12th International EISCAT Workshop, Kiruna, Sweden, 29 August - 3 September 2005

Cosmic radio noise absorption modified by the RF heating in the D region

A. Kero¹, C.-F. Enell¹, Th. Ulich¹, E. Turunen¹, P. T. Verronen², A. Seppälä², M. Rietveld³, F. Honary⁴

¹Sodankylä Geophysical Observatory, Sodankylä, Finland,
²Finnish Meteorological Institute, Helsinki, Finland,
³EISCAT Scientific Association, Tromsø, Norway,
⁴Department of Communication Systems, Lancaster University, U.K.

Abstract

Radio wave absorption in collisional plasma takes place in interaction between electrons, accelerated by the electric field of the wave, and neutrals. Optimal conditions for the absorption process can be found in the ionospheric D region, where the collision frequency is high and the electron density is sufficient. In RF heating experiments the radio wave absorption is used to increase the electron temperature of the plasma. According to our modelling, the maximum effect by the EISCAT heater occurs normally at altitudes around 75 km, where the electron temperature can be raised by a factor of 10.

However, the detection of the heating effect at these altitudes has been difficult for the EISCAT incoherent scatter radars. A different approach is to use narrow beam riometers for the observations. By monitoring the cosmic background radio noise propagated through the heated D region volume, one can deduce electron temperature changes due to heating. In this poster we present a theoretical study of heating effects on cosmic radio noise absorption seen by riometer. The results are compared to the signatures seen by the IRIS riometer (69.0N, 20.8E) during experiments carried out at the EISCAT heating facility (69.6N 19.2E).