Abstract:

In order to qualitatively evaluate the effect of the aircraft artificial rain enhancement in the arid and semi-arid regions of northwest China, the stratiform cloud microphysical structure and its changes before and after the seeding were analyzed by using observation data of an airborne detection, and satellite data. The results are summarized as follows: (1) The stratiform cloud contains a cold layer and a warm layer from the vertical structure perspective and the clouds were thick. The vertical and horizontal distribution of the cloud in the detection area are very uneven. Compared to stratocumulus cloud, the concentration of the small cloud particles in altostratus cloud is low, while the concentration of the large cloud particles is high and the liquid state water content is high. The concentration of the small cloud particles was negatively correlated with its average diameter, particularly in the peak regions. The concentration of small cloud particles greater than 60 individual·cm^-3 and large cloud particles greater than 35 individual·L^-1 depended mainly on the particles whose diameters ranged from 3.5 to 10 μm and from 50 to 200 μm, respectively. (2) The cloud particle spectrum with different heights follows unimodal or bimodal distributions, but shows a declining trend in general. There is difference in the cloud forming and developing. The particle spectrum of the strong seedable, not-seedable and seedable cold cloud basically accords with the monotone decreasing law of negative power exponent, but there are great difference in cloud particles concentration,with the not-seedable ice crystal cloud having the highest concentration,followed by those with seedable cloud,and the strong seedable cloud the lowest. (3) The concentration of the small cloud particles was significantly decreased after seeding,by about two orders of magnitude in the diameter range from 6.5 to 20 μm.The concentration of the large cloud particles was significantly increased after seeding,and the spectral width was expanded,especially in the diameter range larger than 150 μm.

Key words: arid and semi-arid regions of northwest China')"> arid and semi-arid regions of northwest China, stratiform cloud, microphysical structure, microphysical responses after seeding