Effect of Arabian Sea-Surface Temperature Anomaly on Indian Summer Monsoon: A Numerical Experiment with the GFDL Model

Abstract

The global general circulation model of the Geophysical Fluid Dynamics Laboratory has been integrated with and without a cold sea surface temperature (SST) anomaly over the Somali coast and the western Arabian Sea. The temperature anomaly is ?3°C near the Somali coast and linearly decreases eastward having zero anomaly at about 1500 km east of the coast. Comparison of the mean of the two model states indicates that the rainfall over India and the adjoining region is drastically reduced due to the colder SST anomaly over the western Arabian Sea. The other associated features due to the cold anomaly are an increase in sea surface pressure over the Arabian Sea, a decrease in local evaporation, and a reduction in the cross equatorial component of the wind at the surface and hence a reduction in the cross equatorial moisture flux. Statistical analysis of the results has been done by comparing the difference between the two mean states (?signal?) and the standard deviation of the errors (?noise?) in estimating the mean due to the finiteness of the averaging period. It is found that the results of the present numerical experiment are statistically significant.