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Published December 27, 2018 | Supplemental Material + Published
Journal Article Open

Cloud Adiabaticity and Its Relationship to Marine Stratocumulus Characteristics Over the Northeast Pacific Ocean


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.

Additional Information

© 2018 American Geophysical Union. Received 9 JUL 2018; Accepted 13 NOV 2018; Accepted article online 21 NOV 2018; Published online 16 DEC 2018. All aircraft data used in this work can be found in the Figshare database (Sorooshian et al., 2018; https://figshare.com/articles/A_Multi‐Year_Data_Set_on_Aerosol‐Cloud‐Precipitation‐Meteorology_Interactions_for_Marine_Stratocumulus_Clouds/5099983). This work was funded by Office of Naval Research grants N00014‐10‐1‐0811, N00014‐11‐1‐0783, N00014‐10‐1‐0200, N00014‐04‐1‐0118, and N00014‐16‐1‐2567. A. MacDonald acknowledges support from the Mexican National Council for Science and Technology (CONACyT). The Terra/MODIS Clouds 5‐Min L2 Swath 1km and 5km data sets were acquired from the Level‐1 and Atmosphere Archive and Distribution System (LAADS) Distributed Active Archive Center (DAAC), located in the Goddard Space Flight Center in Greenbelt, Maryland (https://ladsweb.nascom.nasa.gov/).

Attached Files

Published - Braun_et_al-2018-Journal_of_Geophysical_Research__Atmospheres.pdf

Supplemental Material - jgrd55112-sup-0001-2018jd029287-si.docx


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Additional details

August 19, 2023
October 20, 2023