LAUSR

We evaluate the impact of natural and anthropogenic loadings on Indian maximum (Tmax) and minimum (Tmin) temperature variabilities during 1901–2015 using multiple spectral and statistical analyses. We compare the significant eigenmodes of temperature with TSI, Ocean and Atmospheric Processes (OAP) such as ENSO, PDO, NAO, AMO and CO2 data to understand their influence on temperature. The present analysis is based on new eigen-weighted correlation coefficient (EWCC) and regression analysis to assess the sensitivity of temperature to TSI, OAP and CO2. The first eigenmodes (EM) of Tmax and Tmin representing the long-term trend correlate well with the first EM of TSI (EWCC: 0.90 and 0.78) and CO2 (EWCC: 0.95 and 0.72), respectively. The CO2 residing throughout the day and night in the atmosphere may produce a similar linearly increasing trend in Tmax and Tmin. However, the trend test revealed non-stationarity in the trends of Tmax and Tmin. In addition, the regression analysis revealed high sensitivity of the Tmax and Tmin trend to TSI compared with CO2. Our study suggests that there is an intermittent change in the running mean of TSI between 1901 and 2015 resulting in observed changes in Tmax. In addition, spectral analysis of the Tmax and Tmin records revealed statistical significant  periodicities of ~ 2–7 years and 11 ± 2 years in Tmax and ~ 2–7 years and 50 ± 4 years in Tmin, which may be associated with OAP and TSI, respectively. Based on the present analyses, we conclude that there are combined responses of (1) intrinsic variation in TSI and CO2, which may be interpreted as the major loading factors on the trend of Tmax and Tmin, respectively; (2) periodic variabilities in different frequency bands may be associated with both solar and ocean atmospheric processes depending upon time scales.