Space weather describes changing environmental conditions in near-Earth space. Magnetic fields, radiation, particles and matter, which have been ejected from the Sun, can interact with the Earth’s upper atmosphere and surrounding magnetic field to produce a variety of effects.
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The auroral oval is expected to be weak and close to background levels at first. However, a slight enhancement of the auroral oval is possible today, mainly during coming night time period, due to the weak influence of a coronal hole high speed stream. The arrival of a CME early on the 25th is much more likely to generate enhancements to the auroral oval, with aurora potentially visible across northern Scotland and perhaps southern Scotland as well.
The auroral oval is expected to be weak and close to background levels at first. However, a slight enhancement of the auroral oval is possible today, mainly during coming night time period, due to the weak influence of a coronal hole high speed stream. The arrival of a CME early on the 25th is much more likely to generate enhancements to the auroral oval, with aurora potentially visible at high latitudes.
Space Weather Forecast Headline: Minor or perhaps Moderate Geomagnetic Storm expected Sunday 25 April. Else, slight chance of moderate X-ray flares resulting in R1 Radio Blackouts of the sunlit side of Earth.
Analysis of Space Weather Activity over past 24 hours
Solar Activity: Solar Activity has been low, with several common-class flares, the largest of which remains that observed at 22/2011UTC. This flare was emitted from a sunspot region which has now rotated off the sun to the northwest. This has left two sunspot regions on the facing side. The more complex of these two groups showed some decay in its intermediate and trailing spots, with this largely counteracted by proliferation and spreading in its leading portion, helping deliver occasional common-class flares. The other group has been analysed as a simple unipolar group, with no significant activity observed.
There were up two potential Coronal Mass Ejections (CMEs) visible on satellite imagery in the period: firstly an eastward-directed event that is probably associated with a 'prominence eruption' (arc of plasma leaving the sun) around the turn of the UTC in the northwestern quadrant. Secondly, a smaller event was seen heading westward in the UTC morning. The latter event's source is uncertain, but it seems likely to be tied to continuing X-ray flare activity in the recently departed sunspot from its far-sided position. Neither of these potential CMEs has been analysed as of yet, however Earth-based effects are considered unlikely from these longitudes.
In terms of earlier CME events, that tied to the common-class X-ray flare at 22/0435 UTC remains a major component of the forecast, due Sunday 25 April. An earlier event from a moderate class X-ray flare on 19 April should pass Earth today (Friday 23 April), and is a minor constituent of the forecast.
Solar Wind / Geomagnetic Activity: The solar wind is now in a slow regime, and the observed solar wind speed fell in the period. The magnetic field associated with particles in the solar wind was small-scale and stable throughout. The north-south component did gradually rotate from co-aligned to become mainly anti-aligned with the Earth's field over the 24 hours. The number of particles comprising the solar wind was at background levels, but with a slight upward trend evident, perhaps hinting at the increase in density that sometimes leads sources of fast wind: 'coronal holes'.
The net effect of the above measures was for mostly quiet geomagnetic activity, peaking in the 21-24UTC interval, perhaps because of anti-aligned magnetic field and relatively large and rapid changes in its orientation seen in this time window.
Energetic Particles / Solar Radiation: No solar radiation storms were observed.
Four-Day Space Weather Forecast Summary
Solar Activity: Solar Activity is expected to be mainly low, with daily common-class flares likely (60% risk), and a 5% slight chance of further moderate-class flares. No further groups should leave or arrive on the disc in the period, and the flare risk is held constant throughout.
Solar Wind / Geomagnetic Activity: There are up to two unassessed CME candidates that do not feature in the following forecast. Any additional contribution to geomagnetism is thought to be unlikely however. There are therefore up to two pre-existing CMEs and a high speed stream from a 'coronal hole' in the forecast.
Firstly, the CME from the moderate-class flare emitted on 19 April is expected to pass just behind Earth, with a residual slight chance of a glancing blow for the remainder of day one (Friday 23 April). This - coupled with the imminent arrival of a minor coronal hole - should give a slight chance of G1 on days one and two.
Finally, the CME from the common class flare emitted 22/0435 UTC is thought to be Earth-directed, and is expected early Day three (Sunday 25 April). Minor geomagnetic storm G1 is expected, and there is a chance of a Moderate Storm G2. There is a residual chance of Minor Storm G1 then seeing out the four days as the effects fade (Monday 26 April).
Energetic Particles / Solar Radiation: There is a slight chance of reaching S1 in the period should any large flares occur, falling a little into the weekend as the recently departed sunspot rotates further from the Earth-facing side, to leave just one noteworthy spot.
This channel highlights the outer atmosphere of the Sun - called the corona - as well as hot flare plasma. Hot active regions, solar flares, and coronal mass ejections will appear bright here. The dark areas - called coronal holes - are places where very little radiation is emitted, yet are the main source of solar wind particles.
This channel is especially good at showing areas where cooler dense plumes of plasma (filaments and prominences) are located above the visible surface of the Sun. Many of these features either can't be seen or appear as dark lines in the other channels. The bright areas show places where the plasma has a high density.