**5. Conclusions**

To reveal the microphysical characteristics of NCCV precipitation, an NCCV coordinate system is firstly introduced in the present study. Under the coordinate system, the horizontal distribution, azimuth distribution, and vertical structures of stratiform and convective precipitation in the NCCV are hereafter explored during 2014–2019. The main findings are listed as follow.

The near-surface rain rate for convective precipitation in the NCCV is stronger than that for stratiform precipitation, while the convective precipitation frequency is lower than stratiform precipitation. The contribution of precipitation frequency and precipitation amount for stratiform precipitation are both larger than those for convection precipitation, which are generally higher than 70% and 60%, respectively. The regions with high convective and stratiform precipitation frequency have a comma-shaped distribution. With the increase in the distance from the NCCV center, the region with frequent stratiform precipitation occurrence shifts from the northeast quadrant to the southeast quadrant, while it is mainly located in the southeast quadrant for convective precipitation. The near-surface droplet sizes of the strong stratiform and convective rain rates inside the NCCV are not larger than those of smaller rain rates, while the droplet concentration is much higher. This indicates the great contribution of high droplet concentration to intense rain rate in the NCCV. The echo top of convective precipitation is higher than that for stratiform precipitation in the NCCV. Below 4 km, the radar reflectivity increases as the altitude decreases for both convective and stratiform precipitation, but with a much more obvious increase for convective precipitation, indicating more efficient collision-growth processes. Above 4 km, hydrometeor particles such as supercooled water and ice crystals in convective and stratiform precipitation grow through the Bergeron process. The stronger updraft in convective precipitation clouds may provide favorable environmental conditions for the growth of precipitation particles. As a result, the droplet concentration of convective precipitation is greater than that for stratiform below 5 km, but above 5 km, the concentration is smaller than stratiform and the droplet diameter is larger. There are shallow and deep convections in the convective precipitation inside the NCCV. Compared to shallow convection, deep convection has a larger droplet diameter, lower concentration, and stronger echo near the surface.

The precipitation and microphysical structures vary in different regions of the NCCV for stratiform and convective precipitation. Convective and stratiform precipitation mostly occurred in the south part of the NCCV, and the near-surface rain rates are also the largest in this region, especially in the southeast quadrant of the NCCV. The peak convective and stratiform rain rates are 6 mm h−<sup>1</sup> and 2.67 mm h−<sup>1</sup> in the southeast quadrant, respectively. In addition, the precipitation frequency in the southeast quadrant of the NCCV is also the

largest, with the azimuthal averages of convective and stratiform precipitation frequencies reaching 1% and 4%, respectively. The frequency and precipitation contribution of stratiform precipitation are the lowest in the southwest of the NCCV and the highest in the northeast quadrant (reaching 92% and 87%, respectively). On the contrary, the contribution peaks of convective precipitation frequency and amount in the southwest quadrant of the NCCV are 19.8% and 37%, respectively. Convective and stratiform precipitation have peak storm-top heights in the southwest quadrant of the NCCV. The peak values of droplet concentration and diameter are in the southeast and west of the NCCV, respectively. In the northwest and southwest quadrants of the NCCV, convective clouds develop deeply, and the radar echo above the melting layer is stronger than those in other quadrants, which increases rapidly as the height decreases, indicating the microphysical processes such as collision-growth and rimming processes of ice crystals and other hydrometeors. Below the melting layer, as the height decreases, the radar echo increases rapidly, indicating collision-growth processes, leading to the prevalence of a low concentration of large-sized droplets at the near-surface, while due to the relatively insufficient water vapor in this quadrant, the near-surface rain rate is relatively low. In the southeast quadrant of the NCCV, the storm-top heights are low for convective and stratiform precipitation. The collision growth of droplets is more significant than that in other quadrants. However, due to the fragmentation of droplets during the falling process, the rain hydrometeors near the surface are mainly composed of high-concentration and small-sized droplets. The high concentrations of hydrometeors together with enough water vapor supply provide favorable conditions for heavy rain rate in this quadrant.

Previous studies have revealed the difference of DSDs in different seasons and regions and different precipitation systems [21,23,24,33]. As a continuation of this work, future work on the microphysical structures of NCCV precipitation in different seasons, and their differences among different precipitation systems (such as Meiyu precipitation) are worthy of further investigation using the joint observations from ground-based and satellite-based instruments, which will help us gain a deeper knowledge of NCCV precipitation.

**Author Contributions:** Conceptualization, X.Z. and F.C.; methodology, X.Z., F.C. and X.C.; software, F.C. and X.C.; validation, X.Z. and F.C.; formal analysis, J.W. and F.C.; investigation, X.Z. and F.C.; resources, X.Z.; data curation, F.C.; writing—original draft preparation, J.W.; writing—review and editing, X.Z. and F.C.; visualization, J.W., X.Z. and F.C.; supervision, X.Z., F.C. and Y.W.; project administration, X.Z; funding acquisition, X.Z. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was financially supported by the National Natural Science Foundation of China (42175006), the Fengyun Application Pioneering Project (FY-APP-2021.0101), Jiangsu Youth Talent Promotion Project (2021-084), the Basic Research Fund of CAMS (2020R002), and the National Natural Science Foundation of China (41805023).

**Data Availability Statement:** The ERA5 data are publicly available at https://cds.climate.copernicus. eu/cdsapp#!/dataset/reanalysis-era5-pressure-levels?tab=overview, accessed on 5 September 2022. The GPM DPR dataset can be obtained from https://gpm.nasa.gov/data/directory, accessed on 4 September 2022. The lists of 20-year NCCVs are available for free at Zenodo via https://doi.org/10.5 281/zenodo.5571340, accessed on 1 September 2022. The Himawari-7 data used in our study can be downloaded from http://weather.is.kochi-u.ac.jp/sat/, accessed on 21 October 2022.

**Acknowledgments:** The authors thank the editors and three reviewers for their helpful comments and valuable suggestions, which improved the manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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