Quantification of tailward cold <formula>O+ beams in the lobe/mantle regions with Geotail data: Constraints on polar <formula>O+ outflows

Details Quantification of tailward cold <formula>O+ beams in the lobe/mantle regions with Geotail data: Constraints on polar <formula>O+ outflows Quantification of tailward cold <formula>O+ beams in the lobe/mantle regions with Geotail data: Constraints on polar <formula>O+ outflows

Dec 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998jgr...10329371s&link_type=abstract

Journal of Geophysical Research, Volume 103, Issue A12, p. 29371-29382

Physics

12

Magnetospheric Physics: Magnetosphere/Ionosphere Interactions, Magnetospheric Physics: Magnetotail, Magnetospheric Physics: Magnetospheric Configuration And Dynamics, Magnetospheric Physics: Polar Cap Phenomena

Scientific paper

Over a wide range of the tailward distances in the lobe/mantle regions (|XGSM'|<=210RE), the Geotail spacecraft sometimes observed cold O+ beams (COBs) streaming tailward at a velocity nearly equal to that of the major proton component. The discovery of the ionospheric ions in the distant lobe/mantle leads us to a reexamination of the conventional view which expects these O+ ions to descend into the plasma sheet because of the E×B drift. In order to clarify the quantitative property of the COBs, we have projected COB parameters onto the polar ionosphere with a simple model which takes into account the velocity filter effect alone. The statistical data set from October 1993 to March 1995 in a solar-minimum period is used in the calculation. The calculated average COB flux in the lobe/mantle corresponds to at least ~108cm-2s-1 O+ flux at the 1000-km altitude. From the comparison with polar outflows, it is suggested that the cusp/cleft originating O+ ions sometimes need significant additional energization(s) so as to supply the COBs in the distant tail. When we assume the typical flux and temperature of polar O+ outflows, the required bulk energy of upward flowing ions (UFIs) turns out to be of the order of 3 keV, which is much higher than the typical energy of cusp/cleft outflows (<= 1 keV). The energy difference between the tail lobe/mantle and the cusp/cleft O+ provides clues to the supply and/or energization mechanisms of the ionospheric ions. Calculations with individual COB events suggest that the rate of COB events in which the ionospheric O+ outflow flux exceeds 109cm-2s-1 increases with the tailward distance, and it corresponds to 27% of all events in the distant tail of |XGSM'|>=150RE.

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