The geomagnetic field was at quiet to active levels on December 18 under the influence of effects associated with CH1335. Solar wind speed at SOHO ranged between 561 and 688 km/sec, averaging 628 km/sec (+19 km/sec compared to the previous day). The high latitude magnetometer at Andenes was at quiet to minor storm 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 115.9 - decreasing 5.3 over the previous solar rotation.
The 365 day average solar flux at 1 AU was 156.79 (183 days ago). The 81 day average solar flux at 1 AU was 144.0 (41 days ago, this is 47.4% of the total SC25 solar flux range from the max 81 day average peak on September 4, 2024 at 227.3 and an average 81 day flux of 69 at solar minimum). SC25 365d peak: 195.9 on October 13, 2024.
The Potsdam WDC planetary A index was 17 (STAR Ap - based on the average of three hour interval ap indices: 17.0). Three hour interval K indices: 43432333 (planetary), 42532322 (Boulder), 53342544 (Andenes).
The background x-ray flux is at the class B5 level (GOES 19).
At the time of counting spots (see image time), spots were observed in 9 active regions using 2K resolution (SN: 133) and in 8 active regions using 1K resolution (SN: 95) SDO/HMI images.
AR 14305 [S25W85] decayed slowly and quietly.
AR 14307 [S16W82] rotated partly out of view while decaying slowly. C1
flares: C1.3 @ 00:11 UT
AR 14308 [N07W24] was mostly quiet and stable. C1 flares: C1.7 @
03:15 UT
AR 14310 [N02W64] was quiet and stable.
AR 14311 [N03W13] decayed slowly and was mostly quiet.
New AR 14312 [N18E60] rotated into view on December 17 and was
numbered the next day by SWPC.
New AR 14313 [S14E29] emerged with a few spots.
Spotted regions not observed (or interpreted
differently) by SWPC/USAF:
AR S11693 [S18W10] was quiet and stable.
New AR S11697 [S16E22] was observed with tiny
spots in an old plage area.
AR 14309 produced a C1.0 flare at 17:09 UT while at the southwest limb.
C2+ flares
| Magnitude | Peak time (UT) | Location | Source | Recorded by | Comment |
| C3.2 | 07:50 | 14312 | GOES18 |
December 16-18: No obviously Earth directed CMEs were observed in available coronagraph imagery.
[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 trans equatorial negative polarity coronal hole (CH1335) rotated across the central meridian on December 14-15. A recurrent positive polarity trans equatorial coronal hole (CH1336) could become Earth facing on December 19-21.
The geomagnetic field is expected to be at quiet to unsettled levels on December 19 due to weakening effects associated with CH1335. Quiet levels are likely on December 20-21. Quiet to minor storm conditions are likely on December 22-24 due to effects associated with CH1336.
| Coronal holes (1) | Coronal mass ejections (2) | M and X class flares (3) |
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.
(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.
| Active region | SWPC date numbered STAR detected |
Spot count | Location at midnight | Area | Classification | SDO / HMI 4K continuum image with magnetic polarity overlays |
Comment | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| SWPC/ USAF |
STAR | SWPC | STAR | Current | Previous | ||||||
| 2K | 1K | ||||||||||
| 14305 | 2025.12.08 2025.12.09 |
1 | 1 | 1 | S25W89 | 0060 | HSX | HSX |
 |
 |
was AR S11671 area: 0070 location: S25W85 |
| 14307 | 2025.12.09 2025.12.11 |
5 | 2 | 1 | S15W88 | 0130 | DAO | CRO |
 |
 |
was AR S11673 area: 0040 location: S16W82 |
| S11676 | 2025.12.09 | S11W44 | |||||||||
| 14308 | 2025.12.11 2025.12.12 |
1 | 7 | 1 | N08W27 | 0010 | AXX | CRO |
 |
 |
was AR S11679 location: N07W24 |
| S11680 | 2025.12.12 | N17W50 | |||||||||
| S11681 | 2025.12.12 | S12W42 | |||||||||
| 14310 | 2025.12.13 2025.12.15 |
2 | 4 | 2 | N02W66 | 0020 | CRO | BXO |
 |
 |
was AR S11684 area: 0010 location: N02W64 |
| S11687 | 2025.12.14 | N10W21 | |||||||||
| S11691 | 2025.12.14 | N19W22 | |||||||||
| S11692 | 2025.12.15 | N00W33 | |||||||||
| S11693 | 2025.12.15 | 6 | S18W10 | 0010 | BXO |
 |
 |
||||
| 14311 | 2025.12.15 2025.12.16 |
5 | 14 | 6 | N03W12 | 0060 | CSO | DRO |
 |
 |
was AR S11694 area: 0030 location: N03W13 |
| 14312 | 2025.12.17 2025.12.18 |
1 | 2 | 1 | N18E62 | 0060 | HAX | CSO |
 |
 |
was AR S11695 area: 0090 location: N18E60 |
| 14313 | 2025.12.18 2025.12.18 |
2 | 4 | 2 | S14E29 | 0010 | AXX | CRO |
 |
was AR S11696 area: 0025 |
|
| S11697 | 2025.12.18 | 3 | 1 | S16E22 | 0005 | AXX |
 |
||||
| Total spot count: | 17 | 43 | 15 | ||||||||
| Sunspot number: | 87 | 133 | 95 | (total spot count + 10 * number of spotted regions) | |||||||
| Weighted SN: | 40 | 65 | 37 | (Sum of total spot count + classification weighting for each AR. Classification weighting: X=0, R=3, A/S=5, H/K=10) | |||||||
| Relative sunspot number (Wolf number): | 95 | 73 | 76 | ||||||||
| Month | Average solar flux | International sunspot number (WDC-SILSO) |
Smoothed sunspot number (4) | Average
ap (3) |
|
|---|---|---|---|---|---|
| Measured | 1 AU | ||||
| 2024.05 | 187.7 | 191.9 | 172.1 | 149.1 (+4.6) | 23.56 (SC25 peak) |
| 2024.08 | 246.1 (SC25 peak) |
252.2 | 216.0 (SC25 peak) | 156.8 (+1.8) | 15.96 |
| 2024.09 | 195.7 | 197.8 | 141.1 | 159.4 (+1.6) | 15.36 |
| 2024.10 | 221.0 | 219.6 | 165.8 | 160.9 (+1.5) (SC25 solar max) | 18.99 |
| 2024.11 | 199.6 | 195.3 | 154.1 | 157.2 (-3.7) | 9.33 |
| 2024.12 | 197.3 | 191.2 | 154.6 | 151.2 (-6.0) | 8.42 |
| 2025.01 | 190.3 | 184.2 | 137.0 | 146.2 (-5.0) | 13.17 |
| 2025.02 | 184.2 | 179.7 | 155.7 | 139.8 (-6.4) | 14.42 |
| 2025.03 | 163.7 | 162.1 | 134.2 | 135.9 (-3.9) | 15.96 |
| 2025.04 | 162.5 | 163.6 | 141.4 | 133.3 (-2.6) | 17.62 |
| 2025.05 | 135.3 | 138.3 | 78.5 | 128.5 (-4.8) | 17.26 |
| 2025.06 | 131.3 | 135.4 | 114.6 | (124.4 projected, -4.1) | 21.43 |
| 2025.07 | 137.8 | 142.3 | 125.6 | (121.7 projected, -2.7) | 11.80 |
| 2025.08 | 154.9 | 158.7 | 133.5 | (118.0 projected, -3.7) | 9.97 |
| 2025.09 | 154.4 | 156.0 | 129.8 | (114.1 projected, -3.9) | 14.02 |
| 2025.10 | 139.5 | 138.6 | 114.6 | (110.1 projected, -4.0) | 15.64 |
| 2025.11 | 140.3 | 137.3 | 91.7 | (107.9 projected, -2.2) | 21.01 |
| 2025.12 | 164.3 (1) | 73.0 (2A) / 125.7 (2B) / 125.1 (2C) | (106.3 projected, -1.6) | (15.0) | |
| 2026.01 | (102.3 projected, -4.0) | ||||
| 2026.02 | (98.2 projected, -4.1) | ||||
| 2026.03 | (93.8 projected, -4.4) | ||||
| 2026.04 | (90.1 projected, -3.7) | ||||
| 2026.05 | (88.9 projected, -1.2) | ||||
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 27 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
Sunspot activity was on a decreasing trend from September
2024 until mid August 2025 (using the average solar flux over 3 solar rotations as a proxy).
Then a strong surge in activity saw solar flux peak in late August 2025 just
below the largest peaks seen in 2024. A slow decrease in activity from the
August level has been observed in September and October 2025.
All 365 day smoothed sunspot numbers reached a maximum on October 11-12, 2024.
This became the peak of SC25 (365 day smoothed peaks: STAR 1K: 236.1, STAR 2K: 364.3, NOAA SN: 156.0, ISN: 163.9),
while the 365d
smoothed solar flux peaked on October 13, 2024, just 1.7% below the SC23
peak, and 62.6% above the SC24 peak.
--------------------------------------------------------------------------------------
This report has been prepared by Jan Alvestad. It is based on the analysis of data from whichever 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.
