Polar wind survey with the Thermal Ion Dynamics Experiment/Plasma Source Instrument suite aboard POLAR

Abstract

Abstract. In February 1996, the POLAR spacecraft was placed in an elliptical orbit with a 9 RE geocentric distance apogee in the northern hemisphere and 1.8 RE perigee in the southern hemisphere. The Thermal Ion Dynamics Experiment (TIDE) on POLAR has allowed sampling of the three-dimensional ion distribution functions with excellent energy, angular, and mass resolution. The Plasma Source Instrument (PSI), when operated, allows sufficient diminution of the electric potential to observe the polar wind at very high altitudes. In this paper, we describe the results of a survey of the polar wind characteristics for H + , He + , and O + as observed by TIDE at -5000 km and -8 RE altitudes over the polar cap during April-

Survey of cold ionospheric outflows in the magnetotail

“…However, our method is much more sensitive to lighter ion species, since their lower energy will make them more affected by the spacecraft potential and thus create a larger wake. Moreover, hydrogen is the dominant ion species in the low-energy high-latitude ion outflows (Su et al, 1998). Our calculated velocity can thus be regarded as the proton velocity, and later comparison of the properties of the outflowing ions to previous measurements will therefore only regard the hydrogen component of the flow.…”

“…The current understanding of the high-latitude ion outflows, including the polar wind, can mainly be attributed to a wealth of studies from Akebono (Abe et al, 1993(Abe et al, , 1996(Abe et al, , 2004Cully et al, 2003a) and Polar (e.g. Moore et al, 1997;Su et al, 1998;Chappell et al, 2000;Lennartsson et al, 2004;Liemohn et al, 2005;Huddleston et al, 2005;Peterson et al, 2006). More details on the previous measurements of the high-latitude ion outflows can be found in the recent review articles by Yau et al (2007) and Moore and Horwitz (2007).…”

“…Olsen (1982) made similar measurements of cold ions when two different spacecraft (Applied Technology Satellite 6 and SCATHA) were in eclipse. By artificially regulating the potential of Polar, Su et al (1998) were able to make a statistical study of the low-energy ion outflow at 8 R E above the northern pole. Engwall et al (2006a) reported the first measurement of low-energy ion flows with energy of the order of 10 eV at a geocentric distance as far as 18 R E using two different methods on the Cluster spacecraft: (1) using a conventional ion detector in a special low-energy mode, and under simultaneous operation of artificial spacecraft potential control, and (2) using a new method, which detects the ions through electric field measurements of the large wake created behind the spacecraft in this flowing plasma.…”

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

“…This has been evidenced by many observational studies and models (Abe et al, 1993;Su et al, 1998a, b;Glocer et al, 2012;Maes et al, 2015). Maes et al (2015), studying outflow above smallscale polar cap arcs using Cluster (Escoubet et al, 2001) measurements, found that the upflow above the polar cap can be roughly divided into two distinct groups based on the solar zenith angle (SZA) of the footpoint of the field line in the ionosphere.…”

“…The low energization also means that it is very difficult for O + ions to escape Earth's gravitational potential via this mechanism, and so very little O + is expected in the polar wind. Nevertheless, O + ions have been observed above the polar caps and in the lobes (Nagai et al, 1984;Waite Jr. et al, 1985;Abe et al, 1993;Su et al, 1998a). Many additional mechanisms have been proposed to explain this (see, e.g., Tam et al, 2007, for an overview).…”