Comparison of Ground-Based and Satellite Geomagnetic Pulsations during Substorms

Magnetic field pulsations in the magnetosphere and the time of their detection and location on the Earth's surface are analyzed. Measurements of magnetic field fluctuations from fluxgate magnetometers of the Cluster II satellites and measurements from ground-based magnetometers in the auroral oval region are used. The substorms on August 13, 2019, are examined. In particular, two substorms and flapping motions of the magnetotail current sheet are analyzed. The measurements from ground-based observatories are selected using the 3DView software, a tool for the visualization of spacecraft position with associated geomagnetic tail field lines. A continuous wavelet transform is used to identify geomagnetic pulsations, and an integrated representation in two frequency bands, 45-150 s (Pc4/Pi2) and 150-600 s (Pc5/Pi3), is considered to determine the pulsation type and estimate the observed shifts between the pulsations recorded in the Earth's magnetotail and in the auroral oval region. Correlated Pi2 and Pc5 pulsations in the auroral region and in the magnetotail are detected. The magnitude of detected pulsations depends on the relative position of ground-based magnetometers and the projection of the field line on which the spacecraft are located. Based on the time delay between the maxima of geomagnetic pulsations at the Earth's surface in relation to disturbances in the magnetosphere, the velocity of disturbance propagation along the magnetic field line is estimated.