Observations of HF-induced instability in the auroral E region
- 1School of Electrical Engineering, Royal Institute of Technology, Teknikringen 31, 10044 Stockholm, Sweden
- 2EISCAT Scientific Association, Rymdcampus 1, 98192 Kiruna, Sweden
- 3Swedish Institute for Space Physics, Uppsala Division, Box 537, 751 21 Uppsala, Sweden
- 4EISCAT Scientific Association, Ramfjordmoen, 9027 Ramfjordbotn, Norway
Abstract. Enhancements were observed in backscattered radar power during an ionospheric heating experiment from two distinct altitude regions in the auroral E region above Tromsø. For the experiment the EISCAT Tromsø heater was operated with O mode and X mode alternated at 4.04 MHz, close to the 3rd electron gyroharmonic. Ion-line data recorded with the EISCAT UHF radar reveal different temporal evolutions as well as different ion-line characteristics for the enhancements from the two altitude regions. The upper layer is dominated by a strong central feature, whereas the lower layer has three peaks corresponding to the central feature and the two ion lines. The altitude region of the two closely spaced (altitude separation ~ 5 km) but distinct enhancements is close to the critical altitude for the heater wave.