The cleft ion fountain

Abstract

Low‐energy (below approximately 50 eV) ionospheric ions, injected into the magnetosphere at the dayside cleft, are studied using data from the retarding ion mass spectrometer (RIMS) experiment on the Dynamics Explorer 1 satellite. It is concluded that upwelling ions at the cleft form an ion fountain and are blown into the polar cap by antisunward convection. At high Kp (>4), convection is generally strong enough to fill the entire polar magnetosphere with low‐energy O+ ions, whereas at low kp (<2) they are largely restricted to the dayside half of the cap. Using a two‐dimensional kinetic ion trajectory model, the locations where RIMS detected O+ within the cap are shown to be consistent with the spatial distributions of O+ density, predicted for an upwelling ion source at the cleft and various dawn‐dusk convection electric fields. A detailed study is made of one polar pass of DE 1, during which RIMS detected He+, N+, O+, and O++ ions, the ion trajectory model being used to trace all these ions back to a common source at an observed upwelling ion event near the cleft. All observed species are deduced to be falling earthward in the nightside of the cap, as predicted from the model, indicating the dominance of gravity over upward field‐aligned acceleration (such as by the ambipolar electric field). Comparison of field‐aligned velocities observed for O+ and O++ ions defines a maximum limit to the upward electrostatic acceleration present within the cap which was only sufficient to eject ionospheric H+ ions, all heavier ions being supplied from the dayside by the cleft ion fountain.

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

“…There are three main regions of outflow at high latitudes: the auroral oval, the cusp, and the polar cap. The auroral oval and the cusp are regions of intense ion outflow in response to strong energy inputs like Poynting flux, particle precipitation, and the work done by strong field-aligned electric fields accelerating ions upwards (Lockwood et al, 1985;Zheng et al, 2005;Moore and Khazanov, 2010;Nilsson et al, 2012). In the absence of such energy inputs, the main source of energy for ion outflow in the polar cap is solar illumination.…”

Survey of cold ionospheric outflows in the magnetotail

“…The outflows in the cusp region form the cleft ion fountain (Lockwood et al, 1985), which is transported over the polar cap by anti-sunward convection and mixes with the other low-energy outflows. When travelling farther out along the magnetic field lines into the lobes, it will be difficult to distinguish the different sources of the outflows, and…”

Modeling transverse heating and outflow of ionospheric ions from the dayside cusp/cleft. 2 Applications

“…The dayside cusp/cleft region has been identified as the major source of ionospheric ions for the magnetosphere (Lockwood et al, 1985). Inside these regions, the energetic, or non-thermal ion outflow is classified into beams and conics.…”