Spatial and Temporal Characteristics of Aerosol Direct Radiative Forcing during Spring in the Indo-china Peninsula

Abstract

Frequent biomass-burning activities occur in the Indo-China Peninsula in spring， and the aerosol generated will affect the atmospheric radiation budget of southwest China through the atmospheric circulation.Exploring its influence on the atmospheric heating rate can provide a basis for studying its influence on weather and climate.Based on the MERRA-2 reanalysis data of hourly aerosol and radiation flux under clear sky， their temporal and spatial characteristics were analyzed first.Secondly， using statistical methods such as EOF and synthetic analysis， the temporal and spatial evolution characteristics of aerosol optical thickness （AOD） and surface aerosol direct radiative forcing （ADRF） over the Indo-China Peninsula and their relationship with atmospheric shortwave heating rate were discussed.The results showed that： （1） During the biomass burning season from March to April， there was an extreme value of AOD in the Indo-China Peninsula and Yunnan Province.The time series trend also showed a high consistency.The central value of AOD in Laos and northern Vietnam was more than 1， and the AOD in Yunnan Province gradually increased from north to south due to its influence.（2） The high-value center of biomass combustion AOD in the Indo-China Peninsula from March to April was consistent with that of total AOD， indicating that it was mainly affected by biomass combustion aerosol at this time.The horizontal flux divergence of biomass burning aerosol is as high as 28 kg·m-1·d-1 in northern Laos， which can be transported northeast to China.（3） The spatial and temporal distribution of surface ADRF and AOD showed a high consistency.The high-value center of surface ADRF also existed in the northern part of Laos and Vietnam in March and April， and its value could reach -36 W·m-2.In the spatial distribution of the first mode of surface ADRF in EOF， the northeast corner of India bordering in Tibet of China， Laos， Vietnam and Thailand are all positive phase regions， with maximum values appearing from March to April.The extreme values decreased in 2017 and 2018 and increased again in 2019.The temporal variation trend of surface ADRF in Yunnan Province is consistent with that in the Indo-China Peninsula.（4） The statistical relationship between the negative surface ADRF and the atmospheric shortwave heating rate is as follows： The more the net radiant flux of the surface decreases， the greater the heating caused by the absorption of shortwave radiation by the lower atmosphere， indicating that the more the shortwave radiation flux trapped by the aerosol in the atmosphere， especially at 700 hPa in March and April.

Keywords

• indo-china peninsula
• biomass burning aerosol
• direct radiative forcing of aerosol
• atmospheric shortwave heating rate