Aerosol-Cloud Interactions in Warm Continental Cumulus During GoMACCS

Aerosol-cloud interactions are a primary topic of study in the cloud physics community. There are many phenomena that require further inquiry, in particular, understanding how aerosols modify clouds and how these modifications relate to precipitation processes. While there has been continual progress towards understanding how aerosols modify warm clouds, some key questions are still left unanswered. Modifications to clouds, via changes in aerosol, are theorized to alter the collision-coalescence pathway by reducing cloud drop sizes and reducing precipitation efficiency. In previous work we observed modifications to entrainment mixing processes as a function of aerosol and how these changes are related to the collision-coalescence process and precipitation initiation in warm maritime cumulus clouds.

In this study, we expand our previous work by utilizing measurements of cloud drop size, concentration, velocity and droplet spacing made with the Phase Doppler Interferometer (PDI) of warm continental cumulus clouds. The aircraft PDI measurements used for this analysis were made during the Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS) in August-September 2006 near Houston, TX and over the Gulf of Mexico. PDI data, in conjunction with atmospheric sounding data and meteorological observations, are used to characterize the environments in which cloud droplets are observed as a function of drop diameter and background aerosol concentration. Environmental characteristics include, for example, vertical velocity, humidity, temperature, observed drop-size distributions, average droplet spacing. All research flights during which PDI measurements were obtained are included, though cloud penetrations with observed precipitation are excluded from this analysis. To provide insight into how aerosol is related to drop-environments, data are sorted into three aerosol categories, low, medium and high. When combined with aerosol information, a thorough understanding of drop-by-drop environments allows us to investigate entrainment mixing process, precipitation initiation, and precipitation suppression.