Denoting regions south of the Antarctic circle, 66° 32′ S. Within the Antarctic circle, the sun does not rise on 21 June (winter solstice in the Southern Hemisphere) or set on 22 December (summer solstice in that hemisphere). Antarctic meteorology is characterized by severe winters with double temperature minima, i.e. two separate occasions of minimum temperature, due to the absence of insolation for several winter months, and to the frequent exchange of air with that of lower latitudes. Blizzards are common. Temperatures rise in late summer as the long waves of the westerlies bring incursions of warmer air. Nevertheless, precipitation is still almost always in the form of snow, since maximum temperatures, occurring at the summer (December) solstice, rarely exceed 0°C. See J. King and J. Turner (1997). Antarctica seems to be part of a single tectonic Antarctic plate, but there is clear palaeomagnetic evidence that in the past there has been a large relative rotation between different parts of the continent (Gordon (2000) Nature 404). Whittaker et al. (2007) Science 318, 83 detail major Australian and Antarctic plate reorganizations.