Subject: Weekly Highlights of Solar and Geomagnetic Activity, 07 - 13 September 2026

:Product: Weekly Highlights and Forecasts
:Issued: 2026 Sep 14 0117 UTC
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# Weekly Highlights and Forecasts
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Highlights of Solar and Geomagnetic Activity
07 - 13 September 2026

Solar activity was at low levels for 07-10 Sep and 12-13 Sep, and
was at very low levels on 11 Sep. The largest flare of the period
was a C5.8/Sf at 12/1720 UTC from Region 4521 (N09, L=266,
class/area Hsx/90 on 06 Sep). This region was responsible for the
majority of the C-flaring activity, producing 6 of the observed 15.
The remainder were produced by Regions 4524 (N12, L=225, class/area
Cao/100 on 06 Sep) and 4528 (S11, L=187, class/area Hsx/120 on 08
Sep).

There were 4 CMEs this period. 3 of these were due to filament
eruptions. First was a filament eruption associated with a C3.4/1f
at 09/0908 UTC from Region 4524, whose slow CME first became visible
in STEREO coronagraph imagery at ~09/1623 UTC and in LASCO C3 at
~09/2106 UTC. Modeling indicated a possible glancing blow on 14 Sep.
Second, a filament centered around approximately S15W30 began
erupting at ~10/0330 UTC, with an associated slow CME first becoming
visible in LASCO C2 at ~10/0524 UTC and GOES CCOR1 at ~10/0730 UTC.
Modeling indicated the majority of the material would likely pass
ahead and below of Earth orbit, however there was the potential for
this eruption also produce a very minor glancing blow on 14 Sep.
Third was an 8 degree long filament at roughly disk center that
began erupting at ~13/1900 UTC, producing a long duration C1.4 at
13/1945 UTC and an associated CME that first became visible in LASCO
C2 at ~13/1948 UTC and SOLAR1 CCOR2 at ~13/2030 UTC. Modeling
indicated a possible glancing blow on 17 Sep.

Lastly, a very slow CME first became visible in LASCO C2 at ~12/1612
UTC and in STEREO at ~12/1638 UTC. Despite triangulation with STEREO
indicating a front-sided eruption, no clear source was found except
for perhaps some faint coronal dimming in the SW quadrant in
GOES/SUVI 195. Modeling indicated the material would pass below
Earth orbit.

The greater than 10 MeV proton flux at geosynchronous orbit was
slightly elevated on 07 Sep due to the continued recovery from the
05 Sep S1 event, but was at background levels for the majority of
the reporting period.

The greater than 2 MeV electron flux at geosynchronous orbit was at normal-moderate levels on 07 Sep and at high levels on 08-13 Sep.

Geomagnetic activity reached active levels and a few isolated
periods of G1 (Minor) storming conditions on 08 Sep due to positive
polarity coronal hole high speed stream (CH HSS) influences,
potentially with embedded effects from CMEs that left the Sun on
either 04 Sep or 06 Sep. The remainder of the reporting period,
09-13 Sep, was at quiet to unsettled levels.

Forecast of Solar and Geomagnetic Activity
14 September - 10 October 2026

Solar activity is expected to be at low levels, with a slight chance
for moderate to high levels throughout the forecast period.

Not proton events are expected at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit is
expected to be at high levels on 14 Sep, 16-23 Sep, 27 Sep-03 Oct,
and 05-10 Oct. Levels are expected to be at normal-moderate levels
on 15 Sep, 24-16 Sep, and 04 Oct.

Geomagnetic field activity is expected to reach active to G1
storming levels on 14-17 Sep due to negative polarity CH HSS effects
with the potential for CME influence from a CME that left the Sun on
09 Sep; 24-27 Sep due to positive polarity CH HSS influences; and
unsettled to active levels on 05-08 Oct due to positive polarity CH
HSS influences. Largely quiet levels are anticipated for all
remaining dates in the forecast period.


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