Irregular structures of the F layer at high latitudes during ionospheric heating

Results on heating the ionospheric F region above Tromso, Norway are presen ted. The ionosphere was monitored by satellite tomography and amplitude sci ntillation methods as well as the EISCAT incoherent scatter radar. No effec t of heating was observed in the daytime. In the evening and in the pre-mid night sector, noticeable tilts of the F region were observed during heating periods. The tilts overlapped the heating cone, where the electron density decreased and irregularities exceeding 10 km in size appeared. Between the heating periods the F layer was restored to its horizontal shape. The anis otropic parameters of small-scale irregularities with scale lengths of hund reds of metres were also determined. It was found that the perpendicular an isotropy points in the direction of F region plasma flow. In some cases the results can be explained by assuming that the small-scale irregularities w ere generated within the heating cone and drifted out of the heating region where they were subsequently observed.