An anomalous cooling event observed in the Bay of Bengal during June 2009

Abstract

Sea surface temperature (SST) variability over the Bay of Bengal (BoB) has the potential to trigger deep moist convection thereby affecting the active-break cycle of the monsoons. Normally, during the summer monsoon season, SST over the BoB is observed to be greater than 28°C which is a pre-requisite for convection. During June 2009, satellite observations revealed an anomalous basin-wide cooling and the month is noted for reduced rainfall over the Indian subcontinent. In this study, we analyze the likely mechanisms of this cooling event using both satellite and moored buoy observations. Observations showed deepened mixed layer, stronger surface currents, and enhanced heat loss at the surface in the BoB. Mixed layer heat balance analysis is carried out to resolve the relative importance of various processes involved. We show that the cooling event is primarily induced by the heat losses at the surface resulting from the strong wind anomalies, and advection and vertical entrainment playing secondary roles.

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Acknowledgment

Authors thank S. Siva Reddy and M. S. Girishkumar of INCOIS for useful discussions and valuable suggestions. The QuikSCAT winds and TMI SST are downloaded from http://apdrc.soest.hawaii.edu. The RAMA data is obtained from http://www.pmel.noaa.gov/tao/data_deliv/deliv.html. GODAS products are used from INCOIS LAS (http://las.incois.gov.in). Argo is a pilot program of the Global Ocean Observing System. Argo floats data were collected and made freely available by the International Argo Project and the national programs that contribute to it (http://www.argo.ucsd.edu, http://argo.jcommops.org). The altimeter products are produced by SSALTO/DUACS and distributed by AVISO. The comments and suggestions of two anonymous reviewers greatly improved the manuscript. Graphics are generated using Ferret. This is INCOIS contribution no. 90.

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Correspondence to Muthalagu Ravichandran.

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Chacko, N., Ravichandran, M., Rao, R.R. et al. An anomalous cooling event observed in the Bay of Bengal during June 2009. Ocean Dynamics 62, 671–681 (2012). https://doi.org/10.1007/s10236-012-0525-9

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Keywords

  • Bay of Bengal
  • Sea surface temperature
  • Mixed layer heat budget
  • Ocean–atmosphere interaction