Excitation of the 5-day Wave by Antarctica

Abstract

The 5-day wave has been detected in composite maps of geopotential height fields of European Centre for Medium-Range Weather Forecasts dataset for 7 years (1984–91, except 1985) and shows a characteristic northwest–southeast meridional phase tilt in the Southern Hemisphere. A numerical integration of Laplace’s tidal equations with periodic forcing of zonal wavenumber 1 only produced the meridional phase tilt when the forcing is located in high latitudes. Such a forcing is created through coupling of the time-fluctuating westerlies with the topography of Antarctica. Numerical simulations that incorporated this mechanism reproduced the observed meridional phase tilt of the 5-day wave, which suggests that Antarctica is responsible for the observed phase tilt through the process of resonance. A linear theory on the meridional phase tilt is given with a nondivergent barotropic model that includes both forcing and dissipation.