The project focuses in particular on feedback from the effect of waves on the atmosphere, a situation in which the flow-profile relationship has been shown to deviate from the classic Monin-Obukhov theory. The challenges are twofold (civil and military) because most atmospheric models, in particular climate forecasting models and models for predicting the performance of optronic and radar systems, use the classical flow-profile relationship, hence the importance of studying the conditions for their validity. To achieve this objective, the project aims to provide accurate and original documentation of the wind profile between the first few metres above sea level and a hundred metres or so above sea level, whatever the sea conditions, particularly in rough seas. This is made possible by the specific use of LiDAR Doppler scanning. As the profiles of speed, temperature, humidity and therefore refractive index are closely linked in the classical model, the documenting the wind profile is of great interest. To this end, the project is therefore planning a campaign spanning several months of in-situ measurements using a LiDAR doppler scanning simultaneously with a wave buoy. In addition to this long-term campaign, there will be two targeted campaigns: the first of which will focus on the detailed measurement of surface conditions, using wave-following platforms (MIOs) to provide better documentation of surface roughness, including wave energy at capillary wavelengths, the wind profile in the first metre above the water and turbulent flows at the surface. The other targeted campaign will document temperature and humidity profiles above the waves using flying drones (CNRM). These original and complementary measurements will provide a new understanding of wind-wave interactions and will serve as a basis for detecting the non-validity conditions of the classical model, for parameterising the profiles and, finally, for proposing a surface model.
To achieve these ambitious objectives, the project is based on an original experimental campaign combining surface measurements (PICCOLO and OCARINA) by the MIO, measurements of temperature and humidity profiles by flying drone (CNRM), which are complementary to the measurement of wind profiles over rough seas using a LiDAR doppler scanner (LHEEA).
The combination of surface measurements and the velocity profile in the surface layer, supplemented by local measurements of the sea state (wave buoy and capillary waves) and environmental variables (temperature, pressure, stability), is intended to provide a database offering the most complete possible view of the processes involved in transferring momentum to the surface in rough sea conditions. The originality of these combined measurements opens the way to detailed analysis of the processes at work in the event of wind-wave interaction and to the parameterisation of speed profiles. The database and its analysis are intended to be used to develop a surface model for use in operational tools at MétéoFrance. Diagram of the in-situ experiment with the various instruments.
Boris Conan (LHEEA)
Dynamics of Urban and Coastal Atmosphere
