Solar Terrestrial Activity Report

Last major update issued on January 2, 2025 at 07:30 UT. Revised on February 25, 2025 based on archived SDO/HMI images

Recent activity

The geomagnetic field was at active to very severe storm levels on January 1 due to strong CME effects. Solar wind speed at SOHO ranged between 401 and 685 km/sec, averaging 531 km/sec (+152 km/sec compared to the previous day). The high latitude magnetometer at Andenes recorded unsettled to extremely severe storm levels. The above 10 MeV proton flux finally returned to background levels.

Solar flux density measured at 20h UT on 2.8 GHz was 219.2 - increasing 44.6 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 190.89. In comparison SC24 peaked on June 28, 2014 at 145.50 while SC23 peaked on February 23, 2002 at 198.15. Current SC25 peak: 190.89 on July 3, 2024 (given a base solar flux level of 65, this is +56.39% compared to the SC24 peak and -5.45% compared to the SC23 peak). The Potsdam WDC planetary A index was 84 (STAR Ap - based on the mean of three hour interval ap indices: 83.5). Three hour interval K indices: 45567874 (planetary), 35467754 (Boulder), 45543965 (Andenes).

The background x-ray flux is at the class C3 level (GOES 18).

At the time of counting spots, spots were observed in 17 active regions using 2K resolution (SN: 382) and in 15 active regions using 1K resolution (SN: 256) images.

AR 13935 [S19W63] decayed slowly and quietly.
AR 13936 [N12W82] rotated partly out of view and produced many C and M flares.
AR 13937 [S11W53] decayed slowly and quietly.
AR 13938 [N19W39] decayed slowly and was mostly quiet.
AR 13939 [S17W20] decayed and was mostly quiet.
AR 13941 [S06W16] decayed and nearly lost all trailing spots.
AR 13943 [S15E46] was mostly quiet and stable.
AR 13944 [S14E20] developed further becoming the largest region on the visible disk. M class flaring is possible.
New AR 13945 [S08E59] rotated into view on December 31 and was numbered by SWPC the next day.

Spotted regions not observed (or interpreted differently) by SWPC/USAF:
S10527 [S12W40] developed slowly and quietly.
S10531 [S18E49] decayed slowly and quietly.
S10532 [S13E67] was mostly quiet and stable.
New region S10534 [N14W42] emerged with several spots to the south of AR 13938.
New region S10535 [N10E80] rotated partly into view and produced several C flares.
New region S10536 [N23E48] emerged with tiny spots.
New region S10537 [N19E67] rotated into view with a tiny spot.
New region S10538 [S05E46] emerged with tiny spots.

C2+ flares

Coronal mass ejections (CMEs)

December 30-31: No obviously Earth directed CMEs.
January 1: A filament eruption early in the day in the southwest quadrant may have been the source of a partial halo CME observed after 02h UT in LASCO imagery. There's a chance of weak CME effects on January 3.

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]

A positive polarity southern hemisphere coronal hole (CH1264) rotated into an Earth facing position on December 31-January 1. A large positive polarity northern hemisphere coronal hole (CH1265) will rotate across the central meridian on January 1-3.

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 to fair.

Forecast

The geomagnetic field is expected to be quiet to active on January 2 due to lingering CME effects. High speed streams from CH1264 and CH1265 could cause quiet to active levels on January 3-5.

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 30, 2024

Sunspot activity increased again during the second half of December 2024, and this will be the eighth consecutive month with average solar flux above 180. The average solar flux at 1 AU since May 1, 2024 is 205. There is an increasing chance solar cycle 25 could have a higher 1 year solar flux average than solar cycle 23. The above plot displays a projected peak for the ISN 365d smoothed sunspot numbers on October 12, 2024. All the other smoothed sunspot number as well as the smoothed 365d solar flux have projected peaks October 12-15. A sudden decrease in activity during the first months of 2025 could move the SC25 max to sometime between July and October 2024.

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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.