Foehn jets over the Larsen C Ice Shelf, Antarctica

• Published in: Quarterly Journal of the Royal Meteorological Society
• Main Authors: Elvidge, Andrew D., Renfrew, Ian A., King, John C., Orr, Andrew, Lachlan‐Cope, Tom A., Weeks, Mark, Gray, Sue L.
• Other Authors: Natural Environment Research Council
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2014
• Subjects: Antarc*; Antarctic; Antarctic Peninsula; Antarctica; Ice Shelf
• Online Access: http://dx.doi.org/10.1002/qj.2382; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fqj.2382; https://onlinelibrary.wiley.com/doi/pdf/10.1002/qj.2382; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/qj.2382; https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/qj.2382

Previously unknown foehn jets have been identified to the east of the Antarctic Peninsula ( AP ) above the Larsen C Ice Shelf. These jets have major implications for the east coast of the AP , a region of rapid climatic warming and where two large sections of ice shelf have collapsed in recent years. During three foehn events across the AP , leeside warming and drying is seen in new aircraft observations and simulated well by the Met Office Unified Model ( MetUM ) at ∼1.5 km grid spacing. In case A, weak southwesterly flow and an elevated upwind inversion characterise a highly nonlinear flow regime with upwind flow blocking. In case C strong northwesterly winds characterise a relatively linear case with little upwind flow blocking. Case B resides somewhere between the two in flow regime linearity. The foehn jets – apparent in aircraft observations where available and MetUM simulations of all three cases – are mesoscale features (up to 60 km in width) originating from the mouths of leeside inlets. Through back trajectory analysis they are identified as a type of gap flow. In cases A and B the jets are distinct, being strongly accelerated relative to the background flow, and confined to low levels above the Larsen C Ice Shelf. They resemble the ‘shallow foehn’ of the Alps. Case C resembles a case of ‘deep foehn’, with the jets less distinct. The foehn jets are considerably cooler and moister relative to adjacent regions of calmer foehn air. This is due to a dampened foehn effect in the jet regions: in case A the jets have lower upwind source regions, and in the more linear case C there is less diabatic warming and precipitation along jet trajectories due to the reduced orographic uplift across the mountain passes.