ULF wave activity from HF pumping experiments at mid and high latitudes

Blagoveshchenskaya, N.1, Borisova, T.1, Kornienko, V.1, Rietveld, M.2, Frolov, V.3, Kosch, M.4, Honary, F.4 and Brekke, A.5

1 Arctic and Antarctic Research Institute, St. Petersburg, Russia
2 EISCAT Scientific Association, Tromsų, Norway
3 Radiophysical Research Institute, Nizhny Novgorod, Russia
4 Lancaster University, Lancaster, England, UK
5 University of Tromsų, Tromsų, Norway

Experimental results from Tromsų and SURA heating experiments in 2005-2006 related to the HF heater-induced and natural ultra low frequency (ULF) waves in the Pc3-5 range (30-300s) are examined. The combination of HF-induced scatter target and bi-static HF Doppler radio scatter remote observations at St. Petersburg is used to examine the ionospheric signatures of a ULF wave. It was found that the amplitude modulated heating by using the HF transmission scheme of 30s on, 30 s off gave rise to the wave variations of Doppler frequency shift, fd, and spectral power of signals scattered from artificial field-aligned irregularities (AFAIs). These waves with period of 1 min were observed from Tromsų heating experiment on 12 October 2005 as well as from SURA experiments on 5 and 7 September 2006. It is interesting that on 12 October 2005 together with an artificial ULF wave with 1 min period there was a ULF wave of natural origin with a period of about 5 min. For this event we have analysed the magnetic field variation data recorded near Tromsų at Kilpisjarvi from SAMNET network of ground-based magnetometers. The correlation between magnetic and Doppler data was found. In the course of SURA heating experiments the period of amplitude modulated heating was close to the eigenperiod for the SURA magnetic flux tube. Here more pronounced fd wave variations as compared with the Tromsų case were observed especially in the evening hours. Natural ULF waves at high latitudes were examined from UK MAZE heating experiment on 3 October 2006. Bi-static HF Doppler radio scatter observations were simultaneously performed at two diagnostic paths allowing to reconstruct two-dimensional vector of plasma velocity in the scattering volume. Ray tracing and Doppler shift simulations were made for this experiment. ULF waves with periods of 3 - 5 min were observed above Tromsų in the morning hours. It was found that the phase velocities of magnitude of about 40-80 m/s were directed to the north-west. The magnitude and direction of the velocity exhibits the wave variations.