Evidence for Nonlinear Coupling of Solar and ENSO Signals in Indian Temperatures During the Past Century

Abstract

Significant fluctuations have been observed in Indian temperatures during past century. In order to identify the statistical periodicities in the maximum and minimum temperature data of different Indian zones, we have spectrally and statistically analyzed the homogeneous regional temperature series from the Western Himalayas, the Northern West, the North Central, the North East (NE), the West Coast, the East Coast, and the Interior Peninsula for the period of 107 years spanning over 1901–2007 using the multitaper method (MTM) and singular spectrum analysis (SSA) methods. The first SSA reconstructed the principal component of all the data sets representing a nonlinear trend (indicating a monotonic rise in temperature probably due to greenhouse gases and other forcing) that varies from region to region. We have reconstructed the temperature time series using the second to tenth oscillatory principal components of all the eight regions and computed their power spectral density using MTM. Our analyses indicate that there is a strong spectral power in the period range of 2–7 years and 53 years, which are matched respectively with the known El Nino–Southern oscillation (ENSO) periods and ocean circulation cycles. Further, the spectral analysis also revealed a statistically significant but riven cycle in a period range of 9.8–13 years corresponding to the Schwabe cycle in all Indiaian maximum and minimum temperature records and almost all the zonal records except in the NE data. In some of the cases, the 22 year double sunspot (Hale cycle) cycle was also identified here. Invariably the splitting of spectral peaks corresponding to solar signal indicated nonlinear characteristics of the data and; therefore, even small variations in the solar output may help in catalyzing the coupled El Nino-atmospheric ENSO cycles by altering the solar heat input to the oceans. We, therefore, conclude that the Indian temperature variability is probably driven by the nonlinear coupling of ENSO and solar activity.