DYNAMICS OF THE GEOMAGNETIC DISTURBANCES IN THE INITIAL PHASE OF THE MAGNETIC STORM: CASE STUDY

Using the global network of ground-based magnetometers, the spatial distributions of bay-like disturbances and geomagnetic pulsations have been investigated in the initial phase of moderate magnetic storm of April 5, 2010. This storm was characterized by high dynamic pressure (up to 15 nPa) and the high solar wind speed (> 800 km / s). According the globally distributed ground-based observations, the huge two-step high latitude geomagnetic disturbances (up to 2700 nT) were observed in the initial phase of this magnetic storm. The first, minor activation, caused by SC, exhibited the significant enhancement of auroral brightening at 67o accompanying by bursts of geomagnetic Pi2-Pi3 pulsations at these latitudes in the evening and morning sectors. The THEMIS A, D, and E probes demonstrated increasing the Bx values. The double auroral oval was observed in the end of this substorm, simultaneously with the geomagnetic pulsation intensification at both sides of the auroral oval. The second, major activation was observed in the very large longitudinal region at high latitudes: from the evening to the noon sector of geomagnetic local time. The most intensive substorm was recorded in the pre-midnight sector 22- 23 MLT at the geomagnetic latitude of ~70o. The substorm onset was accompanied by strong auroral activations. The THEMIS A, D, and E probes showed the dipolarization at XGSM ~ -11 Re. The strong Pi3 magnetic pulsations were recorded during whole substorm from the midnight to the early morning at the auroral latitudes. In recovery phase of substorm the regime of geomagnetic pulsation changed: instead irregular Pi3 pulsations, the regular continuous Pc5 pulsations were observed. Pc5 pulsations had a global character, i.e. they were observed in the large area of the longitude (from early morning until evening hours MLT), as well as in the latitude (from the polar to the equatorial ranges). The spectral analysis of the Pc5 pulsations, observed in the morning magnetosphere (GOES 11) and on the ground, showed the coincidence of the frequency peaks in the spectra.