Links between tropical SST anomalies and precursory signalsassociated with the interannual variability of Asian summer monsoon |
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| Authors: | Biju Thomas S V Kasture V Satyan |
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| Institution: | (1) CNRM/GMME (Meteo-France), 42, Av. G. Coriolis, 31057 Toulouse Cedex, France, FR;(2) Physical Research Laboratory, Ahmedabad-380009, India, IN;(3) Indian Institute of Tropical Meteorology, Pune-411008, India, IN |
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| Abstract: | Summary ?The interannual variability of broad-scale Asian summer monsoon was studied using a general circulation model (GCM) and NCEP
(National Center for Environmental Prediction) data set during 1979–95. In the GCM experiment, the main emphasis was given
to isolate the individual role of surface boundary conditions on the existence of winter-spring time circulation anomalies
associated with the interannual variability of Asian summer monsoon.
In order to understand the role of sea-surface temperatures (SSTs) alone on the existence of precursory signals, we have conducted
17 years numerical integration with a GCM forced with the real-time monthly averaged SSTs of 1979 to 1995. In this experiment,
among the many surface boundary conditions only SSTs are varying interannually. The composite circulation anomalies simulated
by the GCM have good resemblance with the NCEP circulation anomalies over subtropical Asia. This suggests that the root cause
of the existence of winter-spring time circulation anomalies associated with the interannual variability of Asian summer monsoon
is the interannual variability of SST.
Empirical Orthogonal Functions (EOFs) of 200-mb winds and OLR were constructed to study the dynamic coupling between SST anomalies
and winter-spring time circulation anomalies. It is found that the convective heating anomalies associated with SST anomalies
and stationary eddies undergo systematic and coherent interannual variations prior to summer season. We have identified Matsuno-Gill
type mode in the velocity potential and stream function fields. This suggests the existence of dynamic links between the SST
anomalies and the precursory signals of Asian summer monsoon.
Received June 9, 1999/Revised April 7, 2000 |
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