It is well known that VHF echo-intensity data obtained at nonvertical beam directions can be used to retrieve the refractive-index structure parameter Cn2 and that vertical profiles of Cn2 can be used to identify and monitor frontal structures in the free troposphere. In a case study, VHF radar observations of Cn2 are compared with vertical profiles of Mg2 (the square of the vertical gradient of the generalized potential refractive index) obtained from the data of two radiosondes launched from 4 km east of the radar site. The experiment was carried out in the Harz Mountains, north Germany, on October 18, 1993, during a high-pressure period under clear-sky conditions. Well-defined maxima of Cn2 and Mg2 are found at the surface of a warm front at altitudes slightly below 5 km. At altitudes in the immediate vicinity of the front, echo-intensity oscillations are observed, which have an amplitude of up to 9 dB and a period of about 40 min and which are attributed to gravity wave-induced vertical displacements of the frontal surface. Vertical profiles of the outer scale of turbulence, L0, are obtained from the profiles of Cn2 and Mg2. In the stably stratified region below the front (at altitudes between 3 and 5 km), 5--20 m is typical, while in the less stably stratified altitude region between 5 and 7 km, 20--50 m is more representative. It is found that large values of L0 are correlated with low static stability; a relationship between L0 and the Richardson number (dynamic stability), however, was not observed. A continuous temporal increase of Cn2 at altitudes between 5 and 7 km was observed. It is attributed to a temporal increase of the vertical variability of the humidity above the front.¿ 1997 American Geophysical Union