This project is part of the wind energy meteorology efforts of the institute which is closely related to the efforts made to analyse and describe the vertical structure of the atmospheric boundary layer over different surfaces (cities, rural areas, complex terrain, water) as a prerequisite for trace gas and aerosol emission, transformation and dispersion studies.
Highlights from this project:
Drag coefficient in the maine boundary layer
A new formulation for the dependence of the friction velocity and the drag coefficient in the marine boundary layer as function of wind speed. The formulation gives a linear dependence of friction velocity on wind speed for the fully turbulent regime (above about 8 m/s wind speed):
u* = a u10 - b
with the two universal constants a = 0.051 and b = 0.14 m/s. This formulation leads to a drag coefficient which approaches a constant maximum value at high wind speeds. The limit value of the drag coefficient is equal to a2 = 0.0026. Details are given in: Foreman, R., S. Emeis, 2010: Revisiting the Definition of the Drag Coefficient in the Marine Atmospheric Boundary Layer. J. Phys. Oceanogr., 40, 2325-2332.
- This paper has been cited in: Andreas et al. 2012: A New drag relation for aerodynamically rough flow over the ocean. J. Atmos. Sci. Andreas et al. (2012) investigated seven times as much data as Foreman and Emeis (2010) and confirmed the above relation. They got a = 0.058 and b = 0.24 m/s, because they shifted the onset of fully turbulent flow to about 9 m/s.
Updating the "constants" in the Mellor-Yamada-Janjic type of turbulence parameterization
Fokussing on the constant B1 which relates to the turbulent kinetic energy near the surface, a new set of closure constants has been derived using new laboratory data and data from the offshore platform FINO1. The new set of closure constants leads to a much more ralistic description of turbulent kinetic energy (and thus turbulence intensity) in the lower half of the atmospheric boundary layer (i.e., higher turbulence intensity is simulated there). Details are given in: Foreman, R., S. Emeis, 2012a: Method for increasing Turbulent Kinetic Energy in the Mellor-Yamada-Janjić boundary layer parametrization. Bound.-Lay. Meteorol .
Drag coefficient in the marine boundary layer as function of wave steepness
Following a strict dimensional analysis, the drag coefficient must primarily be a function of the steepness of the waves. Data analysis shows that the drag coefficient scales with the square of the wave steepness. Details are given in: Foreman, R., S. Emeis, 2012b: Correlation equation for the marine drag cofficient and wave steepness. Accepted 22 July 2012 for publication in Ocean Dynamics.
Papers from this project
Foreman, R., S. Emeis, 2012: Correlation equation for the marine drag cofficient and wave steepness. Accepted 22 July 2012 for publication in Ocean Dynamics.
Contact: Stefan Emeis
This work has been funded by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety via the PTJ under grant number FKZ 0325060Simultaneously the project has been work package 5 of the RAVE project OWEA