Cloud Adiabaticity and Its Relationship to Marine Stratocumulus Characteristics Over the Northeast Pacific Ocean. Issue 24 (16th December 2018)

• Record Type: Journal Article
• Authors: Braun, Rachel A.; Dadashazar, Hossein; MacDonald, Alexander B.; Crosbie, Ewan; Jonsson, Haflidi H.; Woods, Roy K.; Flagan, Richard C.; Seinfeld, John H.; Sorooshian, Armin
• Is Part Of: Journal of geophysical research. Volume 123:Issue 24(2018)
• Page Start: 13, 790
• Page End: 13, 806
• Publication Date: 2018-12-16
• Subjects: Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2018JD029287
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: Cloud adiabaticity (α) is defined as the ratio of the actual liquid water path (LWPmeasured ) in a cloud to its corresponding adiabatic value (LWPad ). Processes such as drizzle and entrainment can lead to subadiabatic LWPmeasured . 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. Key Points: Average cloud adiabaticity (α) over the Northeast Pacific Ocean was found to be 0.766 ± 0.134 based on airborne analysis of 86 cloud events Cloud droplet number concentration, droplet effective radius, relative dispersion, and rain rate are correlated with α Inclusion of α in calculations from satellite remote‐sensing retrievals results in greater agreement with in situ values