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. Within the interdisciplinary e eld campaign BAYSOFI, measurements of radiation, boundary layer micrometeorology and photochemistry, photosynthesis and transpiration 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, with clouds covering most of central Europe, observational conditions at Weihenstephan 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 signie cant effects of the eclipse on radiation, photolysis rates, OH, the temperature, wind, turbulence structure and stratie cation, ozone and CO 2 e uxes, photosynthesis, transpiration and sap e ow of trees could be observed which are reported and discussed in the following sequence of papers.