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Interannual Sea Level in the Northern and Eastern Indian Ocean

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  • 1 Oceanography Department, The Florida State University, Tallahassee, Florida
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Abstract

Monthly Indian and Pakistani sea level records, adjusted for the effect of atmospheric pressure, were used to examine interannual sea level variability in the northern Indian Ocean. The interannual sea level is correlated along the boundary. The observations hint that interannual sea level propagates along the boundary, but the evidence is not conclusive. Calculations with the Comprehensive Ocean-Atmosphere Data Set wind stress as input to a simple model suggest that the interannual sea level signal occurs along more than 8000 km of Indian Ocean coastline extending from southern Java to Bombay and is generated remotely by zonal interannual winds blowing along the equator.

The eastern Indian Ocean boundary is broken between Indonesia and Australia and examination of north- western Australian interannual sea level shows that it is not well correlated with that in the northern Indian Ocean. The northwestern Australian sea level is larger in amplitude, related to ENSO, and of Pacific origin. Calculations using a simple model and The Florida State University wind stress suggest that the northwestern Australian sea level is generated by zonal ENSO wind stress in the equatorial Pacific. A weighted difference between the northern Indian Ocean and southeastern Indian Ocean sea levels provides a revised estimate of the interannual upper-ocean transport of water between the two oceans. The average amplitude of this interannual transport is about 2.5 Sv (Sv≡106 M3 s−1), which is smaller than estimates of 5–16 Sv for the mean transport. The interannual transport is correlated with ENSO, there being a tendency for flow from the Indian Ocean and into the Pacific during a warm ENSO event. The flow tends to reverse during a cold ENSO event.

Abstract

Monthly Indian and Pakistani sea level records, adjusted for the effect of atmospheric pressure, were used to examine interannual sea level variability in the northern Indian Ocean. The interannual sea level is correlated along the boundary. The observations hint that interannual sea level propagates along the boundary, but the evidence is not conclusive. Calculations with the Comprehensive Ocean-Atmosphere Data Set wind stress as input to a simple model suggest that the interannual sea level signal occurs along more than 8000 km of Indian Ocean coastline extending from southern Java to Bombay and is generated remotely by zonal interannual winds blowing along the equator.

The eastern Indian Ocean boundary is broken between Indonesia and Australia and examination of north- western Australian interannual sea level shows that it is not well correlated with that in the northern Indian Ocean. The northwestern Australian sea level is larger in amplitude, related to ENSO, and of Pacific origin. Calculations using a simple model and The Florida State University wind stress suggest that the northwestern Australian sea level is generated by zonal ENSO wind stress in the equatorial Pacific. A weighted difference between the northern Indian Ocean and southeastern Indian Ocean sea levels provides a revised estimate of the interannual upper-ocean transport of water between the two oceans. The average amplitude of this interannual transport is about 2.5 Sv (Sv≡106 M3 s−1), which is smaller than estimates of 5–16 Sv for the mean transport. The interannual transport is correlated with ENSO, there being a tendency for flow from the Indian Ocean and into the Pacific during a warm ENSO event. The flow tends to reverse during a cold ENSO event.

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