Seasonal Mixed Layer Heat Balance of the Southwestern Tropical Indian Ocean

Type Article
Date 2010-02
Language English
Author(s) Foltz Gregory R.1, Vialard Jerome2, Kumar B. Praveen4, McPhaden Michael J.3
Affiliation(s) 1 : Univ Washington, Joint Inst Study Atmosphere & Oceans, Seattle, WA 98195 USA.
2 : IRD, Lab Oceanog Experimentat & Approches Numer, Paris, France.
3 : NOAA, Pacific Marine Environm Lab, Seattle, WA 98115 USA.
4 : Natl Inst Oceanog, Phys Oceanog Div, Panaji, Goa, India.
Source Journal Of Climate (0894-8755) (Amer Meteorological Soc), 2010-02 , Vol. 23 , N. 4 , P. 947-965
DOI 10.1175/2009JCLI3268.1
WOS© Times Cited 48
Keyword(s) sea surface temperature, pacific ocean, equatorial pacific, interannual variability, bulk parameterization, rainfall variability, atlantic ocean, north pacific, el nino
Abstract Sea surface temperature (SST) in the southwestern tropical Indian Ocean exerts a significant influence on global climate through its influence on the Indian summer monsoon and Northern Hemisphere atmospheric circulation. In this study, measurements from a long-term moored buoy are used in conjunction with satellite, in situ, and atmospheric reanalysis datasets to analyze the seasonal mixed layer heat balance in the thermocline ridge region of the southwestern tropical Indian Ocean. This region is characterized by a shallow mean thermocline (90 m, as measured by the 20 degrees C isotherm) and pronounced seasonal cycles of Ekman pumping and SST (seasonal ranges of -0.1 to 0.6 m day(-1) and 26 degrees-29.5 degrees C, respectively). It is found that surface heat fluxes and horizontal heat advection contribute significantly to the seasonal cycle of mixed layer heat storage. The net surface heat flux tends to warm the mixed layer throughout the year and is strongest during boreal fall and winter, when surface shortwave radiation is highest and latent heat loss is weakest. Horizontal heat advection provides warming during boreal summer and fall, when southwestward surface currents and horizontal SST gradients are strongest, and is close to zero during the remainder of the year. Vertical turbulent mixing, estimated as a residual in the heat balance, also undergoes a significant seasonal cycle. Cooling from this term is strongest in boreal summer, when surface wind and buoyancy forcing are strongest, the thermocline ridge is shallow (<90 m), and the mixed layer is deepening. These empirical results provide a framework for addressing intraseasonal and interannual climate variations, which are dynamically linked to the seasonal cycle, in the southwestern tropical Indian Ocean. They also provide a quantitative basis for assessing the accuracy of numerical ocean model simulations in the region.
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