Specific features of daytime long-period pulsations observed during the solar wind impulse against a background of the substorm of August 1, 1998

Abstract

Long-period geomagnetic pulsations in the (1.7–6.7) mHz frequency range at 18.25–18.48 UT on August 1, 1998, caused by several successive sudden changes in the solar wind (SW) dynamic pressure, are studied against a background of substorm intensification. The data of the ground stations, which were near local noon (the CANOPUS Canadian network) and on the nightside (the auroral stations in Yakutia and at the IMAGE network), and the INTERBALL-1, ACE, WIND, and GOES 8, extramagnetospheric satellites are used. The effect of the SW plasma and IMF parameters, SW inhomogeneity front inclination, and geomagnetic activity on the pulsation propagation and polarization direction and amplitude is discussed. The properties of pulsations, recorded before the substorm, correspond to the pulsation excitation by the inhomogeneity front incident on the magnetopause during the magnetically quiet period: pulsations propagate from the contact point onto the nightside when the amplitude increases and the polarization sense of rotation is opposite on the dawn and dusk sides. Substorm intensification results in the propagation direction reversal and in a more complex behavior of the pulsation amplitude and polarization on the dayside.