Solar Terrestrial Activity Report

Last major update issued on December 17, 2024 at 05:25 UT. Revised on February 5, 2025 based on archived SDO/HMI images

Recent activity

The geomagnetic field was at quiet to active levels on December 16. A high speed coronal hole stream associated with CH1262 was the dominant solar wind source for most of the day. An additional disturbance arrived just after 20h UT, and could be CME related. After the arrival of that disturbance the phi angle varied between away and towards and the geomagnetic disturbance increased in intensity. Solar wind speed at SOHO ranged between 366 and 489 km/sec, averaging 400 km/sec (+11 km/sec compared to the previous day). A strong solar wind shock was observed at ACE at 04:41 UT on December 17, most likely the arrival of the December 14 full halo CME. The high latitude magnetometer at Andenes recorded quiet to minor storm levels. The above 10 MeV proton flux was at background levels most of the day, then became slightly elevated after 18:15 UT.

Solar flux density measured at 20h UT on 2.8 GHz was 166.7 - increasing 9.5 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 188.32. In comparison SC24 peaked on June 28, 2014 at 145.50 while SC23 peaked on February 23, 2002 at 198.15. Current SC25 peak: 188.32 on June 17, 2024 (given a base solar flux level of 65, this is +53.20% compared to the SC24 peak and -7.38% compared to the SC23 peak). The Potsdam WDC planetary A index was 12 (STAR Ap - based on the mean of three hour interval ap indices: 12.5). Three hour interval K indices: 23331234 (planetary), 13442332 (Boulder), 42223545 (Andenes).

At the time of counting spots (see image time), spots were observed in 14 active regions using 2K resolution (SN: 262) and in 8 active regions using 1K resolution (SN: 135) SDO/HMI images.

AR 13920 [N20W53] decayed further losing all penumbra on the leader spots.
AR 13922 [S19W13] developed slowly and produced low level C flares.
AR 13924 [S19W41] gained area and was mostly quiet.
AR 13925 [N11E25] gained tiny spots and was quiet.
AR 13926 [S20E56] was quiet and stable.

Spotted regions not observed (or interpreted differently) by SWPC/USAF:
S10436 [S13W80] gained area and was mostly quiet as the spot group rotated to the southwest limb.
S10463 [S16E27] gained tiny spots and was quiet.
S10464 [N17E11] reemerged with tiny spots.
S10466 [S08E05] was quiet and stable.
S10468 [N21E62] was quiet and stable.
New region S10469 [S03W13] emerged with a tiny spot.
New region S10470 [N06E70] rotated into view with a tiny spot.
New region S10471 [N07E38] emerged with tiny spots.
New region S10472 [S22E17] emerged with tiny spots.

C2+ flares

C1 flares: C1.9 @ 04:18, C1.8 @ 04:33, C1.8 @ 06:19, C1.5 @ 09:13, C1.9 @ 09:23, C1.8 @ 16:04, C1.8 @ 16:25, C1.6 @ 00:03 (on December 17, flare started at 23:59) UT.

Coronal mass ejections (CMEs)

December 15-16: No obviously Earth directed CMEs were observed.
December 14: A faint asymmetrical halo CME was observed in LASCO imagery after a long duration event in AR 13924 peaking at 17:29 UT.

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 an Earth facing location.

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 unsettled to severe storm on December 17 due to CME effects. Quiet to minor storm is likely on December 18 becoming quiet on December 19-20.

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.