Shen, F. F., L. X. Song, J. Z. Min, Z. X. He, A. Q. Shu, D. M. Xu, and J. J. Chen, 2025: Impact of assimilating pseudo-observations derived from the “Z-RH” relation on analyses and forecasts of a strong convection case. Adv. Atmos. Sci., https://doi.org/10.1007/s00376-024-3215-x.
Citation: Shen, F. F., L. X. Song, J. Z. Min, Z. X. He, A. Q. Shu, D. M. Xu, and J. J. Chen, 2025: Impact of assimilating pseudo-observations derived from the “Z-RH” relation on analyses and forecasts of a strong convection case. Adv. Atmos. Sci., https://doi.org/10.1007/s00376-024-3215-x.

Impact of Assimilating Pseudo-Observations Derived from the “Z-RH” Relation on Analyses and Forecasts of a Strong Convection Case

  • Moisture conditions are crucial for the maintenance and development of severe convection. In the indirect assimilation of radar reflectivity, hydrometeors and water vapor retrieved from reflectivity are assimilated to avoid the nonlinearity issues associated with the observation operator. In a widely applied water vapor retrieval scheme, a cloud is assumed to be saturated when the radar reflectivity exceeds a certain threshold. This study replaces the traditional retrieval scheme with the “Z-RH” (radar reflectivity and relative humidity) linear statistical relationship for estimating the water vapor content, which is implemented to reduce the uncertainty caused by empirical relationships. The “Z-RH” relationship is statistically obtained from the humidity and the observations for rainfall rate at different temperature intervals with the use of the Z-R (radar reflectivity-rain rate) relationship. The impacts of these two retrieval approaches are investigated in the analyses and forecasts based on the radar reflectivity. The results suggest that both water vapor retrieval schemes yield similar reflectivity analyses, with “Z-RH” showing slightly stronger reflectivity intensities. Utilizing a “Z-RH” scheme contributes significantly to the improved analyses and forecasts of humidity and wind fields, resulting in more reasonable thermodynamic and dynamic structures. As the “Z-RH” relationship obtained by real-time statistics in a specific area provides a scientific basis for the retrieval of water vapor, a “Z-RH” scheme is beneficial to obtain more accurate reflectivity forecasts. The overall scores for the predicted precipitation of a “Z-RH” scheme are roughly 10%–20% higher compared to those of the traditional scheme.
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