Subject: Weekly Highlights of Solar and Geomagnetic Activity, 17 - 23 April 2023

:Product: Weekly Highlights and Forecasts
:Issued: 2023 Apr 24 1316 UTC
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# Weekly Highlights and Forecasts
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Highlights of Solar and Geomagnetic Activity
17 - 23 April 2023

Solar activity was at low to moderate levels during the period. Low
levels were observed on 17-20 Apr and 22-23 Apr from Regions 3272
(S21, L=102, class/area Eai/280 on 09 Apr), 3280 (S08, L=117,
class/area Dsi/240 on 15 Apr), 3281 (S24, L=019, class/area Dko/350
on 14 Apr), 3282 (N11, L=024, class/area Eki/530 on 16 Apr), 3283
(S20, L=356, class/area Dro/080 on 19 Apr) and 3285 (S17, L=272,
class/area Dao/180 on 22 Apr).

Solar activity reached moderate levels on 21 April due to an M1.7/2n
(R1-Minor) flare from Region 3283 at 21/1812 UTC. Accompanying the
flare were Type II (580 km/s) and Type IV radio sweeps. Subsequent
SOHO LASCO C2 imagery observed a full-halo CME signature beginning
after 23/1812 UTC.

The greater than 10 Mev protons exceeded the S1 (Minor) threshold at
23/1820 UTC with a peak value of 26.2 pfu. This increase was in
response to the passage from a shock ahead of the 21 Apr CME.

The greater than 2 MeV electron flux at geosynchronous orbit was at
normal to moderate levels.

Geomagnetic field activity ranged from quiet to G4 (Severe) storm
conditions during the period. Quiet conditions were observed on 17
Apr through midday on 18 Apr. Unsettled to active conditions were
observed on midday 18 Apr through a majority of 19 Apr due to weak
CME effects. Quiet to isolated unsettled conditions were observed on
20 Apr through the first portion of 23 Apr.

Beginning about midday on 23 Apr, geomagnetic conditions rose
sharply through the day from active to G4 (Severe) geomagetic storm
conditions in response to the arrival of the full-halo CME that left
the Sun on 21 Apr. A sudden impulse (48 nT) was observed at the
Boulder magnetometer beginning at 23/1737 UTC. During this period of
activity, total magnetic field strength increased from about 9 nT to
25 nT during the shock. The Bz component rotated south and
maintained a far southward configuration to -22 nT through 23/2015
UTC at which point Bz rapidly rotated northward. Solar wind speeds
rapidly increased from about 350 km/s to above 600 km/s by about
23/1945 UTC.



Forecast of Solar and Geomagnetic Activity
24 April - 20 May 2023

Solar activity is expected to remain at low levels with a chance for
M-class (R1-R2, Minor-Moderate) flares, and a slight chance for
X-class (R3-Strong), flares on 24-26 Apr and again on 07-20 May.

No proton events are expected at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit is
expected to reach high levels on 25-30 Apr and 01-06 May due to
residual CME effects on 25-26 Apr followed by CH HSS influence.

Geomagnetic field activity is expected to reach G3 (Strong) levels
early on 24 Apr due to CME effects. G1 (Minor) to G2 (Moderate)
levels are expected through the remainder of 24 Apr due to CME
effects. Unsettled to active levels are likely on 25-30 Apr and
01-04 May, 07 May and 11-12 May due to CH HSS effects. Mostly quiet
levels are expected on 05-05 May, 08-10 May and 13-20 May.


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* Origin: NOAA Space Weather Prediction Center (3:633/280.2@fidonet)