The variability of Indian Ocean surface meteorological fields during summer monsoon in EL Nino/La Nina years

Abstract

In the present study, the possible linkages between Indian summer monsoon rainfall and surface meteorological fields (basic fields and heat budget components) were investigated during El Nino years and La Nina years. For this purpose, monthly surface meteorological fields in pre-monsoon month of May and summer monsoon season (June to September) were analyzed using reanalysis data of NCEP/NCAR (National Center for Environmental Prediction/National Center for Atmospheric Research). The statistical significance of the anomaly (difference) between the El Nino years and La Nina years in the surface meteorological fields was also examined. The significant negative precipitation anomalies over Indian landmass show that monsoon activity increases considerably during La Nina years. Significant positive anomalies of mean sea level pressure are observed over India during, Arabian Sea and Arabia in pre-monsoon month of May and monsoon season during El Nino years. Weaker westerlies develop in the west Arabian Sea in the month of may during El Nino years. The stronger southerlies in the monsoon months of La Nina years indicate higher northward transport of moisture. In the month of May, significant negative anomalies of cloud amount are observed over Somali coast, north Bay of Bengal and adjoining West Bengal and Bangladesh. During monsoon season, cloud amount shows negative anomalies over northwest India and Arabian Sea. There is overall reduction in the incoming shortwave radiation flux over northwest India, Arabia and north Arabian Sea during La Nina years. A significant higher magnitude of latent heat flux was also found over northwest India, central India and south Indian Ocean during La Nina years during monsoon season. The distribution of net heat flux is predominantly positive over northwest India and adjoining region, south Indian Ocean during monsoon season.