Review: On the descent of Alpine south foehn (Jansing, Papritz and Sprenger)

Summary

The paper explores why foehn air descends in the lee of topographic obstacles through numerical simulations at the kilometer-scale of 15 south foehn events in the Swiss Alps. The paper is well structured, the writing is clear and the figures are well chosen. However, three fundamental issues exist. (1) The main conclusion that gravity waves trigger foehn descent rests upon a false premise, (2) an alternative hydraulic mechanism is mentioned but not explored, and (3) the numerical simulations are likely incapable of properly reproducing flow separation, which is crucial for how the flow descends.  For these three reasons, the recommendation is to reject the paper. However, the paper could be a fruitful addition to the foehn literature once these three issues have been properly addressed.

The attached pdf file explains the reasons for the rejection in more detail.

The authors present a climatological study of where along the Alpine ridge foehn descent occurs in high resolution model simulations. They present a novel Lagrangian diagnostic to identify foehn descent and thermodynamic history of foehn parcels during descent (temperature and specific humidity). Further, they discuss present a more detailed analysis of foehn descent for two case-studies centered at the Rätikon.

The paper is mostly well structured and clearly written. If the comments detailed in the attached document are addressed, I am recommending the paper to be published.