Meridional Ekman Heat Transport: Estimates from Satellite Data

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  • 1 Department of Meteorology, University of Maryland, College Park, Maryland
  • | 2 Oceans and Ice Branch, Laboratory for Hydrospheric Processes, NASA/Goddard Space Flight Center, Greenbelt, Maryland
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Abstract

Analyses of satellite-derived SSM/I winds and AVHRR sea surface temperatures are used to compute weekly estimates of global meridional ocean Ekman heat transport for the 4-year period 1987–1991. The heat transport is consistently poleward throughout the year over the Atlantic and much of the Pacific between 30°S and 30°N and equatorward at higher latitudes. The zonally integrated Ekman heat transport in the Pacific was weak and equatorward at 10°N in September 1989 and 1990, whereas in other years it is poleward throughout the year. In the Indian Ocean, equatorward heat transport was strongest in Northern Hemisphere summer 1990. The weekly time series provides better temporal resolution than previous studies that at best used monthly averages. The higher-frequency variations are explored through rotated empirical orthogonal functions (REOFs) of nonseasonal heat transport anomalies. The REOFs show large-scale coherence across the tropical and subtropical Pacific and Indian Oceans. The first REOF has a strong spectral peak at periods of 50–60 days and is dominated by the variability in the Southern Hemisphere Indian Ocean. The second REOF is dominated by the variance in the Northern Hemisphere Indian Ocean and western tropical North Pacific. The fist four REOFs, which explain 22.5% of the nonseasonal variance, have spectral peaks at periods consistent with the 30–60 day atmospheric Madden–Julian oscillation. These periods were not resolved in the monthly averaged data from COADS. Singular spectrum analysis has been used as a filter to show the long timescale variations. The early phase of the 1988–89 La Niña has a strong influence on the heat transport, indicating enhanced poleward heat transport in the eastern Indian Ocean, tropical North Pacific, and tropical and subtropical South Pacific and enhanced equatorward heat transport in the midlatitude North Pacific and western tropical Indian Ocean.

Abstract

Analyses of satellite-derived SSM/I winds and AVHRR sea surface temperatures are used to compute weekly estimates of global meridional ocean Ekman heat transport for the 4-year period 1987–1991. The heat transport is consistently poleward throughout the year over the Atlantic and much of the Pacific between 30°S and 30°N and equatorward at higher latitudes. The zonally integrated Ekman heat transport in the Pacific was weak and equatorward at 10°N in September 1989 and 1990, whereas in other years it is poleward throughout the year. In the Indian Ocean, equatorward heat transport was strongest in Northern Hemisphere summer 1990. The weekly time series provides better temporal resolution than previous studies that at best used monthly averages. The higher-frequency variations are explored through rotated empirical orthogonal functions (REOFs) of nonseasonal heat transport anomalies. The REOFs show large-scale coherence across the tropical and subtropical Pacific and Indian Oceans. The first REOF has a strong spectral peak at periods of 50–60 days and is dominated by the variability in the Southern Hemisphere Indian Ocean. The second REOF is dominated by the variance in the Northern Hemisphere Indian Ocean and western tropical North Pacific. The fist four REOFs, which explain 22.5% of the nonseasonal variance, have spectral peaks at periods consistent with the 30–60 day atmospheric Madden–Julian oscillation. These periods were not resolved in the monthly averaged data from COADS. Singular spectrum analysis has been used as a filter to show the long timescale variations. The early phase of the 1988–89 La Niña has a strong influence on the heat transport, indicating enhanced poleward heat transport in the eastern Indian Ocean, tropical North Pacific, and tropical and subtropical South Pacific and enhanced equatorward heat transport in the midlatitude North Pacific and western tropical Indian Ocean.

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