The geomagnetic field was at active to severe storm levels on September 15 under the influence of effects related to CH1316. Solar wind speed at SOHO ranged between 593 and 783 km/sec (on average +286 km/sec compared to the previous day). The high latitude magnetometer at Andenes recorded active to major 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 129.9 - increasing 13.9 over the previous solar rotation. The 365 day average solar flux at 1 AU was 169.19 (183 days ago). The 81 day average solar flux at 1 AU was 148.3 (41 days ago, this is 50.1% 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 48 (STAR Ap - based on the average of three hour interval ap indices: 48.1). Three hour interval K indices: 76545444 (planetary), 56644433 (Boulder), 65544446 (Andenes).
The background x-ray flux is at the class B9 level (GOES 19).
At the time of counting spots (see image time), spots were observed in 9 active regions using 2K resolution (SN: 185) and in 9 active regions using 1K resolution (SN: 142) SDO/HMI images.
AR 14216 [N10E23] decayed slowly and was mostly
quiet.
AR 14217 [S15E58] was mostly unchanged and has polarity
intermixing. C1 flares: C1.7 @ 01:38, C1.7 @ 01:54, C1.1 @ 04:19, C1.2 @
06:42, C1.6 @ 07:09, C1.3 @ 10:27, C1.3 @ 14:06, C1.2 @ 15:02, C1.4 @ 17:21,
C1.4 @ 21:01, C1.3 @ 23:02 UT
AR 14218 [N15W81] developed slowly and rotated partly out of view. C1
flares: C1.3 @ 16:14 UT
New AR 14219 [N26W14] emerged on September 13 and was numbered by
SWPC 2 days later.
New AR 14220 [S18E28] rotated into view on September 12 and received
its NOAA number 3 days later as slow development persisted.
New AR 14221 [N04E57] rotated into view on September 14 and developed
slowly on September 15.
Spotted regions not observed (or interpreted
differently) by SWPC/USAF:
S11435 [N09E08] was quiet and stable.
New AR S11439 [S16E77] rotated into view with small spots. C1 flares:
C1.4 @ 21:08 UT
New AR S11440 [S09E59] emerged with tiny spots to the north of
AR 14207.
AR 14213 produced C flares while rotating over the southwest limb: C1.2 @ 04:37, C1.4 @ 11:39, C1.3 @ 12:08, C1.6 @ 13:17, C1.3 @ 16:51, C1.3 @ 18:06 UT
C2+ flares
| Magnitude | Peak time (UT) | Location | Source | Recorded by | Comment |
| C2.1 | 08:21 | 14217 | GOES19 | ||
| C2.1 | 09:55 | N13E28 | 14216 | GOES18 | |
| C3.5 | 18:31 | behind southwest limb | 14213 | GOES18 | |
| C2.7 | 18:44 | 14217 | GOES18 |
September 13-15: 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 large recurrent trans equatorial negative polarity coronal hole (CH1316) rotated across the central meridian on September 10-13. A recurrent northern hemisphere negative polarity coronal hole (CH1317) could become Earth facing on September 18-19.
The geomagnetic field is expected to be at quiet to minor storm levels on September 16-17 due to effects related to CH1316. Quiet to unsettled levels are likely on September 18.
| 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 | ||||||||||
| S11418 | 2025.09.08 | N23W25 | |||||||||
| S11419 | 2025.09.08 | S10W55 | |||||||||
| S11421 | 2025.09.09 | S08W30 | |||||||||
| S11422 | 2025.09.10 | N20W32 | |||||||||
| 14216 | 2025.09.10 2025.09.11 |
11 | 30 | 16 | N10E24 | 0210 | DAI | CSI |
 |
 |
was AR S11423 area: 0380 locaton: N10E23 |
| S11424 | 2025.09.11 | N09W14 | |||||||||
| S11427 | 2025.09.12 | S17W11 | |||||||||
| S11428 | 2025.09.12 | N08W05 | |||||||||
| 14220 | 2025.09.12 2025.09.15 |
4 | 13 | 7 | S18E28 | 0010 | BXO | CRO |
 |
 |
was AR S11429 area: 0040 |
| 14218 | 2025.09.13 2025.09.14 |
4 | 1 | 1 | N14W86 | 0060 | DSO | HAX |
 |
 |
was AR S11430 location: N15W81 |
| 14219 | 2025.09.13 2025.09.15 |
6 | 13 | 8 | N26W16 | 0020 | CRO | DRO |
 |
 |
was AR S11431 area: 0060 |
| 14217 | 2025.09.13 2025.09.14 |
6 | 20 | 9 | S17E58 | 0200 | DAO | EKI |
 |
 |
beta-gamma was AR S11433 location: S15E58 area: 0350 |
| S11434 | 2025.09.13 | S23W29 |
 |
||||||||
| S11435 | 2025.09.13 | 2 | 1 | N09E08 | 0007 | AXX |
 |
 |
|||
| 14221 | 2025.09.14 2025.09.15 |
3 | 7 | 5 | N04E57 | 0020 | CRO | DAO |
 |
 |
was AR S11436 area: 0080 |
| S11437 | 2025.09.14 | N23E24 |
 |
||||||||
| S11438 | 2025.09.14 | S13E42 |
 |
||||||||
| S11439 | 2025.09.15 | 5 | 4 | S16E77 | 0050 | CAO |
 |
||||
| S11440 | 2025.09.15 | 4 | 1 | S09E59 | 0010 | BXO |
 |
||||
| Total spot count: | 34 | 95 | 52 | ||||||||
| Sunspot number: | 94 | 185 | 142 | (total spot count + 10 * number of spotted regions) | |||||||
| Weighted SN: | 55 | 131 | 88 | (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): | 103 | 102 | 114 | ||||||||
| 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 | 142.2 (1) | 53.1 (2A) / 106.3 (2B) / 134.5 (2C) | (109.7 projected, -4.4) | (14.4) | |
| 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.
