Abstract
AbstractOn 30th January 1982, the research station on Signy Island (South Orkney Islands) reported a daily maximum temperature of 19.8 °C. This is a record maximum for any station south of 60°S. We use surface observations, atmospheric reanalyses and high‐resolution atmospheric model simulations to investigate the drivers of this extreme event. At the time of the record temperature exceptionally warm air was being advected southwards towards the South Orkney Islands from the subtropical South Atlantic. This air mass cooled significantly at levels below 1 km during its long track over the cold Southern Ocean but remained relatively warm above this level. Atmospheric model simulations show that warm air from upper levels was brought down towards the surface over Signy Island in a föhn wind generated by northerly flow over Coronation Island, a mountainous island just to the north of Signy Island. Modelled temperatures over Signy Island are in good agreement with observations and thus support the hypothesis that the record temperature was caused by a combination of exceptional warm advection with conditions suitable for the generation of föhn. Since conditions conducive to föhn occur relatively frequently, föhn warming may have a significant influence on the local climate and ecology of Signy Island.
Highlights
On 30th January 1982, the British Antarctic Survey research station at Signy Island (Figure 1) reported a daily maximum surface air temperature of 19.8 ∘C
On the 30th January, the 1200 UTC temperature was reported as +9.6 ∘C, and the maximum thermometer reading was recorded as +19.8 ∘C
The thermograph chart indicates a maximum temperature of 68 ∘F (20.0 ∘C) at around 0300 UTC on the 30th, in good agreement with the maximum thermometer reading
Summary
On 30th January 1982, the British Antarctic Survey research station at Signy Island (Figure 1) reported a daily maximum surface air temperature of 19.8 ∘C. The World Meteorological Organisation (WMO) has recently recognised this as a record high temperature for the Antarctic region, defined as all land and ice shelves lying south of 60∘S (de los Milagros Skansi et al, 2017) To put this record into a regional context, we note that the absolute maximum temperature for the Antarctic continent (17.5 ∘C on 24th March 2015) was measured at Esperanza station on the Antarctic Peninsula, 660 km southwest of Signy Island. We carry out very high-resolution simulations with a regional atmospheric model to investigate how interaction of the large-scale flow with local orography contributed to the extreme conditions observed We discuss how both regional circulation and local processes contributed to the record event and consider the importance of both for controlling local climate
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