OS41B-0478 0800h
Observations of Coastal Upwelling off the Coast of the South Atlantic Bight in Summer of 2003: An Application of NASA's Remote Sensing Data to Coastal Studies
The Moderate Resolution Imaging Spectroradiometer (MODIS) instruments onboard of Terra and Aqua satellites provide, for the first time, concurrent measurements of sea surface temperature (SST) and ocean color, which are suitable for coastal upwelling studies. The accuracy, the 1-km spatial resolution, and the almost complete daily coverage of the MODIS data compared with historical measurements make it advantageous for resolving important coastal fronts of chlorophyll concentration and temperature. The cold SST anomaly during summer 2003 off the coast of the South Atlantic Bight is an event that is comprehensively covered by NASA's MODIS and SeaWinds satellite observations. These data combined with in situ tide gauge, mooring, and ship measurements can be used to identify important dynamics responsible for the anomalous cold water event. The analysis of the data suggests that coastal upwelling occurs in the climatological summer forced by the climatological southerlies over the South Atlantic Bight area in summer. However, the strong buoyancy barrier in summer prevents the cold water below the thermocline from reaching the ocean surface. In summer 2003, the southwesterlies in July through August were extraordinarily strong and persistent, which generated the upwelling currents strong enough to overcome the buoyancy resistance. The results of this analysis demonstrate the possibility of monitoring and forecasting the event using combination of the satellite and in situ observations. The MODIS data are archived and distributed by the NASA's Goddard Earth Science (GES) Distributed Active Archive Center (DAAC). The data can be accessed via the URL http://www.daac.gsfc.nasa.gov/MODIS.
http://www.daac.gsfc.nasa.gov/MODIS
OS41B-0479 0800h
Lessons Learned With Nowcast/Forecast Systems for Prince William Sound,Alaska (PWS/NFS and EPWS/NFS)
As part of the OSRI (Oil Spill Recovery Institute, Cordova, Alaska) Program, the Princeton Ocean Model (POM) has been implemented on a Cartesian grid (ca. 1.1 km resolution) and in sigma coordinates (15 to 21 levels, with concentrations nearsurface and nearbottom), for Prince William Sound (PWS) per se which is called PWS-POM, and for an extended domain, EPWS, that includes the Alaska Shelf offshore PWS as well as PWS per se, which is called EPWS-POM. These model implementations are run either offline for process and sensitivity studies or online as real-time nowcast/forecast systems, known as PWS/NFS and EPWS/NFS, respectively. The forcing includes synoptic winds from the RAMS mesoscale meteorological prediction system operated at the Univ. of Alsaka Anchorage, climatological monthly surface heating/cooling, climatological snowmelt runoff, eight tidal constituents, and throughflow forcing at the two major ports of PWS, Hinchinbrook Entrance (HE) and Montague Strait (MS), due to the Alaska Coastal Current and the nearby Copper River discharge. The real-time observing system elements consist of two NOS/CO-OPS/NWLON tide gauges (at Valdez and Cordova) and three NWS/NDBC meteorological buoys and three NWS/NDBC/C-MAN meteorological stations supporting the tanker route between Valdez and HE, which are invaluable for model verification though they only observe a limited number of nearsurface variables. In contrast, time-depth series from occasional multi-month deployments of bottom-mounted ADCPs and thermistor arrays have proven invaluable for model validation. Similarly, occasional deployments of upper ocean drifters have provided insights that challenge conventional wisdom. Strong seasonality in the forcing and stratification lead to complex and variable baroclinic flows and counterflows that are intermittently under topographic control. The most uncertain set of forcing functions is associated with the throughflow, which has led to exploration of the use of EPWS-POM as an alternative to PWS-POM, and in preparation for the availability of basin scale fields for open boundary conditions from an operational model
http://pws-nfs-osri.rsmas.miami.edu/
OS41B-0480 0800h
Coastal-Trapped Waves caused by typhoon along the southeast coast of Japan
To clarify the vertical structure of a coastal-trapped wave (CTW) in Sagami Bay located at the southeast coast of Japan, where the CTW was frequently observed, mooring observation using ADCP and memorable temperature was performed at shelf edge (water depth of 95m) and shelf slope (water depth of 250m) from July 28 to October 6 in 2003. Two Typhoons had passed nearby Japanese Island during the observation period. One is Typhoon 0310 (T10) passed through the western side of study area and the other is Typhoon 0315 (T15) passed through the eastern side. The CTWs were caused along the southeast coast of Japan by strong wind associated with T10 and T15, hereafter we call CTW10 and CTW15, respectively. The characteristics of the CTWs observed at the eastern coast of Sagami Bay were as follows; (1) Significant temperature rise and strong inflow in the upper layer were found in the case of CTW15, while strong outflow with little temperature variation were found in CTW10; (2) The current direction in the case of CTW15 changed at 100m depth, whereas the outflow associated with CTW10 was almost homogeneous throughout the water column; (3) The current maxima associated with CTW were appeared at 22 hours for theCTW10 and at 18 hours for the CTW15 after the peaks of the wind at Choshi. The first characteristic was explained by the wind direction associated with each Typhoon. However, the reasons for the second and third characteristics were not clear. To clarify these characteristics, we carried out numerical experiment using a three-dimensional level model with realistic bottom topography. The model result well represented the current structure and propagation speed of the observed CTWs. The CTW15 was the down-welling caused by the southward wind and it propagated as the CTW in the strong stratification. On the other hand, the CTW10 was explained to propagate as the CTW in the weak stratification, because the thermocline outcropped in the surface layer by the significant upwelling.
OS41B-0481 0800h
Modeling bottom mixed layer variability on the mid-Oregon shelf during summer upwelling
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. Data assimilation provides a dynamically significant effect on the intensity and the time of occurrence of the mixing events. 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 45N and a wider shelf area east of Stonewall Bank (44.5N). At 45N, the BML grows in response to downwelling favorable conditions, in agreement with known theories. East of Stonewall Bank, however, 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 computations of bottom stress curl, the vertical pumping velocity in this area may reach 15 m/day following periods of intensified upwelling-favorable winds. A column of denser, near-bottom water upwelled over the Ekman flow convergence area is tilted as a result of vertical shear in horizontal velocities, causing unstable stratification and convective overturning. The bottom stress curl, used as an indicator of the intensity of the bottom Ekman pumping and BML growth east of Stonewall Bank, is difficult to obtain from measurements, but is readily available as an output from the numerical model.
OS41B-0482 0800h
Export and Cycling of Continental Shelf Carbon: A Modeling Study
Continental margins play a significant role in the production and burial of organic carbon in the ocean, but these areas are poorly resolved in global circulation models. In this study, a high-resolution three-dimensional, nonhydrostatic idealized coastal model of the eastern United States after Mahadevan and Archer, 2000, 1998, was modified to simulate organic carbon production and export off the shelf. The model assumes a periodic north and south boundary, solid offshore and bottom boundaries, and a shelf-break density front determined by bathymetry. The model uses a free surface and a sigma grid in the vertical. We are in the process of formulating a carbon and nutrient component for this model. The model is initialized with a vertical nutrient profile taken from the open Atlantic Ocean. Mesoscale wind-driven circulation and vertical diffusion bring nutrients to the euphotic zone. Primary production is based on light availability and nutrient concentration. The particles advect with the flow and sink with a specified velocity. Remineralization is first-order in carbon concentration, and produces ammonia. Ammonia is slowly reoxidized to nitrate in subsurface waters, and used for recycled production in the euphotic zone. We are searching for a model of the production, sinking, and interconversion of multiple types of particles, which predicts the observed trends in f-ratio from coastal to pelagic ecosystems. The model is sensitive to sinking velocity, remineralization rate, vertical diffusivity, the uptake rate of nitrate, the uptake rate of ammonia, and the oxidation rate of ammonia to nitrate. Using the steady state solution of the one-dimensional model to initialize the three-dimensional model, we study the effect of vertical and horizontal advection and three-dimensional oceanographic processes on the distribution and export of carbon from the coastal system. We will compare the sensitivities of a box-budget, a one-dimensional diffusional, and the full 3-D mesoscale physical model.