Lockwood : Auroral Source of Magnetospheric 0 + Ions

Content Provider	Semantic Scholar
Author	Lockwood, Mike
Copyright Year	2007
Abstract	Linear theory, model ion-density stressed the variability of the abundance of profiles and MSIS neutral thermospheric predicthe 0 + ions; for example Peterson et al., tions are used to investigate the stability of [1981] observed 0 + to comprise between 2 and the auroral, topside ionosphere to oxygen 70% of plasma sheet ions having an energy per cyclotron waves: variations of the critical charge of 10 eV/q to 17 keV/q. Circulation of height, above which the plasma is unstable, heavy ions throughout the magnetosphere, owing with field-aligned current, thermal ion density to the convection electric field, was first and exospheric temperature are considered. In suggested by Freeman et al., [1977]. The addition, probabilities are assessed that source of the magnetospheric 0 + is known to be interactions with neutral atomic gases prevent the ionosphere because the solar wind contains 0 + ions from escaping into the magnetosphere practically no 0 + and only small numbers of 06+ after they have been transversely accelerated [Bame et al., 1970]; the fluxes being insufby these waves. The two studies are combined ficient to explain magnetospheric abundances to give a rough estimate of the total 0 + escape even if efficient entry and charge exchange flux as a function of the field-aligned current mechanisms are present [Prange, 1978; Johnson, density for an assumed rise in the perpen1979]. dicular ion temperature. Charge exchange with Upward-flowing ions (UFI's) of ionospheric neutral oxygen, not hydrogen, is shown to be origin are observed over a wide range of altithe principle limitation to the escape of 0 + tudes along auroral field lines [Ghielmetti et ions, which occurs when the waves are driven al., 1978] ß The composition of UFI's varies unstable down to low altitudes. It is found from nearly pure 0 + to nearly pure H + [Kintner that the largest observed field-aligned current et al., 1979; Collin et al., 1981; Lundin et densities can heat a maximum of about 5 x 10 14 al., 1982b] and 0 + fluxes have been observed 0 + ions m -2 to a threshold above which they are out to 35 R E in the magnetotail [Frank et al., subsequently able to escape into the magneto1977; Formisano et al., 1981]. The pitch angle sphere in the following 500s. Averaged over distributions are either conical (with a this period, this would constitute a flux of variety of cone angles between zero and 90 ø ) or 10 12 m -2 s -1 and in steady-state the peak field-aligned (cone angle equals zero, to withoutflow would then be limited to about 1013 m -2 in angular resolution of detector). The mors -1 by frictional drag on thermal 0 + at lower phologies of these conics and beams have been altitudes. Maximum escape is at low plasma studied by Gorney et al., [1981]. Conics are density unless the 0 + scale height is very observed in the topside ionosphere, with cone large. The outflow decreases with decreasing angles close to 90 ø and only small upward field-aligned current density and, to a lesser field-aligned velocity components [Klumpar, extent, with increasing exospheric temperature. 1979; Ungstrup et al., 1979]. The pancake Upward flowing ion events are evaluated as a pitch angle distributions of these transsource of 0 + ions for the magnetosphere and as versely-accelerated ions (TAI' s) indicate that an explanation of the observed solar cycle the observations are made above the region of variation of ring current 0 + abundance. transverse ion heating. Source heights for TAI's as low as 400 km have been observed by
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