Solar Terrestrial Activity Report

Last major update issued on December 31, 2024 at 04:50 UT. Revised on February 23, 2025 based on archived SDO/HMI images

Recent activity

The geomagnetic field was at quiet levels on December 30. Solar wind speed at ACE ranged between 317 and 366 km/sec. The high latitude magnetometer at Andenes recorded quiet to unsettled levels. The above 10 MeV proton flux was at 0.3 pfu at the end of the day, just above background levels.

Solar flux density measured at 20h UT on 2.8 GHz was 223.5 - increasing 49.3 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 190.47. In comparison SC24 peaked on June 28, 2014 at 145.50 while SC23 peaked on February 23, 2002 at 198.15. Current SC25 peak: 190.47 on July 1, 2024 (given a base solar flux level of 65, this is +55.86% compared to the SC24 peak and -5.77% 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: 5.4). Three hour interval K indices: 01211122 (planetary), 02313222 (Boulder), 01210033 (Andenes).

The background x-ray flux is at the class C4 level (GOES 16).

At the time of counting spots, spots were observed in 18 active regions using 2K resolution (SN: 417) and in 15 active regions using 1K resolution (SN: 267) images.

AR 13932 [S18W60] decayed further and was quiet after the X flare.
AR 13933 [S08W82] rotated mostly out of view and produced several M flares.
AR 13935 [S19W36] decayed slowly and quietly.
AR 13936 [N12W58] still has magnetic delta configurations in the intermediate spot section. Some decay was observed during the day. Another major flare is possible.
AR 13937 [S12W26] was quiet and stable.
AR 13938 [N18W13] decayed slowly and produced a few C flares.
AR 13939 [S17E07] produced a few M flares and remains a compact region with reversed polarities.
AR 13940 [S05E04] was quiet and stable.
AR 13941 [S06E12] gained area and develop a small magnetic delta configuration in an intermediate spot section penumbra.
AR 13942 [S13E46] decayed early in the day, then new flux emerged and several spots formed.
New AR 13943 [S15E74] rotated partly into view on December 29 and was numbered the next day by SWPC.

Spotted regions not observed (or interpreted differently) by SWPC/USAF:
S10495 [N14W75] appeared to be developing slowly late in the day.
S10514 [S15W63] decayed slowly and quietly.
S10519 [S09E30] was quiet and stable.
New region S10523 [N15E10] emerged with tiny spots.
New region S10524 [S04W16] emerged with tiny spots.
New region S10525 [N05E41] emerged with a tiny spot.

C2+ flares

Coronal mass ejections (CMEs)

December 28, 30: No obviously Earth directed CMEs.
December 29: Several CMEs were observed during the day, none of them very impressive. A partial halo CME was observed in LASCO imagery following an M2 flare in AR 13939 at 04:34 UT and a subsequent filament eruption. This CME could reach Earth during the latter half of December 31. Another partial halo CME appears to have been associated with an M3.3 flare in AR 13939 at 17:08 UT and could reach Earth on January 1.

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) will rotate into an Earth facing position on December 31-January 1. A positive polarity northern hemisphere coronal hole (CH1265) will like rotate across the central meridian on January 2-3.

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 to fair. Propagation on long distance northeast-southwest paths is poor.

Forecast

The geomagnetic field is expected to be mostly quiet on December 30. CMEs associated with flares in AR 13939 could reach Earth on December 31 and January 1 and cause active to major geomagnetic storming.

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.