Atmosphere Ocean Science Colloquium
Long-range Rossby wave radiation from an unstable ocean current
Speaker: Tom Farrar, WHOI
Location: Warren Weaver Hall 1302
Date: Wednesday, February 20, 2019, 3:30 p.m.
Synopsis:
Tropical instability waves (TIWs) result from instabilities of the swift equatorial current systems in the tropical Pacific and Atlantic Oceans. This presentation focuses on the remote effects of these instabilities in the Pacific Ocean.
Analysis of sea-surface height (SSH) anomalies from satellite altimetry shows variability throughout much of the North Pacific that is coherent with the TIWs near the equator. This variability has regular phase patterns that are 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 30°N. Comparisons with numerical simulations support the conclusion that this remote variability can indeed be attributed to barotropic Rossby waves generated near the equator. Near 40°N, 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 simple result of barotropic wave radiation from the tropical instability waves; for example, there is some wind variability at the higher latitudes that is coherent with both the local SSH and the TIWs near the equator. 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.
Nonlocal effects of current instabilities pose a challenge for parameterization of mesoscale instabilities in climate models. This radiated variability contributes to the mesoscale variability at distant locations. The properties and dynamics of this radiated variability may also have important consequences for the instability process itself by affecting the rate at which energy is removed from the immediate vicinity of the unstable current.