Abstract
ABSTRACTWe have used 1° × 1° resolution maximum temperature (TMAX) data sets developed by India Meteorological Department (IMD) to examine the summer time warming over India during the period 2001–2014 in comparison with the period 1971–2000. The two study periods have been arrived at based on the drastic change of Moisture Index (IM) trends over India between the two epochs. The TMAX variations over India are discussed with the corresponding changes in Potential Evapotranspiration (PET) data of the Climate Research Unit (CRU) and Outgoing Longwave Radiation (OLR) data of NOAA ESRL. The study shows a considerable warming over northern parts of India compared to southern parts. Western Himalayas (WH) and Northwest (NW) regions experienced highest warming with 1.4 °C and 0.8 °C increases during Epoch 2 (2001–2014) as compared Epoch 1 (1971–2000) during the summer (March, April and May). Using MERRA Black Carbon Surface Mass Concentration (BCSMC) data, we have analysed the relation of increasing BCSMC with the TMAX over different homogeneous temperature regions of India and found that BCSMC has increased upto 1.6 times between the two epochs. Strong linear association is found between TMAX, PET and OLR evidenced by Coherence Wavelet Spectral analysis. It is also found that the highest warming occurred in the month of March and is 2.2 °C in WH and 1.4 °C in NW parts of India. We calculated mass stream function based on zonal mean meridional velocity for the two periods. In the recent periods we observed the weakening of polar cell and northward expansion of Hadley cell. These changes may be related to warming conditions of the atmosphere which may explain the intensification and northward expansion of the Ferrel cell with favourable conditions during the summer season.
Published Version
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