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2 Acta Geophysica

2 2021

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Investigating Indian summer heatwaves for 2017–2019 using reanalysis datasets

Hari Manoj, Tyagi Bhishma

Acta Geophysica

2021

Vol. 69, no. 4

1447--1464

Heatwaves are characterized by an increase in temperature to extreme levels, which adversely distress the living organisms. India ranks second in terms of disaster mortality among the world countries, preponderantly by heatwave—infuenced by regional climatology. In this study, the Excess Heat Factor (EHF) index is used to detect the heatwave using the ERA-Interim reanalysis dataset over various states of India during the summer period (April–June of 2017–2019). EHF categorizes heat waves based on the severity, which is an intensity measure created by combining the measures of excess heat, long-term temperatures anomaly characteristics by each location’s unique climatology of heat by various thresholds. The heatwave events are analysed by combining the means of excess heat and heat stress, which has a strong aspect of EHF measure ments. Concerning the intensity of future heatwaves, EHF index helps to analyse the frequency and intensity of heatwave episodes and alert those community most exposed to heat related illness. One of the indices is derived from a climatological background to analyse the severity of heatwave over the Indian states. The analysis over India using the EHF index refected a substantial rate of increase in the intensity and the frequency of heatwaves in the successive years with an average EHF intensity (mean EHF for the analysis period) of ~ 41 °C2 , ~ 38 °C2 and ~ 39 °C2 , especially over the north–western states, eastern coastal states and central and southern states, respectively. The results of this study serve as a drive in the risk and vulnerability planning and assessment.

Aerosol dipole pattern over India: consequences on rainfall and relation with wind circulations

Vissa Naresh Krishna, Tyagi Bhishma

Acta Geophysica

2021

Vol. 69, no. 6

2475--2482

The aerosol concentrations are changing in rapid phase in the recent decades over Indian subcontinent. A general conclusion that is postulated from various studies indicated high aerosol loading over the Indian subcontinent. The aerosol concentrations are found to alter cloud-precipitation chemistry globally. Analysing the trends of aerosol concentrations over the Indian subcontinent is crucial to understand in depth the aerosol–precipitation relationship over these regions. In the present study, the long-term trend (2000–2019) of aerosols, precipitation and winds has been analysed over the Indian subcontinent. The work aims to identify the zones of significant increasing/decreasing Aerosol Optical Depth concentrations and alter the rainfall patterns over these regions. Mann–Kendall test has been employed for trend analysis. An aerosol dipole pattern is observed along the eastern-western boundaries of the monsoon trough over the Indian subcontinent (India, Bangladesh and Pakistan), which shows an inverse relationship with the rainfall patterns. Over the north-western region of the Indian subcontinent, the reduced pollution and enhanced precipitation may further alter the land-sea thermal gradient, resulting in the weakening of monsoonal circulation. Enhanced pollution over eastern India is adjusting the precipitation distribution along with the weakening of low-level jet and moisture transport. The present study provides an evidence of aerosol–precipitation relation over the Indian subcontinent using long-term datasets that has profound application in better understanding the weather systems.