The Role of Katabatic Winds on the Antarctic Surface Wind Regime

Abstract

Antarctica is known for its strong and persistent surface winds that are directed along topographic pathways. Surface winds are especially strong during the winter period. The high directional constancy of the wind and the close relationship of the wind direction to the underlying terrain can be interpreted as evidence of katabatic wind activity. Observations show that the directional constancy of the Antarctic surface wind displays little seasonal variation. Summertime winds cannot be expected to contain a significant katabatic component, owing to enhanced solar heating of the ice slopes. Observations also show that the coastal environs are subjected to wide variation in atmospheric pressure associated with frequent cyclone activity. The robust unidirectional nature of the Antarctic surface wind throughout the year implies that significant topographic influences other than those from katabatic forcing must be acting. Idealized numerical simulations have been performed to illustrate the potential role of the Antarctic topography in shaping the wind. The presence of katabatic winds is dependent on radiative cooling of the ice slopes. Simulations without explicit longwave radiation show that the blocking influence of the Antarctic orography is a powerful constraint to the surface wind regime. Resulting low-level wind fields resemble katabatic winds, with directions being tied to the underlying terrain and speeds dependent on the slope of the ice surface. A numerical simulation of a strong wind event during austral autumn shows that the katabatic component is only a small fraction of the horizontal pressure gradient force for this case. This suggests that the role of katabatic winds in the Antarctic boundary layer may be overemphasized and that the adjustment process between the continental ice surface and the ambient pressure field may be the primary cause of the Antarctic wind field.