In order to evaluate operation effect of artificial precipitation enhancement in Chengdu. The regional historical regression statistical method was applied to test the effect of artificial precipitation enhancement in Chengdu in winter half-year from 2011 to 2019. The results show that the average absolute increments of precipitation in each month of winter half year ranged from 0.14 to 3.53 mm, and the relative precipitation increase ranged from 2.14% to 32.14%. The effect of precipitation enhancement was best in February and November,average absolute increments of precipitation was 2.74 mm and 3.53 mm, and the relative precipitation increase reached 32.14% and 28.06%, respectively. The precipitation enhancement effect in January was poor. The accumulated absolute increment of precipitation of winter half-year in the past 9 years in Chengdu was 88.8 mm, the annual average value was 9.9 mm, and the relative precipitation increase was 19.06%. Evaluating the artificial precipitation enhancement effect in Chengdu play a guiding role on how to scientifically carry out aircraft precipitation enhancement operation and improve precipitation enhancement efficiency.
The weather research and forecasting (WRF) model along with its three-dimensional data assimilation (3D-Var) system was used to improve the initial field by assimilating radar reflectivity and radial velocity from Doppler radars. A rare strong squall line occurring on 4 March 2018 in Jiangxi Province was simulated and studied by using the adjusted initial field. It is found that only assimilation of rainwater, snow, graupel particles retrieved from radar reflectivity and water vapor derived from radar reflectivity could not make a stable improvement in forecasting the composite reflectivity, especially got an opposite effect on forecasting surface gale and precipitation. The assimilation of reflectivity data could significantly improve forecast skill when radar radial velocity was assimilated jointly. The reason is that assimilation of radar reflectivity can efficiently adjust initial hydrometeors and thermal field, but it has little effect on initial dynamic field. As the simulation time went by, the adjustment of dynamic field was unreasonable, a false divergence wind field appeared in the upper troposphere, thus a stratiform cloud area appeared in front of the squall line, which was not captured in reality. So the model could not improve the simulation of vertical wind shear and cold pool as well as rear inflow, and then there was a large gap between forecasted results and observations. Only assimilation of radar radial velocity could improve simulation results, and assimilation of both could efficiently adjust initial hydrometeors and thermal fields as well as dynamic field, and make the physical configuration more compatible with reality.The vertical wind shear and wind field structure were more favorable to occurrence of the strong squall line, and then formed a strong cold pool close to reality, further the forecasting results of radar composite reflectivity, surface wind and precipitation of the squall line agreed much better with observations compared with only assimilation of radar radial velocity.
This paper dynamically discussed the development mechanisms of local rainstorm triggered by gravity waves,and proposed a feasible method,which was verified by a case study,to forecast the propagations of gravity waves. The results showed that:( 1) the propagation of gravity waves strictly consistent with the potential temperature ridge,and by analyzing the isentrope,the forecasting of the generation and evolution of gravity waves would be more effective; ( 2) the waves could travel from higher potential temperature to lower side,or propagate in reverse orientation; ( 3) there were corresponding relations between the propagation path of gravity waves and the surface convergence line. Though the waves propagated along with the convergence line,it did not generate the gravity waves; ( 4) in a case of rainstorm on 9th August 2011 in Shijiazhuang,the gust front generated the gravity waves as a triggering mechanism, and brought about strong rainfall in the west urban.
The PMS p robeswere used to measure microphysical parameters of a summer stratus on August 15, 2007 inMinle of Gansu Provinc. The cloud structure including particle’s vertical distribution, liquid water content and particle spectrum type was analyzed.Results show that: (1) the cloud structure of the stratus is clear, and there is an inversion layer in this cloud; (2) the average of liquid water content is 0. 012 g·m- 3 in the cloud, and mainly concentrated in the layers of 4 100 - 4 200 m and 4 700 - 5 000 m; (3)this cloud accordswith the Bergeron’s catalytic cloud and water cloud interaction model, so we can seed crystals to achieve the objective of increasing p recip itation.
Based on the three - year air observational data, the impact ofweather conditions on aircraft icingwas analyzed, and the general rules of aircraft icing was summed up to enhance flight safety and security. The results show that the aircraft icing frequently occurred in winter and sp ring, and mostly in the areaswith p lenty ofwater vapor; the aircraft icing usually formed in the cloud with the temperature range of 0 to - 11 ℃, and especialy in the range of - 1 to - 8 ℃;when there wasmore supercooled water in the cloud,the aircraft icing would be more intensive.