Wednesday, 6 August 2003: 11:30 AM
Modelling the generation of Haida Eddies
A numerical model forced with average annual cycles of climatological winds, surface heat flux, and temperature and salinity along the open boundaries is used to demonstrate that Haida Eddies are typically generated each winter off Cape St. James, at the southern tip of the Queen Charlotte Islands of western Canada. Annual cycles of sea surface elevation measured at coastal tide gauges and TOPEX/POSEIDON crossover locations are reproduced with reasonable accuracy. Model sensitivity studies show that Haida Eddies are baroclinic in nature and are generated by the merging of several smaller eddies that have been formed to the west of Cape St. James. The generation mechanism does not require the existence of instability processes and is associated with the mean advection of warmer and fresher water from Hecate Strait around the cape. Sustained winds to the north or northwest (typical in winter) are a necessary condition for this advection and strong winds, such as those seen during the 1997-98 El Niņo, have produced eddies with diameters larger than 200km and lifetimes longer than two years after they detach from the coast and drift into the Gulf of Alaska.