The BAYSOFI Campaign - Measurements carried out during the total solar eclipse of August 11, 1999

The total solar eclipse of August 11, 1999 provided a unique opportunity to observe the input of fast day-night and night-day transitions, under high solar elevation around noon, on the earth-atmosphere-biosphere system. With in the interdisciplinary field campaign BAYSOFI. measurements of radiation, boundary layer micrometeorology and photochemistry, photosynthesis and tra nspiration were carried out at Freising-Weihenstephan and several locations nearby focusing on short-term effects of the eclipse. Although the overall grosswetterlage on August 11 was not favourable for viewing the eclipse, w ith clouds covering most of central Europe, observational conditions at Wei henstephan were fair due to a large hole in the cloud layer which appeared just half hour before totality lasting for more than one hour. Thus signifi cant effects of the eclipse on radiation, photolysis rates, OH, the tempera ture, wind, turbulence structure and stratification, ozone and CO2 fluxes, photosynthesis, transpiration and sap flow of trees could be observed which are reported and discussed in the following sequence of papers.