STATISTICAL-ANALYSIS OF THE POSITION OF THE MONSOON TROUGH

Using surface charts at 0330GMT, the movement df the monsoon trough du ring the months June to September 1990 al two fixed longitudes, namely 79 degrees E and 85 degrees E, is studied. The probability distributi on of trough position shows that the median, mean and mode occur at pr ogressively more northern latitudes, especially at 85 degrees E, with a pronounced mode that is close to the northern-most limit reached by the trough. A spectral analysis of the fluctuating latitudinal positio n of the trough is carried out using FFT and the Maximum Entropy Metho d (MEM). Both methods show significant peaks around 7.5 and 2.6 days, and a less significant one around 40-50 days. The two peaks at the sho rter period are more prominent at the eastern longitude. MEM shows an additional peak around 15 days. A study of the weather systems that oc curred during the season shows them to have a duration around 3 days a nd an interval between systems of around 9 days, suggesting a possible correlation with the dominant short periods observed in the spectrum of trough position.