M2.7 flare and earth-directed CME (‘solar storm’)

Update 2026-03-17, 1900 UTC

On 16 March 2026 at 12:15 UTC (peak), a solar flare of magnitude M2.7 occured in the central area of the visible solar disc. The origin is an active region with a large sunspot surrounded by many smaller ones of varying polarity. The region already made its presence felt yesterday with an M-class flare.

Continued and ongoing updates in the next article:
Another M2.7 flare and an Earth-directed CME column (‘solar storm’)

Solar observation (EUV)

Our favourite satellite SDO from NASA is once again delivering magnificent images.

Large-scale dimming and a coronal wave spreading to the north-west can be seen. Indicators for an earth-directed CME.

It can be observed in detail how a filament erupts to the west of the large sunspot.

Once again the flare/eruption in other wavelengths: SDO AIA 193, 211 and 131

The north-south orientation of the posteruptive arcades is an indication of a highly inclined CME with a N-S orientation. This would result in a unipolar CME with either only a northern or only a southern magnetic field (WNE or ESW flux rope).

The PFSS model shows the potential magnetic field of a quiet sun. The loops can be used to predict the trajectory of the ejected material.

Radio emissions

SWPC/NOAA reports the following radio bursts:

• Type II
  • Launch time: 2026 Mar 16 1209 UTC
    Estimated speed: 1227 km/s
    Indicator for CME
• Type IV
  • Start time: 2026 Mar 16 1212 UTC
    Indicator for strong CMEs and released energetic particles
• 10cm radio burst
  • Start time: 2026 Mar 16 1209 UTC
    End time: 2026 Mar 16 1217 UTC
    Duration: 8 minutes
    Peak flux: 380 sfu (base 109 sfu)
    Possible interference with radar, GPS and satellite communication

Energetic particles

Contrary to expectations from the radio emissions, no energetic particles have been detected near the Earth so far.

There may be delays at the moment due to poor connection to the source region (in the east) and the effect of the high-speed stream. But the eruption took place seven hours ago and it is slowly becoming unlikely that we will still see particles of the eruption – probably with the arrival of the shock front. It is therefore not a monster CME for the time being.

Coronographs

CCOR-1 (2026-03-16 1900 UTC)

Unfortunately, triangulation is not possible because STEREO A COR2 has had a data gap for two days. The speed can therefore only be guessed.

This graphic illustrates the problem of missing triangulation:

Source: https://www.swpc.noaa.gov/sites/default/files/images/u59/04%20Craig%20Deforest%20Official.pdf

STEREO A COR2 (2026-03-16 2100 UTC)

STEREO A COR2 data is now available. Consequently, some model runs are likely to be updated.

We are observing a complex CME that is not actually that slow. We can also see that the northward-directed CME is not actually Earth-directed (earth is left) – at least parts of the northward-directed structures do not belong to our CME.

CME analyses and model runs

Without data from STEREO A, it is only possible to make assumptions and the CME analyses can deviate considerably from reality, which is why all model runs without STEREO A data are extremely uncertain.

The estimates for the arrival are from 18 March to 21 March.

NASA M2M (2026-03-16, 1930 UTC)

NASA M2M sees a rather slow CME (483 km/s, preliminary analysis) that could arrive at noon on 19 March (2026-03-19T12:05Z) with rather low impact on the Earth’s magnetic field (Kp 4-5)

SWPC/NOAA (2026-03-16, 2000 UTC)

SWPC/NOAA (2026-03-16, 2030 UTC)

Click to expand for details (arrival in the early hours of 19 March, G2)

The official model run is more in line with NASA M2M, with arrival on 19 March and a G2 watch in place for 19 March.

☞ www.swpc.noaa.gov/products/wsa-enlil-solar-wind-prediction

Met Office UK (2026-03-17, 0030 UTC)

Click to expand for details (arrival on 19 March, G1-G2)

MOSWOC (Met Office Space Weather Operations Centre) is forecasting a CME travelling at 600 km/s, which could arrive in the afternoon of 19 March.

A G1 MINOR to G2 MODERATE STORM is expected.

☞ swe.ssa.esa.int/metoffice-enlil-e-federated

BoM Australia (2026-03-17, 0030 UTC)

Click to expand for details (arrival late on 19 March)

The CME is expected to arrive at BoM at the latest (estimated speed 471 km/s), namely on the evening of 19 March. ACTIVE (G0) to MODERATE STORM (G2) is expected. A G2 Watch has been issued for 19 March.

☞ sws.bom.gov.au

KASA Korea (2026-03-17, 0030 UTC)

Click to expand for details (arrival late on 19 March)

Another run with Impact in the afternoon of 19 March, very similar to the BoM model run.

NASA Ensemble Run (2026-03-17, 0030 UTC)

An ensemble of 27 members with slightly different initial parameters yields a wide range of results.

Arrival from the very early hours of 19 March to the very early hours of 20 March (UTC)

The later the CME arrives, the weaker it will be. Magnetic Field is not expected to exceed 10 nT (generally weak CME).

We will subsequently see the arrival of the Stream Interaction Region from coronal hole CH33+

CME Update: Coronagraphs, Heliospheric Imager (2026-03-17, 1800 UTC)

The CME is slightly more visible in later frames in CCOR-1, but is still not clearly discernible:

The side view of the Sun-Earth axis from the STEREO A Heliospheric Imager I shows the CME at 1100z on 17 March at approximately 0.25 AU. It has thus covered a quarter of the distance in 24 hours. This makes an arrival during 20 March more likely than an arrival on 19 March (UTC day).

Filament eruptions, an M-class flare and 3 CMEs (2026-03-17, 1900 UTC)

During the first half of 17 March (UTC day), there were numerous filament eruptions as well as another M-class flare from Region 4392. This resulted in three relatively small and slow CMEs, more or less directed towards Earth, which may arrive as a single event on 20 or 21 March (glancing blow, Kp 3–5 or more).

NASA M2M has run a combined model simulation (4 CMEs) and predicts they will arrive on 20 March at 0600 UTC (glancing blow). I reckon these CMEs will arrive some time after the main one – probably not until late on 20 March. Hopefully, something will be visible on the Heliospheric Imager later on.

☞ kauai.ccmc.gsfc.nasa.gov/DONKI/view/WSA-ENLIL/45136/1

In STEREO A COR2, several CMEs are faintly visible (Earth is on the left)

On 20 March or 21 March, a Stream Interaction Region from the fast solar wind originating from the negatively polarised coronal hole SWPC No. 33 is also expected to arrive, together with a Sector Boundary Crossing, during which the interplanetary magnetic field changes its polarity from positive (away from the Sun) to negative (towards the Sun). This combination could lead to significantly higher geomagnetic activity than predicted, although this is not certain.

Continued and ongoing updates in the next article:
Another M2.7 flare and an Earth-directed CME column (‘solar storm’)

More updates always on X or bluesky

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