Meridional Asymmetry and Energetics of Tropical Instability Waves

One of the striking features of tropical instability waves (TIWs) is that they appear to be more prominent north of the equator. A linearized, 2½-layer ocean model is used to investigate effects of various asymmetric background states on structures of equatorial, unstable waves. Our results suggest that the meridional asymmetry of TIWs is due to asymmetries of the two branches of the South Equatorial Current (SEC) and of the equatorial, sea surface temperature front; it is not due to the presence of the North Equatorial Countercurrent. Energetics analyses indicate that frontal instability associated with the equatorial, SST front, as well as barotropic instability due to shear associated with the SEC, are energy sources for the model TIWS.