Space Weather Report #130 – Stealthy solar storms (CMEs), rumblings on the sun’s far side

2026-05-09, 0200 UTC

Further fast solar wind, further unnoticed solar storms (CMEs) could arrive, interesting development in the north-west and behind the north-east limb

Sun: Overview

We are under the influence of the positively polarised coronal hole CH50+, whose solar wind has a speed of between 500 and 600 km/s in the vicinity of the Earth. Other coronal holes may continue to increase the speed of the solar wind over the next few days.

The active regions (sunspot groups) of the visible solar disc are small and simple – with the exception of region 4432, which is growing with increasing complexity and flare potential. If the development continues like this, it could produce CMEs before reaching the western limb. Whether this will happen remains to be seen.

In the east we see a very large trans-equatorial coronal hole with negative polarity. In May, this means high geoeffectivity. We could come under its influence in a week or so.

Behind it in the north-east is a complex of active regions that has recently produced stronger solar flares (M2.6) and larger CMEs (Full Halo). We are eagerly following further developments (more on this below).

In the first few days of May, we see an active corona with a lot of movement, filament eruptions, coronal holes opening and closing, large-scale dimming in the south and in the north-east︎ already the roar of the rear side. Some CMEs have left the sun unnoticed, partly because they are difficult to recognise in the high corona or because they have left hardly any traces in the coronographs.

The shape of the equatorial coronal hole also seems to change constantly – this alone is enough to produce stealth CMEs, which leave the Sun’s vicinity very slowly and unnoticed, but are later accelerated by the fast solar wind from the coronal hole that created them and compressed into “real” interplanetary CMEs.

Sun: Roaring at the north-eastern limb

The Solar Orbiter spacecraft currently gives us a view of the mostly empty back side of the sun. To the north, however, there is a large sunspot group cluster, from which active region 4419 produced two major X-class flares and over 10 CMEs during the last rotation before disappearing behind the western limb.

Region 4419 probably no longer exists, but to the west of it a new large one has formed which has recently produced very actively flares and CMEs. It should soon be visible at the eastern limb. It is not possible to estimate exactly how the dynamics of the cluster will develop. However, the potential for significant space weather from this area is probably still high.

Still behind the north-eastern limb, we have already been able to observe a quite astonishing eruption with opening field lines and a dancing filament. Let’s see if there is anything left when cluster is in the earth-strike zone in a few days.

Earth: Aurora 2026-05-04/05

An interplanetary coronal mass ejection (CME, solar storm) on 30.4. with an initially favourably south-facing magnetic field caused some mid-latitude polar light in Europe.

The visible green arc in northern Germany shows that the auroral oval has clearly expanded to the south (equatorwards).

☞ Polarlicht 2026-05-04/05 (AKM-Forum)

☞ More on this in the previous article: Filament eruptions in all directions, including a little towards the earth #2026-05-04 – Luminous substorm

Earth: Aurora 2026-05-07/08

A substorm lasting only a few minutes produced very high-reaching red rays at the Arctic Circle, which could still be seen over 1400 km to the south: 67°N ☞ 54°N (at least photographically). The oval remained stationary north of the Arctic Circle – normally we cannot see the aurora under these circumstances. An exception!

☞ Polarlicht 2026-05-07/08 (AKM-Forum)

The trigger was probably an unexpected CME (stealth CME) that arrived on 7 May. Its magnetic field was predominantly northern, but the axial B_y-component was strong (20nT), so that some energy was transferred to the lobes of the Earth’s magnetotail and red rays could be generated. Nevertheless, there was only one brief substorm in Europe.

ROTI from Norway shows the auroral oval in real time

Kartverket Norway provides a service whose purpose is actually to predict GPS disturbances. It can be used to determine the position and strength of the auroral oval.

(ROTI = Rate of TEC Index – the rate of change of the total electron content of the ionosphere)

Earth: Solar wind analysis

A CME arrived early on 4 May, somewhat earlier and significantly stronger than predicted. At around 1500 UTC, its core reached us with its magnetic field initially orientated to the south, which led to increased geomagnetic activity and aurora. On 5 May, an unexpectedly strong CME followed. The time and place of origin cannot be clearly determined – there are several possibilities. However, its magnetic field remained exclusively to the north, so there was no effect on the Earth’s magnetic field. On 7 May, another CME arrived (this one was also not expected), initially orientated magnetically to the north, later briefly to the south – moderate geomagnetic effects.

We then saw the stream interaction region and subsequently the fast solar wind from the coronal hole CH50+. Both arrived about a day later than expected. As we are now in the positive sector of the interplanetary magnetic field (connection with positively polarised coronal hole), the effects on the Earth’s magnetic field remain small: in May, the Earth prefers negative magnetic fields to produce auroras.

The Jplot shows several CMEs that were (could have been) travelling to Earth and possibly still are. The yellow lines are presumably the CMEs that arrived on 4 and 5 May. To the right we see a whole series of other CMEs, some of which could have grazed the Earth and possibly still will. However, they could also pass ahead and behind the Earth.

So we can expect more surprises, but nothing (nothing at all) is certain.

Three candidates for CMEs that could have hit us. Unfortunately, there were many data gaps in the real-time downlink stream from the STEREO A satellite, as well as from SOHO LASCO. Therefore, not all earth-directed CMEs could be detected and simulated in time. Although NOAA CCOR-1 has fewer data gaps, it has difficulties displaying faint CMEs.

More on eruptions at the beginning of May in the previous article Filament eruptions in all directions, including a little towards the earth:

• CMEs (solar storms) from 30 April slowly travelling towards Earth
• Filament Lift-Off on late 2nd May/early 3rd May

More updates always on X or bluesky

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