North-Eastward propagating 25–50-day mode and its link with Indian summer monsoon activity

Summary Spatio-temporal characteristics of the 25–50-day oscillations are investigated using the empirical orthogonal function (EOF) decomposition and spectral analysis with the Maximum Entropy Method (MEM). Daily pressure values over India during 1978 are used in this study. Power spectra of the temporal coefficients of the two leading EOFs show the existence of a low frequency oscillation with a period range 25–50-day over all India. An analysis using extended empirical orthogonal function (EEOF) indicates North-Eastward propagating 25–50-day mode. The analysis EOF has allowed to establish a relationship between the 25–50-day oscillation and the activity of the summer monsoon. The North-Eastward propagation of this mode is also confirmed by the simple EOF analysis.With 9 Figures