The amazing M7 flare

A strong M7 flare occurred in NOAA 2036 on 18 April (peak at 13:03UT). This sunspot region developed on disk in just a few days (image underneath), was magnetically complex but had not produced any strong flare until that day.

The flare seems to get initiated by a bright jet near the middle cluster of sunspots (image underneath at 12:35UT), apparently destabilizing the overlying magnetic loops (12:43UT) and creating a reconnection and flare. The creation of a transient coronal hole south of the active region can be observed, indicating the ejection of material into space. There was also an EIT-wave associated to this event, which can be seen sweeping towards the Sun's east limb in PROBA2/SWAP difference imagery (one image subtracted from the previous one).

The flare was also accompanied by a proton event (the fifth this year, see this list). The first protons started to arrive about 1 hour after the onset of the flare, and about 30 minutes after the peak. It was a minor event, reaching a maximum of 58pfu (particle flux unit) early on 19 April.

Radio-bursts accompanying this flare event were observed by the Solar Radio Observatory in Humain (image underneath). The type III burst recorded at 12:35UT coincides with the appearance of the jet seen in EUV (extreme ultraviolet) and a brief hick-up in x-ray flux. Also a Type II burst can be seen (from about 12:54 till 13:03UT) which is indicative of a shock wave moving through the solar atmosphere. The speed of this shock wave was determined to be near 800km/s.

Based on the EUV and radio observations, the appearance of a coronal mass ejection (CME) shortly after the flare was no surprise. It showed as a halo around the Sun, indicating that part of this CME was directed towards Earth. The recorded speed was about 1000km/s, but the bulk of the plasma cloud was directed away from the Earth. Around 11:30UT on 20 April, Earth suffered the impact from this CME. Wind speed reached 750km/s, but the magnetic field of the CME was initially positive, eventually resulting in only small negative (southward) excursions. Active conditions were recorded, with a brief episode of a minor geomagnetic storm.

This movie first shows the sunspot regions in white light, then three clips in SDO/AIA filters of increasing temperature (AIA 304-171-131) overlaid on the white light imagery, a clip combining three SDO-filters (AIA 304-171-094), the PROBA2/SWAP difference imagery (EIT-wave), and ends with the combined SDO/AIA and SOHO/LASCO imagery (CME).
Credits - Data and imagery for the movie clips were taken from the PROBA2/SWAP, Humain Radioastronomy Station, SDO, SOHO/LASCO, Staff, and (J)Helioviewer.

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