Wednesday, 6 August 2003: 4:45 PM
Variability in shelf transports in the Gulf of Alaska, Part IV: Response to mesoscale forcing using the Regional Ocean Modeling System (ROMS)
The coastal Gulf of Alaska (CGOA) is characterized by steep coastal mountains which exert strong orographic effects on the local winds. Coastal ocean currents are vigorous, and driven by alongshore winds and runoff. Therefore, trapping of the alongshore winds by the coastal orography is believed to dramatically impact the coastal ocean currents. To explore these mesoscale phenomena, we are utilizing output from a set of nested atmospheric models in conjunction with a regional, primitive equation coastal ocean model of the CGOA. The ocean model used is the Regional Ocean Modeling System (ROMS), with a mean resolution of 12 km. Here we compare the coastal ocean response to the application of two different wind products: 1) low-resolution (2-degree) daily atmospheric hindcasts from NCEP; 2) high-resolution (15-45 km) daily hindcasts from a multiply-nested implementation of MM5, where the NCEP hindcasts serve as a lateral boundary condition on the largest MM5 grid. We have found that the MM5 product leads to 50% or greater enhancement of depth-integrated alongshore currents during strong wintertime coastal wind events; typical values are 20 cm/s with NCEP to greater than 30 cm/s with MM5. This increased flow is accompanied by an additional rise in sea-level of ~20 cm. These are major changes in the coastal circulation, and a comparison with moored current meter records demonstrate enhanced hindcast skill using the MM5 product. These findings confirm that the use of enhanced wind products, which include local orographic effects, offer substantial improvements to coastal ocean simulations in regions with steep coastal mountains.