| East China is one of the most important industrial areas in China, and its climate characteristics are very important to people's production and life, In order to study the effects of cloud condensation nuclei (CCN) on cloud and precipitation in the new atmospheric environment,a short time strong convective weather process occurred in northern Anhui in June 11, 2014, and a continuous winter precipitation duiring 24-27 December 2016 was used as the research object in this paper.Based on the WRF mesoscale numerical model and the NSSL cloud physics scheme, the effects of the change of CCN concentration on the evolution of micro particles in the atmosphere and clouds are discussed. The experiment was divided into clean air(case1,case3) and polluted air(case2,case4), and the concentration of cloud droplets is provided by the formula N=CSk.The CCN concentration of the clean air is the original value in the NSSL, C=600cm-3, k=0.6; The data of polluted air was observed by Wang Hui et al. in the nothern suburb of Nanjing.K=0.47,and the observed value of C is 9957cm-3, which is decreased to 4000cm-3 in the height of cloud base.The results show that:The maximum simulated radar reflectivity of CASE 1 is 50-55, while the CASE2 is 55-60, and the CASE2 is closer to the actual situation than the CASE1 in the intensity and the width of the cloud, and CASE2 reflected stronger echo. That is,the pollution environment, the short time strong weather cloud structure is more consistent with the actual.The precipitation area of CASE2 is closer to reality than the CASE1, and the precipitation intensity is more than CASE1, and the occurrence of multiple strong echo makes the distribution of CASE2 heavy rainfall area wider; Both precipitation centers are derived from the contribution of the two monomers, but the first monomer CASE2 contributed more, resulting in stronger precipitation. The score of TS score was used to find that the CASE1 score was slightly higher than that of CASE2 in the early stage, but lower in the latter stage for the reason the precipitation of CASE2 was down to the west in the initial stage, while in the later period, the precipitation area of CASE1 was in the east.In the early stage of CASE2, greater cloud water number concentration and water content ratio than in CASE1 brings more freezed water particles which generates more ice particles and larger amount of precipitation, and release more heat than in CASE1, makes the cloud develop more exuberant. Trapping in low level negative temperature zone long time,makes more crystals unit mass in CASE1 than in CASE2 and more specific water content in hail graupel particles, accordingly formulates stronger cold cloud precipitation during the melting process. The results show that the increase of pollutant particulates can enhance the precipitation of severe convective weather in East China.Analysis of precipitation difference of strong convective weather shows that,the increase of CCN concentration increases the content of cloud water, accordingly increasing the content of ice crystals. The collision and freezing of larger mount of ice and snow crystal and supercold water brings much larger mount of graupel.For the reason graupel melting is the main source of convective precipitation, the content distribution of graupel particles caused the difference of rainfall area and intensity.Compared with the actual situation, the simulation of radar reflectivity in CASE3, CASE4 are slightly lower, whose maximum reflectivity is only about 45dBZ,and the latter makes slighter impact on the Jiangsu area. There is a slight difference between the trajectory and the range of the impact, and the echo area in CASE4 becomes smaller and smaller than in CASE4 in Nantong.The overall distribution of precipitation is close to that of automatic station data simulated in CASE3 and CASE4 in Jiangsu.In the case of precipitation distribution and strong center distribution, CASE3 simulated precipitation in Nantong area was significantly higher than that in southern Jiangsu.Simulated precipitation in CASE4 in Nanjing, Yangzhou, Taizhou and other places is slightly less than in CASE3,and is significantly less in Nantong,and a strong rainfall over 30mm thick rain zone shows in the northern part of southern Jiangsu in CASE4. So the simulated precipitation effect is better than the former which indicats that increasing the concentration of CCN makes the rain and rainfall fall more accurate. For both precipitation TS score find, the two movements are roughly the same, but CASE4 overall slightly higher than CASE3.CASE4 formed more cloud water and ice crystals than CASE3, which favored the generation of snow crystals in weak convective clouds, which was favorable for the formation of chalas. Higher temperatures will be accompanied by higher saturated vapor pressure, making the unit mass wet air more water vapor.Therefore, when the concentration of CCN increases, there will be more supercooled water in the cloud, which will be more conducive to the increase of precipitation in the cold cloud. At the same time, the increase of CCN concentration makes the cloud droplets smaller and narrowed broadly, which restrains the warm process,and leads to the obvious increase of precipitation along the southern Jiangsu,and reduced the precipitation in the northern part of Jiangsu.Comprehensive comparison on radar echo,precipitation and the evolution of cloud microphysics of the two precipitation events,the addition of CCN observed concentration improve the effects of the both simulation,and this increase is more pronounced for the case of strong convective cases in Anhui in 2014 than in the case of mixed cloud precipitation in December 2016. |
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