Investigating the multiscale variability and teleconnections of extreme temperature over Southern India using the Hilbert–Huang transform

Abstract

This study investigates the variability of annual minimum and maximum surface temperature (T min and T max ) of three temperature homogeneous regions [East Coast (EC), Western Coast (WC) and Interior Peninsular (IP)] in southern India in multiple time scales and examines their teleconnections with different climatic indicators. First, the different temperature time series are decomposed into appropriate number of oscillatory modes using the Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) algorithm. Subsequently, the modes are subjected to spectral analysis employing the Normalized Hilbert Transform—Direct Quadrature (NHT–DQ) scheme to get instantaneous amplitudes and frequencies. Further, a detailed trend analysis of instantaneous amplitudes is performed, which showed that the recent changes in temperature since 1970s, over southern India are mainly attributed to the increase in amplitudes of the IMFs corresponding to inter-decadal periodicity in all the regions. Moreover, data of four climatic indicators such as Pacific Decadal Oscillation (PDO), Sunspot Number (SN), Total Solar Irradiance (TSI) and CO2 concentration are decomposed using CEEMDAN and compared with decompositions of T max and T min time series of all the three regions. From the cross correlation analysis of oscillatory modes, this study established the links of different climatic indicators with the extreme temperature of southern India, which are evident mainly at few low frequency modes and trend component. The close matching of periodicity of different lower modes of PDO series with that of maximum and minimum temperature of the different regions depicted the possible association of PDO with the temperature regime of southern India. This association is further investigated with a recently developed running correlation analysis method namely Time Dependent Intrinsic Correlation (TDIC), which deciphered a long range positive correlation between the PDO and minimum temperature series at inter annual mode of 7 years to inter decadal mode of 15 years at all the three regions of southern India. The association between PDO and maximum temperature at inter annual ranges is positive at EC and IP regions. The association between PDO and maximum temperature at inter decadal scale show regional differences, with no association at WC region, negative association at IP region and positive association at EC region.