Coronal Behavior Before the Large Flare Onset

TL;DR

This study analyzes coronal features before a major solar flare, revealing that upflows, loop expansion, and intensity reductions occur hours to a day prior, aiding flare prediction efforts.

Contribution

It provides new insights into coronal behavior prior to large flares by combining multi-instrument observations of coronal dynamics before the event.

Findings

Upflows grow from 10 to 30 km/s a day before the flare.

Expanding coronal loops observed hours before the flare.

Gradual reduction in soft X-ray and EUV intensities.

Abstract

Flares are a major explosive event in our solar system. They are often followed by coronal mass ejection that has a potential to trigger the geomagnetic storms. There are various studies aiming to predict when and where the flares are likely to occur. Most of these studies mainly discuss the photospheric and chromospheric activity before the flare onset. In this paper we study the coronal features before the famous large flare occurrence on December 13th, 2006. Using the data from Hinode/EUV Imaging Spectrometer (EIS), X-Ray Telescope (XRT), and Solar and Heliospheric Observatory (SOHO) /Extreme ultraviolet Imaging Telescope (EIT), we discuss the coronal features in the large scale (~ a few 100 arcsec) before the flare onset. Our findings are as follows: 1) The upflows in and around active region start growing from ~10 to 30 km /s a day before the flare. 2) The expanding coronal loops are clearly observed a few hours before the flare. 3) Soft X-ray and EUV intensity are gradually reduced. 4) The upflows are further enhanced after the flare. From these observed signatures, we conclude that the outer part of active region loops with low density were expanding a day before the flare onset, and the inner part with high density were expanding a few hours before the onset.