Scripps Institution of Oceanography

This dissertation studies mesoscale ocean-atmosphere interaction using the newly developed Scripps Coupled Ocean-Atmosphere Regional (SCOAR) model. The overall goal of this study is to understand the physical processes that lie behind mesoscale ocean-atmosphere interactions and their connection with the basin-scale climate variability.

SCOAR allows air-sea feedbacks arising from the oceanic mesoscale features. The model is tested in three scenarios in the eastern Pacific Ocean sector: tropical instability waves (TIWs) of the eastern tropical Pacific; mesoscale eddies and fronts of the California Current System; and gap winds of the Central American Coast. The model reproduces aspects of the observed linear response of the atmosphere to the evolving sea surface temperatures (SST). This results in significant anomalies of wind stress curl/divergence, surface heat flux and precipitation that resemble the observations and substantiate the importance of ocean-atmosphere feedbacks involving the oceanic mesoscale.

Extending SCOAR to the tropical Atlantic TIWs shows that air-sea coupling damps the eddy kinetic energy of the waves. TIW-induced wind stress is negatively correlated with the TIW-induced ocean surface current, and this slows down the TIW-currents.

These mesoscale oceanic and atmospheric features alter the large-scale climate variability in the tropical Atlantic. Resolving mesoscale eddies in the ocean leads a cooler equatorial cold tongue and coastal upwelling region. This results in more realistic coastal SST and precipitation. Furthermore, it is shown that synoptic-scale atmospheric African easterly waves capture stronger low-level convergence and convection, only in the higher atmospheric resolution. This triggers heavy precipitation events on the synoptic-scale, which explains a considerable fraction of the total variability. As a result, the simulation of mean rainfall in the Inter-Tropical Convergence Zone (ITCZ) and its seasonality is much improved. This suggests that capturing these transient oceanic mesoscale features and the synoptic-scale atmospheric disturbances is a key ingredient for improving the simulation of the tropical Atlantic SST and ITCZ.