PC index as a proxy of the solar wind energy that entered into the magnetosphere: 4. Relationship between the solar wind dynamic pressure (PSW) impulses and PC, AL indices

Abstract

The solar wind dynamic pressure (PSW) impulses impacting on the magnetosphere were separated on the basis of solar wind parameters measured in the point of libration L1 in 1998–2017. Comparison of the “estimated” PSW impulses reduced to the Earth's magnetopause with the appropriate sudden impulses (SI), revealed in the ground-based 1-min SymH index, showed that features of the really observed sudden impulses (moment of beginning, time evolution, intensity) can be significantly different from characteristics of the estimated PSW impulses. Because of this the preference was given to the real SI events over the estimated PSW impulses. Only the events with sudden impulses starting against the background of steady quiet pressure levels were taken for the analysis (N = 143). Relationship between the positive (leaps) and negative (drops) SI events, on the one hand, and PC and AL indices, on the other hand, were examined under the various solar wind conditions, such as: growing and steady solar wind speed at negative and positive values of the IMF BZ component, fluctuating BZ and solar wind speed, steady solar wind speed and BZ = 0. Analysis of SI events showed that the solar wind dynamic pressure impulses themselves are not promote (or insignificantly promote) the solar wind energy input into the magnetosphere, which is controlled by the interplanetary electric field EKL = Vsw*(BY2+BZ2)1/2 and is displayed by the polar cap magnetic activity PC index. When the PSW impulses (leaps or drops) are accompanied by the corresponding changes in EKL field, the PC index correlates (increases or decreases) with the PSW changes. Inconsistency between the PSW and PC behavior becomes evident as soon as the EKL and PSW courses start to diverge. Development of magnetic disturbances (AL index) is governed only by the EKL field and PC index increase irrespective of the PSW impulses magnitude and time evolution.