ASTRaL Project Overview
Parent Project:
DRI: The Arabian Sea Transition Layer (ASTraL): Exchange across the Air-Sea Interface
Sponsor: Office of Naval Research (Physical Oceanography)
(https://www.nre.navy.mil/organization/departments/code-32/division-322/physical-oceanography/astral)
Indian Ministry of Earth Sciences Partner Project:
Enhancing Knowledge of the Arabian Sea Marine environment through Science and Advanced Training (EKAMSAT)
University of Notre Dame Project
Transition-Layer Physics of the Southeast Arabian Sea Mini Warm Pool
Technical Point of Contact:
Harindra Joseph Fernando
Wayne and Diana Murdy Endowed Professor, Departments of Civil and Environmental Engineering and Earth Sciences, and Aerospace and Mechanical Engineering
University of Notre Dame, Notre Dame, IN 46556; Telephone: 574-631-9346; Facsimile: 574-631-9236; E-mail address: Fernando.10@nd.edu
Subcontracts (Option):
Peter P. Sullivan, Mesoscale and Microscale Meteorology Laboratory, National Center for Atmospheric Research (NCAR), P.O. Box 3000, Boulder, CO, 80307-3000,
email: pps@ucar.edu, phone: 303-497-8953)
NCAR Collaborator: James C. McWilliams, Department of Atmospheric and Oceanic Sciences and Institute of Geophysics and Planetary Physics, UCLA, 405 Hilgard Ave. Los Angeles, California 90095-1565, email: jcm@atmos.ucla.edu, phone: 310-206-2829)
Collaborators:
G.S. Bhat, Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore 560 012, India, bhat@caos.iisc.ernet.in
Priyantha Jinadasa, Ocean University of Sri Lanka, Crow Island, Colombo 15, Sri Lanka; priyanthaj@ocu.ac.lk; Also at National Aquatic Resources Research and Development Agency NARA, Crow Island, Colombo 15, Sri Lanka
Sue Chen (Naval Research Laboratory, Monterey, CA 93943-5502; sue.chen@nrlmry.navy.mil)
Hemantha Wijesekera and Adam Rydbeck, Naval Research Laboratory, Oceanography Division, Stennis Space Center, MS 39529; hemantha.wijesekera@nrlssc.navy.mil and adam.rydbeck@nrlssc.navy.mil
Project Summary:
Every year, during March to May, a compact region of elevated Sea Surface Temperature (SST > 30 degrees C) develops in the Southeastern Arabian Sea (SEAS). This phenomenon has strong implications on biophysical interactions and underwater acoustics in the Arabian Sea (AS) as well as initiation of boreal summer Southwest (SW) monsoons. Known as the Mini Warm Pool (MWP) because of its smaller size compared to other warm pools in the world, MWP develops over an area with solar insolation comparable to the rest of the AS, which suggests that a myriad of interacting multiscale atmospheric and oceanic processes are responsible for the anomalous surface heating leading to MWP. This proposal seeks support to conduct research on dynamical process underpinning the lifecycle (genesis, maturation, and dissolution) of MWP by participating in the ONR-ASTraL research initiative. The origins of MWP can be traced to the collapse of summer SW monsoons of the yesteryear, during which oceanic planetary [Kelvin] waves are generated in the Bay of Bengal. These waves together with low saline water arriving in SEAS during the winter Northeast monsoons produce a large anticyclonic eddy in SEAS, signifying a downwelling Rossby wave. This feature, known as the Lakshadweep high (LH), is the hub of MWP. Accompanying and evolving physical processes therein are numerous: the formation of a thicker and warmer barrier layer topped by a thin low-salinity colder surface layer separated by a pycnocline, air-sea interactions regulated by boundary layers above and below the ocean surface [together known as the transition layer], development of a low-level westerly jet and its instabilities, and development of deep convection in SEAS.
The proposed research is centered on the role of transition layer in the lifecycle of MWP. Four guiding hypotheses are proposed, concerning (i) the development of MWP during the evolution of air-sea fluxes in the transition layer due to evolving large-scale environmental forcing and micro-scale response thereof, (ii) warming of the thin upper mixed layer of LH via entrainment at the pycnocline, temperature inversions and lateral processes, (iii) generation of the SW monsoon onset vortex as a result of instabilities of the low-level westerly jet and amplification of resulting cyclonic vortex via enhanced turbulence and fluxes ensuing from deep convection and breakdown of instabilities, and (iv) rapid dissolution of MWP with the SW monsoon onset due a combination of intense upper ocean turbulence, development of mesoscale structures and migrating planetary waves (e.g., westward migration of LH). The four hypotheses will be tested, and relevant research questions will be addressed by participation in all ASTraL field campaigns wherein an extensive suite of atmospheric and oceanic instruments will be deployed by University of Notre Dame group. Meso- and micro-scale processes active in MWP will be further investigated using a novel large eddy simulation (LES) approach by the PI from the National Center for Atmospheric Research, whose focus will be on the impact of ocean heterogeneity on transition layer. Collaboration with southeast Asian nations (India, Sri Lanka, Maldives), Naval Research Laboratories (Monterey and Stennis) and other ASTraL PIs will be sought, building upon existing partnerships.