Wildfires heat the middle troposphere over the Himalayas and Tibetan Plateau during the peak of fire season

Abstract

Atmospheric pollution from biomass burning contributes to climatic and cryospheric changes by influencing solar radiation and the albedos of snow and ice surfaces over the Himalayas and Tibetan Plateau (HTP). We utilize long-Term Moderate Resolution Imaging Spectroradiometer (MODIS) fire products together with ground-based and satellite-derived aerosol datasets to assess the primary effect of wildfires originating from the southern slopes of the Himalayas on aerosol loading in the HTP. Results reveal consistent interannual and seasonal variation patterns, accompanied by statistically significant correlations between aerosol optical depth (AOD) at 500 nm from AErosol RObotic NETwork (AERONET) stations (Pokhara, Qomolangma (Mt. Everest) Station for Atmospheric and Environmental Observation and Research, Chinese Academy of Sciences (QOMS), Nam Co) and Himalayan fires. Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data further indicate elevated smoke aerosol extinction coefficients at altitudes of 6 to 8 km (middle troposphere) in the southern HTP during the peak fire season (March-April) in 2021. The intense wildfire activity in 2021 likely induced mid-Tropospheric warming and alterations in the vertical temperature structure, evidenced by a pronounced reduction in the absolute lapse rate, representing the rate of temperature decrease with altitude. This reduction was observed at QOMS, South-East Tibetan plateau Station for integrated observation and research of alpine environment, Chinese Academy of Sciences (SETS), and Naqu stations compared to 2022. Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) simulations estimated increased heating rates (0.38-1.32 K d-1) and atmospheric warming (15.03-22.43 W m-2) in the mid-Troposphere due to smoke aerosols. Such warming affects regional atmospheric stability and modulates surface temperatures (∼1/40.04 K). It is crucial to conduct further research into the heating/cooling processes induced by aerosols and their influence on the vertical temperature structure to comprehensively understand the impacts of aerosols on regional climate and the hydrological cycle.