Reexamination of the Near-Surface Airflow over the Antarctic Continent and Implications on Atmospheric Circulations at High Southern Latitudes*

Abstract

Previous work has shown that winds in the lower atmosphere over the Antarctic continent are among the most persistent on earth with directions coupled to the underlying ice topography. In 1987, Parish and Bromwich used a diagnostic model to depict details of the Antarctic near-surface airflow. A radially outward drainage pattern off the highest elevations of the ice sheets was displayed with wind speeds that generally increase from the high interior to the coast. These winds are often referred to as "katabatic," with the implication that they are driven by radiational cooling of near-surface air over the sloping ice terrain. It has been shown that the Antarctic orography constrains the low-level wind regime through other forcing mechanisms as well. Dynamics of the lower atmosphere have been investigated increasingly by the use of numerical models since the observational network over the Antarctic remains quite sparse. Real-time numerical weather prediction for the U.S. Antarctic Program has been ongoing since the 2000-01 austral summer season via the Antarctic Mesoscale Prediction System (AMPS). AMPS output, which is based on a polar optimized version of the fifth-generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model, is used for a 1-yr period from June 2003 to May 2004 to investigate the mean annual and seasonal airflow patterns over the Antarctic continent to compare with previous streamline depictions. Divergent outflow from atop the continental interior implies that subsidence must exist over the continent and a direct thermal circulation over the high southern latitudes results. Estimates of the north-south mass fluxes are obtained from the mean airflow patterns to infer the influence of the elevated ice sheets on the mean meridional circulation over Antarctica.

Multi-year record of atmospheric mercury at Dumont d'Urville, East Antarctic coast: continental outflow and oceanic influences

“…The export of inland air masses towards the coastal regions is not uniform across Antarctica and is concentrated in a few locations -"confluence zones" -such as the Amery Ice Shelf region, the area near Adélie Land at 142 • , the broad region upslope from the Ross Ice Shelf, and the eastern side of the Antarctic Peninsula at ∼ 60 • W (Fig. 1) Bromwich, 1987, 2007). Given its geographic location, DDU in Adélie Land lies close to a confluence zone explaining the extent of the transport of air masses from the Antarctic plateau.…”

An assessment and interpretation of the observed warming of West Antarctica in the austral spring

“…Warren 1996). Near the southern limit of the circumpolar trough at the latitude of *65°S, rising motion occurs and turns polewards aloft (Parish and Bromwich 2007). Slow subsidence occurs over the continent and explains the surface high.…”

“…Climatologically, a surface high is present over the ice sheet, while to the north of the continent at *60°S lies the circumpolar trough. These features are coupled through a thermally direct circulation that represents the mean meridional circulation at the high latitudes (Parish and Bromwich 2007). This circulation and its poleward heat transport must exist to balance the surface energy budget, especially the strong longwave cooling term (e.g.…”

“…Warren 1996;van den Broeke et al 2006). The surface katabatic wind regime, directed equatorwards and down the Antarctic coastal escarpment, closes the lower branch of the circulation (Parish and Bromwich 2007). By definition, a positive phase of the SAM implies lower than normal surface pressure over the Antarctic continent and reduced mean meridional circulation, and negative SAM implies the opposite.…”

“…This basic explanation of reduced meridional heat transport associated with positive SAM is consistent with the modeling study of van den Broeke and van Lipzig (2004). Over the coastal escarpment, the regression coefficients of temperature anomalies with the SAM are an indication that the SAM is tied with the surface energy balance and modulation of the thermally direct circulation as described by Parish and Bromwich (2007); the katabatic winds mix sensible heat towards the surface to balance longwave cooling (van den Broeke et al 2006). Should positive SAM perturb this balance, lower than normal surface temperatures would result.…”