Convective Snowfalls Linked to the Interaction of a Boundary-Layer Front with a Mesoscale Cyclone Near Terra Nova Bay, Antarctica

Abstract

During the XXII Italian expedition in Antarctica, in the summer of 2007, severe weather conditions associated with deep convective instability and heavy coastal precipitation occurred around the Terra Nova Bay area in the presence of an upper level trough and energetic katabatic winds flowing from the Ross Ice Shelf over the open sea. In this case study we document an example of boundary-layer frontal movement across the Ross Sea and mesocyclone development in conjunction with the frontal movement. A westward fast moving boundary-layer front, generated by the leftward turning katabatic airstream to the east of Ross Island, was observed propagating as a baroclinic wave disturbance in an easterly direction across the Ross Sea, merging later with a mesocyclone approaching Terra Nova Bay from offshore. The observed inertial trajectory and an estimation of the radius of curvature suggest that the vigorous katabatic airstream was sustained by the strengthening of a surface mesocyclonic circulation settled over the north-eastern Ross Ice Shelf, triggered by a sub-synoptic upper level trough passing over the area. We hypothesise that baroclinic instability in the low levels plays an important role in the development of a mesoscale vortex and for triggering convective precipitation.

An Analysis of Near-Surface Winds, Air Temperature, and Cyclone Activity in Terra Nova Bay, Antarctica, from 1993 to 2009

“…The atmospheric effects-largely from downslope drainage from the interior of the continent-can alter existing weather patterns or enhance energy fluxes between the ocean and atmosphere Bove and Paolo 2009). The oceanic effects-largely caused by the open ocean water-can change currents in the southern oceans (Buffoni et al 2002).…”

“…The injection of warmer ocean air from the polynya into the atmosphere can cause a convective surface layer to form, initiating the development of mesoscale dynamic systems, such as land breezes or cyclones (Gallé e 1996; Carrasco et al 2003;Bove and Paolo 2009). Cold atmospheric temperatures and strong winds can further the development of this convective layer.…”