Changes in intensity of the regional Hadley cell in Indian Ocean and its impacts on surrounding regions

The impacts of changes in the intensity of the regional Hadley Cell (HC) in the Indian Ocean (HCIO) on its surrounding regions are investigated during the period 1979-2013. A strengthening of the HCIO and the Indian monsoon (IM) is found during austral winter (JJA) and spring (SON) seasons. This is associated with the sea surface temperature (SST) anomalies in the Pacific and Indian Ocean. A La Nia signal started to form in JJA over the equatorial Pacific region, and in SON, it was completely developed. Significant positive SST anomalies are seen over the western Pacific and western Indian Ocean around 10A degrees S in JJA, associated with positive temperature anomalies in the south of China, in the north of the Maritime Continent, and in the southeastern coast of Africa. In SON, they are observed over the western Pacific and eastern Indian Ocean around the equator, associated with positive temperature anomalies observed on a great part of the Maritime Continent and southeastern Atlantic Ocean. Positive rainfall anomalies are seen mainly over the south of India, south of China, Maritime Continent, and eastern coast of Australia. In SON, the connection monsoon-ENSO-Hadley is stronger, because of a series of positive feedbacks that reinforce the initial connection. SST gradients explain much of the variability in the intensity of the HCIO and, especially, of the IM. However, other factors also seem to come into play in determining the changes of the HCIO intensity, whereas the SST changes have a dominant influence on the IM.