The geomagnetic field was at quiet to unsettled levels on September 4. Solar wind speed at SOHO ranged between 419 and 535 km/sec. The high latitude magnetometer at Andenes recorded 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 172.0 - increasing 24.3 over the previous solar rotation (the measurement may have been slightly enhanced by a C3.3 event which peaked at 19:46 UT). The 365 day average solar flux at 1 AU was 171.70 (183 days ago). The 81 day average solar flux at 1 AU was 148.8 (41 days ago, this is 50.4% 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: 195.86 on October 13, 2024. The Potsdam WDC planetary A index was 8 (STAR Ap - based on the average of three hour interval ap indices: 8.4). Three hour interval K indices: 11232323 (planetary), 21334322 (Boulder), 10124454 (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 12 active regions using 2K resolution (SN: 277) and in 12 active regions using 1K resolution (SN: 204) SDO/HMI images.
AR 14197 [S17W80] decayed slowly and produced
several low level C flares. C1 flares: C1.6 @ 02:28, C1.7 @ 06:09, C1.9 @
06:42, C1.6 @ 17:31, C1.6 @ 17:40, C1.9 @ 20:58 UT
AR 14199 [N03W62] decayed slowly and was mostly quiet.
AR 14201 [S21W62] decayed slowly and quietly.
AR 14202 [S15W56] decayed slowly and was mostly quiet. C1 flares:
C1.7 @ 03:31 UT
AR 14205 [N18W12] decayed slowly and quietly.
AR 14206 [N08W10] was mostly quiet and stable.
AR 14207 [N29E07] gained many spots with most of the development
occurring in the intermediate spot section. The spot group has an impressive
longitudinal length of 23 degrees. C1 flares: C1.7 @ 04:51, C1.9 @ 06:52,
C1.9 @ 10:13, C1.9 @ 11:36, C1.6 @ 12:34, C1.8 @ 14:43 UT
AR 14210 [N08E28] matured and was mostly quiet.
AR 14211 [S13E44] was mostly quiet. The trailing spot section could
be split off into a separate spot group.
New AR 14212 [N10E07] emerged with several spots.
Spotted regions not observed (or interpreted
differently) by SWPC/USAF:
S11398 [S07W35] reemerged with tiny spots.
S11404 [N12E12] was quiet and stable.
C2+ flares
| Magnitude | Peak time (UT) | Location | Source | Recorded by | Comment |
| C2.1 | 00:21 | 14211 | GOES18 | ||
| C2.5 | 00:37 | N04W48 | 14199 | GOES18 | |
| C2.0 | 01:15 | 14199 | GOES18 | ||
| C9.2 | 05:32 | N29E11 | 14207 | GOES18 | |
| C2.0 | 08:02 | 14207 | GOES18 | ||
| C2.2 | 08:07 | 14207 | GOES18 | ||
| C2.1 | 09:24 | 14199 | GOES19 | ||
| C2.1 | 10:19 | 14207 | GOES19 | ||
| C2.8 | 10:55 | N29E19 | 14207 | GOES18 | |
| C2.5 | 13:26 | 14211 | GOES18 | ||
| M1.0/1B | 13:44 | 14207 | GOES18 | ||
| C2.0 | 15:39 | 14207 | GOES18 | ||
| C2.4 | 15:57 | 14197 | GOES18 | ||
| C2.0 | 16:05 | 14197 | GOES18 | ||
| C3.3 | 19:46 | 14206 (partly) | GOES18 | ||
| C2.1 | 21:07 | 14197 | GOES18 | ||
| C2.9 | 21:44 | 14197 | GOES18 | ||
| C2.0 | 22:26 | 14197 | GOES18 | ||
| C3.3 | 23:35 | 14210 | GOES18 | ||
| C2.9 | 00:01 | 14197 | GOES18 | flare started at 23:57 UT |
September 2-3: No obviously Earth directed CMEs.
September 4: An asymmetric faint full halo CME was observed after a
C3.3 flare that began at 19:15, peaked at 19:46 and ended at 20:15 UT. The
flare occurred between ARs 14206 and 14212, and affected filaments quite a
distance away. The CME could reach Earth sometime between late on September
6 to the early afternoon of September 7.
[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 southern hemisphere coronal hole (CH1315) will rotate into an Earth facing position on September 2-7. CH1315 has a trans equatorial extension.
The geomagnetic field is expected to be at mostly quiet to minor storm levels on September 5-10 due to effects from CH1315. Major storm intervals are possible late on September 6 and on September 7 if the September 4 CME reaches Earth.
| 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 | ||||||||||
| 14197 | 2025.08.23 2025.08.24 |
14 | 10 | 7 | S18W78 | 0480 | FHI | EHO |
 |
 |
was AR S11375 area: 0580 location: S17W80 |
| 14196 | 2025.08.23 2025.08.24 |
S11W85 |
was AR 11376 location: S12W77 |
||||||||
| 14199 | 2025.08.24 2025.08.25 |
3 | 7 | 4 | N04W63 | 0160 | CSO | HAX |
 |
 |
was AR S11381 location: N03W62 area: 0240 |
| 14201 | 2025.08.24 2025.08.26 |
1 | 3 | 1 | S21W64 | 0045 | HSX | HAX |
 |
 |
was AR S11382 location: S21W62 |
| 14202 | 2025.08.25 2025.08.26 |
3 | 5 | 3 | S15W59 | 0070 | CSO | CSO |
 |
 |
was AR S11385 location: S15W56 |
| 14204 | 2025.08.27 | N03W60 | part of AR 14199 | ||||||||
| 14205 | 2025.08.28 | 1 | 14 | 5 | N17W15 | 0010 | AXX | BXO |
 |
 |
was AR S11389 area: 0020 location: N18W12 |
| 14206 | 2025.08.28 2025.08.29 |
1 | 1 | 1 | N08W12 | 0100 | HSX | HSX |
 |
 |
was AR S11390 location: N08W10 area: 0150 |
| S11391 | 2025.08.28 | N21W57 | |||||||||
| 14207 | 2025.08.29 2025.08.30 |
17 | 55 | 28 | N29E10 | 0390 | FHI | FKI |
 |
 |
was AR S11394 location: N29E07 area: 0450 |
| 14209 | 2025.08.29 2025.09.02 |
N18W70 | was AR S11395 | ||||||||
| S11398 | 2025.08.30 | 4 | 1 | S07W35 | 0007 | AXX |
 |
||||
| S11400 | 2025.08.31 | N18W42 |
 |
||||||||
| 14211 | 2025.09.01 2025.09.02 |
1 | 7 | 6 | S13E43 | 0150 | HSX | CSO |
 |
 |
was AR S11401 area: 0250 location: S13E44 |
| 14210 | 2025.09.01 2025.09.02 |
6 | 24 | 15 | N08E27 | 0140 | DSO | DSI |
 |
 |
was AR S11402 location: N08E28 area: 0280 |
| S11404 | 2025.09.03 | 14 | 7 | N12E12 | 0030 | BXO |
 |
 |
|||
| S11405 | 2025.09.03 | N28W07 |
 |
||||||||
| S11406 | 2025.09.03 | S03E24 |
 |
||||||||
| 14212 | 2025.09.04 2025.09.04 |
3 | 13 | 6 | N11E07 | 0015 | BXO | DRO |
 |
was AR S11407 area: 0025 location: N10E07 |
|
| Total spot count: | 50 | 157 | 84 | ||||||||
| Sunspot number: | 150 | 277 | 204 | (total spot count + 10 * number of spotted regions) | |||||||
| Weighted SN: | 100 | 210 | 137 | (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): | 165 | 152 | 163 | ||||||||
| 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) | 9.8 |
| 2025.09 | 185.2 (1) | 20.6 (2A) / 154.5 (2B) / 154.2 (2C) | (109.7 projected, -4.4) | (15.8) | |
| 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.
