Solar Extreme Events of 2003:
Fundamental Science and Applied Aspects

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Experimental investigations of variations in the electron density in the middle latitude ionospheric D-region during magnetic storms
Gokov A.M., Tyrnov O.F.,

Solar flares, accompained by increasing intensity of the optical, X-ray and corpuscular radiations and by coronal mass emission, form a state of space weather. Problems of solar fenomena affecting the lower Earth ionosphere, D-region, are still little studied. At present, a part playing by corpuscular ionization of the middle latitude ionospheric D-region has been experimentally confirmed. High energy electrons and protons may considerable change the ionosphere ionization at 50-100 km by night and during disturbances of both a natural and an artificial character. Effects of protons on the middle latitude D-region has been little studied. In the paper there are given results of experimental investigations by a partial reflection (PR) technique of variations in the middle latitude D-region electron density during a few magnetic storms. Responses of the D-region to the beginning and end of the storm were considered. Electron density variations in the D-region during the solar proton events (spe) over period of magnetic storms were investigated. The investigations were carried out by means of the PR technique equipment belonging to the Kharkiv National University Radiophysical Observatory. In order to be analysed, PR signals records obtained during a few magnetic storms in 2002-2003 were selected. There were analyzed data obtained in the experiments conducted during 8 spe's into the Earth ionosphere over the periods of solar flares and magnetic storms. The ionospheric D-region response to the magnetic storms is of a complex and ambiguous character as the magnetic storms are followed by a hole number of phenomena coinciding in time, their contributions to the changes in the lower middle latitude ionosphere being difficult or impossible to be determined. The events statistics do not yet allow to determine all (or the most part of them) special features of the response. Among the considered, we note the following ones. 1. It was experimentally found that increasing in the geomagnetic disturbance index, Kp, at the beginning of the magnetic storm (without a sudden commencement) was followed by characteristic changes in PR signals and radio noise and by quasi-harmonic changes in the middle latitude ionospheric D-region electron density, N. The N-cnanges were dozens-hundreds of per cent. 2. In the final phase of the magnetic storms there were found quasi-periodic long-term (some hours) changes in the electron density at 81-90 km. Increasing in N was 100-400%%. 3. During the spe events, there was experimentally found increasing in the electron density by more than 50-100%% in the lower D-region (~70-80 km) for several dozens of minutes. Ionization change rates were estimated. 4. The characteristics of PR signals and radio noise during the events considered have special features clearly differing from those under the undisturbed conditions. 5. On the basis of the hypotisis of electrons and protons precipitating over a period of the magnetic storm, using the experimental data there were calculated energy characteristics of the particle flows, which agree in a good manner with the theoretical estimations and the known data on the particle flows, obtained experimentally under disturbances of different natures.

Skobeltsyn Institute of Nuclear Physics, Moscow State University, 2004