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Generation of Submesoscale Temperature Inversions Below Salinity Fronts in the Bay of Bengal
Author(s) -
Ramachandran Sanjiv,
Tandon Amit
Publication year - 2020
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2020jc016278
Subject(s) - geology , potential vorticity , anticyclone , temperature salinity diagrams , subduction , potential temperature , vorticity , mixed layer , thermal wind , frontogenesis , baroclinity , slab , climatology , geophysics , mesoscale meteorology , mechanics , salinity , seismology , oceanography , tectonics , physics , wind speed , vortex , wind shear
This study uses submesoscale‐permitting simulations to explore the formation of temperature inversions at shallow, salinity‐controlled density fronts representative of conditions in the wintertime Bay of Bengal (BoB). Our simulations complement earlier one‐dimensional studies that have largely used mooring records in the BoB to infer mechanisms for causing temperature inversions, by exploring three‐dimensional frontal processes. We use three different initial conditions with the same lateral and vertical gradients in density, with differing lateral contrasts in temperature within the mixed layer. Our simulations evolve unforced for a few inertial periods, are then forced by weak downfront winds for a few more inertial periods to generate an eddy field, after which the winds are turned off. The formation of inversions proceeds via the subduction of low potential vorticity (PV) fluid from the surface during the forced phase. The inversions result from tilting of horizontal temperature gradients into the vertical direction. Tilting is simultaneously the dominant source of negative vertical vorticity in the Lagrangian vorticity budget. Turning off the winds caps the subducted fluid by overlying stratified fluid, creating temperature inversions with O(1–10 km) lateral scales and O(10 m) thickness. The inversions are pycnostads with anticyclonic rotation. The increase in temperature for the strongest inversion in each simulation is comparable to the initial lateral contrast in temperature. The strongest inversions are associated with anticyclonic rotation and low PV. Our results have potential implications for the vertical thermal structure of the upper BoB in coarse‐resolution models that do not resolve subduction at submesoscale fronts.