The Impacts of Ocean-Atmosphere Coupling Near Ocean Mesoscale Fronts

Abstract

Understanding the interaction between the atmosphere and ocean is crucial to modeling or predicting the dynamics of both systems. Observational studies and numerical simulations of atmospheric responses to ocean mesoscale fronts have found strong correlation between the sea surface temperature (SST) and near surface wind speeds, which is interpreted as the SST driving the atmosphere at these scales. Furthermore, correlations studies have shown that SST fronts are capable of modifying surface turbulent heat and momentum fluxes which can affect winds, clouds and rainfall, as well as have larger scale effects on storm tracks. These larger scale effects have been observed to feed back onto the ocean and further evolve the SST fronts, thus making the need to understand the fully coupled atmosphere-ocean system more significant.

This thesis uses idealized large eddy simulations to investigate the evolution of a coupled atmosphere-ocean model initialized with a filament-like warm SST anomaly in the presence of weak 3 m s⁻¹ winds blowing across the front, as well as no winds, over a period of 24 hours. Uncoupled systems are considered, holding the ocean constant in time for the atmosphere and vice versa, following an analysis of the simulations coupled together to compare. Large scale structures of the potential temperature and zonal velocity are considered alongside the mean and turbulent kinetic energy. To assist in the understanding of dominant factors of both systems a momentum budget and turbulent kinetic energy budget will be analyzed term by term. The coupling is found to have a small impact on the atmosphere over the short time scale, mainly affecting the turbulent kinetic energy strength and distribution, while having a significant impact on the ocean, causing large scale flow changes as well as altering the turbulent kinetic energy distribution.