Abstract
Abstract. Ion escape is of particular interest for studying the evolution of the atmosphere on geological timescales. Previously, using Cluster-CODIF data, we investigated the oxygen ion outflow from the plasma mantle for different solar wind conditions and geomagnetic activity. We found significant correlations between solar wind parameters, geomagnetic activity (Kp index), and the O+ outflow. From these studies, we suggested that O+ ions observed in the plasma mantle and cusp have enough energy and velocity to escape the magnetosphere and be lost into the solar wind or in the distant magnetotail. Thus, this study aims to investigate where the ions observed in the plasma mantle end up. In order to answer this question, we numerically calculate the trajectories of O+ ions using a tracing code to further test this assumption and determine the fate of the observed ions. Our code consists of a magnetic field model (Tsyganenko T96) and an ionospheric potential model (Weimer 2001) in which particles initiated in the plasma mantle region are launched and traced forward in time. We analysed 131 observations of plasma mantle events in Cluster data between 2001 and 2007, and for each event 200 O+ particles were launched with an initial thermal and parallel bulk velocity corresponding to the velocities observed by Cluster. After the tracing, we found that 98 % of the particles are lost into the solar wind or in the distant tail. Out of these 98 %, 20 % escape via the dayside magnetosphere.
Highlights
Before the 1970s, it was believed that the solar wind was the primary source of magnetospheric plasma
This study aims to clarify whether O+ ion outflows observed in the plasma mantle will escape the magnetosphere and be lost into the solar wind as suggested previously from observations (Slapak et al, 2017; Slapak and Nilsson, 2018; Schillings et al, 2018)
Since the bulk perpendicular velocity is much smaller than the parallel bulk velocity in the plasma mantle (Vaith et al, 2004), the O+ ions in the mantle can be characterised by the parallel bulk velocity and the thermal velocity
Summary
Before the 1970s, it was believed that the solar wind was the primary source of magnetospheric plasma. This conception became obsolete a few years later with the studies of Shelley et al (1976) and Sharp et al (1977), who observed ionospheric O+ ions with high velocities in the high-latitude ionosphere. A few decades later, it is well known that ion upflow from the ionosphere is a significant source for the magnetosphere (Hoffman, 1968; Chappell et al, 1987; Abe et al, 1993), and it is accelerated through several processes to reach the high-altitude cusp and plasma mantle. The cold ions – detected with the spacecraft wake technique (Engwall et al, 2009) – are believed to be dominant for the magnetospheric plasma
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