Proceedings with Extended Abstracts (single PDF file) - Radio ...

virtual sensible heat fluxes ( Wm-2)The sensible heat fluxes can also be estimated from UHF profiler data in using the∂ θ ⎛⎞ wheat equation: ⎜∂ θ ∂ θ ∂'u v ⎟ θ'= − + − ± Q . Without advection, the simplified equation∂tx y⎝ ∂ ∂ ⎠ ∂z( w'θ ') − ( w'θ ')∂θzi 0 ∂θ 1,2( w'θ ')becomes: = −and = 0 with an entrainment coefficient∂tz∂tziiequal to 0.2 at the ABL top. Then the sensible heat fluxes can be deduced during convectiveABL (dθ/dt>0):from the heat rate given by the virtual temperature time evolution deducedfrom the UHF/RASS measurement and from Z i deduced from the maximum of reflectivity.3002502001501005001320 3 6 9 12 15 18 21 24Time ( UT)Figure 4: Time evolution of the virtual sensibleheat fluxes deduced from the both methods (1and 2) compared with the sonic anemometerresults (3).Figure 4 presents the time evolution of thevirtual sensible heat fluxes deduced from thetwo methods (symbols 1 and 2) with the UHFdata taken near 300m height and comparedwith the sensible heat fluxes measured withsonic anemometer (black line) at 30 m heightduring a convective day. Compared with thesonic anemometer heat fluxes, a correct timeevolution is obtained for the method using theturbulent kinetic equation and more dispersionfor the heat equation method.6 Concluding remarksThis paper has presented some first results about the determination of the turbulentstructure of the ABL with a UHF/RASS profiler: (i)-the vertical velocity is found negativeduring the day in the convective ABL and very different from the sodar vertical velocity.During the night, they have similar variations ; (ii) the spectral width of the velocity fromUHF and sodar presents the same diurnal variation; (iii) the spectra width of the UHF verticalvelocity of the echo on the acoustic wave is dependant of T '2 , W '2 and W 'T ' ; (iv) themomentum fluxes deduced from spectra width of the opposite beams are underestimatedcompared to fluxes measured with an aircraft; (v) the methods of evaluation of the virtualsensible heat fluxes from the turbulent kinetic and virtual heat equations seems promising in ahomogeneous, without advection and convective ABL.ReferencesAngevine, W. M., A. B. White, S. K. Avery, 1994 : Boundary layer depth and entrainment zonecharacterization with a boundary layer profiler, Bound.-Layer Meteor., 68, 375-385.Bok-Haeng Heo et al, 2003: Use of the Doppler Spectral Width to Improve the Estimation of theConvective Boundary Layer Height from UHF wind Profiler Observations, Journ. Atmos. OceanTechn. 20, 408-424.Girard-Ardhuin F. et al, 2003:Remote sensing and surface observations of the response of theatmospheric boundary layer to a solar eclipse. Boundary-Layer Meteorology, l 106, 93-115.Jacoby-Koaly S.et al 2002 : Estimation of the turbulent dissipation rate from the Doppler spectralwidth measured in the Atmospheric Boundary Layer by a UHF wind profiler: comparison with insitu aircraft data Atmos. Bound. Layer. 103, 361-389.Lothon, M et al, 2002 : Comparison of radar reflectivity and vertical velocity observed with ascannable C-band Doppler radar and two UHF profilers in the lower troposphere. J. Atmos. Ocean.Technol., 19, 899-910.313