Topographic Effects on Stratiform Precipitation Observed by Vertically Pointing Micro Rain Radars at Ridge and Valley Sites in the Liupan Mountains Area, Northwest China
2. Overview of the Liupan Mountains Area
3. Observations and Methods
4. Analysis and Results
4.1. Stratiform Precipitation Statistic Differences
4.2. Vertical Structures Comparisons
4.3. Solid Hydrometeors Frequency Discrepancies
4.4. Melting Layer Characteristics Comparisons
4.5. RSD below the BB Comparisons
5. Summary and Conclusions
- The main weather systems causing precipitation in the Liupan Mountains area include 500 hPa westerly troughs and 700 hPa shear or low vortices, of which 500 hPa trough and 700 hPa shear systems account for 72% of all precipitation events, and 500 hPa trough and 700 hPa low vortex systems account for 17.1%. The movement of precipitating clouds in the Liupan Mountains area is mainly from southwest to northeast, accounting for 51.8% of the total, followed by northwest to southeast, accounting for 23.6%.
- Compared to the rainfall characteristics of two valley sites LD and DW, although the ridge site LPS has a lower percentage of stratiform rainfall, it has a larger percentage of convective and shallow rainfall as well as a larger proportion of the precipitation contribution and average precipitation intensity. The percentages of stratiform and convective precipitation were as large at LD as at DW, but the proportion of the precipitation amount and the average precipitation intensity at DW were slightly larger than those at LD.
- At sub-0 °C, the average MRR-2 Ze at LD, LPS, and DW was 18.96 dBZ, 20.68 dBZ, and 20.86 dBZ, respectively. These circumstances were similar to those inside the melting layer, where the Ze(peak) at the west valley site was 29.8 dBZ, whilst it was 32.4 dBZ and 31.95 dBZ at the ridge east valley sites, respectively. This is because the cooling of saturated air and the resulting condensation by melting snow caused a rise in hydrometeor mass of 6% and, hence, an increase in reflectivity. On the other hand, the Vsnow and Vpeak at all three sites were about 1.68 m s−1 and 5.60 m s−1, but the Vrain at the ridge site (7.15 m s−1) was approximately 19% greater than at the two valley sites. A possible reason might be the deposition and aggregation efficiency and the degree of riming at the ridge and east valley sites were greater than at the west valley site.
- The solid hydrometeors above the sub-0 °C height were mainly snow particles and graupel, and the diameter and density of snow particles and graupel at the ridge and east valley sites were slightly larger than those at the west valley site; plus, there was also a higher occurrence frequency of larger graupel at the ridge site. The key factor causing these differences at the ridge site was the forced uplifting of cloudy air over the mountain area around the ridge site, which might have resulted in a topographic supercooling effect that led to enhanced riming of supercooled liquid water, implying the precipitation often comes from rather more “compact ice”.
- As a whole, the BB was thicker and the sharpness slightly weaker at the ridge site compared to those at the valley sites. The peak reflectivity itself was stronger at the ridge and east valley sites than at the west valley site. Specifically, the variability of these values was obviously larger at the valley sites than at the ridge site. The key factor causing these differences is supposed to be the discrepancies in snow particle densities at the three sites, which are related to, among others, the degree of riming . Based on these results, it was found that the precipitable water vapor is relatively abundant at the ridge and east valley sites. Therefore, the cloud microphysical processes at the west valley site varied significantly from unrimed snow growth, which produced lower density and dimension solid particles, on the contrary, snow particle growth at the ridge and east valley sites tended to be affected by the riming process and the high-density snow particles. Another key factor is that the forced uplifting of cloudy air over the mountain area around the ridge site may play a part in the topographic supercooling that leads to enhanced riming of supercooled liquid water.
- For stratiform precipitation, the values of rainfall diameter below 2.5 mm were dominant, while the maximum value of log (N) reached 19. Compared with the two valley sites, the rainfall diameter was above 4.5 mm at the ridge site and showed relatively larger droplet sizes and log (N) values, which could reach 5.0 mm and 5, respectively.
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Data Availability Statement
Conflicts of Interest
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|Station||BBt *||BBb *||Ze(snow)||Ze(peak)||Ze(rain)||Rpeak||BBsh||BBth||Vsnow||Vrain||Vpeak||Vsnow/Vrain|
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Cao, N.; Yao, Z.; Shu, Z.; Chang, Z.; Mu, J.; Zhu, H.; Lin, T. Topographic Effects on Stratiform Precipitation Observed by Vertically Pointing Micro Rain Radars at Ridge and Valley Sites in the Liupan Mountains Area, Northwest China. Water 2023, 15, 134. https://doi.org/10.3390/w15010134
Cao N, Yao Z, Shu Z, Chang Z, Mu J, Zhu H, Lin T. Topographic Effects on Stratiform Precipitation Observed by Vertically Pointing Micro Rain Radars at Ridge and Valley Sites in the Liupan Mountains Area, Northwest China. Water. 2023; 15(1):134. https://doi.org/10.3390/w15010134Chicago/Turabian Style
Cao, Ning, Zhanyu Yao, Zhiliang Shu, Zhuolin Chang, Jianhua Mu, Haoran Zhu, and Tong Lin. 2023. "Topographic Effects on Stratiform Precipitation Observed by Vertically Pointing Micro Rain Radars at Ridge and Valley Sites in the Liupan Mountains Area, Northwest China" Water 15, no. 1: 134. https://doi.org/10.3390/w15010134