Solar Terrestrial Activity Report

Last major update issued on December 5, 2024 at 06:30 UT. Revised on January 22, 2025 based on archived SDO/HMI images

Recent activity

The geomagnetic field was at quiet levels on December 4. Solar wind speed at SOHO ranged between 449 and 597 km/sec, averaging 489 km/sec (+45 compared to the previous day). The high latitude magnetometer at Andenes recorded quiet to unsettled levels. The above 10 MeV proton flux was at background levels all day.

Solar flux density measured at 20h UT on 2.8 GHz was 174.7 - decreasing 64.5 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 187.22. In comparison SC24 peaked on June 28, 2014 at 145.50 while SC23 peaked on February 23, 2002 at 198.15. Current SC25 peak: 187.22 on June 5, 2024 (given a base solar flux level of 65, this is +51.82% above SC24 peak and -8.21% below SC23 peak). The Potsdam WDC planetary A index was 6 (STAR Ap - based on the mean of three hour interval ap indices: 6.0). Three hour interval K indices: 12122122 (planetary), 11222322 (Boulder), 31010333 (Andenes).

At the time of counting spots (see image time), spots were observed in 16 active regions using 2K resolution (SN: 338) and in 13 active regions using 1K resolution (SN: 204) SDO/HMI images.

AR 13906 [S17W80] decayed slowly and produced several C flares.
AR 13910 [N16W33] decayed slowly and quietly.
AR 13912 [S07W17] was quiet and stable. Note that SWPC moved the center of AR 13912 14 degrees eastwards on December 1 to the location of AR S10418 as AR 13912 decayed substantially. Instead they assigned AR 13913 to what was originally AR 13912. The original numbering will be kept in this report for data consistency.
AR 13914 [N06W38] decayed slowly and quietly.
AR 13915 [N14E38] was mostly quiet and unchanged.
AR 13916 [S15E54] produced several C and M flares. A major flare is possible.
New AR 13917 [S08E65] rotated into view on December 3 and gained many small spots on December 4.

Spotted regions not observed (or interpreted differently) by SWPC/USAF:
S10418 [S05W06] was mostly quiet and stable.
S10420 [S06E08] was quiet and stable.
S10426 [N05W41] was quiet and stable.
S10430 [N20W09] developed slowly and quietly.
S10431 [N09E11] decayed slowly and quietly.
S10433 [S09E27] was quiet and stable.
New region S10434 [S10E13] emerged with tiny spots.
New region S10435 [S18W05] emerged with tiny spots.
New region S10436 [S13E79] rotated into view with tiny spots.

C2+ flares

Coronal mass ejections (CMEs)

December 2-4: No obviously Earth directed CMEs were observed.

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 recurrent positive polarity northern hemisphere coronal hole (CH1259) will likely rotate into an Earth facing position on December 6-7. A southern hemisphere coronal hole was probably too far to the south to cause geomagnetic effects as it rotated across the central meridian on December 4-5.

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 on December 5-8. Effects from CH1259 could cause some unsettled and active intervals on December 9-10.

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 October 27, 2024

Sunspot activity in October 2024 increased over September and looks to be headed for an SSN near 160. The average solar flux for October will become the second highest for a month during SC25. The above plot now displays the peak in 365d smoothed sunspot numbers in mid October 2024. ISN has a peak on October 15, NOAA SN on October 14 while both the 1K and 2K SDO SN peaked on October 16. Assuming that the average sunspot number from October 2024 until April 14, 2025 becomes 150, we would be looking at a 365 days smoothed sunspot maximum of 164.5 centered on October 15. Should the average sunspot number for that period become 160 we would get a peak near 169.7.

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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.