Abstract and keywords
Abstract (English):
Quasi-periodic changes of the geomagnetic field and plasma parameters in the range of Pc 5 pulsations, which occurred immediately after the interaction of interplanetary shock (IPS) with Earth’s magnetosphere in the event of April 24, 2009 at 00:53 UT are examined using ground and satellite observations. The pulsations were localized at latitudes 66–74° in the noon (11 MLT) and evening (20 MLT) sectors. The analysis of hodographs of the geomagnetic field changes both from satellite and ground observations has shown the presence of vortical disturbances. In this event, both the IPS front in the interplanetary medium and the compression wave front in the magnetosphere had a slope in the ZGSM=0 plane; the inclination angle was 14° in the interplanetary medium and 34° in the magnetosphere. The location of the vortical disturbances in the magnetosphere at different radial distances, i.e. X~5.5 Re in the noon sector and X ~–6.3 ÷–7.3 Re in the evening sector, is in agreement with the front inclination. As inferred from satellite observations, the maximum intensity of wave disturbances in both the sectors was registered in the toroidal component of the magnetic field. This suggests the resonant mechanism of excitation of these disturbances. The analysis of distribution of velocities of plasma flow and compression wave front propagation in the magnetosphere’s equatorial plane has revealed that the vortical disturbances occurred in regions where these velocities were noticeably different in magnitude.

interplanetary shock, sudden geomagnetic impulse, geomagnetic pulsations, shear flow
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Sudden geomagnetic impulses (SI) caused by the in-teraction of the solar wind (SW) with Earth’s magneto-sphere, are often accompanied by generation of geomagnetic pulsations in a range 1–1000 mHz, designated as Psi pulsations [Saito and Matsushita, 1967].

Among these pulsations are global magnetospheric oscillations observed in wide latitude and longitude ranges [Samsonov, 2013], and pulsations observed locally due to field line resonances [Nishida, 1980]. Ac-cording to the empirical model [Araki, 1994], global current systems appear during SI. They include magnetospheric (field-aligned) and ionospheric currents. Alfvén waves and corresponding field-aligned currents are assumed to be generated at Alfvén velocity gradients.

Numerical calculations predict the formation of current systems in the ionosphere and their associated plasma flow vortex disturbances in the magnetosphere. Plasma vortices appear at field line apexes corresponding to the field-aligned currents in the magnetosphere due to the accelerated flows in the equatorial plane in the outer magnetosphere [Slinker et al., 1999].

Shi et al. [2014] have studied the generation of Psi pulsations localized in the night plasma sheet. Relying on spatio-temporal characteristics of pulsations and model calculations, the authors suggest that the Psi pulsations occur due to the interaction of a vortex with a resonant field line rather than due to the sharp compres-sion of the magnetosphere by SW.

We analyze Psi pulsations in the Pc5 range localized in the pre-noon and evening sectors during the April 24, 2009 event. Using synchronous satellite and ground observations, we study spatial-temporal characteristics of the pulsations to determine causes of their generation.


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