A wavelet cross-spectral analysis of solar-ENSO-rainfall connections in the Indian monsoons

Abstract

The possible connections between the El Nino-Southern Oscillation (ENSO) phenomenon and Indian monsoon rainfall have been widely discussed in the meteorological literature. We show strong statistical evidence here for connections of ENSO with solar activity. This is particularly evident in a comparison between the two contrasting test periods of 1878-1913 and 1933-1964, representing three complete cycles of lowest and highest solar activity respectively since 1850. Wavelet statistical analysis reveals that the link between solar activity and ENSO is generally stronger than that between ENSO and rainfall but only slightly weaker than that between solar activity and rainfall. Over the two test periods an increase in solar activity is associated with a decrease in ENSO indices and an increase in the monsoon rainfall in the 8-16 y period band. In the 2-7 y period band the effects vary with region. The net effect of solar processes on rainfall thus appears to be the result of counteracting or cooperating influences on shorter (about 5-6 y) and longer (about 11-12 y) time scales, the latter on the whole dominating over the former. The present analysis thus suggests that the influence of solar processes on Indian rainfall operates in part indirectly through ENSO, but on more than one time scale.