IAGA 2005 Scientific Assembly, Toulouse, France, 18-29 July 2005

Artificial heating effects on the cosmic HF radio noise absorption

A. Kero1, C.-F. Enell1, Th. Ulich1, E. Turunen1, T. Raita1, P. T. Verronen2, A. Seppälä2, M. Rietveld3, F. Honary4

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


Radio wave energy absorption in the ionosphere takes place in collisions between the electrons, accelerated by the radio wave electric field, and neutral particles. This process is strongest in the lowest part of the ionosphere, in the D region (50-100km), where the electron density is already significant and the electron-neutral collision frequency is still high. Therefore the radio wave absorption provides tools for remote sensing of the D region, which is otherwise difficult to access experimentally.

Riometers (relative ionospheric opacity meters) are standard instruments in ionospheric monitoring and have been in operation globally for decades. Riometers are radio receivers which detect cosmic background HF radio noise through the ionosphere. There are also active instruments for ionospheric studies, which enhance electron temperatures by transmitting high power HF waves. This method is called artificial ionospheric heating and allows us to modify ionospheric conditions in a controlled manner. Combination of these techniques could be used for active D-region studies even in a case of too low electron density for the radar measurements.

The Sodankylä Ion Chemistry (SIC) model has been developed for detailed modelling of the D region and is used, among many other applications, for interpretation of riometer data. In this poster we present a theoretical study of heating experiment effects on riometer absorption. The results are compared to the signatures seen by the IRIS riometer (69.0N, 20.8E) during heating experiments carried out in the EISCAT heating facility (69.6N 19.2E).