| | |
Summary: Evidence for magnetic reconnection along coronal hole boundaries
M.S. Madjarska 1 , J.G. Doyle 2 and L. van Driel-Gesztelyi 1;3;4
ABSTRACT
The present study reveals for the rst time the existence of bi-directional
jets, which are a signature of magnetic reconnection, occurring along coronal hole
boundaries. The SUMER observations obtained in the N iv 765.15 A (1.3 10 5 K)
and Ne viii 770.42 A (6 10 5 K) emission lines in an equatorial extension of a
polar coronal hole, known as the `Elephant's Trunk' coronal hole, show small
regions of a few arcsec size with strong blue- and red-shifted emission reaching
Doppler shifts of up to 150 km s 1 , i.e. bi-directional jets. The jets' number
density along coronal hole boundaries was found to be of about 4-5 times higher
with respect to the quiet Sun.
Subject headings: Sun: corona|Sun: transition region|Sun: solar wind
1. Introduction
Coronal holes (CHs) are large regions on the Sun that are magnetically open and were
identi ed as the source of the fast solar wind (800 km s 1 ) (Krieger, Timothy & Roelof
1973). They are visible in coronal lines as regions with a reduced emission relative to the
quiet Sun. There are two types of coronal holes: polar and mid-latitudes CHs. During the
minimum of the solar activity the solar atmosphere is dominated by two large CHs situated
at both polar regions. The mid-latitude CHs can be either `isolated' or connected with a
|
