Aerosols exacerbating the heterogeneity of precipitation vertical structures

The vertical structures of precipitation serve as a direct link between clouds and surface precipitation, reflecting the processes of cloud and precipitation formation and development. However, their significance remains debatable, particularly concerning the aerosol effects on these structures. We utilize data from PM2.5 station measurements and the GPM 2A DPR to investigate the impact of aerosols on the vertical structure of precipitation and its microphysical characteristics.

Our findings show that the raindrop size in cold-topped (storm top height more than freezing level) precipitation exhibits three distinct trends from the storm top height to the surface: raindrop size decreases or shows no significant change in the upper layers, increases rapidly in the middle layers, and slightly decreases in the lower layers. Based on the observed turning points in raindrop size changes, we conducted a study on the influence of aerosols on the vertical structure of precipitation.

This study reveals phenomena different from previous views. Conventional wisdom suggests that higher and more extensive cloud development leads to greater surface precipitation intensity. However, our results indicate that for local cold-topped convective precipitation, the correlation between storm top height and precipitation rate at different altitudes decreases gradually with decreasing altitude. Absorbing aerosols are identified as a significant factor exacerbating the heterogeneity of precipitation vertical structures.

Within clouds, aerosols act as cloud condensation nuclei (CCN), influencing the growth of cloud droplets and ice crystals through microphysical effects. The competition between latent heat released and evaporative cooling initially increases storm top height but subsequently reduces it. Above the freezing level, precipitation rates and raindrop sizes remain highly consistent with storm top height. Below the freezing level, however, the vertical structure of precipitation is altered by evaporation. Larger raindrops and higher proportions of absorbing aerosols enhance evaporation, leading to a complex relationship where surface precipitation rates first decrease and then increase with increasing aerosol concentration. This response to aerosol is almost opposite to that observed above the freezing level.

This indicates that aerosols significantly exacerbate the heterogeneity of precipitation vertical structures through both microphysical and radiative effects.