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The influence of Tropical Indian Ocean SST on the Indian summer monsoon
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Abstract
The Indian Summer Monsoon (ISM) is one of the main components of
the Asian summer monsoon. It is well known that one of the starting mechanisms
of a summer monsoon is the thermal contrast between land and ocean
and that sea surface temperature (SST) and moisture are crucial factors for its
evolution and intensity. The Indian Ocean, therefore, may play a very important
role in the generation and evolution of the ISM itself. A coupled general
circulation model, implemented with a high resolution atmospheric component,
appears to be able to simulate the Indian summer monsoon in a realistic
way. In particular, the features of the simulated ISM variability are similar to
the observations.
In this study, the relationships between ISM and Tropical Indian Ocean
(TIO) SST anomalies are investigated, as well as the ability of the coupled
model to capture those connections. The recent discovery of the Indian Ocean
Dipole Mode (IODM) may suggest new perspectives in the relationship between
ISM and TIO SST. A new statistical technique, the Coupled Manifold,
is used to investigate the TIO SST variability and its relation with the Tropical
Pacific Ocean (TPO). The analysis shows that the SST variability in the TIO
contains a significant portion that is independent from the TPO variability.
The same technique is used to estimate the amount of Indian rainfall variability
that can be explained by the Tropical Indian Ocean SST. Indian Ocean
SST anomalies are separated in a part remotely forced from the Tropical Pacific
Ocean variability and a part independent from that. The relationships
between the two SSTA components and the Indian monsoon variability are
then investigated in detail