Influence of Mesoscale and Submesoscale Eddy Structures on the Arabian Sea Mixed Layer Dynamics
Abstract
"During the summer monsoon season from June through September, a strong low-level southwesterly jet forms over the western Arabian Sea, inducing surface turbulence that amplifies the strength of the local eddy field. Though generation mechanism of these eddies is primarilywind-driven (directly through surface turbulence and indirectly through coastal upwelling, which causes the eddy field to strengthen to re-establish stratification), it experiences secondary influence of variability due to Rossby waves and local barotropic instabilities. These eddies transport seawater properties and drive local upwelling (for cyclonic eddies) and downwelling (for anticyclonic eddies). As a result, mesoscale eddies have a distinct sea surface temperature (SST) and sea surface salinity (SSS) footprint characterized by local extremes. A multitude of techniques have been applied to create an algorithm to monitor the development, propagation, characteristics, and dissipation of mesoscale eddies in the Arabian Sea. Due to the availability of satellite-derived altimetric observations from 1993 to present and the well-studied relationship between sea surface height (SSH) anomalies and geostrophic currents, the staunch majority of global eddy tracking algorithms have exclusively utilized gridded SSH fields.However, a more complete analysis requires consideration of other parameters such as SST and sea surface salinity (SSS), which also influence eddy circulation and its influence on local biodiversity. Mesoscale and submesoscale features such as upper-level eddies and fronts directly alter the local mixed layer depths via current-induced upwelling/ downwelling and also through lateral temperature and salinity advection. While mixed layer dynamics in the Arabian Sea also respond strongly to seasonal air-sea fluxes, quantification of mesoscale and submesoscale eddies (Great Whirl and the Socotra Eddy) to the mixed layer variability is currently insufficient. Basin-scale higher significant wave heights and evaporation rates deepen the mixed layer that is locally amplified due to mesoscale eddies|. The objectives of the proposed research are: Developing an eddy-tracking algorithm using multi-parameters (SSH, SST, SSS) to examine mesoscale and submesoscale eddy characteristics in the Arabian Sea. Understanding the influence of mesoscale and submesoscale eddy structures on the Arabian Sea mixed layer variability. High-resolution HYbrid Coordinate Ocean Model (HYCOM) simulations will be used to observe, identify, track, and quantify the features of interest. Temperature and salinity fronts will be identified using a gradient-based approach, while mesoscale and submesoscale eddies will be identified using a closed-contour eddy tracking algorithm that has been proven to detect fewer false eddies than other commonly-used eddy tracking algorithms. HYCOM simulations are available atdaily intervals with 1/12th degree resolution from 1993 to present, which provides appropriate spatial and temporal sampling for the proposed research. To compare atmospheric forcings on mixed layer deepening, fluxes are obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim daily products, of lower biases and better hydrological cycle dynamics."
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 31, 2020
- Source ID
- N000142012742
Entities
People
- Bulusu Subrahmanyam
Organizations
- Office of Naval Research
- United States Navy
- University of South Carolina