Long-term Observations of Turbulent Measurements in the Southern Bay of Bengal

Upper ocean mixing is likely to play an important role in the sea surface temperature (SST) variability within the Bay of Bengal (BoB), closely coupled with the onset and propagation of the Indian Ocean Monsoon (IOM). Long-term measurements of turbulent kinetic energy (TKE) dissipation (ε) and fine-scale temperature variance dissipation (Χ) provide insight into the nature of mixing at the base of the thermocline. Velocity and hydrographic data from five sub-surface moorings, including two moorings equipped with fast thermistors and microstructure shear probes, are used to quantify ε and Χ and to investigate role of mixing on larger scale dynamics. These data sets were collected in the BoB as part of U.S. (Office of Naval Research and Naval Research Laboratory) sponsored programs. Observations reveal that a wide variety of upper-ocean processes contribute to and modulate turbulent mixing levels. We observe TKE dissipation rates of 10^{-7} W/kg corresponding to the relaxation of the southwest monsoon current, and 10^{-6} W/kg during the passage of energetic mesoscale eddies. Further, we observe intermittent increases in dissipation up to 10^{-5} W/kg within highly sheared, wind generated near-inertial waves. Work is ongoing to construct full time series estimates of upper ocean TKE dissipation, temperature variance dissipation and the associated turbulent heat and momentum fluxes on time scales ranging from seasonal to tidal.