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First proton event of 2015

Proton events have already been discussed in earlier news items, such as on 23 January 2014 and on 16 August 2012. It concerns solar eruptions associated with a strong increase in the flux of particles with energies of 10 MeV or more (Note 1). Once this proton flux exceeds the pre-established threshold of 10 pfu (Note 2), it is considered a proton event, if not it is labeled a proton flux enhancement.

Filament eruption

A very nice filament eruption occurred near the north-western solar limb during the morning hours of 3 June 2015. It concerned the long filament already mentioned in the previous news item of 27 May 2015, when it was still in the north-eastern quadrant.


Layer upon layer

Last week, the sunspot activity was again all but exciting. Only a few, very small, and mostly inactive sunspot groups were visible in white light. In H-alpha, which is a filter showing the "cold" inner atmosphere of the Sun, the Sun's outlook was dominated by some long filaments. These are local belts of plasma squeezed together by opposite polarity magnetic fields (see last week's newsletter). Moving up to the hot outer solar atmosphere, the extreme ultraviolet (EUV) imagery from SDO showed darkish patches.

Twisting beauties

Some very nice prominence and filament eruptions were observed over the last week. In this MOVIE, four major events are shown in the combined filters of SDO's AIA 304 ("cool"; about 80.000 degrees; red) and AIA 193 ("hot"; about 1.3 million degrees; green). Prominences and filaments usually lay dormant until the surrounding magnetic fields become unstable and eject the material into space.

A stethoscope for the Sun

The STEREO spacecraft are still in safe mode as they go through their superior conjunction, passing behind the Sun as seen from Earth. This means that for an extended period of time, we cannot receive any imagery from the far-side of the Sun due to radio interference from the Sun. See the STEREO-website for up-to-date information.

The wall


Squeezed between magnetic fields of opposite polarity, a really big blob of plasma (charged particles) rounded the Sun's northeast limb. The prominence offered impressive sights in H-alpha filters, which are suited to observe the inner, "cold" (10.000 degrees) atmosphere of the Sun.

NOAA 2321: one, two or three groups?


At the end of a rather dull week, a cluster of sunspots appeared from behind the northeast limb. The active region was numbered NOAA 2321, had a sunspot area of about 4 times the surface area of the Earth, and produced an M1 flare on 12 April.

Impressive filament eruption


In absence of any large or complex sunspot group, this week's main event was another spectacular filament eruption. This eruption took place late on 4 April and was associated with a long duration C3.8 double ribbon flare that started at 22:16UT, peaked at 00:07UT, and ended at 01:45UT. "Double ribbon" here means that there are two bright ribbons parallel and along the location of the ejected filament.

Divergent


Around noon on 27 March, a giant wall of solar plasma (charged particles) propelled itself into space. A movie of this event can be seen here.

NOAA 2297 targets Earth


Over the last 2 weeks, solar activity was dominated by the small but complex sunspot group NOAA 2297. Under its dictatorship, no less than 97 "common" C-class flares, 23 "medium" M-class flares and 1 "extreme" X-class flare were produced. This makes it one of the most flare productive groups of the current solar cycle so far, very comparable to e.g. NOAA 1515 from July 2012 (see Note 1).

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