Thursday, March 23, 2017

Sea level in Indian Ocean shows abrupt rise, new study says

A CPO-funded study was recently published in the Journal of Geophysical Research. The paper includes data showing sea level rise in the northern Indian Ocean rose twice as fast as the global average since 2003, contrasting starkly with rates of rise in the previous decade.

A team of researchers from the University of Hawai’i Sea Level Center studied two and a half decades of ocean surface height using satellite data. In addition, researchers used computer models to study the cause of the abrupt increase in sea level trends in the region.

The Indian Ocean is home to areas particularly vulnerable to sea level rise, including parts of Bangladesh and Jakarta, a press release form the University of Hawai’i Sea Level Center states.

The colors in this image show trends in ocean height over the equatorial and northern Indian Ocean during 2004-2014. Darker reds indicate a faster rate of rise. The red line in the inset shows the average ocean height in this region since 1994 when satellites began measuring the height of the ocean surface. Courtesy Thompson et al.


Recent decadal sea surface height (SSH) variability across the Equatorial and North Indian Ocean (ENIO, north of 5°S) is spatially coherent and related to a reversal in basin-scale, upper-ocean-temperature trends. Analysis of ocean and forcing fields from a data-assimilating ocean synthesis (ECCOv4) suggests that two equally important mechanisms of wind-driven heat redistribution within the Indian Ocean account for a majority of the decadal variability. The first is the Cross-Equatorial Cell (CEC) forced by zonal wind stress curl at the equator. The wind stress curl variability relates to the strength and position of the Mascarene High, which is influenced by the phase of the Indian Ocean Subtropical Dipole. The second mechanism is deep (700 m) upwelling related to zonal wind stress at the equator that causes deep, cross-equatorial overturning due to the unique geometry of the basin. The CEC acts to cool the upper ocean throughout most of the first decade of satellite altimetry, while the deep upwelling delays and then amplifies the effect of the CEC on SSH. During the subsequent decade, reversals in the forcing anomalies drive warming of the upper ocean and increasing SSH, with the effect of the deep upwelling leading the CEC.

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