Abstract
It is well-known that katabatic winds can be detected as warm signatures in the surface temperature over the slopes of the Antarctic ice sheets. For appropriate synoptic forcing and/or topographic channeling, katabatic surges occur, which result in warm signatures also over adjacent ice shelves. Moderate Resolution Imaging Spectroradiometer (MODIS) ice surface temperature (IST) data are used to detect warm signatures over the Antarctic for the winter periods 2002–2017. In addition, high-resolution (5 km) regional climate model data is used for the years of 2002 to 2016. We present a case study and a climatology of wind-induced IST anomalies for the Ross Ice Shelf and the eastern Weddell Sea. The IST anomaly distributions show maxima around 10–15K for the slopes, but values of more than 25K are also found. Katabatic surges represent a strong climatological signal with a mean warm anomaly of more than 5K on more than 120 days per winter for the Byrd Glacier and the Nimrod Glacier on the Ross Ice Shelf. The mean anomaly for the Brunt Ice Shelf is weaker, and exceeds 5K on about 70 days per winter. Model simulations of the IST are compared to the MODIS IST, and show a very good agreement. The model data show that the near-surface stability is a better measure for the response to the wind than the IST itself.
Highlights
The near-surface wind field over the Antarctic ice sheet (Figure 1a) is dominated by katabatic winds in the stably-stratified boundary layer [1,2,3], which is a climatological feature for the Antarctic continent [4]
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Warm signatures in the surface temperature related to katabatic winds and katabatic surges in the Antarctic have been reported in a number of studies previously. [13] show that the surface temperature field derived from Advanced Very High Resolution Radiometer (AVHRR) infrared imagery for the years 1993 and 1995 typically show a warm thermal belt over the slopes of Coats Land in the Weddell Sea
Summary
The near-surface wind field over the Antarctic ice sheet (Figure 1a) is dominated by katabatic winds in the stably-stratified boundary layer [1,2,3], which is a climatological feature for the Antarctic continent [4]. While the classical katabatic (downslope) winds develop only over the slopes of the ice sheet, they can extend over adjacent (flat) ice shelves, if appropriate synoptic forcing and/or topographic channeling is present. Despite the fact that the katabatic wind is a negatively buoyant air layer, the strong wind associated with katabatic winds and surges leads to a warm signature of the surface temperature The reason for this behavior is the strong turbulence in katabatic winds [7], which destroys or weakens the surface inversion compared to the weak-wind surroundings, where the surface inversion leads to much colder temperatures (Figure 2). The regions of strong wind over ice sheets and ice shelves can be detected as warm signatures in satellite thermal infrared (TIR) imagery, in winter, when the surface inversions are at their strongest (see [8])
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