The semi-annual oscillation and Antarctic climate. Part 3: the role of near-surface wind speed and cloudiness

The interactions between the semi-annual oscillation (SAO), near-surface wind speed and cloudiness at seven Antarctic stations are described, as is how near-surface temperature is affected. A firmly established half-yearly wave, in both the mean annual cycle of wind speed and of cloudiness, was found at two stations with limited local disturbances: Halley and Faraday. Following a significant weakening of the SAO since the late 1970s, the annual cycles of wind speed and cloudiness at these stations have changed accordingly: increased wind speed and cloudiness in solstitial months and a decrease in the equinoctial months. At Halley, where no significant long-term temperature trends are detectable, this explains the observed changes in the seasonal temperature cycle. At Faraday, annual mean wind speed and cloudiness are negatively correlated to SAO strength, and as a result both have recently increased. Based on the correlation between wind speed and temperature changes, we estimate a ‘background’ (independent of circulation changes) Antarctic warming trend of 1.29±0.48°C per century.