Changes in the Alpine boundary layer during the solar eclipse of 11 August 1999

Meteorological data from surface stations in the Alps near Innsbruck, Austria, are used to investigate the effects of the solar eclipse of 11 August 1999 on Alpine meteorology and on the structure and evolution of the Alpine boundary layer. The Innsbruck area was just outside the edge of the zone of totality of the 2 hr 46 min eclipse. Despite extensive cloud cover, observations showed a drop in air temperature of 1-4*C during the eclipse at the slope sites. The formation of a cold air layer over the slopes relative to the largely unaffected air over the adjacent valleys reversed the normal daytime upslope winds to downslope winds. The descending motions suppress cloud cover over the slopes and can produce the unusual effect of the sky brightening during an eclipse.