TURBULENT HEAT FLUXES BY PROFILE AND INERTIAL DISSIPATION METHODS - ANALYSIS OF THE ATMOSPHERIC SURFACE-LAYER FROM SHIPBOARD MEASUREMENTS DURING THE SOFIA ASTEX AND SEMAPHORE EXPERIMENTS/

Heat flux estimates obtained using the inertial dissipation method, an d the profile method applied to radiosonde soundings, are assessed wit h emphasis on the parameterization of the roughness lengths for temper ature and specific humidity. Results from the inertial dissipation met hod show a decrease of the temperature and humidity roughness lengths for increasing neutral wind speed, in agreement with previous studies. The sensible heat flux estimates were obtained using the temperature estimated from the speed of sound determined by a sonic anemometer. Th is method seems very attractive for estimating heat fluxes over the oc ean. However allowance must be made in the inertial dissipation method for non-neutral stratification. The SOFIA/ASTEX and SEMAPHORE results show that, in unstable stratification, a term due to the transport te rms in the turbulent kinetic energy budget, has to be included in orde r to determine the friction velocity with better accuracy. Using the p rofile method with radiosonde data, the roughness length values showed large scatter. A reliable estimate of the temperature roughness lengt h could not be obtained. The humidity roughness length values were com patible with those found using the inertial dissipation method.