2 Data

A disconnection event was found in 47 out of the selected 531 images from The International Halley Watch Atlas of Large-Scale Phenomena (Brandt et al. 1992a), covering the period from 1985 November 13 to 1986 April 15. They were visually and systematically analysed to derive their onset times (Table 1), i.e., the time when the comet supposedly crossed a magnetic sector boundary in the solar wind.

 

 

Table 1: Onset time of 19 DEs

DE number	Onset time (UT)	Possibly related reports
1	1985 Nov. 12.76
2	1985 Dec. 05.61
3	1985 Dec. 13.54	Niedner (1986);
		Yi et al. (1994b)
4	1985 Dec. 14.16
5	1986 Jan. 01.90
6	1986 Jan. 07.52
7	1986 Jan. 09.63	Niedner (1986);
		Tomita et al. (1987);
		Niedner et al. (1991)
8	1986 Jan. 10.16	Niedner (1986);
		Tomita et al. (1987);
		Niedner et al. (1991)
9	1986 Jan. 10.76
10	1986 Feb. 22.17	Niedner (1986);
		Yi et al. (1994b)
11	1986 Mar. 08.90	Niedner (1986);
		Wu & Qiu (1987);
		Niedner &
		Schwingenschuh (1987)
12	1986 Mar. 14.05
13	1986 Mar. 15.87	Feldman et al. (1986);
		Celnik et al. (1988);
		Yi et al. (1994a)
14	1986 Mar. 20.01
15	1986 Apr. 03.38
16	1986 Apr. 06.45	Niedner (1986);
		Celnik et al. (1988)
17	1986 Apr. 07.70
18	1986 Apr. 11.75
19	1986 Apr. 15.34

The 47 DEs documented in these 47 different images allowed the derivation of the 19 DE onsets. The list of them and references to analyses and discussions are given in Table 1.

Figure 1: Carrington-Niedner Diagram. The solid line is the heliospheric current sheet location as determined by Yi et al. (1994b). The sector boundary crossings as determined by spacecraft (ICE, PVO, IMP-8 and Vega-1) are marked as shown in the legend. One sector boundary crossing estimated from the geomagnetic index, $\Sigma$$K_{\rm p}$, is also marked. The onsets of DEs determined in this work (1985 December 13.5: upper panel and 1986 February 22.2: lower panel) are marked with (#) while the onsets calculated by Yi et al. (1994b) are marked with asterisks (*). The $\times$ shows a one day shift corresponding to a one day delay between the sector boundary encounter and the DE for the sunward reconnection model. The + marks the turn-on of plasma activity. The point representing the onset of 1985 December 13.5 (determined in this work) is slightly displaced from the onset determined by Yi et al. (1994b) in order to avoid crowding, since they are at the same time and position. The onset of 1986 February 22.2 has a small offset in relation to the one of 1986 February 21.7 determined by Yi et al. (1994b). The coronal source surface 2.0 solar radii is used for Carrington rotation 1769, and the coronal source surface 2.5 solar radii is used for Carrington rotations 1770-1772