Wind Stress Variations Research Articles

Wind Stress Curl and Wind Stress Divergence Biases from Rain Effects on QSCAT Surface Wind Retrievals

Abstract Surface vector wind datasets from scatterometers provide essential high-resolution surface forcing information for analyses and models of global atmosphere–ocean processes affecting weather and climate. The importance of realistic amplitude, high-wavenumber, surface wind forcing from scatterometer data has been demonstrated in a variety of ocean modeling applications. However, the radar backscatter signal from which surface vector wind estimates are retrieved is attenuated and/or contaminated in heavy rain. The QuikSCAT (QSCAT) dataset flags rain-contaminated wind vector cells where retrievals are either highly uncertain or not available. Zonal and annual averages of wind stress curl and divergence for 2000, 2001, and 2002 are derived and compared across three surface wind datasets: QSCAT only, reanalysis winds from the National Centers for Environmental Prediction (NCEP reanalysis), and blended QSCAT+NCEP. Missing QSCAT surface wind retrievals due to rain contamination lead to statistically sign...

Scatterometer and Model Wind and Wind Stress in the Oregon–Northern California Coastal Zone

Measurements of surface wind stress by the SeaWinds scatterometer on NASA's Quick Scatterometer (QuikSCAT) satellite are analyzed and compared with several different atmospheric model products, from an operational model and two high-resolution nested regional models, during two summer periods, June through September 2000 and 2001, in the coastal region west of Oregon and northern California. The mean summer wind stress had a southward component over the entire region in both years. Orographic intensifications of both the mean and fluctuating wind stress occurred near Cape Blanco, Cape Mendocino, and Point Arena. Substantial differences between the model products are found for the mean, variable, and diurnal wind stress fields. Temporal correlations with the QuikSCAT observations are highest for the operational model, and are not improved by either nested model. The highest-resolution nested model most accurately reproduced the mean observed stress fields, but slightly degrades the temporal correlations due to incoherent high-frequency (0.5–2 cpd) fluctuations. The QuikSCAT data reveal surprisingly strong diurnal fluctuations that extend offshore 150 km or more with magnitudes that are a significant fraction of the mean wind stress. Wind stress curl fields from QuikSCAT and the models show local cyclonic and anticyclonic maxima associated with the orographic wind intensification around the capes. The present results are consistent with the hypothesis of a wind-driven mechanism for coastal jet separation and cold water plume and anticyclonic eddy formation in the California Current System south of Cape Blanco.

Adjustment of Near-Equatorial Wind Stress with Four-Dimensional Variational Data Assimilation in a Model of the Pacific Ocean

Abstract A four-dimensional variational scheme is described in which ocean observations are assimilated into an ocean general circulation model using wind stress forcing fields as control variables. Idealized (“twin”) experiments are performed to evaluate the possibility of reconstructing wind stress variability and its oceanic response from synthetic observations of the ocean state. Two types of wind stress errors are considered: time-varying errors associated with a wind burst and constant errors associated with a wind stress bias. Both sets of experiments demonstrate that the spatial structure of the wind stress variations is well reconstructed, while the estimation of their amplitude and time evolution is less accurate. Sparser equatorial sampling, similar to that of the Tropical Atmosphere–Ocean array, only slightly degrades the analysis. Omitting velocity and salinity observations leads to a less accurate amplitude and time evolution of the wind stress increment. Still, general features are captured...

Seasonal variability of QSCAT-derived wind stress over the Southern Ocean

[1] Seasonal variability of surface wind stress derived from SeaWINDS onboard the NASA's QuikSCAT satellite is mapped over the latitude range 30°–60°S in the Southern Ocean for the period from August 1999 to July 2003. Seasonal variability is pronounced on basin-wide scale which dominates the Atlantic-Indian Ocean sector during austral winter. Harmonic analysis reveals that seasonal harmonic captures larger than 60% of the variance on regional scales. The cyclonic wind stress curl induces divergence around Antarctica and facilitates ACC meandering equatorward in the Atlantic-Indian Ocean sector of the Southern Ocean.

The freshwater transport and dynamics of the western Maine coastal current

Observations in the Gulf of Maine, USA, were used to characterize the freshwater transport, temporal variability and dynamics of the western Maine coastal current. These observations included moored measurements, multiple hydrographic surveys, and drifter releases during April–July of 1993 and 1994. There is a strong seasonal signal in salinity and along-shore velocity of the coastal current, caused by the freshwater inputs of the rivers entering the western Gulf. Surface salinity within the coastal current during the spring freshet is typically 2 psu below ambient, and along-shore currents in the surface layer are directed southwestward at speeds of 0.10–0.20 m s −1, occasionally reaching 0.50 m s −1. The plume thickness is typically 10–20 m in water depths of 50–100 m, thus it is well isolated from the bottom over most of its areal extent. The along-coast freshwater transport within the plume varies considerably due to variations in wind stress, but on time scales of weeks to months it follows the variations of riverine input, with a time lag consistent with the advective velocity. Less than half of the transport of the coastal current is explained by the baroclinic gradient; the barotropic forcing associated with the larger-scale dynamics of the Gulf of Maine accounts for about 60% of the transport. The volume of freshwater transport in the coastal current exceeds the local riverine input of fresh water by 30%, suggesting a significant contribution of freshwater transport from the St. John River, 500 km northeastward. The measurements within the western Maine coastal current, however, indicate a significant decrease in the baroclinic transport of fresh water along the coast, with an e-folding scale of approximately 200 km.

High-frequency wind forcing of a channel model of the ACC: normal mode excitation

The response of the Antarctic circumpolar circulation to wind stress variability is studied in a simple model of the Southern Ocean. The model consists of a zonally reentrant channel with mid-ocean barrier, forced by surface heat flux and stochastic wind stress. The MITgcm code is used to solve for temperature, sea level, and the velocity field. The channel transport responds actively to the stochastic wind forcing through the excitation of several eigenmodes. The fundamental basin mode is excited, which has a period of about 20 days. However, the response is dominated by a topographic mode with a period of 3 days. This barotropic mode is related primarily to topographic Rossby waves propagating on the submarine sill, and Kelvin waves propagating westward on the southern boundary. The mode shares characteristics with numerical predictions of normal modes in the Southern Ocean, as well as with recently observed modes of variability around Antarctica, with periods between 1 and 2 days. These results show that both topographic normal modes and Rossby basin modes can play a role in the adjustment of the ACC to high-frequency wind stress variability. The presence of the resonance in the system leads to interesting phase behavior between the wind stress forcing and the ocean transport: for a considerable frequency range, the transport seems to lead the wind stress variability. This shows that the classical notion of transport passively lagging wind forcing is inadequate when eigenmodes are excited.

High-frequency wind forcing of a channel model of the ACC: normal mode excitation

The response of the Antarctic circumpolar circulation to wind stress variability is studied in a simple model of the Southern Ocean. The model consists of a zonally reentrant channel with mid-ocean barrier, forced by surface heat flux and stochastic wind stress. The MITgcm code is used to solve for temperature, sea level, and the velocity field. The channel transport responds actively to the stochastic wind forcing through the excitation of several eigenmodes. The fundamental basin mode is excited, which has a period of about 20 days. However, the response is dominated by a topographic mode with a period of 3 days. This barotropic mode is related primarily to topographic Rossby waves propagating on the submarine sill, and Kelvin waves propagating westward on the southern boundary. The mode shares characteristics with numerical predictions of normal modes in the Southern Ocean, as well as with recently observed modes of variability around Antarctica, with periods between 1 and 2 days. These results show that both topographic normal modes and Rossby basin modes can play a role in the adjustment of the ACC to high-frequency wind stress variability. The presence of the resonance in the system leads to interesting phase behavior between the wind stress forcing and the ocean transport: for a considerable frequency range, the transport seems to lead the wind stress variability. This shows that the classical notion of transport passively lagging wind forcing is inadequate when eigenmodes are excited.

Intraseasonal variability of wind-forced coastal upwelling off central Chile (30°S)

Satellite-derived along-shore windstress variability off subtropical Chile at intraseasonal periods has been recently associated with the corresponding wind variability over the tropical Pacific. Along the coastal strip in which satellite winds can not be resolved, wind-driven upwelling might be in principle modulated through large-scale intraseasonal changes in the strength of the subtropical anticyclone and by intraseasonal ocean coastal-trapped waves (CTWs) through associated changes in coastal sea-surface temperatures. Daily anomalies of band-passed outgoing long-wave radiation over the central equatorial Pacific have been selected to represent Madden–Julian Oscillations, as the dominant mode of equatorially sourced, intraseasonal variability in the atmosphere and coastal ocean. Afternoon alongshore pseudo-windstresses at a representative coastal site in central Chile (30°S) describe the upwelling-favourable wind field over a 30–40 km coastal strip. The subtropical anticyclone strength is expressed as a 900-km offshore sea-level pressure (San Felix Island), and the sea-level pressure difference with the coast. CTWs are represented by the smoothed sea-level at 27°S. The intermittent nature of intraseasonal variability led to statistical procedures as Wavelet and Singular-Spectrum (SSA) analyses to search for associations among those series. Cross-correlation analysis of the SSA-reconstructed series with the two principal oscillatory modes (40–100-day, and 28–50-day periods, respectively), shows that intraseasonal variability in the subtropical anticyclone strength, partially associated with the Pacific South America teleconnection pattern, has the best association with coastal windstress variability. CTWs appeared to be important in their association with coastal winds only during strong MJO activity in connection with El Niño in the low-frequency intraseasonal band, while in the high-frequency one a fraction of the ASL variability appears to be locally wind-forced.

Variability in satellite winds over the Benguela upwelling system during 1999–2000

Wind stress variability over the Benguela upwelling system is considered using 16 months (01 August 1999 to 29 November 2000) of satellite‐derived QuikSCAT wind data. Variability is investigated using a type of artificial neural network, the self‐organizing map (SOM), and a wavelet analysis. The SOM and wavelet analysis are applied to an extracted data set to find that the system may be divided into six discrete wind regimes. The wavelet power spectra for these wind regions span a range of frequencies from 4 to 64 days, with each region appearing to contain distinct periodicities. To the north, 10°–23.5°S, the majority of the power occurs during austral winter, with a 4–16 day periodicity. Further investigation of National Centers for Environmental Prediction reanalysis outgoing longwave radiation data indicates that the winter intensification of wind stress off the Angolan coast is linked with convective activity over equatorial West Africa. The summer activity appears to be linked with the intensification of the Angolan heat low. Convective activity over the Congo basin appears to impact upon wind stress variability, off the Angolan coast, throughout the year. Farther south, 24°–35°S, the majority of the power occurs in the summer. Here a bimodal distribution occurs, with peaks of 4–12 and 25–50 days. The southernmost regions appear to be forced at higher frequencies by both midlatitude cyclones (austral winter) and mesoscale coastal lows (austral summer). At lower frequencies, eastward propagating periodic wind events that originate over eastern South America appear to be important to the forcing of wind stress over the southern Benguela.

Exchange through the Bab el Mandab

During the last 10 years there have been a number of important developments in the understanding of the exchange flow in the Bab el Mandab. New and improved estimates of the fluxes of mass, heat and salt through the Strait have been made directly from oceanographic measurements and indirectly from air–sea flux data. Hydraulic theory has been applied to explain the seasonal variations in the exchange flow, and in particular the three-layer summer circulation. The effects of wind stress, friction, and seasonal sea-level variability on hydraulic control are addressed in this paper. Analyses of oceanographic data have failed to provide direct evidence of hydraulic control, but they have highlighted the importance of tidal scale variability and differences between real continuously stratified fluids and idealised layer flows often used in hydraulic theory. Other studies have investigated the coupling between the flow in the Strait and the circulation within the Red Sea.

Coastal transition zone off Chile

Seven years of subsurface current observations at deep‐sea and continental slope moorings off Chile (30°S), satellite sea surface anomaly, and satellite wind stress are used to examine space, time, and propagation characteristics of the mesoscale eddy activity in the coastal transition zone off Chile. This zone off Chile extends from the coast to ∼600–800 km offshore and can be separated into two latitudinal regions. The first region, between 29° and 39°S off central Chile, is characterized by high eddy kinetic energy and strong but variable equatorward wind stress. The second region, between 19° and 29°S off northern Chile, is characterized by low eddy kinetic energy and weak but persistent equatorward wind stress. Low‐frequency mesoscale variability off central Chile is mainly associated with baroclinic instability of coastal currents and westward propagation of Rossby waves from the eastern boundary and is strongly modulated over El Niño/La Niña cycles. Application of a new rotary wavelet spectrum method to the recording current meter data and the use of current estimates from satellite altimeter data show that mesoscale eddies and meanders in the coastal transition zone fluctuate with periods centered on 120 days and with length scales centered on ∼200 km. Cross‐rotary wavelet analyses of currents and wind stress indicate that fluctuations of coastal currents with periods longer than 220 days propagated westward as free Rossby waves during 1995–1996 and as forced Rossby waves during 1999–2001.

Formation of an aggregate scale in Arctic sea ice

The ice pack covering northern seas is a mixture of thick ridged and rafted ice, undeformed ice, and open water. Conventional Eulerian Arctic sea ice models use a plastic yield surface to characterize the constitutive behavior of the pack. An alternative is to adopt a discontinuous Lagrangian approach and explicitly model the formation of leads and pressure ridges. We use a Lagrangian ice model that consists of thousands of discrete polygonal floes 1–4 km in width. At the beginning of a simulation the ice floes are frozen together in a square domain. We apply a linearly varying wind stress that deforms the pack by stretching the viscous‐elastic joints between adjacent floes. Fractures propagate along joints forming a crack pattern in the model ice pack. The crack pattern defines a system of large plates 10–100 km in width that are aggregates of many individual floes. The average size of the plates is determined by a competition between the rate of crack creation and the speed of the relaxation wave that travels outward from a newly broken joint and reduces stresses in the surrounding pack. Simulation results are used to characterize the formation of the aggregate structure and to determine how the rate of crack creation and the average area of the aggregate plates depends on tensile strength, the wind stress gradient, and the size of the individual floes. After the formation of the aggregate‐scale plate structure, subsequent deformation occurs at the plate boundaries. Since the usual state of the ice pack is a state of failure, an interesting situation is created in which the initial wind‐driven deformation creates the material conditions or aggregate structure under which subsequent deformation occurs.

Propagation and the Vertical Structure of the Madden–Julian Oscillation

The Madden–Julian oscillation (MJO) dominates tropical variability on time scales of 30–70 days. During the boreal winter–spring it is manifested as an eastward propagating disturbance, with a strong convective signature over the Eastern Hemisphere. The space–time structure of the MJO is described using the National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis, Advanced Very High Resolution Radiometer outgoing longwave radiation, observed sea surface temperature, and the Climate Prediction Center Merged Analysis of Precipitation. Empirical orthogonal function analysis is used to identify the convective signature of the MJO, and regression is used to identify key relationships with the convection. Compared to analyzing successive years of data, the selection of years of strong MJO activity results in a more robust lead–lag structure and an increase in explained variance. The MJO exhibits a rich vertical structure, with low-level moisture convergence being well defined when the convective anomalies are strong, and there is evidence that free-tropospheric processes also play a role in the MJO life cycle. The westward vertical tilt is most apparent over the western Pacific. Over the Indian Ocean the system is more vertically stacked, principally because of the strong subsidence of the inactive phase of the MJO, which lies to the east of the convection. As the Kelvin wave decouples from the convection near the date line, a sea level low pressure surge, previously discussed by A. J. Matthews, transits the eastern Pacific and Atlantic Oceans. Here the link of the zonal wind stress and low-level divergence to the pressure surge is explored. The pressure gradient gives rise to westerlies that propagate rapidly to the east, and it may play role in the development of the MJO convection in the western Indian Ocean, which occurs in an easterly basic state, and conditions not consistent with the low-level moisture convergence paradigm.

Separation of quasi-semiannual Rossby waves from the eastern boundary of the Indian Ocean

Westward propagating features, identified as semiannual Rossby waves, have been observed in the southern subtropical Indian Ocean between 20S and 35S. A previous study based on ERS satellite scatterometer wind stress data in this region has shown that the Rossby waves were not forced by local Ekman pumping in the ocean interior nor by local variations in wind stress near the Australian coast. In the present study, we investigate a third possible source, in the form of remotely forced semiannual coastal waves propagating along the Australian coast. Altimetric and tide gauge data show consistent semiannual anomalies along the northwestern and western coast, with a phase lag between the northernmost station and about 25S, producing a poleward phase speed of ∼0.4 m s -1 . South of the critical latitude for semiannual Rossby wave radiation at 27S, we still observe a significant sea level signal along the coast at the semiannual frequency that appears nearly in phase between the stations. Semiannual sea level anomalies lead the semiannual wind forcing by about one month, confirming that the signal is not locally forced. These semiannual coastal variations are in phase with the offshore radiation of Rossby waves observed between 20S and 35S. We suggest that, south of the critical latitude of 27S, the observed coastal wave signal could interact with the poleward coastal Leeuwin Current and that this wave-current interaction could stimulate nonlinear instabilities of this density-driven current and may be a key mechanism for the Rossby wave radiation in the subtropical Indian Ocean.

Interannual variability of the sea‐air exchange of CO2 from 1961 to 1998 simulated with a global ocean circulation‐biogeochemistry model

Interannual variability of global sea‐air CO2 flux is investigated by use of a numerical model for general and biogeochemical circulation with the observed interannual variations in sea surface temperature and wind stress from 1961 to 1998. The global variability is 0.23 GtC yr−1 as the standard deviation, and is governed by the variability of 0.13 GtC yr−1 in the equatorial Pacific through the El Niño‐Southern Oscillation (ENSO) cycle. The variability in the Southern Ocean is the second largest, 0.07 GtC yr−1. These features are reproduced in both the experiments using the wind stress from an atmospheric circulation model reanalysis (National Centers for Environmental Prediction (NCEP)) and that from an observational data set (Atlas of Surface Marine Data, 1994). Our results agree with the previous ocean‐based estimates on the points that the global variability is much smaller than the atmosphere‐based estimates (∼1 GtC yr−1) and that the global variability is governed by the equatorial Pacific. The variability in the equatorial Pacific is mostly influenced by the surface dissolved inorganic carbon (DIC) convergence in the wind‐driven velocity field; the reduced DIC convergence by the weakened easterly causes the reduced sea‐to‐air CO2 flux during El Niño. Variability of export production has an opposite effect to that of the surface DIC convergence in controlling the sea‐air CO2 flux in the ENSO cycle but is smaller than a half of the variability of the surface DIC convergence. Effect of surface temperature through the CO2 solubility is also opposite but is smaller by an order of magnitude. The sea‐air CO2 flux variability influenced by the ENSO is almost the same in both the early period (1961–1979) and the late period (1980–1998). The simulated variability in the equatorial Pacific is smaller, about 70% of the observational estimate. This deficiency is partly due to the underestimated effect of surface salinity variation on pCO2 caused by the climatological salinity boundary condition and partly due to the overestimated export production by the neglect of the effect of micronutrients in our production parameterization.

Surface forcing on the southern flank of Georges Bank, February–August 1995

Surface wind stress, heat, and freshwater fluxes were estimated over the southern flank of Georges Bank during February–August 1995 using moored measurements made at ST1 located on the 76‐m isobath, roughly halfway between the tidal mixing and shelf/slope fronts. Wind stress variability was dominated by a succession of atmospheric lows that passed Georges Bank during the deployment. A transition between frequent lows and strong wind stress events (“winter”) to less frequent lows and weaker wind stresses (“summer”) occurred in mid‐May. In winter, wind stress fluctuations tended to be omnidirectional, with maximum stresses above 0.5 N/m2 during four storms, one a classic “nor'easter”, while summer fluctuations were weaker but strongly polarized in the along‐bank direction. The ST1 surface heat flux was dominated by shortwave heating, which increased from a winter mean of 130 W/m2 to 230 W/m2 in summer. Long‐wave cooling decreased from 50 W/m2 (winter) to 30 W/m2 (summer), while mean sensible and latent fluxes increased from −20 and −40 W/m2 (winter) to +10 and 0 (summer) respectively. Overall, winter was characterized by weak net heating (30 W/m2) with shortwave gain offset by long‐wave, latent, and sensible heat loss. In summer, increased shortwave gain and reduced long‐wave loss and weak sensible and latent fluxes combined to produce strong net heating (210 W/m2). ST1 precipitation was highly episodic with little seasonality while evaporation occurred mostly during winter, resulting in a net evaporation of −15 cm and net freshwater flux of +48 cm over the deployment.

A Model of the Wind-Driven Seasonal Variability in the Tropical North Pacific, with Validation through Altimeter Data

Abstract The wind-driven seasonal variability in the tropical North Pacific Ocean is analyzed by means of a two-layer primitive equation ocean model implemented in an idealized Pacific extending from 30°S to 52°N and forced by an analytic seasonally varying wind stress field derived from ECMWF winds. The oceanic response in the tropical region is found to be mainly in the form of annual beta-refracted baroclinic Rossby waves radiating from the eastern boundary. Validation of these results with TOPEX/Poseidon (T/P) altimeter data is carried out. Zonal longitude–time diagrams of sea surface height anomalies and zonally integrated meridional transports computed from T/P data and from the winds through the Sverdrup relation by Stammer are compared with the corresponding quantities obtained from the model results. Such comparison shows that the model does capture the essential features of the wind-driven seasonal variability in the tropical North Pacific. The analysis of the model results, based also on sensit...

Ocean distribution of dungeness crab megalopae and recruitment patterns to estuaries in Southern Washington State

We investigated the distribution of meroplankton and water properties off southern Washington and simultaneously measured time series of larval abundance and water properties in two adjacent estuaries, Grays Harbor and Willapa Bay. The cruise period, in late May 1999, coincided with large variation in the alongshore wind stress that caused dynamic change in the position of the Columbia River plume, coastal upelling and downwelling, and offshore phytoplankton production. In the coastal ocean, meroplankton groups responded differently to this wind event and the associated advection of water masses. Dungeness crab (Cancer magister) megalopae were largely indifferent to the wide salinity variation, and were found throughout the surveyed area in both plume and recently upwelled waters. Megalopae of kelp crab (Pugettia producta) and hermit crab (Pagurus spp). were more abundant in upwelled water and low numbers were caught in the plume water. Barnacle cyprids appeared to track the advective transport suggesting that they may be more passively dispersed. Within the estuaries, hydrography responded rapidly and synchronously to variation in wind stress. Intrusions of both plume and newly upwelled waters were detected at estuarine sites, depending on the type of water present at the coast, indicating a tight link between the estuaries and the coastal ocean in this region. A 90-d record ofC. magister megalopae abundance was made at 3 estuarine sites using light traps. The bulk of theC. magister recruitment was limited to a relatively brief period in late May through June. Within this window, megalopae occurred in distinct pulses of 3–5 d interspaced with periods of low or zero abundance.C. magister megalopae recruited to the estuaries over a wide range of wind forcing, and were transported into the estuary within varied water types. There were no periodic patterns indicative of spring-neap tidal variations in the abundance time series. Abundance was only weakly cross-correlated between the adjacent Grays Harbor and Willapa Bay estuaries, which contrasts with the more synchronous estuarine-coastal linkages measured for water properties. These results suggest the interaction of larval aggregation size in the ocean with estuary-ocean exchange processes likely controls patterns of estuarine recruitment.

Observations of SST-Induced Perturbations of the Wind Stress Field over the Southern Ocean on Seasonal Timescales

Abstract The surface wind stress response to sea surface temperature (SST) over the latitude range 30°–60°S in the Southern Ocean is described from the National Aeronautics and Space Administration's QuikSCAT scatterometer observations of wind stress and Reynolds analyses of SST during the 2-yr period August 1999 to July 2001. While ocean–atmosphere coupling at midlatitudes has previously been documented from several case studies, this is the first study to quantify this relation over the entire Southern Ocean. The spatial structures of the surface wind perturbations with wavelengths shorter than 10° latitude by 30° longitude are closely related to persistent spatial variations of the SST field on the same scales. The wind stress curl and divergence are shown to be linearly related, respectively, to the crosswind and downwind components of the SST gradient. The curl response has a magnitude only about half that of the divergence response. This observed coupling is consistent with the hypothesis that SST modification of marine atmospheric boundary layer (MABL) stability affects vertical turbulent mixing of momentum, inducing perturbations in the surface winds. The nonequivalence between the responses of the curl and divergence to the crosswind and downwind SST gradients suggests that secondary circulations in the MABL may also play an important role by producing significant perturbations in the surface wind field near SST fronts that are distinct from the vertical turbulent transfer of momentum. The importance of the wind stress curl in driving Ekman vertical velocity in the open ocean implies that the coupling between winds and SST may have important feedback effects on upper ocean processes near SST fronts.

Spatial overlap and distribution of anchovies ( Anchoa spp.) and copepods in a shallow stratified estuary

Juvenile pelagic fishes are integral members of many coastal river communities. Many of these systems are strongly influenced by variable wind stress and freshwater inputs that can increase heterogeneity in estuarine habitat for fishes. We use mobile sonar surveys within the Neuse River Estuary System, NC, USA to assess the distribution and behavioral patterns of juvenile anchovies, Anchoa spp. 25-65 mm TL, over a broad range of spatial scales in relation to diel and seasonal changes in water quality including stratification, hypoxic events and copepod distribution. Results from our study indicate that episodic stratification-induced hypoxic events can reduce suitable habitat volume for anchovies by more than 50%. Furthermore, our sampling suggests that hypoxia causes spatial separation between plankton and the grazing fishes. Under stratified oxygen conditions, we observe higher densities of copepods in hypoxic bottom water. Finally, we report that reductions in available habitat caused an increase in local densities of fishes and may result in increased competition for resources. These spatially explicit data are critical for developing trophic dynamic models that predict the response of fish communities to natural and anthropogenic impacts on the system.