RP0225 – Moisture trend over the Arabian Sea and its influence on the Indian summer monsoon rainfall

Division ODA - Ocean modeling and Data Assimilation


  • Satyaban Bishoyi Ratna
  • Annalisa Cherchi
  • P V Joseph
  • Swadhin Behera
  • B Abish
  • Simona Masina
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Indo-Pacific Ocean has been experiencing a basin wide warming since the 1950s but the large-scale summer monsoon rainfall over India is decreasing. At the same time the moisture over the Arabian Sea is also decreasing. In this study we intend to investigate how the decrease of moisture over the Arabian Sea is related with the Indo-Pacific Ocean warming and how this could affect the variability of the Indian summer monsoon rainfall. We performed the analysis for the period 1951-2012 based on the observed precipitation, sea surface temperature and atmospheric reanalysis products. The decreasing trend of the moisture over the Arabian Sea coincides with an increasing trend of moisture over the western Pacific region. This is accompanied by the strengthening (weakening) of the upward motion over the western Pacific (Arabian Sea/East Africa) that, consequently, contributes in strengthening the western Pacific-Indian Ocean Walker circulation. Associated with it, the low-level westerlies are weakening over the peninsular India, thus contributing to the reduction of moisture transport towards India. Therefore, rainfall has decreased over the Western Ghats and central-east India. In the very last decade of the analyzed time-series, moisture over the Arabian Sea started to increase accompanied by strengthening of vertical motion. At the same time, the SST over the western Pacific is cooling and causing the reduction of convection that in turn weakens the vertical motion compared to the decades before.

  • Keywords: Indian summer monsoon, Indo-Pacific ocean warming, Arabian Sea, low-level moisture, climate trends

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