Solar Terrestrial Activity Report

Last major update issued on December 26, 2024 at 06:55 UT. Revised on February 16, 2025 based on archived SDO/HMI images

Recent activity

The geomagnetic field was at quiet levels on December 25. Solar wind speed at SOHO ranged between 446 and 542 km/sec, averaging 473 km/sec (-77 km/sec compared to the previous day). The high latitude magnetometer at Andenes recorded quiet to unsettled levels. The above 10 MeV proton flux was at 0.8 pfu at the end of the day, slowly decreasing.

Solar flux density measured at 20h UT on 2.8 GHz was 252.7 - increasing 39.5 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 189.07. In comparison SC24 peaked on June 28, 2014 at 145.50 while SC23 peaked on February 23, 2002 at 198.15. Current SC25 peak: 189.07 on June 26, 2024 (given a base solar flux level of 65, this is +54.13% compared to the SC24 peak and -6.82% compared to the SC23 peak). The Potsdam WDC planetary A index was 5 (STAR Ap - based on the mean of three hour interval ap indices: 4.6). Three hour interval K indices: 22121010 (planetary), 22122220 (Boulder), 32310023 (Andenes).

The background x-ray flux is at the class C2 level (GOES 16).

At the time of counting spots, spots were observed in 20 active regions using 2K resolution (SN: 549) and in 16 active regions using 1K resolution (SN: 354) images.

AR 13926 [S20W60] decayed slowly and quietly.
AR 13927 [S07W29] was quiet and stable.
AR 13928 [S14W22] decayed slowly and quietly.
AR 13929 [N16W37] was quiet and stable.
AR 13932 [S18E04] decayed slowly losing spots and area.
AR 13933 [S07W19] produced the largest flare of the day and has minor polarity intermixing.
AR 13934 [N13W00] decayed slowly and quietly.
AR 13935 [S18E14] decayed slowly and quietly.
AR 13936 [N13E27] gained spots and area and could produce a major flare.
AR 13937 [S12E39] was quiet and stable.
AR 13938 [N19E53] produced several C flares and one M flare. There is a magnetic delta configuration in a northwestern penumbra.
New AR 13939 [S17E72] rotated into view on December 24 and was mostly quiet when it was numbered by SWPC the next day.

Spotted regions not observed (or interpreted differently) by SWPC/USAF:
S10495 [N16W10] reemerged with tiny spots.
S10499 [S12W63] reemerged with tiny spots.
S10501 [N17W43] decayed slowly and quietly.
S10502 [N31E21] was quiet and stable.
S10506 [S05E68] was quiet and stable.
New region S10507 [N02E18] was observed with a tiny spot in an old plage area.
New region S10508 [S27E37] emerged with a tiny spot.
New region S10509 [S13E28] was observed with a tiny spot in an old plage area.

C2+ flares

Coronal mass ejections (CMEs)

December 23: A partial halo CME was observed after the M9 flare in AR 13932 just before noon.
December 24: An unimpressive CME was observed after the M4.1 flare in AR 13932 at 08:41 UT. Components of this CME could reach Earth on December 26.
December 25: A CME was observed after an M4.9 flare in AR 13933 early in the day. There's a minor chance this could cause a solar wind shock on December 27.

Coronal holes

[Coronal hole history (since October 2002)]
[Compare today's report to the situation one solar rotation ago: 28 days ago 27 days ago 26 days ago]

No obvious coronal holes are currently in or near Earth facing positions.

Propagation

Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over upper middle and high latitudes is poor. Propagation on long distance northeast-southwest paths is poor.

Forecast

The geomagnetic field is expected to be mostly quiet on December 26-28 with a chance of unsettled and active intervals should components of the December 24 and 25 CMEs reach Earth.

1) Effects from a coronal hole could reach Earth within the next 5 days. When the high speed stream has arrived the color changes to green.
2) Effects from a CME are likely to be observed at Earth within 96 hours.
3) There is a possibility of either M or X class flares within the next 48 hours.

Green: 0-30% probability, Yellow: 30-70% probability, Red: 70-100% probability.

Active solar regions

(Click on image for 2K resolution). 4K resolution. Compare to the previous day's image. 0.5K image

When available the active region map has a coronal hole polarity overlay where red (pink) is negative and blue is positive.

Data for all officially numbered solar regions according to the Solar Region Summary provided by NOAA/SWPC, all other regions are numbered sequentially as they emerge using the STAR spot number. Comments are my own, as is the STAR spot count (spots observed at or inside a few hours before midnight) and data for regions not numbered by SWPC or where SWPC has observed no spots. SWPC active region numbers in the table below and in the active region map above are the historic SWPC/USAF numbers. SWPC data considered to be not sufficiently precise (location, area, classification) are colored red.

Monthly solar cycle data

1) Running average based on the daily 20:00 UTC observed solar flux value at 2800 MHz and any corrections applied to that measurement.
2A) Current impact on the monthly sunspot number based on the Boulder (NOAA/SWPC) sunspot number (accumulated daily sunspots / month days).
2B) Boulder SN current month average to date.
2C) STAR SDO 1K Wolf number 30 day average.
3) Running average based on the quicklook and definitive Potsdam WDC ap indices. Values in red are based on the definitive international GFZ Potsdam WDC ap indices.
4) Source: WDC-SILSO, Royal Observatory Of Belgium, Brussels

Solar cycles 24-25

Update on the progress of solar cycle 25 as of December 10, 2024

Sunspot activity in November 2024 decreased compared to October and there is a trend towards lower levels since August 2024. The average solar flux for November was the fourth highest for a month during SC24. The above plot displays a projected peak for the ISN 365d smoothed sunspot numbers in October 15, 2024. All the other smoothed sunspot number have projected peaks either in late November or early December. Assuming that the average sunspot numbers in December 24 decreases significantly over the previous months, and then slowly until mid 2025, an earlier peak near July 9, 2024 becomes possible. Currently SC25 is tracking much closer to SC23 than to SC24.

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This report has been prepared by Jan Alvestad. It is based on the analysis of data from whatever sources are available at the time the report is prepared. All time references are to Universal Time. Comments and suggestions are always welcome.

SDO images are courtesy of NASA/SDO and the AIA, EVE, and HMI science teams.