Sack Lunch Seminar (SLS)

Tom Farrar (WHOI)
Date Time Location
March 21st, 2018 12:00pm-1:00pm

Planetary scalepropagation of oceanic mesoscale instabilities

Tropical instability waves (TIWs) result from instabilitiesof the swift equatorial current systems in the tropical Pacific and AtlanticOceans.  This analysis focuses on theremote effects of these instabilities in the Pacific Ocean.

Analysis of sea-surface height (SSH) anomalies fromsatellite altimetry shows variability throughout much of the North Pacific thatis coherent with the TIWs near the equator. This variability has regular phasepatterns that are consistent with barotropic Rossby waves radiating energy awayfrom the unstable equatorial currents, and the waves clearly propagate from theequatorial region to at least 30°N. Comparisons with numerical simulations support the conclusion that thisremote variability can indeed be attributed to barotropic Rossby wavesgenerated near the equator.  Near 40°N,the SSH field remains coherent with the near-equatorial SSH variability, but itis not as clear whether the variability at the higher latitudes is a simpleresult of barotropic wave radiation from the tropical instability waves; forexample, there is some wind variability at the higher latitudes that iscoherent with both the local SSH and the TIWs near the equator.  There are even more distant regions, as farnorth as the Aleutian Islands off of Alaska, where the SSH variability issignificantly coherent with the near-equatorial TIW signal.

These nonlocal aspects of current instabilities pose achallenge for parameterization of mesoscale instabilities in climatemodels.  This radiated variabilitycontributes to the mesoscale variability in SSH in the midlatitudes.  The properties and dynamics of this radiatedvariability may also have important consequences for the instability processitself by affecting the rate at which energy is removed from the immediatevicinity of the unstable current.