alongshelf variability of inner shelf circulation along the central oregon coast during summer the spatial and temporal variability of inner shelf circulation along the central oregon coast during the 2004 upwelling season is described using a 70 km long array of moorings along the 15 m isobath circulation at three stations located onshore of a submarine bank differed from that of a station north of the bank despite the relatively uniform wind forcing and inner shelf bathymetry present during upwelling favorable winds strong southward alongshelf flow occurred north of the bank no alongshelf flow occurred onshore of the northern part of the bank and increasing southward flow occurred onshore of the southern part of the bank during downwelling favorable winds strong northward flow occurred in the inner shelf onshore of the bank while weak flow occurred north of the bank these alongshelf differences in inner shelf circulation were due to the effects of the bank which isolated the inner shelf onshore of the bank from the regional upwelling circulation that was evident at the northernmost station as a result circulation onshore of the bank was drivenprimarily by local wind forcing whileflow north of the bank was only partiallydriven by local winds a secondary mode of variability attributed to the movement of the regional upwelling jet due to remote forcings contributed the bulk of the variability observed north of the bank with the time dependent wind forcing present acceleration was an important term in the depth averaged alongshelf momentum equation at all stations during upwelling bottom stress and acceleration opposed the wind stress north of the bank while bottom stress was weaker onshore of the bank where the across shelf momentum flux and the alongshelf pressure gradient balanced the residual of the acceleration and stresses during downwelling waters onshore of the bank surged northward at magnitudes much larger than that found north of the bank these spatial variations developed as the season progressed and the regional upwelling circulation intensified explaining known variations in growth and recruitment of nearshore invertebrate species

models of coastally trapped disturbances during the spring and summer the climatological northerly flow along the u s west coast is occasionally interrupted by transitions to southerly flow that have a limited offshore scale and appear to be manifestations of marine layer flow that is rotationally trapped by the coastal mountains existing climatological and observational studies suggest that a synoptic scale offshore flow initiates these coastally trapped disturbances ctds using idealized simulations produced with a 3d nonhydrostatic model the authors find that an imposed offshore flow will produce ctds in idealized coastal environments the imposed flow first weakens the prevailing northerly flow in the marine layer and lowers the pressure at the coast the marine layer flow around this low pressure evolves toward geostrophic balance but is retarded as it encounters the coastal mountains to the south of the low and subsequently deepens the marine layer in this region the elevated marine layer then begins progressing northward as a kelvin wave and later may steepen into a bore or gravity current this progression being the ctd many observed features accompanying ctds are found in the numerical simulations including the formation of a mesoscale pressure trough offshore and deep southerlies in the ctd at the coast stability in the atmosphere above the marine layer can give rise to topographically trapped rossby waves and stronger ctd winds in these stable conditions propagation of wave energy away from the disturbance does not preclude strong quasi steady propagating ctds

mapping the u s west coast surface circulation a multiyear analysis of high frequency radar observations signals with phase speeds of o 10 and o 100 to 300 km day 1 and time scales of 2 to 3 weeks the signals with slow phase speed are only observed in southern california it is hypothesized that they are scattered and reflected by shoreline curvature and bathymetry change and do not penetrate north of point conception the seasonal transition of alongshore surfacecirculationforcedbyupwelling favorablewindsandtheirrelaxationiscapturedinfine detail submesoscaleeddies identifiedusingflowgeometry haverossbynumbersof0 1to3 diameters in the range of 10 to 60 km and persistence for 2 to 12 days the hfr surface currents resolve coastal surface ocean variability continuously across scales from

moored wind temperature and current observations made during coastal ocean dynamics experiments 1 and 2 over the northern california continental shelf and upper slope moored observations of winds currents and temperature made over the northern california shelf and upper slope during the 1981 and 1982 upwelling seasons as part of the coastal ocean dynamics experiment code are described in both field experiments code 1 and code 2 the onset of the upwelling season is triggered by the strengthening of the north pacific high off northern california and signalled by the presence of water colder than 9 c near the bottom over the shelf vertical temperature stratification over the shelf is reduced during active upwelling local winds and subtidal currents over the shelf are strongly polarized in the alongshelf direction and the mean wind stress is directed equatorward response of alongshelf currents to wind forcing is similar at all depths over the shelf the response of the cross shelf current is more complex in the surface layer offshelf flow is significantly and positively correlated with the upwelling favorable alongshelf wind stress beneath this layer a weak return flow exists the thickness of the upper mixed layer varies greatly reaching 60 m during upwelling events thus direct wind forcing affects a substantial fraction of the water over the shelf low frequency wind stress current and temperature fields are adequately described by a few energetic empirical orthogonal functions with simple spatial structure the most energetic mode typically accounts for 75 or more of the variance of wind stress and temperature over the middle and inner shelf the most energetic current mode accounts for 90 or more of the variance is dominated by he alongshelf component and veers to the left with depth the low frequency alongshelf flow fluctuations are quasi barotropic with some vertical shear but no reversal with depth vertical shear in alongshelf current and the cross shelf density gradient obey the thermal wind relation the simple structure of the subdiurnal currents allow estimation of the alongshelf volume transport between the 60 and 130 m isobaths through three cross shelf transects in code 2 volume transport over the shelf is often nearly two dimensional but occasional large differences indicate significant mass exchange between the shelf and the adjacent upper slope correlation of low frequency currents and alongshelf wind stress shows the response of alongshelf current to be maximum near the surface and near midshelf where a 15 cm 1 alongshelf flow lags a 1 dyn cm 2 alongshelf wind stress by the order of 10 hours currents over the upper slope are not significantly correlated with local wind alongshelf transport over the shelf is highly correlated with local wind stress explaining 80 of the variance in the low frequency transport during code 2 volume transport is best correlated with wind stress approximately 30 km to the south winds in the code area during spring and summer are characterized by strong and persistent upwelling favorable winds interrupted by shorter periods of weak winds regression analysis indicates that in the absence of wind a poleward barotropic current jet exists over the shelf with a maximum amplitude over the inner shelf in the code area an upwelling favorable wind counters this jet over the shelf so that the alongshore flow is everywhere equator ward during strong wind events since the maximum response to wind forcing is found at midshelf and near surface the mean current over the upwelling season is strongly sheared in both the vertical and cross shelf directions mean flow over the outer shelf is surface intensified and is directed offshelf and equatorward while the deeper flow at midshelf and through most of the water column over the inner shelf is directed poleward

large scale forcing of summertime monsoon surges over the gulf of california and the southwestern united states synoptic forcing of the gulf of california summertime low level wind field is described using a nested regional modeling system under appropriate synoptic conditions strong surge events develop that are characterized by persistent vertically extensive 1 2 km southerly flow extending along the entire gulf of california and into arizona california and even southern nevada these surge periods are initiated either by tropical cyclone activity to the south of baja california or by the westward propagation of lower tropospheric troughs from over the sierra madre occidental to the eastern pacific the flow over the gulf is primarily geostrophic and is associated with the presence of these low pressure centers to the south and west of baja california

26al 10be systematics in deep sea sediments we report the development of a naoh leaching technique to extract the authigenic al and be in marine sediments which should allow the sedimentary signals of cosmogenic 26al and 10be to be more effectively studied as geochemical geophysical tracers the technique has been applied to the study of 26al and 10be in opal rich sediments from the north pacific the 26al 27al and 10be 9be ratios of 3 10 14 and 1 10 7 leached from the sediments are higher than those in the total sediments by factors of 3 10 and 2 3 respectively the authigenic 10be 9be ratios are similar to those in deep waters at the study site pointing to the potential usefulness of the ratios in paleoceanographic studies the fractions of total be and al in the sediment studied that are of authigenic origin average about 40 and 17 respectively estimated 26al 27a1 ratios in detrital sediments are 10 15 low enough to indicate that the source of 26al in the ocean mainly comes from atmospheric production in the study area the deposition flux of 26al is comparable to its atmospheric supply however the deposition flux of 10be is about threefold higher than the atmospheric input signifying lateral transport of 10be from the open ocean to this area of relatively high particle flux the 26al 10be ratio being insensitive to the oceanic influx of lithogenic particles may serve as a valuable proxy for paleoproductivity both the authigenic and total sediment 26al 27al and 10be 9be ratios decreased significantly at 6 ka which could reflect an enhanced input of windblown lithogenic particles to the north pacific while the enhanced dust input did not significantly alter the deep water 9be concentration it contributed to the observed increase of authigenic 9be flux to the sediment

failure to bloom intense upwelling results in negligible phytoplankton response and prolonged co2 outgassing over the oregon shelf during summer upwelled water with elevated co2 partial pressure pco2 and nutrients outcrops over the oregon or inner shelf as this water transits across the shelf high rates of primary production fueled by the upwelled nutrients results in net atmospheric co2 drawdown upwelled source waters typically have pco2 approaching 1000 atm that is then reduced to 200 atm for almost the entire month of july 2008 strong and persistent upwelling brought cold 8 c saline 33 5 high pco2 600 atm water to our midshelf buoy site and high pco2 water was broadly distributed over the shelf chlorophyll levels as a proxy for phytoplankton biomass were low 2 mg m 3 on the shelf during the period of most intense upwelling and satellite data showed no evidence of a downstream phytoplankton bloom a small chlorophyll increase to 4 mg m 3 was observed at our buoy site following a decrease in the strength of southward wind stress 10 days after upwelling initiated chlorophyll levels further increased to 10 mg m 3 only after a cease in upwelling these higher levels were coincident with the appearance of water masses having temperature and salinity properties distinct from recently upwelled water we suggest that rapid offshore transport and subsequent subduction before phytoplankton populations could respond is the most likely explanation for the persistent low chlorophyll and elevated surface water pco2 throughout the july upwelling event this mechanism likely dominates under conditions of strong and persistent upwelling favorable winds that coincide with close proximity of low density offshore waters which may have implications for the biogeochemical functioning of this system under future climate scenarios

aircraft observations of the 12 15 july 2004 moisture surge event during the north american monsoon experiment abstract this paper describes aspects of a strong moisture surge over the gulf of california that was observed during the 2004 north american monsoon experiment although a variety of special observation platforms aid the analyses the authors focus on observations collected during two noaa research aircraft flights made on 12 and 13 july these flights sampled the initial and mature phases of a strong surge associated with tropical storm blas the first flight is identified by both a convective outflow and another feature both deeper and with larger spatial scale ahead of the outflow in association with the surge s leading edge the surge speed 18 m s 1 was identified from anomaly analysis of surface station pressure data observations show interesting multiscale features associated with the surge during its initial stages but do not allow for unambiguous identification of the surge s forcing mechanism or dynamical properties data from the second flight were used to describe the along and cross gu

time dependent wind driven flow over a shallow midshelf submarine bank 1 during summer 2001 high resolution hydrographic velocity and bio optical surveys were conducted over heceta bank off central oregon north of the bank upwelling over simple bottom topography exhibited a classic response with a midshelf baroclinic coastal jet and upwelled isopycnals the coastal upwelling jet follows the bank topography as it widens offshore before reaching the southern end of the bank where the shelf break turns almost 90 back toward the coast the ensuing adjustment involves the offshelf transport of coastal water and the material it contains the jet meanders anticyclonically in the lee of the bank before resuming its equatorward path seaward of the shelf break a pool of high chlorophyll 15 mg m 3 near surface water is found in the low velocity lee region created by the bank a low temperature high salinity bottom water pool supplied primarily from the south lies over the inshore region of the bank this bottom pool is up to 40 m thick and contains elevated levels of suspended material by creating an east west perturbation in the coastal upwelling front the flow topography interaction introduces an alongshore pressure gradient when southward upwelling favorable winds relax this alongshore pressure gradient can drive flow back to the north this leads to northward flow on the inshore side of the bank ultimately setting up the potential for recirculation around the entire bank complex on a timescale of about 10 days strong northward winds during summer lead to downwelling within 15 km of the coast accompanied by significant 0 2 m s 1 wind driven northward currents

particulate removal of230th and231pa in the biologically productive northern north pacific settling particles were collected by sediment traps at four stations in the high latitudes of the north pacific and analyzed for234th 232th 230th 228th and231pa in the northern north pacific including the bering sea the average activity ratio of unsupported230th to231pa in settling particles was 5 5 whereas that in the gulf of alaska in the eastern north pacific was about 14 the northern north pacific may be an efficient sink for231pa relative to230th because the average ratio in the world ocean is equal to the production ratio of 10 8 in seawater the activity ratios of230th 231pa of the settling particles agree well with those of the surface sediments at the respective stations this indicates that both nuclides in the surface sediments originated from settling particles and their dissolution or uptake during early diagenesis are not effective the ratio of the particulate nuclide flux f to the overlying water column production rate p did not correlate well with the total mass flux for230th however that for231pa increased almost linearly with increase in total mass flux and reached unity when the total mass flux was about 110 mg m2 d this suggests that231pa transported from oligotrophic regions is being actively removed in the biologically productive northern north pacific

structure and dynamics of the arizona monsoon boundary abstract the arizona monsoon boundary is defined as the boundary separating two distinctly different air masses over mexico and the adjacent pacific during the summer the structure and dynamics of this boundary are examined by cross sectional analysis using three different data sources 1 a composite cross section through the boundary constructed from the fleet numerical oceanography center fnoc analysis 2 a time height cross section constructed using radiosonde observations at the time the boundary passed through tucson in 1984 and 3 a cross section through the boundary on 22 july 1985 using high resolution fields of temperature moisture and geopotential height obtained from the vissr atmospheric sounder vas all draw cross sections showed similar structure in some respects the arizona monsoon boundary resembles a midlatitude front i e there is a distinct and relatively sharp air mass change forced almost entirely by confluence a direct ageostrophic circulation is produced by this f

coastal wind driven circulation in the vicinity of a bank part ii modeling flow over the heceta bank complex on the oregon coast abstract this study investigates wind driven circulation in the vicinity of the heceta bank complex along the oregon shelf numerical experiments forced with steady winds 0 1 pa are conducted upwelling and downwelling cases are compared the asymmetric bank bathymetry is the only configurational difference from the symmetric bank runs analyzed in part i whitney and allen upwelling favorable winds generate an upwelling front and southward baroclinic jet model results indicate the upwelling jet is centered on the 100 m isobath along the straight shelf the jet follows this isobath offshore around the northern part of the bank but separates from sharply turning isobaths in the southern half and flows over deeper waters the jet turns back toward the coast farther downstream inshore of the main jet currents reverse and flow back onto the bank these reversed currents turn southward again at the bank center and join a secondary southward coastal upwelling jet this secondary coastal jet converges wi

chernobyl radioactivity found in mid water sediment interceptors in the n pacific and bering sea fission product nuclides 134cs 137cs and 103ru originated from the chernobyl accident have been detected in sediment traps deployed at mid water depths ranging from 110 to 780 m in the n pacific and the bering sea the detected radioactivities originally associated with fine airborne particles have apparently been incorporated into much larger aggregates of predominantly biogenic material formed in the surface ocean and transferred downward through the water column with velocities of the order of 100 m day

principal component analysis of the summertime winds over the gulf of california a gulf surge index a principal component analysis of the summertime near surface quick scatterometer quikscat winds is used to identify the leading mode of synoptic scale variability of the low level flow along the gulf of california during the north american monsoon season a gulf surge mode emerges from this analysis as the leading eof with the corresponding principal component time series interpretable as an objective index for gulf surge occurrence this index is used as a reference time series for regression analysis and compositing meteorological fields of interest to explore the relationship between gulf surges and precipitation over the core and marginal regions of the monsoon as well as the manifestation of these transient events in the large scale circulation it is found that although seemingly mesoscale features confined over the gulf of california gulf surges are intimately linked to patterns of large scale variability of the eastern pacific itcz and greatly contribute to the definition of the northward extent of the monsoonal rains

the circulation and water masses in the gulf of the farallones abstract six adcp and ctd ship surveys of the continental shelf and slope in the vicinity of the gulf of the farallones ca were conducted in 1990 1992 adcp data provide much more detail on the structure of the currents over the slope and shelf in the gulf and reveal a persistent largely barotropic poleward flow with a complex mesoscale flow field superimposed the directly measured currents are not well represented by the geostrophic velocity fields derived from hydrographic casts important upper ocean circulation features include a slope countercurrent scc variable shelf circulation and submesoscale eddy like features the scc was present in all seasons and is believed due to a strong year round positive wind stress curl enhanced by point reyes its flow was poleward throughout the upper 300 m and often surface intensified poleward transport in the upper 400 m was 1 3 sv much greater than previous geostrophic estimates for the california current system constrained to a 500 dbar reference level the shelf circulation was much more variable than the scc and generally exhibited a pattern consistent with classic ekman dynamics responding to synoptic wind forcing submesoscale vortices or eddies often dominated the general flow field these eddies are thought to be generated by the frictional torque associated with current topography interactions their centers typically have a distinct water type associated with either the scc or the southward flowing california current higher spiciness anomalies representing a higher percentage of pacific equatorial water pew were typically found in the core of the scc or within anticyclonic eddies lower bland spiciness anomalies characteristic of a higher percentage of pacific subarctic water psaw were associated with cyclonic eddies while these circulation features were largely barotropic the flow also adjusted baroclinically to changes in the density field as different water types were advected by the general flow field or by mesoscale instabilities in the large scale boundary currents as they interacted with topography despite a seasonal cycle in regional wind and ocean temperature time series there is no obvious seasonal pattern in the circulation most of the temporal variability in the current appears to be due to synoptic and interannual variations in atmospheric forcing because of the very dynamic three dimensional nature of the regional circulation the gulf of the farallones is likely to be a center for active mixing and exchange between the coastal and california current waters relative to most us west coast locales

new appraisal of radium 226 as a large scale oceanic mixing tracer radium 226 and ba data in the eastern and central indian ocean collected during the geochemical ocean sections study geosecs expeditions are reviewed and used to delineate the geochemical cycle of both species the data show that although particulate uptake of 226ra and ba occurs in the surface ocean their regeneration may largely take place near or below the sediment water interface therefore over much of the deep ocean save close to the bottom 226ra can be regarded as being chemically conservative taking advantage of this geochemical aspect of 226ra enables us to compute the vertical z and horizontal meridional x eddy diffusivities kz and kx and advective velocities vz and vx and their variability in the eastern and central parts of the indian ocean the absolute magnitudes of these mixing parameters are calibrated against the decay rate of 226ra the computation is done by numerically solving the mass continuity equations for three properties 226ra total salt and mass of seawater the grid size used in the calculations in which the advective transport is taken to be along the isopycnal surface has dimensions of x 700 km and z 400 m the model calculation shows that in the eastern and central indian ocean along the geosecs traverses values of diapycnal diffusivity kz of 1 10 cm2 s 1 are found near the surface and the bottom minima occur in the thermocline region where kz falls to about 10 2 cm2 s 1 below kz has values largely in the range 0 1 1 cm2 s 1 and increases downward the horizontal isopycnal diffusivity varies between 104 and 108 cm2 s 1 mainly in the range 106 107 cm2 s 1 upwelling velocities are mostly in the lower end of the range 1 10 m yr 2 whereas downwelling unlike upwelling which tends to be localized occurs with velocities of 0 1 1 m yr 2 the meridional component of subsurface currents is in the range of 0 01 0 1 cm s 1 mostly toward the south and not restricted to a particular depth interval the current field deduced in the study area provides a broad picture of the strength and pattern of return flows of the deep water introduced from the south and thought to be principally transported northward via the relatively narrow intense currents along the western boundaries of the basins the present study as well as recent developments in the high precision and high sensitivity mass spectrometric analysis of 226ra suggests that this naturally occurring isotope warrants further exploitation as a rate tracer for large scale ocean circulation and mixing processes

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

ensemble based estimates of the predictability of wind driven coastal ocean flow over topography abstract the predictability of coastal ocean circulation over the central oregon shelf a region of strong wind driven currents and variable topography is studied using ensembles of 50 day primitive equation ocean model simulations with realistic topography simplified lateral boundary conditions and forcing from both idealized and observed wind time series representative of the summer upwelling season the main focus is on the balance relevant to practical predictability between deterministic response to known or well predicted forcing uncertainty in initial conditions and sensitivity to instabilities and topographic interactions large ensemble and single simulation variances are found downstream of topographic features associated with transitions between along isobath and cross isobath flow which are in turn related both to the time integrated amplitude of upwelling favorable wind forcing and to the formation of small scale eddies simulated predictability experiments are conducted and model fo

seasonal differences in the current and temperature variability over the northern california shelf during the coastal ocean dynamics experiment a long term moored array was maintained over the northern california continental shelf from april 1981 to april 1983 as part of the coastal ocean dynamics experiment to determine the seasonal differences in the current and water temperature characteristics the array consisted of two midshelf moorings and one upper slope mooring from april 1981 through july 1982 and one midshelf mooring from august 1982 to april 1983 the two summers were characterized by southeastward mean wind stresses upwelling favorable cold water isotherms sloping upward toward the coast and a sheared equatorward mean shelf current the intervening fall and winter were characterized by a weak mean wind stress relatively warm shelf water level isotherms and a more barotropic poleward mean shelf current in contrast to the differences in the characteristics of the means many of the characteristics of the current and temperature variability are the same for the summer and winter the vertical structure of the largest current empirical orthogonal functions eofs for each of the shelf moorings which account for more than 75 of the subtidal variance do not vary with season the current is vertically sheared oriented 15 20 clockwise relative to local isobaths near the surface and along isobaths near the bottom currents at the two shelf moorings alongshore separation 29 37 km are correlated with each other and with the local wind stress and these relationships do not exhibit a seasonal variation denser arrays of wind and current sensors during the two summers indicated that there were strong persistent variations in the wind field over relatively small scales tens of kilometers with corresponding variations in the shelf current field during the summer of 1981 but not during the summer of 1982 over the slope the largest eofs account for 56 72 of the current variance and have a vertical structure which is relatively uniform with depth during the summer fall and winter of 1981 but is strongly sheared in the upper 100 m during the summer of 1982 current observations over the slope are not correlated with either the shelf currents or the local wind stress during any season in contrast the temperature variability as described by eofs does exhibit a seasonal variation in vertical structure with the variability concentrated in the upper 20 30 m in summer and more uniform with depth in winter the near surface temperature variability over the slope is correlated with the shelf temperature variability estimates of the cross shelf heat flux due to the wind driven ekman transport accounts for a large part of the shelf temperature variability observations from the midshelf mooring maintained through the fall and winter of 1982 1983 showed evidence of the 1982 1983 el nino with persistent onshore and poleward currents and water temperatures typically above 12 c

dynamics of a simulated north american monsoon gulf surge event abstractgulf surges are transient disturbances that propagate along the gulf of california goc from south to north transporting cool moist air toward the deserts of northwest mexico and the southwest united states during the north american monsoon they have been shown to modulate precipitation and have been linked to severe weather and flooding in northern mexico and the southwest united states the general features and progression of surge events are well documented but their detailed dynamical evolution is still unclear in this study a convection permitting simulation is performed over the core monsoon region for the 12 14 july 2004 gulf surge event and the dynamics of the simulated surge are examined initially convection associated with the tropical easterly wave precursor to tropical cyclone blas creates a disturbance in the southern goc on early 12 july this disturbance is a precursor to the gulf surge on 13 july and is a kelvin shock internal bore under the influence of rotation that diss

the relationship between tropical easterly waves and surges over the gulf of california during the north american monsoon abstract coastally trapped disturbances which occur over the gulf of california and are commonly referred to as gulf surges are an important mechanism in the transport of low level moisture into the southwestern united states to determine whether or not gulf surges develop in association with the passage of tropical easterly waves as hypothesized in previous studies standard surface observations and european centre for medium range weather forecasts reanalysis data during the months of july and august over a 14 yr period are examined results indicate that tropical easterly wave troughs often cross western mexico 1 3 days prior to surge onset at yuma arizona indicating a strong correlation between these two events this analysis documents yet another mechanism by which the tropics influences convection in the midlatitudes

on the spatial structure of coastal circulation off newport oregon during spring and summer 2001 in a region of varying shelf width 1 a time series of hourly surface current maps in the shelf waters off newport oregon was made during april september 2001 using five seasonde hf current mappers during coastal advances in shelf transport coast the surface currents responded rapidly to the changing winds in repeated patterns that were strongly affected by bottom topography an equatorward current jet repeatedly formed in response to upwelling winds its strength but not its trajectory covarying with the meridional wind stress near cape foulweather 44 8 n where the shelf begins to widen the jet rotates weakens and trends offshore to the south first along then across the isobaths below cape foulweather inshore of the jet a lee region of generally weak currents was commonly observed the equatorward jet core was most commonly observed near the 80 m isobath between 45 0 n and 44 4 n but transited offshore between spring and summer over heceta bank at newport 44 6 n it was rarely observed less than 8 km from the coast a second inshore equatorward jet previously unknown was observed repeatedly south of waldport 44 4 n sustained downwelling wind episodes produced poleward currents though less responsively north of cape foulweather strongest poleward flow was generally trapped near the coast surface currents were correlated with the northward wind except regionally far from shore over heceta bank responding within half a day response to the wind varies spatially being intensified in the narrow shelf northern region the equatorward jet persists through periods of zero wind forcing coastal sea level covaries with the meridional wind and the primary mode of ocean current response

the interaction of easterly waves orography and the intertropical convergence zone in the genesis of eastern pacific tropical cyclones the interaction of an idealized easterly wave with an orographic feature representing the sierra madre of mexico and a large scale meridionally sheared zonal flow representing the itcz in the eastern north pacific is examined through numerical integration of the shallow water equations on an equatorial beta plane channel the model simulations show that as a wave approaches the orography from the east the relative vorticity in the lee increases due to the wave being modified by the orography this relative vorticity maximum increases the northward advection of the itcz in the lee of the mountain that occurs due to the influence of the mountain anticyclone the result of this interaction is the development of a localized region of enhanced cyclonic vorticity that moves parallel to the contours of the model orography there is a minimal increase in the amplitude of the vorticity occuring during interactions between the wave and orography itcz and orography and wave and itcz the position of the incident wave upstream of the orography at the time that the disturbance in the lee begins to develop and the subsequent motion of the leeside vorticity maximum are in agreement with an observed case of eastern pacific tropical cyclogenesis which is also presented

the spatial structure of tidal and mean circulation over the inner shelf south of martha s vineyard massachusetts abstractthe spatial structure of the tidal and background circulation over the inner shelf south of martha s vineyard massachusetts was investigated using observations from a high resolution high frequency coastal radar system paired with satellite ssts and in situ adcp velocities maximum tidal velocities for the dominant semidiurnal constituent increased from 5 to 35 cm s 1 over the 20 km wide domain with phase variations up to 60 a northeastward jet along the eastern edge and a recirculation region inshore dominated the annually averaged surface currents along with a separate along shelf jet offshore owing in part to this variable circulation the spatial structure of seasonal sst anomalies had implications for the local heat balance cooling owing to the advective heat flux divergence was large enough to offset more than half of the seasonal heat gain owing to surface heat flux tidal stresses were the largest terms in the mean along and across shelf momentum equations in the area of the reci

poleward propagating subinertial alongshore surface currents off the u s west coast 1 the network comprising 61 high frequency radar systems along the u s west coast uswc provides a unique high resolution and broad scale view of ocean surface circulation subinertial alongshore surface currents show poleward propagating signals with phase speeds of o 10 and o 100 300 km d 1 that are consistent with historical in situ observations off the uswc and that can be possibly interpreted as coastally trapped waves ctws the propagating signals in the slow mode are partly observed in southern california which may result from scattering and reflection of higher mode ctws due to curvature of shoreline and bathymetry near point conception california on the other hand considering the order of the phase speed in the slow mode the poleward propagating signals may be attributed to alongshore advection or pressure driven flows a statistical regression of coastal winds at national data buoy center buoys on the observed surface currents partitions locally and remotely wind forced components isolates footprints of the equatorward propagating storm events in winter off the uswc and shows the poleward propagating signals year round

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

dynamic mechanisms of the gulf surge 1 the gulf surge is a summertime phenomenon associated with the north american monsoon that transports moisture from the gulf of california into western portions of the united states this phenomenon has been acknowledged operationally and by researchers for over 30 years the surge is typically linked to the presence of some sort of low pressure system such as an easterly wave mesoscale convective system or hurricane located near the southern end of the gulf of california proposed mechanisms for the gulf surge are gravity currents ageostrophic flows kelvin or rossby edge waves the purpose of this paper is to describe the fundamental dynamics of each of these mechanisms and assess their plausibility through scale analyses and idealized numerical simulations and to suggest signatures that may appear in data and output of more sophisticated numerical models

intensified diurnal tides along the oregon coast abstractintensified diurnal tides are found along portions of the oregon shelf u s west coast based on analyses of high frequency hf radar surface current data and outputs of a 1 km resolution ocean circulation model the k1 tidal currents with magnitudes near 0 07 m s 1 over a wider part of the shelf heceta bank complex 44 44 5 n previously predicted by erofeeva et al are confirmed here by newly available hf radar data intensified diurnal tides are also found along the narrow shelf south of heceta bank in the close vicinity of cape blanco 42 8 n diurnal tidal currents k1 and o1 constituents combined may reach 0 3 m s 1 appreciable differences in diurnal tide intensity are found depending on whether the model is forced with tides and winds tw or only tides also diurnal variability in wind forcing is found to affect diurnal surface velocities for the case forced by tides alone results strongly depend on whether the model ocean is stratified tides only stratified tos or not t

the interaction of planetary scale tropical easterly waves with topography a mechanism for the initiation of tropical cyclones abstract the interaction of a basic state flow consisting of a planetary scale easterly wave superimposed on a uniform easterly zonal wind with an isolated topographic feature is examined by numerical integration of the shallow water equations in an equatorial beta plane channel the topographic parameters are chosen to represent the sierra madre mountains of mexico the zonal wavelength and phase speeds of the basic state easterly waves are chosen to correspond with previously published observations the topographic modification of a slow rossby mode in which the basic state vorticity maximum is located near 15 latitude is characterized by the generation of a cyclonic vorticity maximum in the lee of the mountain which extends the entire length of the ridge and a secondary maximum which propagates downstream a fast mixed rossby gravity mode in which the vorticity maximum is located at the equator interacts less strongly with the mountain with a lee vorticity maximum that is confined near the southern

time dependent wind driven flow over a shallow midshelf submarine bank wind driven circulation and ecosystem response off the oregon coast results from the coastal ocean advances in shelf transport coast program during summer 2001 high resolution hydrographic velocity and bio optical surveys were conducted over heceta bank off central oregon north of the bank upwelling over simple bottom topography exhibited a classic response with a midshelf baroclinic coastal jet and upwelled isopycnals the coastal upwelling jet follows the bank topography as it widens offshore before reaching the southern end of the bank where the shelf break turns almost 90 back toward the coast the ensuing adjustment involves the offshelf transport of coastal water and the material it contains the jet meanders anticyclonically in the lee of the bank before resuming its equatorward path seaward of the shelf break a pool of high chlorophyll 15 mg m 3 near surface water is found in the low velocity lee region created by the bank a low temperature high salinity bottom water pool supplied primarily from the south lies over the inshore region of the bank this bottom pool is up to 40 m thick and contains elevated levels of suspended material by creating an east west perturbation in the coastal upwelling front the flow topography interaction introduces an alongshore pressure gradient when southward upwelling favorable winds relax this alongshore pressure gradient can drive flow back to the north this leads to northward flow on the inshore side of the bank ultimately setting up the potential for recirculation around the entire bank complex on a timescale of about 10 days strong northward winds during summer lead to downwelling within 15 km of the coast accompanied by significant 0 2 m s 1 wind driven northward currents

modeling bottom mixed layer variability on the mid oregon shelf during summer upwelling abstract results from a model of wind driven circulation are analyzed to study spatial and temporal variability in the bottom mixed layer bml on the mid oregon shelf in summer 2001 the model assimilates acoustic doppler profiler velocities from two cross shore lines of moorings 90 km apart to provide improved accuracy of near bottom velocities and turbulence variables in the area between the mooring lines model results suggest that the response of the bml thickness to upwelling and downwelling favorable winds differs qualitatively between an area of simple bathymetric slope at 45 n and a wider shelf area east of stonewall bank 44 5 n at 45 n the bml grows in response to downwelling favorable conditions in agreement with known theories east of stonewall bank the bml thickness is increased following upwelling events in this area the southward upwelling jet detaches from the coast and flows over a wider part of the oregon shelf creating conditions for ekman pumping near the bottom based on

the relative importance of wind strength and along shelf bathymetric variations on the separation of a coastal upwelling jet abstract a high resolution numerical model with idealized topography is used to investigate the degree to which a coastal upwelling jet separates from the shelf as it flows around a submarine bank depending on the wind strength and the horizontal scale of the bank experiments were run using several wind forcing magnitudes and submarine banks with different geometries so as to explore a wide range of the flow strength as measured by the rossby number ro and the ratio of the squares of the internal rossby radius of deformation and curvature of the topography as denoted by the burger number bu the intensity of the jet separation is strongly dependent on both parameters with maximum separation with increasing ro and bu close to 1 when large amounts of upwelled water are exported toward deeper waters for small bu separation is minimal and independent of ro for high ro the degree of separation decreases at large bu since the bank acts only as a small perturbation to the flow term balances in the a

large scale structure of the spring transition in the coastal ocean off western north america past measurements off the coast of central oregon and washington have shown that the rapid change from northward monthly mean winter winds to southward summer winds forces a spring transition of the coastal ocean sea levels and temperatures drop and mean surface currents shift from northward to southward current and water temperature data from 35 n to 48 n from 1981 and 1982 and sea level and wind stress data from 1971 1975 and 1980 1983 show the transition to have a large alongshore scale typically 500 to 2000 km the large scale wind stress appears to be the forcing mechanism at latitudes north of approximately 37 n south of 37 n sea level usually falls more gradually before the northern transition event both wind and sea level events generally progress from south to north over a 3 to 10 day period but this is not always true several aspects of the spring transition reflect coastal trapped wave dynamics previous studies at 45 n found persistent vertical shear of the southward summer current associated with a cross shelf density gradient during 1982 the shear and the density front develop over the shelf break immediately after the transition at 43 n and to the south but they are much less persistent than at 48 n the stronger winds between 38 n and 42 n and the narrower shelf result in an offshore displacement of the density front and vertical shear past the shelf break leaving the water over the shelf less stratified and more subject to barotropic reversals of the current than that farther north where the front stays closer to the coast

evidence of kelvin waves in california s marine layer and related eddy generation abstract evidence suggests that an internal solitary kelvin wave exists in the marine layer along california the marine layer is lifted over the central coast by a weak cyclonic circulation this bump initially 850 m high moves to the north along the coast at 6 m s 1 the undisturbed layer depth is 100 200 m thick the crest height of the wave decreases to 500 m farther north winds under the raised marine layer are southerly the leading edge of the wave is easily followed by satellite as the thickened marine layer is marked by overcast stratus a greatly curved offshore leading edge indicates that nonlinear effects are important offshore scale in the overcast is about 300 km in the south and 50 km in the north surface pressure gradient alongshore is closely related to the marine layer depth the surface wind shifts when the leading and trailing edge of the wave passes northerly wave progression ceases at the sharp bend formed by cape mendocino at this time a vortex is formed in the marine laye

estimates of sea surface height and near surface alongshore coastal currents from combinations of altimeters and tide gauges 1 present methods used to retrieve altimeter data do not provide reliable estimates of sea surface height ssh in the nearshore region resulting in a measurement gap of 25 50 km next to the coast in the present work gridded ssh fields produced by archiving validation and interpretation of satellite oceanographic data aviso in the offshore region are combined with coastal tide gauge time series of ssh to improve estimation in that gap along the west coast of the united states in the northern california current system between 40 and 45n and 123 8 and 126w to assess the increase in skill provided by this procedure the geostrophic alongshore currents calculated from the new ssh fields in the gap region are compared to three in situ nearshore current measurements resulting in correlation coefficients of 0 73 0 83 and standard deviations of the differences of 11 6 12 6 cm s substantially improved from the aviso only results when the ekman current components are estimated and added to the geostrophic currents comparisons to the 10 m deep acoustic doppler current profiler velocities are only slightly improved the ekman components make a more significant contribution when compared to hf radar surface current measurements providing correlations of 0 94 and standard deviations of the differences of 6 4 9 5 cm s these results represent a dramatic improvement in the quality of the ssh fields and estimated alongshore currents when additional realistic ssh data from the coastal region are added here we use coastal tide gauges to provide the additional ssh data but also discuss more general approaches for altimeter ssh retrievals in coastal regions where tide gauge data are not available

residual and tidal circulation revealed by vhf radar surface current measurements in the southern channel isles region english channel abstract two very high frequency radars vhfrs operating in the southern channel isles region english channel in february march 2003 provided a continuous 27 day long dataset of surface currents at 2 km resolution over an area extending approximately 20 km offshore the tidal range in the region of study is one of the highest in the world and the coastal circulation is completely dominated by tides the radar data resolve two modes which account for 97 of the variability of the surface current velocities with the major contribution of the first mode this mode accounts for oscillating tidal currents whereas the second mode represents motions emerging from the interaction of tidal currents with capes and islands eddy in the vicinity of the point of grouin and jet south of chausey a fortnightly modulation of the modal amplitudes causes the exceptional more than 600 variability of currents which is well captured by the vhfr observations the radar data revealed that tidal circulation in the region is flood dominated with a strong asymmetry of current velocity curve wind events and fortnightly variability affect the course of tidal cycle by modifying the magnitude and duration of ebb and flood in addition to expected features of coastal circulation tidally dominated flow eddies and high wind current coupling the residual currents revealed a strong cross shore structure in the mean and a significant variability which has the same order of magnitude

surges over the gulf of california during the mexican monsoon abstract northward surges of relatively cool moist maritime air from the tropical pacific into the southwestern united states occur via the gulf of california every summer during the mexican monsoon season these surges advect large amounts of moisture northward and promote increased convective activity in arizona mesoscale model output from 32 successive 24 h simulations are used to examine both the large scale and mesoscale features associated with surge events model data are compared to high resolution aircraft measurements on two days showing clearly that the model is capable of reproducing many of the detailed structures found in the observations results from a large scale analysis indicate that strong surges are produced in the model when a midlatitude trough is in the proper phase relationship with a tropical easterly wave weak surges occur when this relationship is missing

influence of varying upper ocean stratification on coastal near inertial currents the influence of varying horizontal and vertical stratification in the upper layer o 10 m associated with riverine waters and seasonal atmospheric fluxes on coastal near inertial currents is investigated with remotely sensed and in situ observations of surface and subsurface currents and realistic numerical model outputs off the coast of oregon based on numerical simulations with and without the columbia river cr during summer the directly wind forced near inertial surface currents are enhanced by 30 60 when the near surface layer has a stratified condition due to riverine water inputs from the cr comparing model results without the cr for summer and winter conditions indicates that the directly wind forced near inertial surface current response to a unit wind forcing during summer are 20 70 stronger than those during winter depending on the cross shore location which is in contrast to the seasonal patterns of both mixed layer depth and amplitudes of near inertial currents the model simulations are used to examine aspects of coastal inhibition of near inertial currents manifested in their spatial coherence in the cross shore direction where the phase propagates upward over the continental shelf bounces at the coast and continues increasing upward offshore toward surface and then downward offshore at the surface with magnitudes and length scales in the near surface layer increasing offshore this pattern exhibits a particularly well organized structure during winter similarly the raypaths of clockwise near inertial internal waves are consistent with the phase propagation of coherence showing the influence of upper layer stratification and coastal inhibition

modeling upwelling circulation off the oregon coast 1 time dependent three dimensional upwelling circulation on the continental shelf off the oregon coast is studied using a primitive equation numerical model a limited area domain with a high resolution curvilinear grid is utilized the response of the coastal ocean to forcing by observed wind stress and heat flux during the summer 2001 time period of the coastal ocean advances in shelf transport coast field experiment is investigated model results are compared to coast current and hydrographic measurements the shelf velocity and density fields are generally characterized by the presence of a southward alongshore coastal jet with an upwelling density front on the shoreward side of the jet the large variability in shelf topography associated with heceta bank exerts a major influence on the shelf velocity and density fields over the bank the alongshore coastal jet is displaced offshore and colder upwelled water extends farther from the coast northward mean flow and upward motion are found inshore of the jet three dimensional flow structures in response to variable shelf bottom topography are presented and an analysis of time and space dependent alongshore momentum balances is applied to clarify the associated dynamics in general northward pressure gradients set up over the bank during southward upwelling winds accelerate currents on the inshore side of the jet northward when the winds relax analysis of term balances in the depth averaged equation for potential temperature shows that during upwelling across shore advection makes the major contribution to cooling over most of the region except inshore over heceta bank where alongshore advection also plays a significant role

near surface dynamics of a separated jet in the coastal transition zone off oregon 1 three dimensional circulation in the coastal transition zone ctz off oregon is studied using a 3 km resolution model based on the regional ocean modeling system the study period is spring and summer 2002 when extensive observations were available from the northeastern pacific component of the global ocean ecosystems dynamics project our main focus is on near surface transports particularly in an area off cape blanco where an energetic coastal current is separated in the ctz comparisons with available observations velocities from midshelf moorings surface velocities from high frequency radars satellite sea surface temperature maps along track sea surface height altimetry and seasoar hydrography show that the model reproduces qualitatively correctly the flow structure and variability in the study area the near surface flow behavior during 26 july to 21 august a late summer time period of strong time variable southward winds is examined during that period the coastal jet separates from the continental shelf around cape blanco 43 n the energetic separated jet continues to flow southward in a near coastal region between 42 2 n and 43 n it subsequently turns around 42 n to flow westward offshore past 127 w relatively vigorous up and downwelling is found concentrated in the region of the separated jet frontogenesis secondary circulation nonlinear effects of the relative vorticity on the ageostrophic ekman transport and submesoscale instabilities contribute to the vertical circulation within the jet vertical velocities are found to reach 50 m d 1 in the offshore part of the jet and 100 m d 1 in the near coastal part where the jet is aligned with the wind direction

on the accuracy of hf radar surface current measurements intercomparisons with ship based sensors high frequency hf radar systems can provide periodic two dimensional vector current estimates over an area approaching 1000 km as the use of these hf systems has gained wider acceptance a number of attempts have been made to estimate the accuracy of such systems however comparisons of hf radar current estimates with in situ sensors are difficult to interpret since hf systems measure currents averaged over an area of 1 km 2 and to a depth of only 50 cm while in situ sensors measure currents at a point and somewhat greater depths 1 to 10 m previous studies of the accuracy of hf radar technology have thus attributed the differences observed between hf radar and in situ sensors to an unknown combination of vertical shear horizontal inhomogeneity in situ instrument errors and hf radar system errors this study examines the accuracy of hf radar current measurements using data from the 1993 high resolution remote sensing experiment conducted off cape hatteras north carolina data from four shipborne in situ current meters are compared with data from an ocean surface current radar oscr a commercial current measuring radar we attempt to discern the predominant sources of error in these data by using multiple simultaneous measurements from different sensors and by examining the variation of observed current differences as a function of location the results suggest an upper bound on the accuracy of the oscr derived radial currents of 7 to 8 cm s the measurement of near surface currents in the coastal environ ment is an important problem

intensified upwelling over a widened shelf in the northeastern south china sea 1 observational and three dimensional modeling studies reveal that the intensified upwelling in the northeastern south china sea nscs is formed as a result of intensified upslope advection of dense deep waters that cross the middle shelf toward the inner shelf over a distinctly eastward widened shelf the strongest advection occurs over the converging isobaths near the head of the widened shelf as these dense deep waters advance shoreward they are advected downstream by the quickly developed upwelling current over the inner shelf and eventually outcropped at the lee of a coastal cape dynamically the shoreward cross isobath transport over the widened shelf is geostrophically enhanced by a quasi barotropic negative westward along isobath pressure gradient force as a result of the net rate of the momentum influx and by an intensified bottom frictional transport owing to the flow confluence near the head of the widened shelf a negative pressure gradient also exists at the lee of the coastal cape over the inner shelf and locally amplifies shoreward motion induced by the respective widened shelf and the coastal promontory the along isobath variations of cross isobath transport in the water column over the middle and inner shelves interactively characterize intensified upwelling in the nscs

a poleward jet and an equatorward undercurrent observed off oregon and northern california during the 1997 98 el nino abstract the timing and intensity of the effects of the 1997 98 el nino on sea surface temperature sst and coastal sea level along the us west coast are examined using in situ time series measurements and the effects on upper ocean currents on the continental shelf and slope off oregon and northern california are examined using repeated shipborne adcp transects a mid shelf mooring off newport oregon and an hf surface current radar an initial transient positive anomaly was observed in both adjusted sea level and sst during may june 1997 followed by anomalously high coastal sea levels generally strongest during september 1997 through february 1998 and abruptly returned to normal in late february 1998 and by positive temperatures anomalies over the mid shelf that persisted longer into april 1998 low frequency coastal sea level anomalies propagated poleward at 2 1 m s poleward flow over the shelf and slope was enhanced at most depths during the el nino compared with following years northward currents in the upper 12 m over the continental shelf off newport oregon averaged 13 7 cm s stronger during august 1997 through february 1998 than during the same period the following year enhanced poleward flow was present at all latitudes sampled during november 1997 and february 1998 particularly over the continental slope these transects also provided clear views of a fall winter equatorward undercurrent which was both strongest and had the most alongshore similarity of form during the enso finally subsurface intensified anticyclonic eddies originating in the poleward undercurrent appear to be a recurrent feature of the circulation off newport late in the upwelling season

analysis of the 13 14 july gulf surge event during the 2004 north american monsoon experiment abstract gulf surges are disturbances that move northward along the gulf of california goc frequently advecting cool moist air from the goc or eastern tropical pacific ocean into the deserts of the southwest united states and northwest mexico during the north american monsoon nam little attention has been given to the dynamics of these disturbances because of the lack of reliable high resolution data across the nam region high temporal and spatial observations collected during the 2004 north american monsoon experiment are used to investigate the structure and dynamical mechanisms of a significant gulf surge on 13 14 july 2004 integrated sounding systems deployed along the east coast of the goc and an enhanced network of rawinsonde sites across the nam region are used in this study observations show that the 13 14 july gulf surge occurred in two primary stages the first stage was preceded by anomalous low level warming along the northern goc on 13 july sharp cooling moistening and increased

a modeling study of shelf circulation off northern california in the region of the coastal ocean dynamics experiment 2 simulations and comparisons with observations 1 this is the second part of a modeling study of wind forced flow on the continental shelf off northern california in the region 37 40 n of the coastal ocean dynamics experiment code gan and allen 2002 analyzed the shelf flow response to idealized wind stress forcing in a process oriented study the study here applies forcing from observed winds and heat flux for april may 1982 and compares the model results with moored current and temperature measurements the princeton ocean model pom is used in a three dimensional limited area domain with a high resolution curvilinear grid approximately 1 km horizontal spacing 60 vertical levels and realistic coastline and bottom topography the objectives of the study are to simulate the response of the shelf circulation field to time varying observed wind stress and heat flux to compare model results with oceanographic observations to establish confidence in the model and to subsequently analyze the model fields and the model dynamical balances to help understand the behavior of the observed flow the model variables show overall good agreement with corresponding observations similar to the conclusions by gan and allen 2002 it is found that the alongshore variability of upwelling is mainly controlled by the interaction of the wind forced shelf flow with the coastline and bottom topography different dynamical regimes in the regions north and south of the coastal capes formed by pt reyes and pt arena and in the more uniform region between these capes are identified and investigated the results demonstrate that the coastal capes play a dominant role in causing alongshore variability of the upwelling flow including the setup of an alongshore pressure gradient that forces northward currents during relaxation of southward upwelling favorable winds an analysis of the balance of terms in the equation for potential temperature indicates that across shore temperature advection is the major contributor to the cooling of coastal water during upwelling with a larger magnitude to the south of the capes to the north of the capes however alongshore temperature advection is the dominant contributor to the colder water near the coast

relaxation from upwelling in the coastal ocean dynamics experiment a relaxation of the upwelling system on the northern california shelf occurs when upwelling favorable winds decay or reverse observations from the coastal ocean dynamics experiment are used to investigate this process with emphasis on the near surface temperature evolution models of relaxation warming are tested for the surface layer 0 30 m over midshelf with the result that the surface heat flux and poleward alongshelf advection can account for the observed temperature behavior onshore advection of the upwelled isopycnal field is a relatively unimportant contribution the warming patterns that are observed and which provide the gradients for the advective process have wedgelike shapes warmest inshore and in the south of the experimental area these patterns appear to be related to a topographic influence of point reyes possibly through the generation of gradients in the wind field remote advection of warm water from as far south as san francisco occasionally occurs as well the nature of the relaxation mechanism has general implications a new warm saline nutrient rich water mass may be formed in the surface layer since the warming processes are not the reverse of the cooling an important asymmetry is present it causes time variable upwelling to generate conditions very different from steady upwelling a new upwelling front is created during each event with upwelled water seaward of it and reversed alongshelf flow contributes to the warming and exchange mechanisms the system cannot be described or understood without the irreversible processes during upwelling and relaxation or without a mixed layer

flow topography interactions in the northern california current system observed from geostationary satellite data 1 data from geostationary operational environmental satellites are used to study the seasonal evolution of temperature fronts in the northern california current system ccs focusing on the interactions with topographic features fronts first appear close to the coast in response to upwelling winds moving offshore with the continuous input of energy to the system late in the upwelling season after july the upwelling front is persistently found over deeper waters south of heceta bank oregon than north of it suggesting that the equatorward jet separates from the shelf at heceta bank inshore of the upwelling front weak gradients are found on the bank the interaction of the equatorward flow with heceta bank and cape blanco oregon farther south substantially increases the mesoscale activity and oceanic frontal habitat downstream to the south in the ccs where fronts are persistently found greater than 100 km from the coast

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

a modeling study of shelf circulation off northern california in the region of the coastal ocean dynamics experiment response to relaxation of upwelling winds 1 a two part modeling study of the wind forced flow on the continental shelf off northern california in the region 37 40 n of the coastal ocean dynamics experiment code is pursued this paper involves a process oriented study with idealized wind stress forcing gan and allen 2002 involves forcing with observed winds and heat flux for april may 1982 and comparison of model results with code observations a characteristic but previously unexplained response observed during code following the weakening or relaxation of southward upwelling favorable winds is the time dependent development of northward currents over the inner shelf next to the coast the presence of northward winds is not necessary for this occurrence the objective in this paper is to investigate the dynamics of the shelf flow response to upwelling wind relaxation events under idealized conditions in the basic case experiment a spatially uniform upwelling favorable southward wind stress of 0 1 pa is applied to the ocean initially at rest the stress is held constant for 10 days and then decreased linearly to zero over 3 days in response to the southward wind stress southward alongshore currents develop on the shelf accompanied by upwelling of cold dense water near the coast considerable spatial variability in the shelf flow clearly related to the alongshore variations in coastline and bottom topography is found the alongshore currents tend to separate from the coast south of capes and the coldest surface water is found at those locations as the winds decrease northward currents similar to those observed develop on the inner shelf next to the coast at many alongshore locations examination of the alongshore momentum balances shows that the northward currents are forced by a northward pressure gradient force associated with negative alongshore pressure gradients these pressure gradients are set up by the interaction of the wind forced flow with the alongshore variations in shelf topography in general negative alongshore pressure gradients intensified off pt reyes and pt arena by the gradient wind balance are found south of capes the negative pressure gradients geostrophically balance onshore flow at depth and upwelling is strengthened in these locations north of capes positive pressure gradients that are primarily in balance with nonlinear advective effects are found after the winds cease the forced across shelf circulation weakens and the resulting unbalanced negative pressure gradients south of the capes accelerate the alongshore currents northward processes with similar dynamics are found embedded in the more complex coastal ocean response to observed time varying winds by gan and allen 2002

coastal wind driven circulation in the vicinity of a bank part i modeling flow over idealized symmetric banks abstract this study examines how coastal banks influence wind driven circulation along stratified continental shelves numerical experiments are conducted for idealized symmetric banks the standard bank 200 km long and 50 km wide has dimensions similar to the heceta bank complex along the oregon shelf model runs are forced with 10 days of steady winds 0 1 pa upwelling and downwelling cases are compared the bank introduces significant alongshelf variability in the currents and density fields upwelling favorable winds create an upwelling front and a baroclinic jet flowing opposite coastal trapped wave propagation that bend around the standard bank approximately centered on the 90 m isobath the upwelling jet is strongest over the upstream bank half where it advects a tongue of dense water over the bank there is a current reversal shoreward of the main jet at the bank center upwelling is most intense over the upstream part of the bank while there is reduced upwelling and even downwelling over

the influence of large scale topography on barotropic vortex motion abstract the motion of a barotropic vortex in the vicinity of a large scale topographic feature is examined through numerical integration of the shallow water equations in an equatorial beta plane channel the topographic parameters are chosen to represent the sierra madre mountains of mexico the motion of the vortex is affected through modification of the asymmetric circulation by vortex stretching associated with divergence of the horizontal velocity field as the air flows across the mountain a vortex that approaches the topography from the east is accelerated and deflected toward the south and a vortex initially west of the mountain recurves and moves toward the cut this motion is in contrast to the northwestward motion of a vortex over level terrain the vortex motion is also compared to the direction of the imposed potential vorticity gradient the topographic effects described in this paper may be important in forecasting hurricane motion in the eastern north pacific and western gulf of mexico

connectivity and larval dispersal along the oregon coast estimated by numerical simulations 1 connectivity and larval dispersal is explored off the oregon coast during the summer upwelling season of 2001 using numerical ocean circulation simulations the study region with strong wind driven currents and variable topography is modeled using the regional ocean modeling system roms forced by the coupled ocean atmosphere mesoscale prediction system a large number of passive particles as models of planktonic larvae are released daily for 120 days from 1 may to 28 august at depths of 1 7 15 20 50 and 75 m at every grid point shoreward of the 200 m isobath on average 32 km offshore the particles are transported by the three dimensional currents of the model simulation the competency time window for larval settlement is assumed to be in between days 15 and 35 after larvae are released larval settlement occurs at the shallowest location during the competency time window connectivity matrices reveal that some of the places of highest retention are similar to the proposed oregon marine reserve sites especially cape perpetua the heceta bank region has high probabilities as both a source and a destination for settled larvae larvae released in the heceta bank region often settle at higher latitudes than their release location there are strong correlations between the number of settled larvae shallower than the 50 m isobath and a 6 to 8 day running mean of the alongshore wind stress larvae are retained near the shore when the winds averaged over the previous 6 to 8 days are relaxed or downwelling favorable

variation in the position of the upwelling front on the oregon shelf 1 as part of an experiment to study wind driven coastal circulation 17 hydrographic surveys of the middle to inner shelf region off the coast of newport or 44 65 n from roughly the 90 m isobath to the 10 m isobath were performed during summer 1999 with a small towed undulating vehicle the cross shelf survey data were combined with data from several other surveys at the same latitude to study the relationship between upwelling intensity and wind stress field a measure of upwelling intensity based on the position of the permanent pycnocline is developed this measure is designed so as to be insensitive to density modifying surface processes such as heating cooling buoyancy plumes and wind mixing it is highly correlated with an upwelling index formed by taking an exponentially weighted running mean of the alongshore wind stress this analysis suggests that the front relaxes to a dynamic geostrophic equilibrium on a timescale of roughly 8 days consistent with a similar analysis of moored hydrographic observations this relationship allows the amount of time the pycnocline is outcropped to be estimated and could be used with historical wind records to better quantify interannual cycles in upwelling

enhanced turbulence due to the superposition of internal gravity waves and a coastal upwelling jet to vertical aspect ratios of 10 2 to 10 3 median value 300 these patches are clearly defined by regions of low richardson number and occur where and when the linear superposition of the three dominant shear constituents near inertial m2 and thermal wind interferes constructively this is most pronounced at the base of the coastal jet where the thermal wind shear is largest while the effect of the turbulence stress divergence on the jet is small compared to geostrophy 1 it is significant in the second order force balance governing secondary circulation the timescale associated with the decay of the thermal wind shear via turbulence stress is o 10 days we confirm that the vertical salt flux due to mixing is comparable to the net ekman transport of salt onto the shelf within the bottom boundary layer because numerical models of coastal circulation lack turbulence in midwater column any vertical transport of scalars including salt and heat must be achieved inshore of the 40 m isobath this is inconsistent with the observations presented in this study in which significant vertical turbulent salt transport is found to exist across the entire shelf

transport and retention in an upwelling region the role of across shelf structure abstract the paradox of upwelling is the relationship between strong wind forcing nutrient enrichment and shelf productivity here we investigate how across shelf structure in velocity and hydrography plays a role in the retention inshore and export offshore of particles such as nutrients plankton and larvae we examine the spatial structure of the coastal currents during wind driven upwelling and relaxation on the northern californian shelf the field work was conducted as part of the wind events and shelf transport west project a 5 year nsf coop funded study of the role of wind driven transport in shelf productivity off bodega bay northern california from 2000 to 2003 we combine shipboard velocity profiles adcp and water properties from hydrographic surveys during the upwelling season to examine the mean across shelf structure of the hydrography and velocity fields during three contrasting upwelling seasons and throughout the upwelling relaxation cycle we also present results from two winter seasons that serve as contrast to the upwelling seasons during all three upwelling seasons clear spatial structure is evident in velocity and hydrography across the shelf exemplified by current reversals inshore and the presence of a persistent upwelling jet at the shelf break this jet feature changes in structure and distance from the coast under different wind forcing regimes the jet also changes from the north of our region where it is a single narrow jet adjacent to the coast and to the south of our region where it broadens and at times two jets become evident we present observations of the california under current which was observed at the outer edge of our domain during all three upwelling seasons the observed across shelf structure could aid both in the retention of plankton inshore during periods of upwelling followed by relaxation and in the export of plankton offshore in the upwelling jet

evaluation of directly wind coherent near inertial surface currents off oregon using a statistical parameterization and analytical and numerical models directly wind coherent near inertial surface currents off the oregon coast are investigated with a statistical parameterization of observations and outputs of a regional numerical ocean model and three one dimensional analytical models including the slab layer ekman and near surface averaged ekman models the transfer functions and response functions statistically estimated from observed wind stress at ndbc buoys and surface currents derived from shored based high frequency radars enable us to isolate the directly wind forced near inertial surface currents concurrent observations of the wind and currents are crucial to evaluate the directly wind forced currents thus the wind stress and surface current fields obtained from a regional ocean model which simulates variability of the wind and surface currents on scales comparable to those in observations are analyzed with the same statistical parameterization to derive the point by point transfer functions and response functions model and data comparisons show that the regional ocean model describes near inertial variability of surface currents qualitatively and quantitatively correctly the estimated response functions exhibit decay time scales in a range of 3 5 days and about 40 of the near inertial motions are explained by local wind stress among the one dimensional analytical models the near surface averaged ekman model explains the statistically derived wind current relationship better than other analytical models

coastal ocean response to summer upwelling favorable winds in a region of alongshore bottom topography variations off oregon 1 repeated mesoscale surveys of waters over the shelf and slope off oregon were conducted during spring and summer of 2001 to study the spatial structure of the velocity and hydrographic fields the ocean response to wind forcing is compared between a region of relatively simple topography with alongshore uniformity and a region of complex topography including a shallow submarine bank heceta bank in the simple topography region the upper water column is influenced by upwelling and fresh water from the columbia river during spring with the low salinity water located farther offshore during summer variability in the fields is mostly confined within 30 km from the coast over heceta bank the region of higher variability is broader spanning most of the shelf the coastal upwelling jet is located inshore of the pinnacle of the bank during spring moving offshore during summer the region inshore of the bank is characterized by low velocities and flow recirculation near surface fields show that the circulation evolves considerably between seasons in both regions the area influenced by upwelled water is much broader during summer dense waters found over midshelf off newport are upwelled to the north and advected south dense waters inshore of heceta bank are substantially influenced by water from the north during spring but their source is mostly from the south during summer south of the bank the separation of the jet significantly increases the cross isobath transport constituting an efficient mechanism for transport of material from the shelf into deeper waters

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

mesoscale surveys over the shelf and slope in the upwelling region near point arena california repeated mesoscale surveys of a 40 km wide 100 km long coastal region near point arena california were conducted during the upwelling season april august in 1981 and 1982 each survey included conventional conductivity temperature depth casts at standard locations over the continental shelf and slope between 38 n and 39 10 n and continuous operation of a doppler acoustic log to obtain velocity profiles in the 20 to 150 m depth range synoptic surveys covered the entire grid in 2 3 days winds were strongly favorable for upwelling during the three 1981 surveys and were weak or variable during the three 1982 surveys surface temperature and salinity fields reflect the influence of both the seasonal winds and day to day variations in the wind persistently low surface salinities offshore reflect the general southward advection of subarctic waters and sporadic low salinities over the inner shelf reflect north ward advection of local runoff through an intermittent narrow countercurrent along the coast circulation patterns during all but one of the surveys were very complex and included meandering equatorward flow cyclonic and anticyclonic eddies and inshore countercurrents the simple two dimensional equatorward baroclinic coastal jet usually associated with coastal upwelling was observed during only one of our surveys overall average fields are relatively simple they show broad equatorward surface flow a very weak inshore countercurrent and a definite poleward undercurrent at the shelf break average temperature salinity and density fields are generally congruent with the average flow pattern average isotherms and isohalines are not strictly parallel to the coastline south of the coastline bend at point arena they diverge gradually from the coast comparison of average sections calculated from 10 matched pairs of central and arena lines separated by 50 km shows there are systematic differences between them warmer fresher waters lie nearer shore and in shallower water off point arena than on the central line this suggests that the surface waters flowing past point arena have sufficient southward momentum to cross isobaths comparison of average velocity sections on these two lines shows some differences in structure since the variability is large these may not be significant comparison of the measured and geostrophic average shears suggests there is a significant ageostrophic component in the upper layers above 40 m it may be the signature of an average wind driven ekman spiral

observations on the circulation of the saronikos gulf a mediterranean embayment sea border of athens greece 1 the saronikos gulf three dimensional flow structure is mapped by objective analysis in 12 acoustic doppler current profiler surveys 4 seasonal surveys per period for the periods may 1998 may 1999 may 2000 may 2001 may 2003 may 2004 under various winds robust seasonal flows throughout the gulf are basically induced by thermohaline effects winter water subduction different responses to atmospheric heating of shallow and deeper areas of the gulf and density contrasts with inflowing aegean waters inner gulf observations show that the seasonal flows are modified by the wind while recurrent structures cyclonic and anticyclonic appear between the seasonal flows and the coast of attica in summer an anticyclonic and a cyclonic flow exists throughout the gulf above and below the pycnocline respectively with a jet observed to meander within the inner gulf in winter and early spring an anticyclonic flow prevails in the upper 100 m in late spring early summer cyclonic and anticyclonic flow occurs in the upper 0 40 m and deeper 60 100 m layers respectively the predominant northerly winds in summer and winter push the inner gulf eastward seasonal jet to the south and favor the formation of a recurrent cyclonic upwelling structure between this jet and attica northwesterly westerly and southerly winds favor the northward meandering of the seasonal jet in the inner gulf and no recurrent structures appear in the limited space between this jet and attica in the southeast area of the inner gulf the wind driven flow fluctuations at 30 m have time scales of 3 5 4 days observed meandering period is 13 days meandering characteristics are close to instability predictions time scales of flows due to recurrent structures are 8 days

a separating coastal upwelling jet at cape blanco oregon and its connection to the california current system the coastal upwelling region near cape blanco oregon 433n o the west coast of the united states was studied using a towed ctd on seasoar a shipboard acoustic doppler current pro ler adcp satellite sea surface temperature maps and surface drifters during august 1995 the equatorward upwelling jet was inshore of the shelfbreak north of cape blanco meandered gently o shore around the cape and then veered sharply o shore just to the south of the cape analysis of vertical sections of density velocity and spicinessa con rmed the separation of an upwelling jet and front the jet was followed from over the shelfbreak north of the cape to 100 km o shore downstream of the cape the separating jet originates from the coastal upwelling jet leaving the shelf but is augmented by an o shore branching of the poleward undercurrent by combining information from adcp streamfunction maps with analysis of hydrographic data including distributions of the tracer like quantity spicinessa a conceptual model of the three dimensional circulation near the cape emerges a mid shelf upwelling jet encounters a coastal promontory then turns o shore stretching and deepening as it crosses the continental margin the jet then turns back shoreward cyclonically where the deepened equatorward ow encounters the top of the poleward undercurrent owing along the continental slope this causes a portion of the undercurrent to turn o shore to join and strengthen the equatorward transport in the separated jet throughout the separation process the coastal upwelling front and jet are continuous robust features separation of a coastal upwelling jet is an important mechanism for cross shelf transport from the coast to the deep ocean cape blanco appears to be the northernmost point where an equatorward jet regularly separates from the coast to become an oceanic jet and thus serves as the northern boundary of the region where an intense meandering current characteristic of the california current system