Abstract
Abstract. Heavy ion injection events (registered in the C+/N+/O+ mass channel) into the ionosphere at 1700km height are surveyed using the Swedish-German Freja satellite data. Heavy ion injections from the inner magnetosphere are mostly found in the nightside sector with a few exceptions that occur on the dayside. We report on these exceptional cases, particularly two specific events which seem to have a different generation/transport mechanism of heavy ions from the majority of cases: 1) mono-energetic heavy ion injection near local noon with oxygen first and protons later; and 2) a multiple heavy ion dispersion event at 9 MLT. Both events are unique without any similar events in terms of dispersion pattern during the more than 2 years of the entire Freja operation, and these events are found during the main phase of major magnetic storms (peak Dst is -144nT and -105nT). The first event is probably of dayside origin but the exact mechanism to make both energy filter and mass filter is unknown. The second event can be traced back to one localized energization of dense oxygen with strong pitch-angle anisotropy within 1000km distance from the spacecraft.
Highlights
Magnetospheric heavy ion injections into the ionosphere have rarely been discussed they were already detected in the early 1970’s (Shelley et al, 1972). One reason for this lack of reports may be related to the fact that no past low-altitude (
Since the escape of ionospheric ions is a common feature over the polar region in the form of ion beams or conics (e.g. Lundin et al, 1987; Norqvist et al, 1998; Moore et al, 1999), and since the inner magnetosphere is eventually filled with heavy ions during magnetic storms (Hamilton et al, 1988; Blanc et al, 1999), it is not surprising to observe heavy ion injections into the ionosphere from the inner magnetosphere
This characteristic normally implies a velocity filter, but in this case we expect that the ions which are slower than a certain velocity are lost through the polar cap and only fast ions can stay within the closed magnetosphere
Summary
Magnetospheric heavy ion injections into the ionosphere have rarely been discussed they were already detected in the early 1970’s (Shelley et al, 1972). Freja’s three-dimensional ion composition spectrometer (TICS) provides high spatial/temporal resolution (about 80 m or 10 ms per energy step, and 3 km or 0.4 s per energy sweep) data for heavy ions and protons (Eliasson et al, 1994) with 30% energy resolution in its normal mode It sometimes suffers from contamination from protons (this is inevitable for almost all mass-resolving ion spectrometers when the flux is high), it is capable of identifying primarily injecting species between proton and heavy ions, as shown in Fig. 1 (see the section for details). No similar phenomenon has been found during more than 2 years of Freja observation, nor has it been reported in the past
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