DETECTION OF TURBULENCE AROUND JET STREAMS USING A VHF RADAR

Two methods for detecting turbulence near jet streams are investigated using a VHF radar-the corrected spectral width of the vertical echo a nd the anisotropy of the signal returned. It is found that turbulent d issipation rates in excess of 0.2 mW kg(-1) may be detected using the spectral width, but uncertainties in the derivation of this parameter preclude detection of weak turbulence. Anisotropy of the signal is cap able of detecting some turbulence in regions of high static stability, but the method is not quantitative and is best employed to confirm th e spectral-width estimates when these are near the detection limit. In dependent confirmation that atmospheric conditions were favourable for turbulence was provided by Richardson number profiles derived from th e radar and a Raman lidar. Measurements of static stability by the lid ar and spectral widths by the radar allow an estimate of the turbulent -dissipation rate. The application of these techniques to two jet stre am passages is discussed.