Research Article

Investigation of pre-flare dynamics using the weighted horizontal magnetic gradient method: From small to major flare classes

¹ Solar Physics & Space Plasma Research Center (SP2RC), School of Mathematics and Statistics, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH, UK
² Debrecen Heliophysical Observatory (DHO), Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Science, P.O. Box 30, 4010 Debrecen, Hungary
³ Department of Astronomy, Eötvös Loránd University, Pázmány P. sétány 1/A, Budapest, H-1117, Hungary
⁴ CAS Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China
⁵ School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, PR China

^* Corresponding author: m.korsos@sheffield.ac.uk

Received: 15 June 2017
Accepted: 10 January 2019

Abstract

There is a wide range of eruptions in the solar atmosphere which contribute to space weather, including the major explosions of radiation known as flares. To examine pre-event behavior in δ-spot regions, we use here a method based on the weighted horizontal gradient of magnetic field (WG_M), defined between opposite polarity umbrae at the polarity inversion line of active regions (ARs) as measured using from the Debrecen Heliophysical Observatory catalogues. In this work, we extend the previous analysis of high-energy flares to include both medium (M) and low-energy (C and B) flares. First, we found a logarithmic relationship between the log value of highest flare class intensity (from B- to X-class) in a δ-spot AR and the maximum value of WG_M of the 127 ARs investigated. We confirm a trend in the convergence-divergence phase of the barycenters of opposite polarities in the vicinity of the polarity inversion line. The extended sample, (i) affirms the linear connection between the durations of the convergence-divergence phases of barycenters of opposite polarities in δ-spot regions up to flare occurrence and (ii) provides a geometric constraint for the location of flare emission around the polarity inversion line. The method provides a tool to possibly estimate the likelihood of a subsequent flare of the same or larger energy.