Subject: Weekly Highlights of Solar and Geomagnetic Activity, 28 September - 04 October 2026

:Product: Weekly Highlights and Forecasts
:Issued: 2026 Oct 05 0139 UTC
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# Weekly Highlights and Forecasts
#
Highlights of Solar and Geomagnetic Activity
28 September - 04 October 2026

Solar activity was at very low to low levels throughout the summary
period. Region 4535 (N11, L=351, class/area Dao/060 on 30 Sep)
produced the strongest flare of the period; an impulsive C8.6/1f
event at 30/0246 UTC. This event also produced a 523 km/s Type II
and a Type IV Sweep. All other regions remained simple and absent of
any significant activity. No Earth-directed CMEs were observed in
available coronagraph imagery.

No proton events were observed at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit reached
high levels on 28-30 Sep and 01 Oct with a peak of 5,620 pfu
observed at 29/1620 UTC. Moderate levels were observed on 02-04 Oct.

Geomagnetic field activity was at quiet levels on 28-30 Sep and
01-03 Oct with some isolated unsettled periods observed early on 03
Oct. On 04 Oct, solar wind parameters became enhanced due to the
influence of a positive polarity CH HSS. Total magnetic field
strength increased to a peak of 22 nT and Bz observed several
southward deflections, the maximum being -20 nT early on 04 Oct.
Solar wind speeds steadily increased from about 300 km/s to a peak
of 644 km/s later on 04 Oct. The phi angle was predominately
positive.

Forecast of Solar and Geomagnetic Activity
05 October - 31 October 2026

Solar activity is likely to continue at very low to low levels
throughout the outlook period.

No 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 06-11 Oct, 14-17 Oct, and 23-28 Oct
due to anticipated incluence from multiple, recurrent CH HSSs.

Geomagnetic field activity is expected to reach G1 (Minor)
geomagnetic storm levels on 22 and 31 Oct. Active levels are likely
on 06, 21, and 23 Oct. Unsettled levels are likely on 07, 11-14, and
24 Oct. All increases in geomagnetic activity are associated with
anticipated influence from multiple, recurrent, coronal hole HSSs.
The remainder of the outlook period is likely to be at mostly quiet
levels.


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