Nonlocal effects of an unstable ocean current
Event: 2019 Ocean Surface Topography Science Team Meeting
Session: Science III: Mesoscale and sub-mesoscale oceanography
Presentation type: Type Poster
We analyze sea-surface height (SSH) anomalies from satellite altimetry to show that the instability of the Pacific equatorial current system trigger oceanic Rossby waves that affect the variability in distant regions. SSH variability throughout much of the North Pacific is coherent with the SSH signal of tropical instability waves (TIWs) near the equator that result from instabilities of the swift equatorial current system. This variability has regular phase patterns that are consistent with barotropic Rossby waves radiating energy away from the unstable equatorial currents, and the waves can be clearly seen to propagate from the equatorial region to at least 30°N. Comparisons with numerical simulations further support this interpretation. North of 40°N, 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. There are even more distant regions, as far north as the Aleutian Islands off of Alaska, where the SSH variability is significantly coherent with the near-equatorial instabilities. In the period band associated with tropical instability waves, a surprisingly large amount of the geostrophic eddy kinetic energy at distant midlatitude locations can be ascribed to the remote effects of the unstable equatorial currents. The fact that instabilities of strong ocean currents can radiate waves that affect mesoscale variability at distant locations poses an important challenge for parameterization of mesoscale variability in climate models.