A New Look at the Daily Cycle of Trade Wind Cumuli

• Published in: Journal of Advances in Modeling Earth Systems
• Main Authors: Jessica Vial, Raphaela Vogel, Sandrine Bony, Bjorn Stevens, David M. Winker, Xia Cai, Cathy Hohenegger, Ann Kristin Naumann, Hélène Brogniez
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union (AGU) 2019
• Subjects: daily cycle; diurnal time scale; trade wind cumuli; shallow clouds; observations; high‐resolution models; Physical geography; GB3-5030; Oceanography; GC1-1581; North Atlantic
• Online Access: https://doi.org/10.1029/2019MS001746; https://doaj.org/article/47ca9f97ef49406fb6184e83e05aff3d

Abstract A description of the daily cycle of oceanic shallow cumulus for undisturbed boreal winter conditions in the North Atlantic trades is presented. Modern investigation tools are used, including storm‐resolving and large‐eddy simulations, run over large domains in realistic configurations, and observations from in situ measurements and satellite‐based retrievals. Models and observations clearly show pronounced diurnal variations in cloudiness, both near cloud base and below the trade inversion. The daily cycle reflects the evolution of two cloud populations: (i) a population of nonprecipitating small cumuli with weak vertical extent, which grows during the day and maximizes around sunset, and (ii) a population of deeper precipitating clouds with a stratiform cloud layer below the trade inversion, which grows during the night and maximizes just before sunrise. Previous studies have reported that cloudiness near cloud base undergoes weak variations on time scales longer than a day. However, here we find that it can vary strongly at the diurnal time scale. This daily cycle could serve as a critical test of the models' representation of the physical processes controlling cloudiness near cloud base, which is thought to be key for the determination of the Earth's climate response to warming.