Highlights of Solar and Geomagnetic Activity
Covering the period: 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.

Space Weather and Propagation Forecast
Prepared by the US Dept. of Commerce, NOAA,
and the Space Weather Prediction Center

Three Day Forecast of Solar and Geomagnetic Activity
(as of 2200Z on 07 Dec 2014)

Solar Forecast:

Solar activity is expected to be low with a chance for M-class flares on days one, two, and three (08 Dec, 09 Dec, 10 Dec).

Geomagnetic Forecast:

The geomagnetic field is expected to be at quiet to minor storm levels on day one (08 Dec), quiet to active levels on day two (09 Dec) and quiet levels on day three (10 Dec).

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.