Lake-atmosphere exchanges: the LATEX field experimental campaign

Understanding the interaction of the atmosphere with underlying water surfaces is of great importance for a wide range of scientific fields such as water resources management, climate simulations and change impact studies, and regional weather forecasting in coastal areas. However, atmospheric dynamics over water surfaces have generally received less attention than land-atmosphere interactions, partially due to logistical difficulties in operating in-situ field studies. The Lake-Atmosphere Turbulent EXchanges (LATEX) field measurement was designed to address the issues of air-water interactions over lakes. The experiment was performed over Lake Geneva (Switzerland) on a 10 meter high tower situated 100 meters offshore. The main instrumentation consisted of a vertical array of four sonic anemometers and four open path gas analyzers measuring wind speed, temperature, and humidity at 20 Hz. Additional supporting measurements included net radiation, water surface temperature, relative humidity and temperature of air, and wave height and speed. The diurnal trends of momentum, heat, and water vapor fluxes for the whole experimental period are presented and several evaporation models of varying complexity are tested. A new model based on the Penman approach and sensible heat flux measurement is also proposed and tested. The roughness lengths of the surface (for momentum, heat, and water vapor) are investigated. The focus is then turned to the coherent structures over the lake and results from a quadrant analysis for momentum, heat and water vapor fluxes are analyzed. Under neutral and stable stratification, ejections and sweeps contribute equally to the vertical fluxes; as the atmospheric boundary layer turns to unstable, ejections begin to clearly dominate.