Role of aerosols on prolonged extreme heatwave event over India and its implication to atmospheric boundary layer

Abstract

The extreme heatwave event is a major threat to living beings in the warming climate which demands immediate quantification of the meteorological factors triggering its amplification. In this study, we explored the role of absorbing and scattering aerosols in the occurrence of extreme heatwave events as well as changes in the atmospheric boundary layer (ABL) over the northwest (NW) and east coast (EC) India during March–June 2017–2022. Ten dry (RH < 33 %) and nine moist (RH > 55 %) heatwave events are observed over the study period. Among these cases, a dry heatwave over NW region prolonged from 27 May to June 11, 2019 is explored in detail. In this case, the increased ABL height from ∼2.0 to 3.0 km to ∼4.0–5.0 km is observed and the entire ABL depth shows enhanced temperature by ∼4 K. The latent and sensible heat fluxes are found to be reduced by 50 W/m² and enhanced by 80 W/m² respectively during heatwave. The total aerosol optical depth (AOD) is gradually enhanced to 0.6 leading to enhanced atmospheric warming of ∼8.5–11.5 W/m² during the heatwave event. Furthermore, the heating rates for moist heatwave cases (∼2 K/day) are higher than those for dry heatwave cases (∼1.8 K/day). In addition, the moist heatwaves exhibit a higher concentration of PM2.5 (∼80–120 μg/m³) compared to the dry heatwave (∼60–100 μg/m³) posing a greater threat to public health and air quality.