A study on macro and micro physical structures of convective-stratiform mixed clouds associated with a cold front in autumn and their catalytic responses in North China

Making use of the Particle Measuring System (PMS) observations collected in the middle-upper stratocumulus clouds over Laiyuan in Zhangjiakou region on 13 October 2013, the vertical microphysical structure, the seedability of clouds and the variation of total number concentrations of liquid cloud particles, ice crystals and precipitation particles are analyzed. The results show that the clouds have a cold-warm structure with a dry layer and a deep cloud layer. The average value of cloud particle concentrations in cold clouds is 62 cm^-3 and the max value of liquid water content is 0.05 g/m³. The mean concentrations of ice crystals and precipitation particles detected by 2DC and 2DP are 1.9 L^-1 and 2.2 L^-1, respectively. The average value of cloud particle concentrations in warm clouds is 300 cm^-3, and the value of liquid water content is 0.1 g/m³. The horizontal distribution of cloud particle concentrations in the study area is very uneven. Using the value of liquid water content and the mean concentration of ice crystals to identify cloud seeding ability, it is found that stratiform clouds are the most seedable. By comparing the average concentration and diameter of cloud particles before and after the seeding, the results show that the average concentration of cloud particles before the seeding is 31 cm^-3, which is much higher than that after the seeding (17.6 cm^-3). But the average diameter has little change. After seeding, ice crystals can grow by consuming the supercool water. The concentration of ice crystals increased from 0.86 L^-1 to 4.27 L^-1, and the mean diameter also increased to 550 μm. Ice crystal particles gradually grew, and precipitation particle concentration also increased and the particle spectral broadened.