EXPERIMENTAL INVESTIGATION OF ATMOSPHERIC BOUNDARY-LAYER TURBULENCE

This paper describes how to measure turbulence in the atmospheric boun dary layer (ABL) in order to address certain problems in modern atmosp heric physics. These problems mainly relate to the Earth's energy budg et (including the hydrological cycle) and biogeochemical cycles. Start ing from the main characteristic numbers and the basic equations of at mospheric turbulent flow, we show what turbulence parameters are impor tant to measure. Special attention is given to the various methods use d to compute the turbulent fluxes. We analyse the range of scales whic h has to be measured to properly capture the eddies contributing to th e turbulent transfers. This range of scales determines what sensors ca n be used in the atmospheric surface layer and in the ABL. We describe the most widely used instruments and their performances. The principa l platforms used to deploy these instruments are examined. Aircraft ar e described in more details, because they allow a thorough exploration of the ABL. In the last section, some examples of ABL turbulence sign als measured in various conditions are presented. These examples illus trate horizontally homogeneous turbulence as well as inhomogeneous sig nals for which standard analysis techniques cannot be used. We show ho w some recent techniques, like wavelet transforms, can help to investi gate this kind of signal. At the end, we present what would be interes ting to do in the near future for the study of ABL turbulence. (C) 199 7 Elsevier Science B.V.