Interannual variability in sea surface height at southern mid-latitudes of the Indian Ocean

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  • 1 Japan Agency for Marine-Earth Science and Technology, Yokosuka, Kanagawa, Japan
  • 2 National Oceanic and Atmospheric Administration/Pacific Marine Environmental Laboratory, Seattle, Washington, USA
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Abstract

This study examines interannual variability in sea surface height (SSH) at southern midlatitudes of the Indian Ocean (10°-35°S). Our focus is on the relative role of local wind forcing and remote forcing from the equatorial Pacific Ocean. We use satellite altimetry measurements, an atmospheric reanalysis and a one-dimensional wave model tuned to simulate observed SSH anomalies. The model solution is decomposed into the part driven by local winds and that driven by SSH variability radiated from the western coast of Australia. Results show that variability radiated from the Australian coast is larger in amplitude than variability driven by local winds in the central and eastern parts of the south Indian Ocean at mid latitudes (between 19° and 33°S), whereas the influence from eastern boundary forcing is confined to the eastern basin at lower latitudes (10° and 17°S). The relative importance of coastally forced variability at mid latitudes is due to the weakness of wind stress curl anomalies in the south Indian Ocean. Our analysis further suggests that SSH variability along the west coast of Australia originates from remote wind forcing in the tropical Pacific, as is pointed out by previous studies. The zonal gradient of SSH between the western and eastern parts of the south Indian Ocean is also mostly controlled by variability radiated from the Australian coast, indicating that interannual variability in meridional geostrophic transport is driven principally by Pacific winds.

Corresponding author: Motoki Nagura (nagura@jamstec.go.jp)

Abstract

This study examines interannual variability in sea surface height (SSH) at southern midlatitudes of the Indian Ocean (10°-35°S). Our focus is on the relative role of local wind forcing and remote forcing from the equatorial Pacific Ocean. We use satellite altimetry measurements, an atmospheric reanalysis and a one-dimensional wave model tuned to simulate observed SSH anomalies. The model solution is decomposed into the part driven by local winds and that driven by SSH variability radiated from the western coast of Australia. Results show that variability radiated from the Australian coast is larger in amplitude than variability driven by local winds in the central and eastern parts of the south Indian Ocean at mid latitudes (between 19° and 33°S), whereas the influence from eastern boundary forcing is confined to the eastern basin at lower latitudes (10° and 17°S). The relative importance of coastally forced variability at mid latitudes is due to the weakness of wind stress curl anomalies in the south Indian Ocean. Our analysis further suggests that SSH variability along the west coast of Australia originates from remote wind forcing in the tropical Pacific, as is pointed out by previous studies. The zonal gradient of SSH between the western and eastern parts of the south Indian Ocean is also mostly controlled by variability radiated from the Australian coast, indicating that interannual variability in meridional geostrophic transport is driven principally by Pacific winds.

Corresponding author: Motoki Nagura (nagura@jamstec.go.jp)
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