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Shear Flow Instabilities and Unstable Events Over the North Bay of Bengal
Author(s) -
Jampana Venkata,
Ravichandran M.,
Sengupta Debasis,
D'Asaro E. A.,
Rahaman Hasibur,
Joseph Sudheer,
Sreelekha J.,
Chaudhuri Dipanjan
Publication year - 2018
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2017jc013272
Subject(s) - buoyancy , bay , richardson number , shear (geology) , wind shear , neutral buoyancy , instability , geology , monsoon , context (archaeology) , climatology , shear flow , atmospheric sciences , meteorology , oceanography , mechanics , physics , wind speed , petrology , paleontology
A year‐long mooring data are used to study the upper ocean unstable events and instabilities at 18°N 89°E, which is a climatologically important region in the North Bay of Bengal. Near‐surface stability is studied from the context of the buoyancy frequency normalized shear ( V z / N ) and reduced shear ( S 2 −4 N 2 ) which are convenient measures to quantify flow stability, compared to the more widely used Richardson number ( R i ). The analysis is carried out across three contrasting time periods, the monsoon, postmonsoon, and the winter of year 2012. Although it is well known that the flow stability changes from stable to unstable at R i = R i c r =0.25, the relative importance of the perturbations of shear and buoyancy frequency in driving the unstable events is not well studied over the open oceans and more particularly over the Bay of Bengal. At 18°N, 89°E both higher than average shear and lower than average buoyancy frequency perturbations are crucial in driving the unstable events during the summer and premonsoon period. However, at increasing depths, the influence of shear perturbations becomes more dominant. Invoking the Miles‐Howard criteria for flow instability, it is seen that during the postmonsoon period, the buoyancy frequency perturbations are more critical than shear perturbations in driving the unstable events. In winter, the unstable events are influenced by both the buoyancy frequency and shear perturbations.