On Assessing ERA5 and MERRA2 Representations of Cold-Air Outbreaks Across the Gulf Stream

• Published in: Geophysical research letters Vol. 48; no. 19
• Main Authors: Chellappan, Seethala, Zuidema, Paquita, Edson, Jim, Brunke, Michael, Chen, Gao, Li, Xiang-Yu, Painemal, David, Robinson, Claire, Shingler, Taylor, Shook, Michael, Sorooshian, Armin, Thornhill, Lee, Tornow, Florian, Wang, Hailong, Zeng, Xubin, Ziemba, Luke
• Format: Journal Article
• Language: English
• Published: Goddard Space Flight Center Wiley 16.10.2021; American Geophysical Union (AGU)
• Subjects: ACTIVATE; cold‐air outbreaks; ERA5; Gulf Stream; MERRA2; Meteorology And Climatology; surface fluxes; Era5; Merra2; Cold-Air Outbreaks; Surface Fluxes; Moisture Transfer; Marine Low Clouds; Temperature Projections; Carbon Monoxide; Activate; Heat Transfer; Gulf Stream; Warm Ocean Temperatures
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL094364

The warm Gulf Stream sea surface temperatures (SSTs) strongly impact the evolution of winter clouds behind atmospheric cold fronts. Such cloud evolution remains challenging to model. The Gulf Stream is too wide within the ERA5 and MERRA2 reanalyses, affecting the turbulent surface fluxes. Known problems within the ERA5 boundary layer (too-dry and too-cool with too strong westerlies), ascertained primarily from ACTIVATE 2020 campaign aircraft dropsondes and secondarily from older buoy measurements, reinforce surface flux biases. In contrast, MERRA2 winter surface winds and air-sea temperature/humidity differences are slightly too weak, producing surface fluxes that are too low. Reanalyses boundary layer heights in the strongly-forced winter cold-air-outbreak regime are realistic, whereas late-summer quiescent stable boundary layers are too shallow. Nevertheless, the reanalysis biases are small, and reanalyses adequately support their use for initializing higher-resolution cloud process modeling studies of cold-air outbreaks.