The geomagnetic field was at quiet levels on September 26. Solar wind speed at SOHO ranged between 399 and 495 km/sec, averaging 443 km/sec (-57 km/sec compared to the previous day). The high latitude magnetometer at Andenes recorded quiet to active 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
165.1 -
decreasing 54.3
over the previous solar rotation.
The 365 day average solar flux at 1
AU was 169.08 (183 days ago). The 81 day average solar flux at 1 AU was
153.3 (41 days ago, this is 53.3% 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 6 (STAR Ap - based on the average of three hour interval ap indices: 5.5). Three hour interval K indices: 22121022 (planetary), 32113221 (Boulder), 43111144 (Andenes).
The background x-ray flux is at the class C1 level (GOES 19).
At the time of counting spots (see image time), spots were observed in 17 active regions using 2K resolution (SN: 329) and in 13 active regions using 1K resolution (SN: 203) SDO/HMI images.
AR 14225 [N09W51] was quiet and stable.
AR 14226 [S11W08] decayed slowly and was mostly quiet. The region
produced an M1.0 flare at 03:57 UT on September 27. C1 flares: C1.6 @ 02:02,
C1.7 @ 08:31 UT
AR 14227 [S19W10] decayed slowly and was mostly quiet.
AR 14228 [N04E02] decayed slowly and quietly.
AR 14229 [S03W73] decayed slowly and was mostly quiet. C1 flares:
C1.9 @ 13:59 UT
AR 14230 [S11E14] was mostly unchanged and quiet.
AR 14231 [S07W65] decayed slowly and quietly.
New AR 14232 [N02E77] rotated into view before noon. While the region
appears to be magnetically simple structured, several flares have been
recorded including an M1.1 event at 07:14 UT on September 27. C1 flares:
C1.7 @ 00:21, C1.6 @ 13:12 UT
Spotted regions not observed (or interpreted
differently) by SWPC/USAF:
S11444 [S12W80] developed slowly and was mostly quiet. C1 flares:
C1.7 @ 00:57, C1.3 @ 11:34, C1.5 @ 12:05 UT
S11445 [N07W36] was quiet and stable.
S11459 [S20W25] reemerged with tiny spots.
S11460 [S20E17] was quiet and stable.
S11461 [N17E75] is unstable and has only small and tiny spots. The
region was the most active spot group on the visible disk on September
26. A
small trailing magnetic delta configuration appears to be the source of most
flares including an M1.1 flare at 04:23 UT on September 27. C1 flares: C1.7
@ 09:26, C1.9 @ 04:34 UT
New AR S11463 [S17W14] emerged with several small and tiny spots. The
region has a weak trailing magnetic delta configuration.
New AR S11464 [N17W09] was observed with tiny spots in an old
plage area.
New AR S11465 [S08E47] emerged with a tiny spot.
New AR S11466 [S30E35] was observed with tiny
spots in an old plage area.
AR 14217 produced C1 flares while at the southwest limb: C1.7 @ 03:20, C1.9 @ 04:02, C1.6 @ 08:22 UT
C2+ flares
| Magnitude | Peak time (UT) | Location | Source | Recorded by | Comment |
| C2.4 | 06:28 | S11461 | GOES18 | simultaneous flare in AR S11444 | |
| C2.5 | 10:19 | 14227 | GOES18 | ||
| C2.0 | 10:50 | 14226 | GOES18 | ||
| C2.0 | 13:52 | 14229 | GOES18 | ||
| C2.2 | 14:43 | 14229 | GOES18 | ||
| C2.7 | 15:01 | 14229 | GOES18 | ||
| C2.1 | 16:20 | S11461 | GOES18 | ||
| C2.9 | 17:16 | S11461 | GOES18 | ||
| C2.3 | 18:05 | S11444 | GOES18 | ||
| C2.4 | 18:09 | S11461 | GOES18 | ||
| C7.8 | 19:05 | 14221 | GOES18 | ||
| C2.4 | 19:33 | S11461 | GOES18 | ||
| C2.1 | 19:52 | S11444 | GOES18 | ||
| M1.6 | 20:01 | S11461 | GOES18 | weak type II radio sweep | |
| C4.0 | 20:55 | S11461 | GOES18 | ||
| C2.1 | 21:17 | 14226 | GOES18 | ||
| C4.1 | 22:27 | S11461 | GOES18 | ||
| C2.8 | 23:15 | S11444 | GOES18 | ||
| C2.2 | 23:52 | S11444 | GOES18 |
September 24-26: No obviously Earth directed CMEs.
[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 small recurrent southern hemisphere negative polarity coronal hole (CH1318) rotated across the central meridian on September 24. A small northern hemisphere negative polarity coronal hole (CH1319) was Earth facing on September 25. A trans equatorial positive polarity coronal hole (CH1320) will probably rotate across the central meridian on September 29. A recurrent southern hemisphere positive polarity coronal hole (CH1321) will likely become Earth facing on September 29.
The geomagnetic field is expected to be at quiet to unsettled levels on September 27-29 due to weak effects from CH1318/CH1319.
| 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 | ||||||||||
| 14217 | 2025.09.13 2025.09.14 |
2 | S18W88 | 0070 | CSO |
 |
was AR S11433 rotated out of view |
||||
| 14223 | 2025.09.15 2025.09.16 |
S18W75 |
was AR S11439 location: S18W66 SWPC location is way off |
||||||||
| 14224 | 2025.09.15 2025.09.16 |
2 | S14W80 | 0060 | DSO |
was AR S11440 SWPC data correspond to that of AR S11444. actual location: S11W89 |
|||||
| 14225 | 2025.09.16 2025.09.16 |
2 | 5 | 3 | N09W53 | 0120 | HSX | CSO |
 |
 |
was AR S11442 area: 0220 location: N09W51 |
| S11444 | 2025.09.18 | 8 | 4 | S13W80 | 0190 | DAI |
 |
 |
SWPC moved AR 14224 to this AR on 2025.09.19 |
||
| S11445 | 2025.09.18 | 2 | N07W36 | 0003 | BXO |
 |
 |
||||
| 14231 | 2025.09.19 2025.09.25 |
2 | 4 | 1 | S08W66 | 0020 | CSO | CRO |
 |
 |
was AR S11446 area: 0030 |
| 14227 | 2025.09.19 2025.09.20 |
4 | 24 | 9 | S18W11 | 0030 | HAX | CRO |
 |
 |
was AR S11448 location: S19W10 area: 0060 |
| 14226 | 2025.09.19 2025.09.20 |
9 | 19 | 10 | S10W07 | 0130 | CAO | CAO |
 |
 |
was AR S11449 area: 0230 location: S10W08 |
| S11450 | 2025.09.19 | S27W41 | |||||||||
| S11452 | 2025.09.20 | N21W41 | |||||||||
| 14228 | 2025.09.20 2025.09.21 |
2 | 26 | 14 | N05E01 | 0020 | HSX | CRO |
 |
 |
was AR S11453 location: N04E02 |
| S11454 | 2025.09.21 | N01W43 | |||||||||
| S11455 | 2025.09.21 | N30W05 | |||||||||
| 14230 | 2025.09.22 2025.09.23 |
9 | 24 | 14 | S10E16 | 0080 | ESO | EAI |
 |
 |
beta-gamma was AR S11456 location: S11E14 area: 0220 |
| 14229 | 2025.09.22 2025.09.23 |
3 | 7 | 4 | S03W74 | 0050 | DSO | DAO |
 |
 |
was AR S11457 area: 0130 location: S03W73 |
| S11458 | 2025.09.22 | S22W00 | |||||||||
| S11459 | 2025.09.23 | 4 | S20W25 | 0005 | AXX |
 |
|||||
| S11460 | 2025.09.24 | 7 | 3 | S20E17 | 0020 | BXO |
 |
 |
|||
| S11461 | 2025.09.25 | 10 | 4 | N17E75 | 0030 | DRI |
 |
 |
beta-delta | ||
| 14232 | 2025.09.26 2025.09.26 |
2 | 3 | 1 | N02E78 | 0010 | HAX | HHX |
 |
was AR S11462 area: 0250 location: N02E77 |
|
| S11463 | 2025.09.26 | 9 | 4 | S17W14 | 0040 | DRI |
 |
beta-delta | |||
| S11464 | 2025.09.26 | 2 | N17W09 | 0004 | AXX |
 |
|||||
| S11465 | 2025.09.26 | 1 | S08E47 | 0001 | AXX |
 |
|||||
| S11466 | 2025.09.26 | 4 | 2 | S30E25 | 0006 | AXX |
 |
||||
| Total spot count: | 37 | 159 | 73 | ||||||||
| Sunspot number: | 137 | 329 | 203 | (total spot count + 10 * number of spotted regions) | |||||||
| Weighted SN: | 87 | 209 | 123 | (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): | 151 | 181 | 162 | ||||||||
| Month | Average solar flux | International sunspot number (WDC-SILSO) |
Smoothed sunspot number (4) | Average
ap (3) |
|
|---|---|---|---|---|---|
| Measured | 1 AU | ||||
| 2024.03 | 154.4 | 152.9 | 103.7 | 141.4 (+4.5) | 11.03 |
| 2024.04 | 161.3 | 162.6 | 137.0 | 144.5 (+3.1) | 9.69 |
| 2024.05 | 187.7 | 191.9 | 172.1 | 149.1 (+4.6) | 23.56 (SC25 peak) |
| 2024.06 | 184.3 | 190.2 | 164.1 | 152.8 (+3.7) | 10.24 |
| 2024.07 | 196.6 | 203.0 | 196.8 | 155.0 (+2.3) | 7.13 |
| 2024.08 | 246.1 (cycle 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 | 157.1 (-3.8) | 9.33 |
| 2024.12 | 197.3 | 191.2 | 154.6 | 151.3 (-5.8) | 8.42 |
| 2025.01 | 190.3 | 184.2 | 137.0 | 146.3 (-5.0) | 13.17 |
| 2025.02 | 184.2 | 179.7 | 155.7 | 139.9 (-6.4) | 14.42 |
| 2025.03 | 163.7 | 162.1 | 134.2 | (135.6 projected, -4.3) | 15.96 |
| 2025.04 | 162.5 | 163.6 | 140.6 | (132.5 projected, -3.1) | 17.62 |
| 2025.05 | 135.3 | 138.3 | 79.2 | (127.6 projected, -4.9) | 17.26 |
| 2025.06 | 131.3 | 135.4 | 116.3 | (122.8 projected, -4.8) | 21.43 |
| 2025.07 | 137.8 | 142.3 | 125.6 | (118.9 projected, -3.9) | 11.80 |
| 2025.08 | 154.9 | 158.7 | 133.6 | (114.1 projected, -4.8) | 9.97 |
| 2025.09 | 150.9 (1) | 106.6 (2A) / 122.5 (2B) / 153.2 (2C) ISN average to date: 130. At this level the SSN for March 2025 will become 136.0 |
(109.7 projected, -4.4) | (11.9) | |
| 2025.10 | (105.8 projected, -3.9) | ||||
| 2025.11 | (103.6 projected, -2.2) | ||||
| 2025.12 | (101.9 projected, -1.7) | ||||
| 2026.01 | (97.8 projected, -4.1) | ||||
| 2026.02 | (93.7 projected, -4.1) | ||||
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 has been on a decreasing trend since September
2024 (using the average solar flux over 3 solar rotations as a proxy).
Compared to the peak of SC25 solar flux has been at a low level in both May
and June 2025. Taking a closer look at the 81 day (3 solar rotations)
average solar flux proxy, its peak was in early September 2024 and had on
May 12 decreased to less than half of the solar cycle flux range.
Subtracting the 81 day average of approximately 69 at solar cycle minimum
from all measurements, the SC25 range is 0 - 158.3.
All 365 day smoothed sunspot numbers peaked on October 11-12, 2024,
very likely making this the peak of SC25 (365 day smoothed peaks: STAR 1K: 236.1, STAR 2K: 364.3, NOAA SN: 156.0, ISN: 163.9). 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.
