Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 479-509, doi:10.1175/JPO-D-16-0283.1.
Lateral submesoscale processes and their influence on vertical stratification at shallow salinity fronts in the central Bay of Bengal during the winter monsoon are explored using high-resolution data from a cruise in November 2013. The observations are from a radiator survey centered at a salinity-controlled density front, embedded in a zone of moderate mesoscale strain (0.15 times the Coriolis parameter) and forced by winds with a downfront orientation. Below a thin mixed layer, often ≤10 m, the analysis shows several dynamical signatures indicative of submesoscale processes: (i) negative Ertel potential vorticity (PV); (ii) low-PV anomalies with O(1–10) km lateral extent, where the vorticity estimated on isopycnals and the isopycnal thickness are tightly coupled, varying in lockstep to yield low PV; (iii) flow conditions susceptible to forced symmetric instability (FSI) or bearing the imprint of earlier FSI events; (iv) negative lateral gradients in the absolute momentum field (inertial instability); and (v) strong contribution from differential sheared advection at O(1) km scales to the growth rate of the depth-averaged stratification. The findings here show one-dimensional vertical processes alone cannot explain the vertical stratification and its lateral variability over O(1–10) km scales at the radiator survey.
S. Ramachandran acknowledges support from the National Science Foundation
through award OCE 1558849 and the U.S. Office of
Naval Research, Grants N00014-13-1-0456 and N00014-17-
1-2355. A. Tandon acknowledges support from the U.S.
Office of Naval Research, Grants N00014-13-1-0456 and
N00014-17-1-2355. J. T. Farrar and R. A. Weller were
supported by the U.S. Office of Naval Research, Grant
N00014-13-1-0453, to collect the UCTD data and process
theUCTD and shipboard meteorological data. J. Nash, J. Mackinnon, and A. F. Waterhouse
acknowledge support from the U. S. Office of Naval Research,
Grants N00014-13-1-0503 and N00014-14-1-0455.
E. Shroyer acknowledges support from the U. S. Office of
Naval Research, Grants N00014-14-10236 and N00014-15-
12634. A. Mahadevan acknowledges support fromthe U. S.
Office of Naval Research, Grant N00014-13-10451.
A. J. Lucas and R. Pinkel acknowledge support from the
U. S. Office of Naval Research, Grant N00014-13-1-0489.
Oceanic mixed layer
Woods Hole Open Access Server