The impacts of biomass burning activities on convective systems over the Maritime Continent

Hsiang-He Lee,Chien Wang

doi:10.5194/acp-20-2533-2020

Abstract

Abstract. Convective precipitation associated with Sumatra squall lines and diurnal rainfall over Borneo is an important weather feature of the Maritime Continent in Southeast Asia. Over the past few decades, biomass burning activities have been widespread during summertime over this region, producing massive fire aerosols. These additional aerosols, when brought into the atmosphere, besides influencing the local radiation budget through directly scattering and absorbing sunlight, can also act as cloud condensation nuclei or ice nuclei to alter convective clouds and precipitation over the Maritime Continent via so-called aerosol indirect effects. Based on 4-month simulations with or without biomass burning aerosols, conducted using the Weather Research and Forecasting model coupled with a chemistry module (WRF-Chem), we have investigated the aerosol–cloud interactions associated with biomass burning aerosols over the Maritime Continent. Results from selected cases of convective events have specifically shown the significant impact of fire aerosols on weak convections by their increasing of the quantities of hydrometeors and rainfall in both the Sumatra and Borneo regions. Statistical analysis over the fire season also suggests that fire aerosols have impacts on the nocturnal convections associated with the local anticyclonic circulation in western Borneo and weaken nocturnal rainfall intensity by about 9 %. Such an effect is likely to have come from the near-surface heating due to absorbing aerosols emitted from fires, which could weaken land breezes and thus the convergence of anticyclonic circulation.

Highlights

Biomass burning in Southeast Asia has become a serious environmental and societal issue in the past decade due to its impact on the local economy, air quality, and public health (Miettinen et al, 2011; Kunii et al, 2002; Frankenberg et al, 2005; Crippa et al, 2016; Lee et al, 2018)
By comparing WRF-Chem modeling results including or excluding biomass burning emissions (FFBB versus FF), we have identified certain detailed impacts of fire aerosols on convective events within two study regions over the Maritime Continent during a 4-month period (June 2008–September 2008)
We have focused our analyses on two rainfall features: (1) convective precipitation associated with Sumatra squall lines and (2) diurnal rainfall over western Borneo

Summary

Introduction

Biomass burning in Southeast Asia has become a serious environmental and societal issue in the past decade due to its impact on the local economy, air quality, and public health (Miettinen et al, 2011; Kunii et al, 2002; Frankenberg et al, 2005; Crippa et al, 2016; Lee et al, 2018). Abundant aerosols emitted from such fires cause environmental issues and affect regional weather and climate through the direct and indirect effects of biomass burning aerosols (Grandey et al, 2016; Hodzic and Duvel, 2017; Jeong and Wang, 2010; Ramanathan and Carmichael, 2008; Taylor, 2010; Tosca et al, 2013) Carbonaceous compounds such as black carbon (BC) in biomass burning aerosols can reduce sunlight through both absorption and scattering to warm the atmosphere while cooling the Earth’s surface (Fujii et al, 2014; Andreae and Gelencsér, 2006; Satheesh and Ramanathan, 2000; Ramanathan et al, 2001).

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