Kim et al. (2026) Comparison of RTTOV-SCATT simulations of brightness temperature for NOAA-21/ATMS water vapor channels with different WRF microphysics schemes: the case study of heavy rain event in the Amnok River basin on 27 July 2024

Identification

• Journal: Modeling Earth Systems and Environment
• Year: 2026
• Date: 2026-04-06
• Authors: Song-Ryong Kim, Kwang-Chol Yu, Chang-Bok Rim, Chol-Ho Ryang, Hyon-Il Ryang
• DOI: 10.1007/s40808-026-02766-z

Research Groups

Kim Il Sung University, Pyongyang, Democratic People’s Republic of Korea

Short Summary

This study compared RTTOV-SCATT simulations of NOAA-21/ATMS brightness temperature using six different WRF microphysics schemes for a heavy rain event. It identified the Thompson scheme as providing the most suitable all-sky brightness temperature simulations, exhibiting the best agreement with observations and closest to a Gaussian Observation Minus Background distribution after quality control.

Objective

• To compare and evaluate the impact of six different WRF microphysics (MP) schemes on RTTOV-SCATT simulations of NOAA-21/ATMS brightness temperature (BT) for water vapor channels during a heavy rain event in the Amnok River basin.
• To analyze the Observation Minus Background (O-B) statistics and Gaussian characteristics of simulated BTs depending on MP schemes, both before and after Z-score based outlier removal.

Study Configuration

• Spatial Scale: Amnok River basin, Democratic People’s Republic of Korea. WRF domain: 598 × 561 grid cells with 4 km horizontal grid spacing, 51 vertical sigma levels up to 10 hPa. ATMS nadir field of view (FOV) sizes: 75 km (channels 1-2), 32 km (channels 3-16), 16 km (channels 17-22).
• Temporal Scale: Heavy rain event on 27 July 2024. WRF model integrated from 12:00 UTC to 21:00 UTC on 27 July 2024, with products generated every 10 minutes. ATMS scanning time around 17:20 UTC on 27 July 2024.

Methodology and Data

• Models used:
  • Numerical Weather Prediction (NWP) model: Advanced Research WRF (ARW-WRF) model version 4.5.1.
  • Radiative Transfer Model (RTM): RTTOV v13.2, specifically RTTOV-SCATT for all-sky conditions.
  • Microphysics (MP) schemes tested: Ferrier, WDM5, WSM6, Thompson, Morrison, and NSSL-2.
• Data sources:
  • Satellite observations: NOAA-21/ATMS (Advanced Technology Microwave Sounder) water vapor channels (17-22, centered around 183.31 GHz). Data obtained from Global Data Assimilation System (GDAS) at rda.ucar.edu/datasets/ds735.0.
  • Verification observations: NOAA-19/MHS, Metop-B/MHS, Metop-C/MHS, and NOAA-20/ATMS.
  • Initial and Boundary Conditions for WRF: National Centers for Environmental Prediction (NCEP) GFS (Global Forecast System) at 0.25° × 0.25° resolution from rda.ucar.edu/datasets/ds335.0.

Main Results

• The Ferrier microphysics scheme showed the smallest Mean Absolute Error (MAE) of 2.36 K and Root Mean Square Error (RMSE) of 3.11 K for the whole scan domain, but significantly underestimated the brightness temperature depression over the rainband region, simulating much warmer BTs than observed.
• The Thompson and NSSL-2 schemes simulated the coldest BT centers over the ocean, with linear regression slopes between observed and simulated BTs closest to 1, indicating better correlation. However, they exhibited biases in the location of these cold centers.
• Observation Minus Background (O-B) values showed channel dependence, generally decreasing as the height of the weighting function peak rose from lower to higher atmospheric levels.
• After Z-score based outlier removal and normalization, the O-B distribution of the Thompson scheme was most similar to a Gaussian distribution, with skewness and kurtosis values closest to ideal Gaussian characteristics.
• The study confirmed that the choice of microphysics scheme significantly impacts RTTOV-SCATT simulations of brightness temperature in all-sky conditions.
• Verification with other microwave instruments (NOAA-19/MHS, Metop-B/MHS, Metop-C/MHS, NOAA-20/ATMS) showed consistent O-B patterns across different satellites.

Contributions

• This study is the first (to the authors' knowledge) to investigate the effect of hydrometeors generated by different microphysics schemes on microwave radiation simulation for initial field improvement before data assimilation in the Amnok River basin.
• It identifies the Thompson scheme as the most suitable microphysics scheme for RTTOV-SCATT simulation of ATMS brightness temperatures in the context of heavy rain events in the study area.
• The research demonstrates the channel dependence of O-B and highlights the effectiveness of Z-score based quality control in normalizing O-B distributions, which is crucial for all-sky data assimilation.

Funding

Not applicable.

Citation

@article{Kim2026Comparison,
  author = {Kim, Song-Ryong and Yu, Kwang-Chol and Rim, Chang-Bok and Ryang, Chol-Ho and Ryang, Hyon-Il},
  title = {Comparison of RTTOV-SCATT simulations of brightness temperature for NOAA-21/ATMS water vapor channels with different WRF microphysics schemes: the case study of heavy rain event in the Amnok River basin on 27 July 2024},
  journal = {Modeling Earth Systems and Environment},
  year = {2026},
  doi = {10.1007/s40808-026-02766-z},
  url = {https://doi.org/10.1007/s40808-026-02766-z}
}