Importance of Upper Tropospheric Thermal Anomalies for Long-Range Forecasting of Indian Summer Monsoon Activity

R. K. Verma Indian Institute of Tropical Meteorology, Poona-411005. India

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Abstract

Upper tropospheric monthly mean values of geopotential height at selected Indian stations during the pre-months of April and May, and the monsoon months of June, July and August, have been used to study the interannual variation in the upper tropospheric thermal field for the years 1968–77. The 300–100 mb thickness anomalies averaged over these stations reveal that 1) the anomalies observed during the pre-monsoon period of April-May generally persist through the subsequent monsoon months of June, July and August; and 2) a warm (cold) anomaly over northern India during the pre-monsoon months is followed by above-normal (below-normal) monsoon rainfall activity. The study may be useful in long-range forecasting of Indian summer monsoon rainfall activity.

Abstract

Upper tropospheric monthly mean values of geopotential height at selected Indian stations during the pre-months of April and May, and the monsoon months of June, July and August, have been used to study the interannual variation in the upper tropospheric thermal field for the years 1968–77. The 300–100 mb thickness anomalies averaged over these stations reveal that 1) the anomalies observed during the pre-monsoon period of April-May generally persist through the subsequent monsoon months of June, July and August; and 2) a warm (cold) anomaly over northern India during the pre-monsoon months is followed by above-normal (below-normal) monsoon rainfall activity. The study may be useful in long-range forecasting of Indian summer monsoon rainfall activity.

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