Survey of cold ionospheric outflows in the magnetotail

Abstract

Abstract. Low-energy ions escape from the ionosphere and constitute a large part of the magnetospheric content, especially in the geomagnetic tail lobes. However, they are normally invisible to spacecraft measurements, since the potential of a sunlit spacecraft in a tenuous plasma in many cases exceeds the energy-per-charge of the ions, and little is therefore known about their outflow properties far from the Earth. Here we present an extensive statistical study of cold ion outflows (0-60 eV) in the geomagnetic tail at geocentric distances from 5 to 19 R E using the Cluster spacecraft during the period from 2001 to 2005. Our results were obtained by a new method, relying on the detection of a wake behind the spacecraft. We show that the cold ions dominate in both flux and density in large regions of the magnetosphere. Most of the cold ions are found to escape from the Earth, which improves previous estimates of the global outflow. The local outflow in the magnetotail corresponds to a global outflow of the order of 10 26 ions s −1 . The size of the outflow depends on different solar and magnetic activity levels.

Seasonal variations and north–south asymmetries in polar wind outflow due to solar illumination

“…Moreover, integrated over the polar cap area, these H + flux densities lead to fluxes similar to those found by other studies of the polar wind (see e.g. Nagai et al, 1984;Cully et al, 2003;Huddleston et al, 2005;Engwall et al, 2009;André et al, 2015).…”

“…Moreover, during geomagnetically quiet times, the polar cap is the main cold ion source for the magnetospheric lobes . These ions have temperatures generally not much higher than the ion temperature in the ionosphere and flow at relatively small velocities (Engwall et al, 2009). As a consequence, they are very difficult to measure with satellites flying through the lobes, because these cold ions often have energies too low to overcome the spacecraft potential, which can go up to several tens of electronvolts in these regions.…”

Outflow of low-energy O<sup>+</sup> ion beams observed during periods without substorms

“…Based on these numbers the escaping fluxes correspond to a flow rate of 10 19 -10 21 ions s −1 . This number is less than the cold ions escaping the polar cap, 10 26 ions s −1 (Engwall et al, 2009). However, considering that the quiet auroral oval can persist for hours, the number of ions escaping here (> 10 24 ions) can be higher than that predicted by Seki et al (2001) and comparable to the number of energetic ions escaping during substorms (Yan and .…”

“…The polar cap ions include the polar wind (Engwall et al, 2009;Li et al, 2012) and cusp origin O + Liao et al, 2010Liao et al, , 2012. Cold polar cap ions sometimes consist of mainly H + ions and can dominate the lobe outflow fluxes (Engwall et al, 2009;Nilsson et al, 2010). Ions flowing out with transpolar arcs (TPAs, also known as theta auroras) are field-aligned and observed when the interplanetary magnetic field (IMF) is northward (Kullen, 2012).…”

“…These escaping ions have been observed by experiments from radars on the ground (Wahlund et al, 1992) and on numerous satellites including DE1, Polar, Geotail and Cluster (Yan and André and Yau, 1997;Moore et al, 1999;Maggiolo et al, 2006Maggiolo et al, , 2011Nilsson et al, 2006;Seki et al, 2001). The polar cap ions include the polar wind (Engwall et al, 2009;Li et al, 2012) and cusp origin O + Liao et al, 2010Liao et al, , 2012. Cold polar cap ions sometimes consist of mainly H + ions and can dominate the lobe outflow fluxes (Engwall et al, 2009;Nilsson et al, 2010).…”