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Cloud Adiabaticity and Its Relationship to Marine Stratocumulus Characteristics Over the Northeast Pacific Ocean
Author(s) -
Braun Rachel A.,
Dadashazar Hossein,
MacDonald Alexander B.,
Crosbie Ewan,
Jonsson Haflidi H.,
Woods Roy K.,
Flagan Richard C.,
Seinfeld John H.,
Sorooshian Armin
Publication year - 2018
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2018jd029287
Subject(s) - drizzle , liquid water content , liquid water path , effective radius , environmental science , moderate resolution imaging spectroradiometer , cloud top , atmospheric sciences , cloud computing , marine stratocumulus , aerosol , cloud height , meteorology , spectroradiometer , cloud cover , satellite , physics , reflectivity , precipitation , optics , quantum mechanics , astronomy , galaxy , computer science , operating system
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.