Arabian Sea upper ocean stratification and dynamics from broad-scale temperature/salinity profiling
Abstract
The proposed work is analysis of (a) large-scale, time-dependent dynamical controls on the circulation including the Somali Current, and (b) relation of regional/time-dependent diapycnal mixing and the destabilizing salinity stratification to upper ocean stratification and seasonal SST/SSS in the Arabian Sea. Profiling float and glider T/S profiles will be utilized, and can be augmented with oxygen profiles where available. While analysis here can be stand-alone, collaboration with NASCar modeling and in situ microstructure will enhance the impact and usability of the results. (a) The western Indian Ocean tropics, with strongly ?-dominated zonal PV distribution, are dynamically separated from the northern Arabian Sea with its more homogenized PV distribution (McCarthy and Talley, 1999). It is hypothesized here that this must impact Rossby wave propagation and spinup of the Somali Current, and the reversing monsoon currents in the tropics and northern Arabian Sea. Novelty: connection of well-known dynamical regimes with PV distribution, which may provide new physical understanding of Somali Current seasonality. Method: PV/T/S/velocity, and oxygen where available, will be mapped from basin-wide profiling floats, surface drifters, altimetry, including data assimilation, permitting analysis of the propagation of planetary waves relative to the mapped underlying PV structure. Close collaboration with NASCar modeling is expected. (b) Vertical mixing of heat, salt, and momentum, central to upper ocean stratification, are affected by diapycnal diffusivity ?, which can be estimated from T/S finestructure. ? just below the mixed layer has been shown recently to be related to wind strength, tides/bottom roughness, eddy kinetic energy, and latitude. In the Arabian Sea, ? is higher in the west (boundary currents) and in the tropics, and is very low in the east. Because ? has a large range in the Arabian Sea, mechanisms that result in this range can be evaluated. An additional factor in vertical mixing in the A.S. is the destabilizing salinity stratification, which affects mixing, air-sea heat and freshwater fluxes, and SST gradient; the associated air-sea heat and freshwater fluxes affect the monsoon winds. A.S. stratification is subject to both double diffusion (warm salty over cold fresh) and barrier layers (warm fresh over warm salty), depending on region and season. Unaligned salinity/temperature fronts can create localized subduction. Novelty: relate A.S. diapycnal diffusivity variability and salinity stratification to monsoonal winds, seasonal stratification, Somali Current variability (Great Whirl, Socotra Gyre, etc) and Rossby wave activity, bottom roughness/tides, latitude. Double diffusive processes will also be evaluated. Method: calculate finestructure diffusivity below the mixed layer as a function of time and space, and relative to salinity stratification, and compare with in situ microstructure measurements, both to provide improved distribution for modeling. Close collaboration with NASCar microstructure observations and modelers is expected.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 12, 2016
- Source ID
- N000141512566
Entities
People
- Lynne Talley
Organizations
- Office of Naval Research
- United States Navy
- University of California, San Diego