Large-scale April pressure index connected with the southern oscillation and its potential for prediction of large-scale droughts over India

Abstract

The large-scale April pressure index (PI), which can be regarded as a measure of the southern oscillation, has been devised with the combination of surface pressures at Jakarta, Bombay, Santiago and Perth. The fluctuations of PI covering a period of 89 years (1891-1979) and its relation to the areal extent of droughts over India during the following monsoon season have been examined by spectral and cross-spectral analysis. The areal extent of drought is significantly negatively correlated with the PI. This implies that the large negative PI during April, signifying weakening of the southeast trades over the Indo-Pacific region, coincides with large areal extent of drought during the following monsoon season and vice versa. The significant correlation between the areal extent of drought and PI is mostly due to the oscillations in the range of 3 to 6 years. Furthermore, ~ 3 year oscillation in the areal extent of drought arises primarily due to the influence of the southern oscillation. The southern oscillation appears to be one possible causal climatic phenomenon for introduction a common period anything from 3 to 6 years for the recurrence of large-scale droughts over India.