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|Record Value||19.8°C (67.6°F)|
|Date of Record||30/1 (January) /1982|
|Length of Record||1947-present (summer only: 1996 on)|
|Instrumentation||Maximum and minimum thermometers in Stevenson Screen|
|Geospatial Location||Signy Research Station (UK) [60°43'S, 45°36'W, elevation: 9m (23ft)]|
Eos Earth and Space Science News of the American Geophysical Union (AGU) published on 1 March 2017.
Between 25 and 27 January 1982, 1200 UTC temperatures remained just above freezing but rose on and after 28 January. On 30 January the 1200 UTC temperature was reported as +9.6°C, and the maximum thermometer reading (0000 UTC 30 Jan – 1200 UTC 30 Jan) is recorded as +19.8°C (67.6°F), a record for Signy station. At the time of the observed record temperature, a trough of low surface pressure lay across the Drake Passage, connecting low pressure centres to the west of the Antarctic Peninsula and to the west of southern Chile. Together with ridge of high pressure extending southwards from the South Atlantic that drove a strong northwesterly geostrophic flow in the vicinity of the South Orkney Islands, based on the ERA Interim Reanalysis. This flow resulted in the southward advection of warm mid-latitude air from the South Atlantic sector. While this advection of warm air was almost certainly a necessary condition for achieving these record temperatures, it is likely that local orographic effects also played a role. With a northwesterly flow, Signy lies in the lee of Coronation Island, which rises to 1265 m and may thus experience a significant föhn (warm adiabatic descent) effect. The DRT record shows a rapid increase in temperature around 2100 local and a rapid decrease at around 0230 local, both of which are characteristic of föhn events. Additionally, the hygrograph record shows two very rapid decreases in humidity on 29 January, the first around 0900, the second around 2100, which would support this high temperature extreme event as a föhn event. While the anemograph does not show particularly marked wind speed changes at these times, there is a transition from almost calm conditions to very gusty, moderate winds at around 2230 on 29 January, followed by a dramatic increase in wind speed at around 0230 on 30 January. The importance of föhn in driving Antarctica warm events has been noted in research (e.g. Elvidge and Renfrew 2016, Cape et al. 2015, Speirs et al. 2010).
WMO Region VII (Antarctica)