Doppler investigations of short-period ionospheric variations produced by magnetic disturbances.
Abstract
In the report the results of experimental researches on excitation magnetospheric Alfven resonator by sudden magnetic disturbances and related with this an ionosphere effects are presented. The experiments were conducted with the help of the multifrequency Doppler installation of IZMIRAN since 1998. The research program consist in monitoring ionospheric disturbances related to solar activity. The measurements were conducted by a method of vertical radio sounding simultaneously on 4 frequencies. The set of selected frequencies would provide the signal reflection from Å, F1 and F2 layers of an ionosphere. The data processing consist in dynamic Doppler spectra calculation, which one allows receive the information on time responses of ionospheric disturbances. The effect, which one is discussed in the report, was watched already in the maiden experiments in April, 1998 at the moment of a substorm beginning in the polar ionosphere. It was revealed, that at the moment of a beginning of magnetic disturbance - which arrived from Tiksi Bay region (or substorm ignition area) - the Doppler displacements of sounding signal frequency (at Moscow) exhibit the synchronic variations (the observed period was about one minute duration) on all frequencies. During researches under the program HIRAC/SolarMax, which one was directed on analysis of influencing of solar activity on an ionosphere, it was possible to snap solar flare of April 26, 2001, which one has generated classic effects in an ionosphere -- sharp rise of an electron density and strong absorption of radio waves (black-out effect). The Doppler spectra on all active frequencies have shown in an instance of ignition considerable (more than 1 Hz) displacement of frequency. However most interesting events have begun after 2 day after a flash, when the magnetic disturbance began. At this time on Doppler spectra the quasiperiodic frequency drifts of radio echoes have appeared. Thus the quasiperiodic variations of Doppler displacement of frequency descended synchro on all search frequencies to the period some les 1 minute and were prolonged during more than 10 min. That fact, that such variation descended on all frequencies simultaneously testifies that the factor, disturbing an ionosphere, affects at once all ionosphere layers: from E up to F2 layer. The period of observed quasiperiodic frequency drifts (or ionosphere parameters variation) is the same for both as substorm and as solar flare action and is equal to one minute or bounce time for Alfven oscillation of magnetic field tube above the IZMIRAN region. It means that during magnetic disturbance the local Alfven resonator would be exñitated and in result the quasiperiodic precipitations of energetic particles are expected.
- Publication:
-
35th COSPAR Scientific Assembly
- Pub Date:
- 2004
- Bibcode:
- 2004cosp...35.2661K