Abstract's details

Model analysis of barotropic Rossby waves radiated from Tropical Instability Waves

Ted Durland (Oregon State University, United States)


Tom Farrar (Woods Hole Oceanographic Institution, USA)

Event: 2022 Ocean Surface Topography Science Team Meeting

Session: Science II: Large Scale Ocean Circulation Variability and Change

Presentation type: Type Forum only

An analysis of satellite altimetry shows that sea surface height (SSH) throughout large parts of the North Pacific is significantly coherent with Tropical Instability Waves (TIWs) in the 33-34 day period band (Farrar and Durland, 2021). A qualitative comparison of the coherence gain patterns with the output of a simple barotropic model suggests that much of the observed variability can be attributed to barotropic Rossby waves radiating northward from the TIWs to far reaches of the basin. The SSH variability is patchy on the scale of a few degrees, but in both the observations and in various configurations of the model, this patchiness is organized in a larger ridge-trough-ridge pattern. Based on analyses of a flat-bottom model and the early evolution of a topographic model, Farrar and Durland attributed the ridge-trough-ridge pattern to interference between the short-wave field radiating directly from the TIW region and a long-wave field generated when short waves reflect from the North American coast. This mechanism is robust in the flat-bottom model, and it appears to be important during the early evolution of the topographic model. We show here, however, that by a month or so into the evolution of the topographic model, refraction and partial trapping by bottom topography tends to reduce the amount of wave energy reaching the coast and hence the wave interference due to coastal reflection. Given the annual cycle of the TIWs, the coastal reflection is probably important for brief fractions of the TIW life cycle, but the topographic effects probably play the dominant role in determining the SSH patterns.

Ted Durland
Oregon State University
United States