Response of A Small, Two-Strait Semi-Enclosed Sea to External Forcings

Located at the northern edge of the Northern Gulf of Alaska (NGOA), Prince William Sound(PWS) is a small, two-strait semi-enclosed sea. The general ocean circulation pattern inside PWS is significantly affected by external forcings, for instance, the large-scale circulation in NGOA, atmospheric pressure and surface winds, surface heating/cooling, runoff, and tides. Motivated by multi-year experience with a well-validated, quasi-operational ocean circulation nowcast/forecast system for PWS (viz., Extended PWS Nowcast/Forecast System (EPWS/NFS)), the present study addresses some aspects of the PWS response to various external forcings, via numerical simulations. Based on the Princeton Ocean Model (POM), four numerical implementations have been examined, viz., PWS-POM, Extended PWS-POM (EPWS-POM), Idealized PWS-POM (IPWS-POM), and a 2-D tidal model. These implementations are used to simulate physical processes with various spatial and temporal scales in PWS. A series of numerical simulations are conducted, driven by various external forcings ranging from large scale and mesoscale circulation in NGOA represented by the Global Navy Coastal Ocean Model (NCOM), to atmospheric pressure observed by National Data Buoy Center (NDBC) buoys and mesoscale winds predicted by Regional Atmospheric Modeling System (RAMS), and to tides simulated by the 2-D tidal model. These simulations, along with analysis from a Helmholtz resonance model, demonstrate and help interpret some phenomena in PWS; for instance, barotropic Helmholtz resonance in coastal sea levels, and volume transports through the two PWS straits, and a dominant cyclonic gyre in the Central Sound in August and September. The simulation results are used to study a wide range of oceanic phenomena in PWS; e.g., two-layer/three-layer baroclinic transports through the straits, a "transition band" in the coherence pattern between volume transports through the two straits, mesoscale circulation in the Central Sound, the deep water circulation, and the annual tidal energy budget.