Assimilation of AIRS observations to improve the initial condition for the Asian dust model

This study focuses on assimilating Atmospheric Infrared Sounder (AIRS) observations for improving the initial condition for the Asian Dust Aerosol Model (ADAM) in the Korean Meteorological Administration (KMA). Assimilating the AIRS observations, the dust top height (Z_dust) and infrared aerosol optical thickness (AOT) are first produced from AIRS observations by using a one-dimensional variational analysis (1D-Var) scheme. Background field is needed as input to 1D-Var and is obtained from ADAM forecasts at the previous assimilation cycle. After performing 1D-Var by applying the ratio between the retrieved visible AOT converted from retrieved infrared AOT and background visible AOT, the vertical number concentration of dust in the background field is updated. In addition to the number concentration of dust, the averaged dust top height of background field is adjusted by using retrieved Z_dust. From the comparison with collocated Moderate Resolution Imaging Spectrometer (MODIS) visible AOTs for the Asian dust events in 2015, it has been noted that the retrieved visible AOTs are significantly improved. Especially, over the Asian dust source regions such as Taklamakan Desert, the tendency of underestimating the AOT in the background field has been considerably reduced. For trial experiments using ADAM model, the use of updated initial condition improves the accuracy of dust forecast at the Asian dust events.