The phase relation of solar wind parameters with a solar activity proxy

Abstract

Manifestations of the solar magnetic activity in several forms, such as coronal mass ejections (CMEs), energetic particles and solar wind slow or high speed streams, strongly affect the terrestrial and circumterrestrial electromagnetic environments. Such phenomena primary affect the Earth's magnetosphere, which is perturbed and compressed, but subsequently they can have cascading effects on all the underlying systems, down to the upper atmosphere and the planetary surface. Because of the impact on the human activities too, it is of paramount importance to try to predict the time windows in which high speed solar wind is expected to occur. We study here the phase relation of a proxy of the solar activity, the Ca II K index, with solar wind parameters, such as speed and dynamic pressure. An unexpected relation between the parameters is found once the phases of the signals are considered, opening to the possibility to predict at least the expected mean solar wind conditions from the mentioned solar activity proxy. In this respect, it is essential to take into account for the presence of transients, which are responsible for the observed changes in the phase of the solar wind parameters. The method allows at least to predict the phase of the solar cycle in which high speed solar wind streams have the greatest probability of occurrence, as well as how their amplitudes are related to the solar cycle's one.