[1] Modifications to surface winds by currents and sea surface temperature (SST) gradients near frontal boundaries of Gulf Stream rings are analyzed using satellite SST and scatterometer (NASA's Quick Scatterometer (QuikSCAT), NASA scatterometer (NSCAT)) wind observations. A component of scatterometer wind approximately equal and opposite to the surface current vector is observed and attributed to the fact that scatterometers detect relative motion of water and air. Warm-core ring (WCR) SSTs act to destabilize the marine atmospheric boundary layer (MABL), increasing surface wind magnitude by 10-15% and decreasing veering angle by 5-15°relative to large-scale mean winds. Cold-core ring (CCR) SSTs cause impacts of similar magnitude and opposite sense. Magnitudes and directions of modifications are accounted for by MABL dynamics of a nonlinear planetary boundary layer model forced by air-sea temperature differences. Wind modifications occur within tens of kilometers of SST fronts, implying a wind response timescale of order 1 hour. By contrast, uniformity of modified winds across the larger area within rings suggests the response time for the MABL to return to equilibrium downstream from a front exceeds 10 hours. Over WCRs, strong divergence (convergence) occurs on the upwind (downwind) side; curl is strongly negative (positive) to the right (left) side facing downwind. Opposite patterns are generally seen over CCRs. Divergence (curl) peaks where winds blow perpendicular (parallel) to SST fronts. SST image analysis indicates enhanced cloudiness occurs with downwind convergence over WCRs. Wind stress curl due to ring modifications causes dipolar Ekman pumping sufficient to influence ring translation and decay processes.

[1] Surface current (HF radar) and velocity profile observations, obtained as part of the Front-Resolving Observational Network with Telemetry (FRONT) project over an approximately 2-year period, are used to describe the seasonal variability of a coastal jet in the Long Island Sound outflow region. The jet is observed in an area of the continental shelf where surface thermal fronts are frequently detected during both summer and winter. The current jet is coincident with a band of high summer frontal probability, and apparently arises from the interaction between Long Island Sound outflow and larger-scale alongshore currents on the shelf. The jet reaches peak strength in summer (transport of $0.07 Sv) and is weak or non-existent in winter. Flow is strongest near the surface and weakens with depth, with only moderate seasonal variations in the vertical shear. The relatively long data set of currents combined with historical hydrographic measurements and buoy wind observations is analyzed to examine the seasonal variability of the terms in the depth-averaged momentum balance. The depth-averaged pressure gradient is partitioned into a steric component, evaluated from the hydrography, and a non-steric component that is estimated as the residual of the computed terms in the momentum equation. The depth-averaged momentum balance is found to be approximately geostrophic in the across-shore direction. The seasonal variability in the jet arises due to the shifting balance between buoyancy-driven flow that is always downshelf but intensifies somewhat in summer and wind-driven flow which dominates in winter when wind stress becomes strongly upwelling favorable.

Low dissolved oxygen events were characterized in Narragansett Bay (NB), a moderate-size (370 km 2 ) temperate estuary with a complex passage/embayment geometry, using time series from 2001 to 2006 at nine fixed-site monitoring stations. Metrics for event intensity and severity were the event-mean deficit relative to a threshold (mg O 2 l −1 ) and the deficit-duration (mg O 2 l −1 day; product of deficit and duration [day]). Hypoxia (threshold 2.9 mg O 2 l −1 ) typically occurred intermittently from late June through August at most stations, as multiple (two to five per season) events each 2 to 7 days long with deficit-duration 2 to 5 mg O 2 l −1 day. Conditions were more severe to the north and west, a pattern attributed to a northsouth nutrient/productivity gradient and east-west structure of residual circulation. Spatial patterns for suboxic and severely hypoxic events (thresholds 4.8 and 1.4 mg O 2 l −1 ) were similar. The view that different processes govern event variability in different regions, each influenced by local hydrodynamics, is supported by both weak spatial synchronicity (quantified using overlap of event times at different sites) and multiple linear regressions of biological and physical parameters against event severity. Interannual changes were prominent and season-cumulative hypoxia severity correlated with June-mean river runoff and Junemean stratification. Benthic ecological implications for areas experiencing events include: NB hypoxia classifies as periodic/episodic on a near-annual basis; highest direct mortality risk is to sensitive and moderately sensitive sessile species in the northern West Passage and western Greenwich Bay, with some risk to Upper Bay; direct risk to mobile species may be ameliorated by weak spatial synchronicity; and indirect impacts, including reduced growth rates and shifts in predator-prey balances, are very likely throughout the sampled area due to observed suboxic and hypoxic conditions.

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The response to wind events in the Long Island Sound (LIS), a large macrotidal estuary influenced by rotation and stratification, is studied using long-term ferry-based current observations near the mouth, unstratified and stratified numerical simulations forced with along-estuary winds, and analytic solutions based on linear barotropic theory. The observed wind-event velocity anomalies for down-estuary winds have surfaceintensified downwind flows flanking a deeper central upwind flow. Response to up-estuary wind events has a weaker magnitude and a broader and thicker downwind flow. The downwind and upwind flows are more laterally aligned than vertically layered, as determined by a newly defined dimensionless lateral alignment index. Simulation results and analytic solutions share the gross spatial patterns of the observed response, though statistical measures indicate weak agreement. Along-estuary variations in the simulation results and analytic solutions follow similar trends and are strongly influenced by variations of the bathymetric cross section. Wind-event anomalies in the section-averaged dynamics are dominated by the along-estuary pressure gradient opposing wind stress. In the stratified simulation, wind-driven density advection, isopycnal straining, and stirring modify stratification, eddy viscosities, and baroclinic pressure gradients. The wind-event response of the baroclinic pressure gradient is 15% of the barotropic gradient but is dynamically linked to response differences to up-estuary and down-estuary winds. The wind-event response asymmetries near the mouth are in qualitative agreement with observations and are opposite to asymmetries closer to the head.