Abstract/Summary

A previous study explored land–ocean differences in the warm-rain formation process. In that study, aerosol effects were removed, or at least partially removed, but some land–ocean differences remained. Therefore, the study hypothesized that the land–ocean difference in the microphysical structure of warm clouds and in the formation of warm rain can be explained by differences in the nature of updraughts. To test this hypothesis, this study provides a detailed analysis of the land–ocean differences in warm clouds using a combination of CloudSat and MODerate-resolution Imaging Spectroradiometer (MODIS) observations, ground-based measurements obtained from Atmospheric Radiation Measurement (ARM), as well as a simple model framework. Our results show that a stronger updraught increases the height at which significant coalescence begins, and also prolongs the lifetime of falling drops promoting larger droplet growth. A consequence of this difference is that drizzle is less frequently observed at cloud base over land. Our results point to the critical role of the strength of the convective updraught in the warm-rain formation process.