Strong-wind events and their impact on the near-surface climate at Kohnen Station on the Antarctic Plateau

Strong-wind events occur 10–20 times per year at Kohnen Station, East Antarctica (75°00′S, 0°04′E, 2892 m above sea level), and are often caused by warm-core cyclones in the north-eastern Weddell Sea. An uncommon event occurred in January 2002, when blocking both in the south Atlantic Ocean and in the south Tasman Sea caused a split-up of the circumpolar vortex, and large amounts of heat and moisture were transported onto the Antarctic Plateau. During strong-wind events over the plateau the near-surface temperature can increase by tens of degrees, which is partly caused by the advection of heat, but for an important part by the destruction of the stable temperature-deficit layer by enhanced vertical mixing. The temperature rise is larger during the winter/night than during the summer/day, due to a better-developed temperature deficit. Snowdrift during the January 2002 event linearly increased surface roughness for momentum with friction velocity, for values over about 0.18 m s-1. The cloud cover during the event reduced down-welling solar radiation by 32%, and increased the albedo from about 0.86 to 0.92. Changes in longwave radiation largely cancelled the daytime changes in shortwave radiation, thus net radiation was most affected at night.