Extension of all‐sky radiance assimilation to hyperspectral infrared sounders

Abstract This study accomplished the all‐sky infrared (IR) radiance assimilation of the hyperspectral IR sounders of the IR atmospheric sounding interferometer in the Japan Meteorological Agency's global system. Essential assimilation procedures, including cloud‐dependent quality control, bias correction, and observation‐error modeling, were directly adapted from the all‐sky assimilation of geostationary satellite imagers in our previous study, without any sophisticated modifications. Data assimilation experiments conducted in different seasons demonstrated that, compared with clear‐sky radiance assimilation, the all‐sky radiance assimilation of three channels sensitive to mid and upper tropospheric water vapor yielded significant forecast improvements in not only humidity but also temperature, wind, and geopotential height. These improvements originated from more than twofold increments in the number of globally assimilated observations under the all‐sky approach and better observation coverages. Increasing the number of assimilated channels to nine further amplified these improvements. The incorporation of an upper tropospheric channel mitigated upper tropospheric humidity biases that were originally exacerbated during three‐channel assimilation. These results underscore the broad applicability of the all‐sky assimilation approach to various IR instruments.