Heliospheric Current Sheet (HCS) Crossings and Disconnection Events (DEs) in Comet Halley 1985-1986

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Session 14 -- Comets, Asteroids, Meteoroids
Oral presentation, Monday, 30, 1994, 10:00-11:30

[14.03] Heliospheric Current Sheet (HCS) Crossings and Disconnection Events (DEs) in Comet Halley 1985-1986

J.C. Brandt (LASP/U. Colorado), F.M. Caputo (LASP/U. Colorado), J.T. Hoeksema (Stanford U.), M.B. Niedner, Jr. (NASA/Goddard), Y. Yi (LASP/U. Colorado)

Evidence is presented for the clear association of HCS crossings with the DEs observed in Halley's comet, 1985-1986. This report ex-tends the pre- vious work (Brandt et al. 1992, BAAS, 24, 1270 and Yi et al. 1994, PASS, in press) from 16 to 19 DEs and is now thought to include all the major DEs observed in comet Halley.

Improvements to the analysis include use of the latest current-sheet loca- tions and a different fitting technique that significantly reduces the uncer- tainties as determined by comparing the extrapolated HCS location with locations directly measured by spacecraft. The RMS dispersion of the spacecraft measurements around the extrap-olated HCS locations is lower than the corresponding value for DEs. These values can be completely reconciled if the DE process (from HCS crossing to actual disconnection) has a dispersion of about 1/2 day.

The comet Halley interval in 1985-1986 was exceptionally favorable for this type of study with excellent imaging coverage of the comet, solar- wind data available from several spacecraft, and HCS loca-tions available for coronal source surfaces. These favorable circum-stances are unlikely to be repeated anytime in the foreseeable fu-ture.

If we assume that DEs have a common cause and that the DEs ob-served in comet Halley are representative, then the result that they are associated with HCS crossings, and apparently no other prop-erty of the solar wind (such as high-speed streams), gives clear di-rection to theoretical efforts.

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