Estimation of oceanic subsurface mixing under a severe cyclonic storm using a coupled atmosphere–ocean–wave model
A coupled atmosphere–ocean–wave model was used to examine mixing in the upper-oceanic layers under the influence of a very severe cyclonic storm Phailin over the Bay of Bengal (BoB) during 10–14 October 2013. The coupled model was found to improve the sea surface temperature over the uncoupled m...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-04-01
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| Series: | Ocean Science |
| Online Access: | https://www.ocean-sci.net/14/259/2018/os-14-259-2018.pdf |
| Summary: | A coupled atmosphere–ocean–wave model was used to examine
mixing in the upper-oceanic layers under the influence of a very severe
cyclonic storm Phailin over the Bay of Bengal (BoB) during 10–14 October
2013. The coupled model was found to improve the sea surface temperature over
the uncoupled model. Model simulations highlight the prominent role of
cyclone-induced near-inertial oscillations in subsurface mixing up to the
thermocline depth. The inertial mixing introduced by the cyclone played a
central role in the deepening of the thermocline and mixed layer depth by 40
and 15 m, respectively. For the first time over the BoB, a detailed analysis
of inertial oscillation kinetic energy generation, propagation, and
dissipation was carried out using an atmosphere–ocean–wave coupled model
during a cyclone. A quantitative estimate of kinetic energy in the oceanic
water column, its propagation, and its dissipation mechanisms were explained
using the coupled atmosphere–ocean–wave model. The large shear generated by
the inertial oscillations was found to overcome the stratification and
initiate mixing at the base of the mixed layer. Greater mixing was found at
the depths where the eddy kinetic diffusivity was large. The baroclinic
current, holding a larger fraction of kinetic energy than the barotropic
current, weakened rapidly after the passage of the cyclone. The shear induced
by inertial oscillations was found to decrease rapidly with increasing depth
below the thermocline. The dampening of the mixing process below the
thermocline was explained through the enhanced dissipation rate of turbulent
kinetic energy upon approaching the thermocline layer. The wave–current
interaction and nonlinear wave–wave interaction were found to affect the
process of downward mixing and cause the dissipation of inertial
oscillations. |
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| ISSN: | 1812-0784 1812-0792 |