Astron. Astrophys. Suppl. Ser. 139, 311-320

A survey of flares and current helicity in active regions

S.D. Bao - H.Q. Zhang - G.X. Ai - M. Zhang

Send offprint request: S.D. Bao

Correspondence to: bshd@sun10.bao.ac.cn

Beijing Astronomical Observatory, Chinese Academy of Sciences, Beijing 100080, China
National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China

Received February 9; accepted June 9, 1999

Abstract:

We examine the spatial and temporal relationship between chromospheric H$_{\beta}$ flares and photospheric current helicities in active regions. All of the data were obtained by the vector magnetograph system at Huairou Solar Observing Station of Beijing Astronomical Observatory. We focus our analysis on NOAA Active Region 6233, which was observed on 30 August 1990. The result shows that rapid and substantial changes of distribution of current helicity in an area or in its vicinity are most likely to trigger flares, but no compelling correlation between peaks of current helicity and flare sites. Furthermore, we study the influence of flares on helicity for several other active regions. We find that the time variations of current helicity in the active regions with highly productive flares are more significant than those of the poorly flare-productive active regions, and that the magnitude of current helicity does not always decrease after flares. Therefore we conclude that the rate of variation of current helicity may be considered as an indicator of flare activity.

In this paper we describe the specification of the instrumentation and data used, and we describe the methods for computing helicity. The noises and errors in our data are estimated to be at the $2-3 \sigma$ level.

Key words: Sun: activity -- Sun: flares -- Sun: magnetic fields