:Product: Weekly Highlights and Forecasts
:Issued: 2024 May 20 0143 UTC
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# Weekly Highlights and Forecasts
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Highlights of Solar and Geomagnetic Activity
13 - 19 May 2024

Solar activity ranged from low to high levels during the period.
High levels were reached 13-15 May; moderate levels 16-17 May; and
low levels on 18 May. Levels returned to moderate by 19 May. There
were at least 15 M-class flares and 5 X-class flares during the
reporting week - sub-peaks and re-enhancements made firm
correlations difficult. Region 3664 (S17, L=347, Fkc/BGD on 11 May)
was the primary X-class flare producer and erupted with the largest
solar flare thus far in solar cycle 25, an X8.7 at 14/1651 UTC as it
reached the western limb. Nineteen sunspot groups littered the solar
disk, with Region 3664 rotating beyond the limb 14 May. Even though
Region 3664 rotated beyond the limb, it continued producing M and
X-class flares on 15 May, to include an X3.4 flare at 15/0818 UTC.
Another active region just beyond the east limb was the source of an
X2.9 flare on 15/1438 UTC. This region rotated into view on 16 May
and was designated as Region 3685 (S13 L=152, Ehi/BG on 16 May.

Radio activity was aplenty during the week - main highlights include
Region 3664 eruption of solar radio bursts on 14 May that included
Castelli U signature bursts twice, once with an X1.7 flare at
14/0209 UTC and again with the X8.7 flare. The first radio burst was
the more massive, with a peak frequency flux centered on 245 MHz of
63,000 sfu. Tenflares were also observed, as well as Type II and IV
radio sweeps with each of these events. Radio activity of note
continued on 15 May with early activity still from well beyond the
limb Region 3664, however, later on 15 May, the source region
shifted to the east limb, with Type II and IV sweeps associated with
the X2.9 flare from soon to be assigned Region 3685.

Many CMEs were noted through the week, most were sourced to Region
3664 and were determined to be misses ahead of Earth. However, even
though an asymmetric halo CME on 13 May from Region 3664 was
analyzed and modeled as mainly a miss, possible shock arrival and
glancing or near-proximity influences were possible on 14-15 May due
to its fast speed. Additionally, on 14 May, a filament eruption
centered over the far northeastern solar disk was modeled and a
glancing blow was suggested by 17 May. Yet another filament eruption
occurred from a source location in the northwest quadrant on 16 May.
This associated CME analysis and model results suggested a glancing
blow possible on 20 May.

A proton event was observed at geosynchronous orbit. The event began
on 13 May as the greater than 10 MeV levels reached 10 pfu at
13/1400 UTC and breached 100 pfu by 14/0335 UTC. These events were
most likely associated with flare and CME activity from region 3664.
Peak flux reached was 121 pfu on 14/0505 UTC and decreased below 10
pfu at 16/1455 UTC.

The greater than 2 MeV electron flux reached 1,000 pfu on 15/1525
UTC with a peak flux of 1,500 pfu at 15/1840 UTC and returned to
normal levels on 16 May.

Geomagnetic field activity ranged from quiet to G2 (Moderate) storm
levels. 13 May began with G2 levels in response to continued CME
influences as solar wind speeds were still highly elevated and near
850 km/s with total IMF strength between 5-10 nT and favorable
periods of southward Bz component. Solar wind speed slowly declined
and eventually reached near 450 km/s on 15 May, while the total IMF
strength weakened and returned to more ambient levels. This led to a
period of mainly quiet to unsettled levels 14-15 May. Another
enhancement in the solar wind field occurred on 16 May due to CME
effects (likely from one of Region's 3664 CMEs of 13 May) as
total field intensified to 17 nT, while the Bz component shifted
southward - this led to G1 (Minor) to G2 storm levels. Yet another
CME arrival disturbed and enhanced the IMF again, with a favorable
southward connection on 17 May that led to G1-G2 storm levels again.
The origin of this CME is somewhat in doubt, but the most likely
candidate is one of the CMEs from Region 3664 on 14 May. The solar
wind field gradually returned to a less disturbed and more ambient,
background state on 18 May with quiet to active levels noted and
quiet to unsettled conditions on 19 May.

Forecast of Solar and Geomagnetic Activity
20 May - 15 June 2024

Solar activity is likely to be moderate (R1-R2; Minor-Moderate),
with a slight chance for high levels (R3; Strong) through 21 May as
Region 3685 (S13 L=155, Ehi/BG as of 18 May) continues to produce
low-level M-class flares (R1). The region will take some time to
rotate to the western limb - rotating beyond the limb by 30 May.
Meanwhile eight other regions will rotate beyond the limb beginning
21 May through 26 May. A good number of former spot regions are
timed to rotate back into Earth-view through much of the outlook
period - the most anticipated is former Region 3664 (S17, L=347,
Fkc/BGD on 11 May) that is expected to return by 26-27 May. The
litany of returning regions, to include 3664, could lead to
increasing solar activity levels back to moderate to high levels as
early as 26 May.

There will be a slight chance of S1 (Minor) solar radiation storms
through 30 May until Region 3685 rotates beyond the western limb. If
Region 3664 survives to its return to the visible solar disk 26-27
May, there is a possibility of an increase to a chance of an S1
storm by 7-15 June.

The greater than 2 MeV electron flux is likely to be normal to
moderate with a chance for high levels 20 May - 15 Jun.

Geomagnetic activity is anticipated to be at quiet to active
conditions, with likely G1 (Minor) storm levels 20 May due to CME
effects. Conditions are expected to wane on 21 May and primarily
quiet to active levels are expected. A period of quiet conditions
follows 22-23 May, with CH HSS effects leading back to active levels
24-25 May. The remainder of the period is anticipated to be
primarily a mix of quiet to active conditions in varying response to
occasional recurrent CH HSS effects.


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