Variability and teleconnectivity of northeast monsoon rainfall over India

Abstract

The spatial and temporal variabilities of rainfall over Peninsular India during the northeast monsoon (NEM) season is studied using a high resolution gridded data, for the period 1951–2003. The dominant modes of the NEM rainfall were identified using Empirical Orthogonal Function (EOF) analysis and the power over the identified scales was extracted using wavelet analysis (scale averaged wavelet power-SAP). Homogenous regions of variability of the SAP of NEM rainfall (smoothed NEM) were studied using EOF. Excluding the subdivisions of Karnataka, the leading mode of EOF explains the spatio-temporal variability of NEM rainfall over Peninsular India. Dominant frequency of smoothed NEM is in the 4 year period and the second dominant mode is in the 8 year period. The energy of the principal components (PCs) is consistent with the above/below-normal rainfall received over the NEM region. Even though PC1 explains the variability over the core region of NEM rainfall, the energy of the WET year 1956 is not captured by PC1. The excess rainfall of this year was contributed by the subdivisions of Karnataka, whose variability is explained by PC2. EOF analysis was also applied on the SAP of SST (smoothed SST) for the months from January to September, over the Indian Ocean (30° S–30° N, 40° E–110° E), the Atlantic Ocean (30° S–30° N, 60° W–10° E) and the Pacific Ocean (30° S–30° N, 120° E–60° W). Correlation between PC1 of smoothed SST for the months of January to September and smoothed NEM averaged over Peninsular India was found and the month that bears high correlation was selected to explain the teleconnections. Thus the smoothed SST for the months of February, March and August over Indian, Atlantic and Pacific Oceans respectively was selected to explain their relations with the smoothed NEM rainfall.