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Analysis of the Ross Ice Shelf Airstream Forcing Mechanisms Using Self-Organizing Maps

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  • 1 Cooperative Institute for Research in Environmental Sciences and Department of Atmospheric and Oceanic Sciences, University of Colorado Boulder, Boulder, Colorado
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Abstract

The Ross Ice Shelf airstream (RAS), a prominent transport mechanism of cold, continental air to the north, is the most common wind pattern over the Ross Ice Shelf, Antarctica. The forcing mechanisms of the RAS include katabatic drainage, mesoscale forcing, and synoptic forcing. This paper uses the 15-km output from the Antarctic Mesoscale Prediction System (AMPS) and the method of self-organizing maps (SOM) to analyze how the combination of these forcing mechanisms impacts the strength and position of the RAS. It is found that the strength and position of the RAS is mainly driven by the thermal forcing in the region of the Transantarctic Mountains. This forcing includes the pressure gradient associated with cold air pooling at the base of the Transantarctic Mountains, as well as, the pressure gradient associated with the temperature contrast between the cold air located over the East Antarctic Plateau and the warm ambient air over the Ross Ice Shelf. These forcing mechanisms are analyzed in a region near the southern tip of the Ross Ice Shelf. In this region, the pressure gradient associated with the temperature contrast between the East Antarctic Plateau and the ambient air over the ice shelf is usually present during RAS events, while the pressure gradient associated with the cold air pooling varies between RAS events. The analysis shows that, in the region of the southern Ross Ice Shelf, RAS events can occur without the presence of cold air pooling.

Corresponding author address: Melissa A. Nigro, University of Colorado, 216 UCB, Boulder, CO 80309. E-mail: melissa.nigro@colorado.edu

Abstract

The Ross Ice Shelf airstream (RAS), a prominent transport mechanism of cold, continental air to the north, is the most common wind pattern over the Ross Ice Shelf, Antarctica. The forcing mechanisms of the RAS include katabatic drainage, mesoscale forcing, and synoptic forcing. This paper uses the 15-km output from the Antarctic Mesoscale Prediction System (AMPS) and the method of self-organizing maps (SOM) to analyze how the combination of these forcing mechanisms impacts the strength and position of the RAS. It is found that the strength and position of the RAS is mainly driven by the thermal forcing in the region of the Transantarctic Mountains. This forcing includes the pressure gradient associated with cold air pooling at the base of the Transantarctic Mountains, as well as, the pressure gradient associated with the temperature contrast between the cold air located over the East Antarctic Plateau and the warm ambient air over the Ross Ice Shelf. These forcing mechanisms are analyzed in a region near the southern tip of the Ross Ice Shelf. In this region, the pressure gradient associated with the temperature contrast between the East Antarctic Plateau and the ambient air over the ice shelf is usually present during RAS events, while the pressure gradient associated with the cold air pooling varies between RAS events. The analysis shows that, in the region of the southern Ross Ice Shelf, RAS events can occur without the presence of cold air pooling.

Corresponding author address: Melissa A. Nigro, University of Colorado, 216 UCB, Boulder, CO 80309. E-mail: melissa.nigro@colorado.edu
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