Other
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsh13a0299c&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #SH13A-0299
Other
2101 Coronal Mass Ejections (7513), 2111 Ejecta, Driver Gases, And Magnetic Clouds, 2134 Interplanetary Magnetic Fields
Scientific paper
Studies that use suprathermal electrons to determine the distribution of open and closed fields in ICMEs imply that about 40% open during the CME release process and that the remainder open over a much longer period of months to years. The opening mechanism is understood to be interchange reconnection between an open field line and one leg of an ICME field-line loop back at the Sun. The argument that ICME fields must eventually open is based upon the finding that signatures of the alternative means of preventing a build-up of flux in the heliosphere, disconnection through reconnection between open fields elsewhere on the Sun, are seemingly far too rare to account for the flux involved. Ironically, the requirement that ICME fields must continue to open at a slow rate, based upon a negligible decrease in the percentage of open ICME flux at 5 AU compared to 1 AU, implies that the signature of that interchange reconnection might be indistinguishable from the signature of disconnection, thus re-opening the question of why more signatures of disconnection are not observed. If interchange reconnection occurs when the apex of an ICME loop is far from the Sun, beyond some as yet unknown distance, it is unlikely to carry the counterstreaming electron signature that presumably signals connection to the Sun at both ends because the sunward electron beam will have disappeared owing to scattering along the lengthy path it has to travel to reach the observing spacecraft situated much closer to the Sun. Without counterstreaming, the loop will appear to be open, and the signature of interchange reconnection will look like that of reconnection between two open fields, that is, like disconnection. One way to approach this dilemma is to question whether counterstreaming is a valid signature of closed fields at 5 AU, as has recently been suggested. Another way, adopted here, is to extend the search for disconnection signatures to high-time resolution data. Preliminary results show clear evidence of small-scale disconnection signatures within larger-scale heat flux dropouts (HFDs) that were earlier dismissed as disconnection signatures because of a residual strahl in the averaged data. A survey of 96-sec 3DP Wind data in 68 HFDs indicates that 52 (76%) have within them some flat pitch-angle distributions at background (halo) level intensities, ranging from about 5-40% of their durations. Whether these are signatures of interchange reconnection in ICME legs or true disconnection elsewhere cannot be determined, but the question becomes irrelevant since either acts to balance the flux added by CMEs. Whether the magnetic flux in these disconnection signatures is sufficient to balance the budget has yet to be determined.
Crooker Nancy U.
Pagel Christina
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