Estimating the capture and loss of cold plasma from ionospheric outflow

Haaland, Stein
Eriksson, Anders
Engwall, Erik
Lybekk, Bjørn
Nilsson, Hans
Pedersen, Arne
Svenes, Knut Ragnar
André, Mats
Förster, Matthias
Li, K.
Johnsen, Christine
Østgaard, Nikolai
Date Issued
Haaland, Stein; Eriksson, Anders; Engwall, Erik; Lybekk, Bjørn; Nilsson, Hans; Pedersen, Arne; Svenes, Knut Ragnar; André, Mats; Förster, Matthias; Li, K.; Johnsen, Christine; Østgaard, Nikolai. Estimating the capture and loss of cold plasma from ionospheric outflow. Journal of Geophysical Research - Space Physics 2012 ;Volum 117. s. -
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An important source of magnetospheric plasma is cold plasma from the terrestrial ionosphere. Low energy ions travel along the magnetic field lines and enter the magnetospheric lobes where they are convected toward the tail plasma sheet. Recent observations indicate that the field aligned ion outflow velocity is sometimes much higher than the convection toward the central plasma sheet. A substantial amount of plasma therefore escapes downtail without ever reaching the central plasma sheet. In this work, we use Cluster measurements of cold plasma outflow and lobe convection velocities combined with models of the magnetic field in an attempt to determine the fate of the outflowing ions and to quantify the amount of plasma lost downtail. The results show that both the circulation of plasma and the direct tailward escape of ions varies significantly with magnetospheric conditions. For strong solar wind driving with a southward interplanetary magnetic field, also typically associated with high geomagnetic activity, most of the outflowing plasma is convected to the plasma sheet and recirculated. For periods with northward interplanetary magnetic field, the convection is nearly stagnant, whereas the outflow, although limited, still persists. The dominant part of the outflowing ions escape downtail and are directly lost into the solar wind under such conditions.
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