Dependence of the Solar Wind Plasma Density on Moderate Geomagnetic Activity Elucidated by Potential Learning

Abstract

Abstract In this study, the relationship between a moderate range of geomagnetic activity, represented by the Kp index (2- – 5+), and solar wind conditions were revealed based on Potential Learning (PL), a newly developed neural network, and dependence of particular solar wind plasma density on moderate geomagnetic conditions was discussed. It has poorly been understood from what stage of geomagnetic activity the solar wind density begins to control the Kp level. We utilized the PL protocols that were improved for the research of space plasma physics in our previous study. As a result, we succeeded in specifying the most influential solar wind parameters at an extremely low (0–1+) and high (6- – 9) Kp ranges under southward interplanetary magnetic field (IMF) conditions. The IMF three components (Bx, By, and Bz), solar wind flow speed (Vx) in geocentric solar magnetospheric (GSM) coordinates, and solar wind plasma density (Np) obtained from the OMNI solar wind database (1998–2019) were used as input parameters for PL. Based on PL, the solar wind velocity is the most significant parameter for the moderate Kp range under southward IMF conditions and the solar wind number density is the second most influential parameter. Based on the examination of the statistical relationship between the solar wind speed and plasma density under extremely low, high, and moderate Kp ranges using the PL database, geomagnetic conditions remain high while the plasma number density becomes large, even if the solar wind velocity decreases (or remains similar). This shows that both solar wind velocity and plasma number density govern geomagnetic activity, following the relational equation between Kp index and the solar wind plasma parameter. We investigated the relation between the solar wind velocity and plasma density and revealed that the solar wind density begins to affect the Kp level from moderate geomagnetic activity level (2- – 5) based on PL and incidental statistical studies using PL input data. Our results would greatly help understand general relationship between solar wind conditions and geomagnetic activity under various IMF conditions.