Improvements of the Microwave Gaseous Absorption Scheme Based on Statistical Regression and Its Application to ARMS.

An improved microwave gaseous absorption scheme based on statistical regression is proposed in this study. In the new scheme, Monochromatic Radiative Transfer Model (MonoRTM) replaces the Millimeter‐wave Propagation Model (MPM) to train the new scheme and the effect of real Spectral Response Functions is included in the training process. After the replacement, results of the new scheme are closer to observations from Advanced Technology Microwave Sounder (ATMS) onboard Suomi National Polar‐orbiting Partnership satellite in low level channels while MPM has some advantages in upper level channels. Introducing ozone absorption can cause a systematic bias but results in small standard deviations in channels with frequency 183 ± 1.8 GHz and 183 ± 1 GHz. In addition, the new scheme updates the vertical interpolation of water vapor and optimizes the vertical distribution of Planck function. These updates can reduce biases caused by vertical interpolation, especially for water vapor absorption channels. The bias associated to vertical interpolation can reach 0.25 K whereas the new scheme can decrease it to 0.003 K. To further validate the accuracy of the new scheme, we apply the new scheme to Advanced Radiative transfer Modeling System and compare simulated results to RTTOV 13.2 under 37 and 137 level (L) atmosphere (atm). Observations from ATMS onboard NOAA‐20 are used as true values. Results show that the new scheme agrees with RTTOV 13.2 well in accuracy and performs even better in upper level channels and water vapor absorption channels. Plain Language Summary: Fast radiative transfer (RT) models play a crucial role in satellite data assimilation as well as remote sensing. Gaseous absorption calculation is a fundamental aspect of fast RT models. With the capability of new‐generation spaceborne microwave instruments to observe spectra beyond 200 GHz, Monochromatic Radiative Transfer Model (MonoRTM) is utilized to train the microwave gaseous absorption scheme. The absorption of oxygen, ozone, water vapor and nitrogen is considered. In addition, the mismatch of vertical coordinates between fast RT models and input profiles requires fast RT models to do vertical interpolation during simulations. Vertical interpolation may introduce notable biases in microwave water vapor absorption channels. In this study, we enhance the vertical interpolation of water vapor and optimize the vertical distribution of the Planck function to mitigate these biases. The accuracy of the new scheme is assessed by comparing it with MonoRTM and satellite observations. Key Points: A new microwave gaseous absorption scheme, trained using Monochromatic Radiative Transfer Model (MonoRTM), is developed and the effect of ozone and nitrogen absorption is evaluatedThe accuracy of the new scheme is enhanced through updates to water vapor interpolation and the vertical distribution of Planck functionAfter application in Advanced Radiative transfer Modeling System (ARMS), the new scheme aligns with RTTOV and gets greater accuracy in upper‐level and water vapor absorption channels [ABSTRACT FROM AUTHOR]