the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
The spatial distribution of convective precipitation – an evaluation of cloud microphysics schemes with polarimetric radar observations
Abstract. The representation of cloud microphysics in numerical weather prediction models contributes significantly to the uncertainty of weather forecasts. Polarimetric radar observations are increasingly used to evaluate numerical weather simulations, due to their sensitivity to microphysical properties. Typically, this evaluation is performed for individual case studies, which limits the generalizability of the results. This is particularly problematic for convective precipitation events, which are characterized by high variability due to their small scale and rapid error growth of initial uncertainties, and are often associated with severe weather phenomena. In this study, the performance of microphysics schemes in the simulation of convective precipitation events is evaluated statistically over a 30-day dataset. The aim is to assess the distribution of precipitation into convective and stratiform regions, and the microphysical properties in these regions based on polarimetric radar signals. Within a Weather Research and Forecasting model setup, 5 different microphysics schemes of varying complexity are evaluated. The choice of microphysics schemes has a significant impact on the distribution of precipitation; the median convective area fraction varies by an order of magnitude between the microphysics schemes. These differences are attributed to differences in rain drop size distributions. In the convective core, the FSBM and Morrison schemes frequently lack large rain drops, while the Thompson and P3 schemes simulate too many. Statistical evaluations are important to address the prevailing uncertainty surrounding cloud microphysics. The framework presented in this study can serve as a guide for future statistical evaluations of weather models with polarimetric radar observations.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2025-2475', Anonymous Referee #1, 07 Aug 2025
- AC1: 'Reply on RC1', Gregor Köcher, 16 Sep 2025
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RC2: 'Comment on egusphere-2025-2475', Anonymous Referee #2, 22 Aug 2025
This manuscript highlights the value of polarimetric radar observations for evaluating cloud microphysical parameterizations within numerical weather prediction models. Cloud microphysical parameterizations are statistical representations of our understanding of sub grid scale processes, and as the authors highlight, the creation and validation of these parameterizations are limited by observations. In this study, polarimetric radar observations, together with inline reflectivity diagnostics (CRSIM), are used to understand the partitioning of the cloud fields into stratiform and convective parts across five cloud microphysical parameterizations. The authors show that these five cloud microphysical parameterizations are in somewhat close agreement with the distribution of total precipitation across the study area. However, the convection cloud fraction varies greatly across parameterizations, suggesting the partitioning into convective/stratiform is problematic. Additionally, they attribute that the rain drop size distributions within the microphysics parameterizations are a source of the differences in rain particle sizes within convective/stratiform regions.
This manuscript is well written and generally easy to follow. This framework for microphysics evaluation within NWP/GCMs provides a great tool for future cloud microphysics parameterization development and evaluation.
Minor Comments:
For both figures 5 and 6, panels a-b (upper-row) are labeled with 5500m, whereas panels c-d (lower-low) are labeled with 1500m. However, the figure caption has upper-low labeled with 1500m and lower-row labeled with 5500m. The Figure and references in the text appear to be correct, but the caption is not.Citation: https://doi.org/10.5194/egusphere-2025-2475-RC2 - AC2: 'Reply on RC2', Gregor Köcher, 16 Sep 2025
Data sets
A gridded 30-Day dataset of convective precipitation from radar and WRF simulations with 5 microphysics schemes Gregor Köcher https://opendata.physik.lmu.de/2rvyDFh8t2W4QNX/
Convection-permitting WRF simulations with 5 microphysics schemes over 30 days Gregor Köcher https://opendata.physik.lmu.de/gmjQaVOkkmbQCqC/
Model code and software
Software for data analysis Gregor Köcher https://doi.org/10.5281/zenodo.15519860
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"The spatial distribution of convective precipitation - an evaluation of cloud microphysics schemes with polarimetric radar observations" by Köcher and Zinner
This manuscript presents a statistical evaluation of five different cloud microphysics schemes within the Weather Research and Forecasting (WRF) model, focusing on their ability to simulate the spatial distribution of convective and stratiform precipitation. The study utilizes a 30-day dataset of precipitation events in the Munich region with 400m horizontal resolution, comparing WRF simulations with polarimetric radar observations. The authors employ a cell-tracking algorithm to differentiate between convective and stratiform regions and analyze reflectivity and differential reflectivity histograms, as well as simulated rain drop size distributions. The integration of polarimetric radar observations is crucial, as these data are highly sensitive to microphysical properties and allow for a more in-depth assessment of the simulated precipitation characteristics. It is concluded that the differences in convective and stratiform precipitation between the 5 different microphysics are mainly attributed to the differences in rain drop size distribution. This is a well-structured and important study that makes a valuable contribution to the field of numerical weather prediction and cloud microphysics. The statistical evaluation using polarimetric radar observations is a robust approach for assessing and improving microphysics schemes. The findings provide clear insights into the strengths and weaknesses of different microphysics schemes in simulating convective precipitation, particularly concerning rain drop size distributions and their impact on precipitation partitioning. The manuscript is clearly written and the figures are informative. It is suggested to accept this manuscript after some minor revisions.
Minor:
1). Line 143: is shown in 1 → is shown in Figure 1?
2). Line 327: Figure 6c → Figure 6a?
3). Line 348: Figure 6d → Figure 6b?