Escape of suprathermal O⁺ ions in the polar cap

Abstract

Instruments on board the Dynamics Explorer (DE) 1 and 2 spacecraft have been used to investigate the characteristics of a very low‐energy (less than 10 eV) outflow of O+ ions at high altitudes over the polar cap. The measured O+ outflow has a relatively high Mach number (2–6) and a large flux (∼2×108 cm−2 s−1). A statistical study using 50 orbits of retarding ion mass spectrometer (RIMS) data indicates that the outflows occur during active magnetic conditions, lasting for several hours over large areas of the polar cap. The observations are then discussed and analyzed in a framework based on polar wind models with particular attention paid to the new information obtained by the DE 2 Fabry‐Perot interferometer (FPI), and the impact these flows have on the composition of the magnetosphere. The observed suprathermal outflow of O+ suggests a scenario requiring both significant compositional changes in the high latitude thermosphere and significant heating of the ions and electrons in the topside ionosphere.

Combined ESR and EISCAT observations of the dayside polar cap and auroral oval during the May 15, 1997 storm

“…As it increased with height it is interesting to speculate that this ion up¯ow may be associated with an out¯ow at the topside ionosphere and higher altitudes (Lookwood, 1982; Shelly et al, 1982;Yau et al, 1985;Waite et al, 1985). If this is indeed the case, the observation would be in agreement with Waite et al (1985) stating that the out¯ow of O + in the polar cap exhibits a wide spatial and temporal extent under active magnetic conditions, and that it is strongest in the 1000±1600 MLT sector. Satellite data are needed for a ®nal proof to identify any ion out¯ow above 1000 km during the corresponding period.…”

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

“…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).…”

Electrodynamics in the duskside inner magnetosphere and plasmasphere during a super magnetic storm on March 13–15, 1989

“…Satellite observations of ion outflow at high altitudes (>5000 km) have been extensively studied in many previous works (e.g., Shelley et al, 1976;Lockwood et al, 1985;Waite et al, 1985;Yau et al, 1985;Chappell et al, 1987). Lockwood et al (1985) showed that occurrence of the heavy ion outflow depends on K p index by using the retarding ion mass spectrometer (RIMS) data obtained from the DE-1 satellite for 2 years.…”