Long-distance radiation of Rossby waves from the equatorial current system
Event: 2020 Ocean Surface Topography Science Team Meeting (virtual)
Session: Science III: Mesoscale and sub-mesoscale oceanography
Presentation type: Type Forum
(This is a finalized version of the project presented at the previous OSTST meeting.) Sea-surface height (SSH) variability throughout much of the North Pacific is coherent with the SSH signal of the tropical instability waves (TIWs) that result from instabilities of the equatorial currents. This variability has regular phase patterns consistent with barotropic Rossby waves radiating energy away from the unstable equatorial currents, and the waves clearly propagate from the equatorial region to at least 30N. Numerical simulations further support this interpretation. North of 40N, more than 6000 km from the unstable equatorial currents, the SSH field remains coherent with the near-equatorial SSH variability, but it is not as clear whether the variability at the higher latitudes is a simple result of barotropic wave radiation from the tropical instability waves. Even more distant regions, as far north as the Aleutian Islands off of Alaska and the Kamchatka Peninsula of eastern Russia, have SSH variability that is significantly coherent with the near-equatorial instabilities. The variability is not well represented in a widely used gridded SSH data product, and this appears to be a result of the assumed form of the autocovariance function used for the objective mapping scheme. The pattern of SSH variance at TIW frequencies exhibits remarkable patchiness on scales of hundreds of kilometers, which we interpret as being due to the combined effects of wave interference topographic refraction.