The remote sensing of radiative forcing by light-absorbing particles (LAPs) in seasonal snow over northeastern China

Light-absorbing particles (LAPs) deposited on snow can decrease snow albedo and affect climate through snow-albedo radiative forcing. In this study, we use MODIS observations combined with a snow-albedo model (SNICAR - Snow, Ice, and Aerosol Radiative) and a radiative transfer model (SBDART - Santa Barbara DISORT Atmospheric Radiative Transfer) to retrieve the instantaneous spectrally integrated radiative forcing at the surface by LAPs in snow (RF^LAPs_MODIS) under clear-sky conditions at the time of MODIS Aqua overpass across northeastern China (NEC) in January-February from 2003 to 2017. (RF^LAPs_MODIS) presents distinct spatial variability, with the minimum (22.3 W m^-2) in western NEC and the maximum (64.6 W m^-2) near industrial areas in central NEC. The regional mean RF^LAPs_MODIS ∼ 45.1 ± 6.8 W m^-2 in NEC. The positive (negative) uncertainties of retrieved RF^LAPs_MODIS. We attribute the variations of radiative forcing based on remote sensing and find that the spatial variance of RF^LAPs_MODIS in NEC is 74.6 % due to LAPs and 21.2 % and 4.2 % due to snow grain size and solar zenith angle. Furthermore, based on multiple linear regression, the BC dry and wet deposition and snowfall could explain 84 % of the spatial variance of LAP contents, which confirms the reasonability of the spatial patterns of retrieved RF^LAPs_MODIS using in situ radiative forcing estimates. We find that the biases in RF^LAPs_MODIS are negatively correlated with LAP concentrations and range from ∼ 5 % to ∼ 350 % in NEC.