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Register a new userIonospheric manifestations of geomagnetic pulsations at high latitudes
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In this paper the interrelation between geomagnetic pulsations and variations in frequency Doppler shift (Fd) of the ionosphere-reflected radio signal is under investigation. The experiment on simultaneous recording of Fd variations and geomagnetic pulsations was organised at high latitude station in Norilsk (geomagnetic latitude and longitude 64.2 N, 160.4 E, L=5.3) during Febrary-April of 1995-98. Thirty cases of simultaneous recording of duration from 10 min to two hour were analysed: 6 cases of simultaneous recording of variations Fd and regular geomagnetic pulsations Pc5; and 25 cases of recording of Fd variations and irregular pulsations Pi2. On the basis of experimental results, the following conclusions have been drawn: a) Hydromagnetic waves in the range of regular Pc5 pulsations, when interacting with the ionospheric F2 layer, make the main contribution to short-period Fd variations. The possible mechanism of Fd variations are oscillations of electron density, associated with distribution of a hydromagnetic wave in an ionosphere. b) There exists an unquestionable interrelation between Fd variations of the sporadic E layer-reflected radio signal and irregular Pi2 pulsations, but for some reasons it is traced poorly.
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In this paper an attempt is made to verify the hypothesis on the role of geomagnetic disturbances as a factor determining the intensity of traveling ionospheric disturbances (TIDs). To improve the statistical validity of the data, we have used the based on the new GLOBDET technology method involving a global spatial averaging of disturbance spectra of the total electron content (TEC). To characterize the TID intensity quantitatively, we suggest that a new global index of the degree of disturbance should be used, which is equal to the mean value of the rms variations in TEC within the selected range of spectral periods (of 20-60 min in the present case). It was found that power spectra of daytime TEC variations in the range of 20-60 min periods under quiet conditions have a power-law form, with the slope index k = -2.5. With an increase of the level of magnetic disturbance, there is an increase in total intensity of TIDs, with a concurrent kink of the spectrum caused by an increase in oscillation intensity in the range of 20-60 min. It was found that an increase in the level of geomagnetic activity is accompanied by an increase in total intensity of TEC; however, it correlates not with the absolute level of Dst, but with the value of the time derivative of Dst (a maximum correlation coefficient reaches -0.94). The delay of the TID response of the order of 2 hours is consistent with the view that TIDs are generated in auroral regions, and propagate equatorward with the velocity of about 300-400 m/s.
Basic properties of the mid-latitude large-scale traveling ionospheric disturbances (LS TIDs) during the maximum phase of a strong magnetic storm of 6-8 April 2000 are shown. Total electron content (TEC) variations were studied by using data from GPS receivers located in Russia and Central Asia. The nightglow response to this storm at mesopause and termospheric altitudes was also measured by optical instruments FENIX located at the observatory of the Institute of Solar-Terrestrial Physics, (51.9 deg. N, 103.0 deg. E) and MORTI located at the observatory of the Institute of Ionosphere (43.2 deg. N, 77.0 deg. E). Observations of the O (557.7 nm, 630.0 nm, 360-410 nm, and 720-830 nm) emissions originating from atmospheric layers centered at altitudes of 90 km, 97 km, and 250 km were carried out at Irkutsk and of the O_2 (866.5 nm) emission originating from an atmospheric layer centered at altitude of 95 km was carried out at Almaty. Variations of the f_0F2 and virtual altitude of the F2 layer were measured at Almaty as well. An analysis of data was performed for the time interval 17.00-21.00 UT comprising a maximum of the Dst derivative. Results have shown that the storm-induced solitary large-scale wave with duration of 1 hour and with the front width of 5000 km moved equatorward with the velocity of 200 ms-1 to a distance of no less than 1000 km. The TEC disturbance, basically displaying an electron content depression in the maximum of the F2 region, reveals a good correlation with growing nightglow emission, the temporal shift between the TEC and emission variation maxima being different for different altitudes.
We have performed an analysis of case events and statistics of positive ionospheric storms in the dayside region of the equatorial ionization anomaly during recurrent geomagnetic storms (RGSs), which dominate in geomagnetic and ionospheric conditions on the declining phase of solar activity in 2004 to 2008. It is shown that total electron content (TEC) has a tendency to minimize before the beginning of RGSs and to peak 3 to 4 days after, i.e. on the RGS recovery phase produced by high-intensity long-duration continuous auroral activity. The maximum of TEC coincides with the maximum of solar wind velocity within high-speed solar wind streams. An analysis of electron content vertical profiles, derived from two independent methods using ionosondes and COSMIC/FORMOSAT-3 radio occultation, showed that in the maximum of an ionospheric storm on 28 March 2008, the F2 layer thickens, NmF2 increases by ~50% and hmF2 elevates by a few tens of kilometers. The response of positive ionospheric storms to solar, heliospheric and geomagnetic drivers reveals a prominent longitudinal asymmetry. In the longitudinal range from -90 deg to 90 deg, the solar illumination plays a major role, and in the range from 90 deg to -120 deg, the influence of heliospheric and geomagnetic drivers becomes significant. The highest correlations of the TEC enhancements with the heliospheric and geomagnetic drivers were found during December - February period (r increased from ~ 0.3 to ~0.5). We speculate that the dynamics controlling this might result from an effect of solar zenith angle, storm-time effects of thermospheric Sum(O/N2) enhancement, and penetrating electric fields of interplanetary and magnetospheric origin.
In this paper we show that the simple analysis of the local geomagnetic field behaviour can serve as reliable imminent precursor for regional seismic activity increasing. As the first step the problem was investigated using one- component Dubna fluxgate magnetometer. The result of 2001-2004 Sofia monitoring confirmed many old papers for connection between Earth tide (Sun- Moon tides as earthquakes trigger) and jump (Geomagnetic quake) of daily averaged one minute standart deviation of the geomagnetic field. The second step (2004-present), which included analisys of three-component Danish fluxgate magnetometer data, worked in Skopje Seismological observatory, confirmed the first step result. The analysis of INTERMAGNET data stations around which was happened stronger earthquakes also confirmed our result. The distribution of time difference between the times of such earthquakes and local daily averaged tide vector movement for impending tide extreme confirms our estimate that the increasing seismicity is realized in time window about +/- 2.7 days. The Complex program for researching the possibility for when, where and how earthquakes prediction is proposed as well as the short description of FORTRAN codes for analysis of earthquakes, geomagnetic and tide data, their correlations and visualization.
The time evolution of the strength of the Earths virtual axial dipole moment (VADM) is analyzed by relating it to the Fokker-Planck equation, which describes a random walk with VADM-dependent drift and diffusion coefficients. We demonstrate first that our method is able to retrieve the correct shape of the drift and diffusion coefficients from a time series generated by a test model. Analysis of the Sint-2000 data shows that the geomagnetic dipole mode has a linear growth time of 13 to 33 kyr, and that the nonlinear quenching of the growth rate follows a quadratic function of the type [1-(x/x0)^2]. On theoretical grounds, the diffusive motion of the VADM is expected to be driven by multiplicative noise, and the corresponding diffusion coefficient to scale quadratically with dipole strength. However, analysis of the Sint-2000 VADM data reveals a diffusion which depends only very weakly on the dipole strength. This may indicate that the magnetic field quenches the amplitude of the turbulent velocity in the Earths outer core.
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