Large‐eddy simulation of a warm‐air advection episode in the summer Arctic

• Published in: Quarterly Journal of the Royal Meteorological Society
• Main Authors: Sotiropoulou, Georgia, Tjernström, Michael, Savre, Julien, Ekman, Annica M. L., Hartung, Kerstin, Sedlar, Joseph
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2018
• Subjects: albedo
• Online Access: http://dx.doi.org/10.1002/qj.3316; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fqj.3316; https://onlinelibrary.wiley.com/doi/pdf/10.1002/qj.3316; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/qj.3316; https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/qj.3316

While there is an increasing scientific interest in the role of advection of warm and moist air into the Arctic, there is little understanding of the interactive processes between the advected air, boundary‐layer clouds and turbulence during such events and almost all studies refer to winter conditions. We use large‐eddy simulation (LES) to investigate these processes for an extreme warm‐air advection episode observed during summer 2014. The results indicate that moisture advection is the critical factor for cloud formation; shutting off this supply resulted in cloud dissipation, regardless of heat advection being present or not. The dissipation of the cloud reduced the surface energy budget by up to 37 W/m 2 . Advection of heat suppresses cloud‐driven mixing through enhancement of the atmospheric stability. Turning off the large‐scale heat transport therefore resulted in a somewhat optically thicker cloud, on average increasing the liquid water path by ∼10 g/m 2 . The results showed little sensitivity to a number of assumptions and simplifications in the LES set‐up, such as the prescribed cloud condensation nuclei concentration, friction velocity, surface albedo and the available moisture above the cloud layer.