Cloud adiabaticity (α) is defined as the ratio of the actual liquid water path (LWP measured ) in a cloud to its corresponding adiabatic value (LWP ad ). Processes such as drizzle and entrainment can lead to subadiabatic LWP measured . This study examines α and its relationship to microphysical properties for 86 cloud events over the Northeast Pacific Ocean based on data collected during four separate summertime airborne campaigns. For the study region, α was found to be 0.766 ± 0.134. For most cases, clouds with a low value of α were found to have lower droplet number concentration (N d ), higher droplet effective radius (r e ), higher relative dispersion (d), and higher rain rate (R). The subcloud aerosol concentration (N a ) was often less for the low-α cases. The relationship between α and the vertical profiles and cloud-top characteristics for both the cloud droplet-only spectrum and full spectrum (cloud and rain droplets) is also examined. Inclusion of rain droplets produced a larger change in d for the low-α clouds as compared to the high-α clouds. On average, R increased at cloud top for high-α clouds but decreased at cloud top for low-α clouds. Accounting for α when estimating N d from Moderate Resolution Imaging Spectroradiometer retrievals results in better agreement with in situ N d values. Results of this work motivate the need for additional focus on the factors governing α, such as cloud type, and implications of its value, especially for remote-sensing retrievals.
ASJC Scopus subject areas
- Atmospheric Science
- Earth and Planetary Sciences (miscellaneous)
- Space and Planetary Science