The first detailed validation of maximum temperature of Modern‐Era Retrospective analysis for Research and Application Version 2 (T_MERRA‐2) against Indian Meteorological Department (T_IMD) has been carried out for 35 years (1981–2015) over India. For this purpose, India has been divided into seven different zones, i.e Western Himalaya (WH), Northwest, North Central, Northeast (NE), West Peninsula India, East Peninsula India, and South Peninsula India. The descriptive statistics and correlation between T_MERRA‐2 and T_IMD have been determined for monthly, seasonal, and annual basis. A significant correlation (>0.9) has been found for monthly T_MERRA‐2 and T_IMD with a root‐mean‐square error value closer to 1 except for WH where a high root‐mean‐square error value of 18.2 is obtained. Seasonal analysis also indicates a significant correlation for all the zones except for WH and NE with a correlation value of <0.3 during monsoon season; this may be due to sparse network, cold climate, and heterogeneity due to topography. Percent bias indicates that T_MERRA‐2 generally overestimates the T_IMD monthly observations for all the zones, that is, Northwest, North Central, NE, West Peninsula India, East Peninsula India, and South Peninsula India by 4.1%, 2.4%, 1.6%, 0.5%, 0.2%, and 0.8%, respectively, except WH where an underestimation (−82.5%) is determined. Thus, after calibration, MERRA‐2 Reanalysis maximum temperature may be used for further study of extreme weather events.

Dynamic and thermodynamic characteristics of the Asian summer monsoon during the onset phase over the Indian Peninsula (Kerala coast) and its variability are examined with reanalysis data sets. For this study, daily averaged (0000 and 1200 UTC) reanalysis data sets of National Centre for Environmental Prediction–National Centre for Atmospheric Research for the period 1948–99 are used. Based on 52 years of onset dates of the Indian summer monsoon, we categorized pre-onset, onset and post-onset periods (each averaged 5 days) to investigate the mean circulation characteristics and the large-scale energetics of the Asian summer monsoon. It is found that the strength of the low-level Somali jet and upper tropospheric tropical easterly jet increase rapidly during the time of evolution of the summer monsoon over India. Over the Bay of Bengal and the Arabian Sea, predominant changes are noticed in the large-scale balances of kinetic energy, heat and moisture from the pre-onset to the post-onset periods. Prior to the onset of the summer monsoon over India, a zone of flux convergence of heat and moisture is noticed over the eastern sector of the Bay of Bengal and this intensifies in the onset and post-onset periods. During onset of the monsoon over India, the horizontal flux convergence of heat and moisture, as well as diabatic heating, are enhanced over the Arabian Sea. These subsequently increase with the evolution and advancement of the monsoon over India. Further, the dynamics of the evolution processes (15 days before and 30 days after the onset date of the monsoon over Kerala for each annual cycle) are studied over various sectors, such as the Arabian Sea, Bay of Bengal and Indian Peninsula region. The study reveals that the low-level kinetic energy, vertically integrated generation of kinetic energy and net tropospheric moisture over Arabian Sea can be used as potential predictors for the prediction of the possible onset date of the summer monsoon over the Indian Peninsula. Copyright © 2005 Royal Meteorological Society

An endeavour is made to investigate the performance of convective parameterization schemes on the simulation of South Asian summer monsoon features through a regional climate model (RegCM). For this purpose, RegCM version 4.3 developed by International Center for Theoretical Physics (ICTP) is used for the simulation experiments in the Coordinated Regional Climate Downscaling Experiment (CORDEX) framework over the South Asia domain. Four convective schemes, namely, Emanuel, Grell, Tiedtke and a mixed scheme (Emanuel over land and Grell over the ocean) are evaluated in RegCM4.3 at 45 km horizontal resolution. The simulated results of precipitation, temperature and wind fields are systematically evaluated respectively with Tropical Rainfall Measurement Mission (TRMM), Climate Research Unit (CRU) and ECMWF re‐analysis (ERA) Interim datasets. The results reveal that the response of a mixed convective scheme is better in simulating precipitation and temperature realistically over the Indian subcontinent and is in close agreement with the TRMM observations, compared with the three other schemes. The circulation features are also properly represented with the mixed convection scheme. Furthermore, the annual cycle of precipitation and temperature averaged over the Indian region are well estimated in the mixed scheme, compared with the CRU observations. The northward propagation of monsoon intra‐seasonal oscillations in extreme monsoon seasons is simulated reasonably in a mixed convection scheme as compared with three other schemes. The inter‐annual variability of area averaged JJAS precipitation over the Indian region is simulated well by the model for the combination of Emanuel over land and Grell over the ocean. Grell scheme overestimates the JJAS precipitation, whereas Emanual and Tiedtke schemes underestimate it.

Diurnal temperature range (DTR) is an important indicator of climatic change and a critical thermal metric to assess the impact on agriculture and human health. This study investigates the seasonal, annual and decadal changes in the spatio‐temporal trend in DTR and air temperatures (maximum: T_max and minimum: T_min) during 1951–2016 and solar radiation (Srad) during 1984–2016 over 14 different agro‐climatic zones (ACZs) in India. The changes in the DTR trend between two time periods:1951–2016 and 1991–2016 (recent period) are also assessed. The results indicate an overall increasing trend in DTR (0.038°C/decade), T_max (0.078°C/decade, significant), T_min (0.049°C/decade) during 1951–2016 and Srad (0.10 MJ/m²/day/decade) during 1984–2016. However, a decreasing trend in DTR (−0.02°C/decade) and a significant increasing trend in T_min (0.210°C/decade) was noted during 1991–2016. The decadal changes showed an evident decline in DTR during the recent period since 1991. The relative increase in T_min (0.21°C/decade, significant) compared to T_max (0.18°C/decade) resulted in a decreasing DTR trend. This was evident across the 5 out of the 14 agro‐climatic zones for the 1991–2016 period. The seasonal analysis showed a significant (95%) increasing trend in DTR during pre‐monsoon and monsoon (1951–2016), and a negative trend for the post‐monsoon and monsoon since 1991. There were also interesting spatial differences found with the ACZs in the north‐west, parts of Gangetic plain, north‐east, and central India exhibiting negative DTR trends. The effect of Srad is larger on T_max than T_min; therefore, the decrease in Srad in parts of Gangetic plain likely contributed to a smaller increase in T_max relative to T_min and led to a decreasing trend in DTR. At the same time, the west coast, east coast, and southern region show positive trends. The observational analysis finds a distinct increase in the T_min and also highlights the need for future assessments to continue investigate the causes of these spatio‐temporal changes found in this study.