Characteristics of the Ross Ice Shelf air stream as depicted in Antarctic Mesoscale Prediction System simulations

Abstract

Streamlines of the mean annual near‐surface winds over the Antarctic continent suggest a confluent channeling of the drainage flows off the ice sheets and onto the Ross Ice Shelf. A persistent cyclonic circulation to the north of the ice shelf supports a large‐scale pressure field that reinforces the continental drainage flows. Owing to these two processes, an enhanced low‐level airflow is present along the southern and western sections of the Ross Ice Shelf. The resulting air stream, known as the Ross Ice Shelf air stream (RAS), is one of the persistent and prominent low‐level wind features seen in the Antarctic. Real‐time mesoscale simulations of the Antarctic atmosphere and high southern latitudes using a modified version of the Pennsylvania State University/National Center for Atmospheric Research Mesoscale Modeling System have been ongoing since the 1999–2000 austral field season. Model results from the 1‐year period November 2001 to October 2002 have been analyzed to investigate the mean structure and modulation of the Ross Ice Shelf air stream. Analyses of model results show the low‐level air stream over the western Ross Ice Shelf has a wind speed maxima that is linked to the steep topography to the west. Individual cases of strong wind events appear to contain a significant barrier wind component that arises from cold air damming against the Transantarctic Mountains. Cyclones that frequently form in the Ross Sea are shown to establish conditions that promote barrier wind dynamics and thus significantly modulate the intensity of the RAS.