everywhere weak pattern 1 it can blow at large speeds in a uniform pattern pattern 2 or finally the structure of the northerly surface wind can be complex with large changes in the wind speed and corresponding changes in the surface pressure over short spatial scales pattern 3 the latter pattern which o

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

effects of viscosity and bottom friction on recirculating flows a recent set of coastal experiments pattiaratchi et al 1987 found that the horizontal eddy reynolds number did not adequately describe the wakes found in the lee of coastal islands other flow parameters formulated on bottom friction were found to be much better at describing these wakes in this paper it is suggested that these findings are caused by the extraction of energy from the flow due to bottom friction which is the net result of the vertical viscous transfer of momentum through the water column to the seabed this is in contrast to the horizontal viscous transfer of momentum which results in negligible energy loss to the coast because of the far larger horizontal scales it is hypothesized that this difference results in fundamentally different flow regimes and this hypothesis is investigated both analytically and numerically conditions for the existence of steady zones of barotropic recirculation under the influence of both horizontal viscosity and bottom friction in the wake behind a bluff body are examined analytically it is found that such steady recirculation requires the presence of horizontal viscosity and is hindered by the loss of energy due to bottom friction a numerical model is used to verify and quantify this analytical result for the case of two dimensional flow around a circular cylinder and it is concluded that an appropriate bottom friction number based on the ratio of scales of the nonlinear and bottom friction terms may often govern the nature of the recirculation in the lee of coastal islands instead of the eddy reynolds number based on horizontal eddy viscosity as is sometimes assumed

tidally induced clouds of suspended sediment connected to shallow water coral reefs abstract the bay of banten west java indonesia represents a shallow coastal embayment harboring coral reefs subject to extremely turbid conditions the sedimentary regime and flow structure of two contrasting coral reef islands in the embayment were investigated to identify the mechanisms responsible for mean and peak levels of suspended sediment concentration ssc around the reefs arrays of in situ calibrated optical backscatter obs sensors were deployed across the reef slopes far field conditions were simultaneously monitored using an acoustic doppler current profiler adcp and a conductivity temperature and depth ctd probe equipped with an obs sensor in addition hydrographic surveys were conducted using the adcp attached to a small fishing boat navigating transects perpendicular to the reef islands the direct influence of river plumes was found to be insignificant waves act only in the uppermost few meters of the reef slopes where coral growth is most abundant and little sediment is available for resuspension tidal currents are the primary cause of high turbidity which was inferred from peaks in the diurnal and semidiurnal frequency bands of ssc spectra and the large depths where the turbidity variation sometimes initiates the entrained sediment disperses upward across the reef slopes which is likely due to a secondary current associated with bending of the flow along the curved hydraulically rough reef slopes in weakly stratified ambient waters changes in sediment availability variable critical shear stresses for erosion and deposition and the formation and evanescence of island wakes may explain the high variability of ssc at the reef slopes

on the generation and propagation of the southern african coastal low the time height variability of the lower marine atmosphere during the eastwards propagation of coastal lows around the coast of southern africa is presented these coastal lows are shallow mesoscale disturbances that are trapped vertically by a strong subsidence inversion and horizontally through coriolis effects against the steep escarpment that fringes the subcontinent prior to the event warm offshore flow descending off this escarpment at about the inversion level provides an input of buoyancy which together with the cyclonic vorticity acquired during the descent acts to generate a coastal low rather than a high analysis of the data shows that coastal lows are characterized by a marked lowering of the inversion level a switch in the direction of the winds below the inversion and a drop in the near surface temperature which are all consistent with the hypothesis that the coastal low is an internal kelvin wave propagating in the marine layer good agreement between the observed propagation speed of the coastal low and the theoretical phase speed of such a wave reinforces this hypothesis a model of the vertical buoyancy advection into the marine atmosphere that results from the warm offshore flow is presented it is illustrated that an internal kelvin wave in the form of a coastal low results from this buoyancy advection comparisons are made between coastal low dynamics and those characteristics of other mesoscale coastally trapped disturbances which propagate in the marine layers of california and south eastern australia

coastally trapped wind reversals along the united states west coast during the warm season part ii synoptic evolution abstract this paper describes the synoptic evolution associated with coastally trapped wind reversals along the west coast of the united states from april through september gridded national centers for environmental prediction formerly national meteorological center synoptic analyses are composited relative to the initiation of both weak and strong coastal southerlies at four coastal buoys offshore of oregon and california a similar composite synoptic evolution accompanies the transition from northerlies to southerlies at each site at 500 mb there is anomalous ridging over the eastern pacific while at 850 mb and the surface the east pacific high extends into southwestern canada and the pacific northwest the result is offshore flow and subsidence along the mountainous west coast that produces a strengthening and coastal extension of the trough normally resident over the interior of southern and central california this anomalous coastal troughing weakens the offshore gradient and establishes an alon

supercritical marine layer flow along a smoothly varying coastline abstract a model for hydraulically supercritical atmospheric marine layer flow along a smoothly varying coastline is formulated and solved numerically the model is motivated by a recent comparison of code observations to a simple hydraulic theory which suggested the presence of an expansion fan and a compression jump downstream of topographic features the marine layer is modeled as a homogeneous rotating fluid layer decelerated by surface friction and forced by imposed upper level pressure gradients the equations are solved by a characteristic based gridpoint scheme the results indicate that the expansion fan is a robust feature that persists under most conditions in the present more realistic model but is dramatically altered in structure by the presence of friction while the jump may weaken rapidly offshore due mainly to offshore variations of the layer height upstream of the jump the agreement between observations and model predictions is good enough to suggest that a first order description of

surface boundary layer variability off northern california usa during upwelling abstract a five element mooring array is used to study surface boundary layer transport over the northern california shelf from may to august 2001 in this region upwelling favorable winds increase in strength offshore leading to a strong positive wind stress curl we examine the cross shelf variation in surface ekman transport calculated from the wind stress and the actual surface boundary layer transport estimated from oceanic observations the two quantities are highly correlated with a regression slope near one both the ekman transport and surface boundary layer transport imply curl driven upwelling rates of about 3 10 4 m s 1 between the 40 and 90 m isobaths 1 5 and 11 0 km from the coast respectively and curl driven upwelling rates about 1 5 10 4 m s 1 between the 90 and 130 m isobaths 11 0 and 28 4 km from the coast respectively thus curl driven upwelling extends to at least 25 km from the coast in contrast upwelling driven by the adjustment to the coastal boundary condition occurs primarily inshore of the 40 m isobath the upwelling rates implied by the differentiating the 40 m transport observations with the coastal boundary condition are up to 8 10 4 m s 1 the estimated upwelling rates and the temperature nitrate relationship imply curl driven vertical nitrate flux divergences are about half of those driven by coastal boundary upwelling

high resolution real time modeling of the marine atmospheric boundary layer in support of the aosn ii field campaign abstract the navy s coamps atmospheric model has been used to provide twice daily real time forecasts of 72 h duration in support of the aosn ii field campaign during august 2003 the model was configured with four grid meshes with a minimum horizontal grid increment of 3 km a statistical analysis of the model forecasts using available buoy observations demonstrates the skill of the atmospheric model predictions with characteristic wind speed rms and bias errors of 1 3 m s 1 and less than 0 5 1 0 m s 1 respectively and temperature rms errors of 1 2 c and biases typically less than 1 0 c the highest resolution mesh provides more accurate wind speed variances during the upwelling periods in the nearshore region where the wind speed gradients and diurnal variations are the largest persistent and strong low level winds from a northwesterly direction were associated with a mid tropospheric trough and jet stream that was substantially stronger than the overall mean monthly conditions during the relaxation periods which were relatively infrequent during august 2003 the trough was weaker than the mean conditions with a closed low west of the coast that resulted in southerlies near the coast during upwelling favorable conditions the mean marine inversion was substantially stronger than during the relaxation periods with the surface stress field exhibiting maxima in the lee of prominent coastal capes and topography particularly during the periods of strong larger scale low level flow the persistent mean stress pattern that is topographically locked yields maxima in the stress curl pattern that induce favorable regions of coastal upwelling near and downwind of the coastal promontories and headlands