Analysis Of Rain-reduction Seeding Effect On Raindrop And Application Of Weather Radar In It

Artificial weather modification is an important measure to implement meteorological support at present,It is of great significance to check and evaluate the cloud seeding effect.In this paper,we take the rain-reduction seeding of the opening ceremony and the closing ceremony of Nanjing Youth Olympic Games on August 16 and 28,2014 as objects,to evaluate the rain-reduction seeding effect by analyzing the effect of rain-reduction seeding on raindrop.Firstly,take the target area of the seeding as the center,use the sounding data to calculate the optimal rocket seeding height and the optimal distance between the operating point and the target area,and combined with the time and place of the rocket rain-reduction seeding to calculate the diffusion time of each point from the implementation of the seeding to the effect of rain mitigation on the target area,finally get the specific period of time affected by the rain-reduction seeding in the target area.Then,we use the observed data of OTT raindrop spectrometer at Nanjing disdrometer site to calculate the dominant diameter,median diameter and other characteristic diameters of raindrop,and the total concentration of raindrop particles,the weighted mean diameter of particle mass and the parameter ?(reflecting the size distribution of raindrops)of raindrop,to compare the change characteristics of raindrop before and after the effect of the rain reduction seeding in the target area,and use the analysis results to provide the evaluation basis for the effect of rain reduction seeding.On the analysis of rain reduction seeding at the opening ceremony,for the similarity of the properties of precipitation echo,we take the Wuhu disdrometer site which is not affected by the rain reduction seeding as the contrast area,compare and analysis the variation trend of the characteristic parameters of the raindrop with time series in two sites in Nanjing and Wuhu,and illustrate the effect of seeding by this comparison.The results show that:(1)Under the influence of rain reduction seeding at the opening ceremony,the raindrop of Nanjing disdrometer site is narrower than that of before seeding,and the small raindrop particle whose diameter is smaller than 1mm increases,and the large raindrop particle whose diameter is larger than 1mm decreases.And the characteristic diameters of raindrops are smaller than those before seeding.In the period affected by seeding,the total concentration of raindrops inNanjing disdrometer site and the weighted average diameter of raindrop were smaller than those in Wuhu disdrometer site,and the spectral parameter ? was larger than that in Wuhu.The trend of variation with time is opposite to that of Wuhu disdrometer site.And the radar echo intensity data show that the radar reflectance factor of the area affected by the rain reduction seeding is obviously smaller than that of the contrast area in the upstream area affected by the rain reduction seeding.(2)Under the influence of rain reduction seeding at the closing ceremony,the raindrop of Nanjing site is also characterized by narrow spectrum width,increase of small raindrop particle and decrease of large raindrop particle.After the seeding,the example scale of raindrop decreases,the rain droplet particles that contribute to the precipitation are reduced,and the rain droplets that contribute less to the precipitation increase.Due to the suppression effect of rain reduction on precipitation,after the target area is no longer affected by the seeding,the particle number concentration increases sharply and the spectral parameter ? decreases significantly.These characteristics show that twice of artificial rain reduction seeding have obviously changed the size and concentration distribution of raindrop in the target area,and effectively reduced the large droplet particles in the raindrop cluster,indicating that the seeding has successfully restrained the development of rainfall,and play a rain abatement effect.On the basis of the above analysis,we further discusses the problem to retrieve raindrop spectrum from weather radar reflectivity factor observations at other heights other than the ground level and to apply it to the analysis of rain reduction seeding.Then we based on the method for retrieving particle spectra in weakly precipitation stratus cloud by using radar reflectivity factor,we use the echo intensity data of Nuist-C radar to retrieve the precipitation raindrop spectrum of the opening day of the Olympic Games,and get the inversion raindrop spectra at altitudes below 3.5 km.The inversion result is in good agreement with the observed raindrop spectrum near the ground.The obtained raindrop information is applied to the analysis of the effect of artificial rain reduction on the raindrop,and the conclusion is basically consistent with the analysis of the measured particle spectrum.It turns out that,the particle spectrum information of strati form cloud precipitation obtained from radar reflectivity factor data by this inversion method can be referred to,other raindrop spectra obtained from inversion can also be used to analyze the effects of artificial weather modifications.