Session 1B Lectures by Fellows/Associates

A Possible Cause for Change in Indian Monsoon & El-Nino Relationship

The Indian Summer Monsoon (ISM) governs the pulse of our nation. The monsoon varies from year-to-year. There are various phenomena associated with the variability of ISM, the major ones being the El-Nino over the Central Equatorial Pacific (EnSO), and fluctuations of Rainfall over the Eastern and Western parts of Indian Ocean. Studies have shown that the strength of association between ISM and EnSO varies with time. We afind that fluctuation of West African Monsoon (WAM) is also associated with EnSO and the relationship of WAM-EnSO and ISM-EnSO seem to be out-of-phase. We notice that during the period prior to 1980, the relationship between WAM and EnSO was weak and strengthened in the post-80s. EnSO-ISM relationship weakened in the post-80s period. We find that EnSO affects both ISM and WAM through upper tropospheric temperature anomalies. This anomaly was quite strong and located to the northwest of India during the pre-80s period. In the post-80s, we observe a westward shift of this anomaly and it is also more diffuse. The relationship between EnSO and Atlantic Nino also changed in the post-80s.. The effect of all these on the changing nature of EnSO relationship with ISM and WAM will be discussed.