Flare productivity of newly-emerged paired and isolated solar active regions

¹ School of Physics and Astronomy, University of Manchester, PO Box 88, Manchester M60 1QD, UK e-mail: s.dalla@manchester.ac.uk
² Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK
³ Institute of Astronomy, University of Cambridge, Cambridge CB3 OHA, UK

Received: 26 January 2007
Accepted: 7 April 2007

Abstract

Aims.We investigate whether sunspot regions that emerge near existing ones are more flare productive than those that emerge isolated.

Methods.We analyse a sample of 2115 new regions obtained from the USAF/Mount Wilson catalogue of sunspot regions. For our analysis we use AstroGrid, a Virtual Observatory developed in the UK, to build a series of workflows that perform queries to catalogues of solar regions and flares, and operations on the results of the queries. If a new region emerged through the solar surface within 12° of a pre-existing one, we classify it as paired, otherwise as isolated.

Results.We find that paired regions are more flare productive than isolated ones, although this is a small effect. Here only soft X-ray flares of magnitude greater than C1.0 are considered, and flare productivity is characterised by the percentage of regions that produced at least one flare over 4 days since emergence, and by the average number of flares over the same period. For paired regions, we also consider the flare productivity of the nearby companion region and find that if a flare does happen within the pair, it will more likely take place in the companion region than in the newly-emerged one. Our results show that although emergence in proximity to another region can slightly increase the probability of a flare taking place, presumably by increasing the likelihood of magnetic reconnection and significant change in magnetic topology, this is not a large effect. It appears that intrinsic properties of the region are the key factor in determining whether or not it will produce flares, as opposed to interaction with pre-existing regions.