Observed seasonal and interannual variability of the near-surface thermal structure of the Arabian Sea Warm Pool |
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| Affiliation: | 1. International CLIVAR Monsoon Project Office, Indian Institute of Tropical Meteorology, Pune 411 008, India;2. Department of Meteorology and Oceanography, Andhra University, Visakhapatnam 530 003, India;1. Department of Mathematics, University of Wisconsin-Madison, Madison, WI 53706, USA;2. Department of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison, Madison, WI 53706, USA;3. Department of Mathematics and Center for Atmosphere Ocean Science, Courant Institute of Mathematical Sciences, New York University, New York, NY 10012, USA;1. Climate Dynamics Research Center (CDRC) of the College of Atmospheric Sciences/Key Laboratory of Meteorological Disaster of the Ministry of Education (ELME)/Joint International Research Laboratory of Climate and Environment Change (ILCEC)/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC-FEMD), Nanjing University of Information Science & Technology, 219 Ningliu Road, Nanjing, 210044, China;2. Hubei Province Public Meteorological Service Center, Wuhan, 430074, China;1. Center for Ocean-Atmospheric Prediction Studies, Florida State University, Tallahassee, FL, USA;2. Department of Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee, FL, USA;3. Florida Climate Institute, Florida State University, Tallahassee, FL, USA;4. CIRES, University of Colorado, Boulder, CO, USA;5. Earth System Research Laboratory, NOAA, Boulder, CO, USA;1. USEPA National Health and Environmental Effects Research Laboratory, Gulf Ecology Division, 1 Sabine Island Drive, Gulf Breeze, FL 32561, United States;2. University of South Alabama, Dauphin Island Sea Lab, Dauphin Island, AL 36528, United States;3. CSRA Inc., supporting the USEPA, Research Triangle Park, NC 27709, United States |
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| Abstract: | The observed seasonal and interannual variability of near-surface thermal structure of the Arabian Sea Warm Pool (ASWP) is examined utilizing a reanalysis data set for the period 1990–2008. During a year, the ASWP progressively builds from February, reaches its peak by May only in the topmost 60 m water column. The ASWP Index showed a strong seasonal cycle with distinct interannual signatures. The years with higher (lower) sea surface temperature (SST) and larger (smaller) spatial extent are termed as strong (weak) ASWP years. The differences in the magnitude and spatial extent of thermal structure between the strong and weak ASWP regimes are seen more prominently in the topmost 40 m water column. The heat content values with respect to 28 °C isotherm (HC28) are relatively higher (lower) during strong (weak) ASWP years. Even the secondary peak in HC28 seen during the preceding November–December showed higher (lower) magnitude during the strong ASWP (weak) years. The influence of the observed variability in the surface wind field, surface net air–sea heat flux, near-surface mixed layer thickness, sea surface height (SSH) anomaly, depth of 20 °C isotherm and barrier layer thickness is examined to explain the observed differences in the near-surface thermal structure of the ASWP between strong and weak regimes. The surface wind speed is much weaker in particular during the preceding October and February–March corresponding to the strong ASWP years when compared to those of the weak ASWP years implying its important role. Both stronger winter cooling during weak ASWP years and stronger pre-monsoon heating during strong ASWP years through the surface air–sea heat fluxes contribute to the observed sharp contrast in the magnitudes of both the regimes of the ASWP. The upwelling Rossby wave during the preceding summer monsoon, post-monsoon and winter seasons is stronger corresponding to the weak ASWP regime when compared to the strong ASWP regime resulting in greater cooling of the near-surface layers during the summer monsoon season of the preceding year. On the other hand, the downwelling Rossby wave is stronger during pre-monsoon months during the strong ASWP regime when compared to weak ASWP regime leading to lesser cooling during strong ASWP regime. |
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