The geomagnetic field was at quiet to unsettled levels on May 31, under the weakening influence of a high speed stream associated with CH1298. Solar wind speed at SOHO ranged between 603 and 795 km/sec, averaging 675 km/sec (-68 km/sec compared to the previous day). The high latitude magnetometer at Andenes recorded unsettled to minor storm levels. The above 10 MeV proton flux was at background levels until 07:55 UT, then protons associated with the M8 LDE began to arrive. Event levels were reached at 17:10 UT and the above 10 MeV flux was at 63 pfu at the end of the day. As I write this 86 pfu has been reached (05:10 UT on June 1).
Solar flux density measured at 20h UT on 2.8 GHz was 164.2 - increasing 5.2 over the previous solar rotation. The 365 day average solar flux at 1 AU was 189.88 (183 days ago). SC25 peak: 195.86 on October 13, 2024 (subtracting a baseline solar flux level of 65, this is +62.6% compared to the SC24 peak and -1.7% compared to the SC23 peak). The Potsdam WDC planetary A index was 13 (STAR Ap - based on the mean of three hour interval ap indices: 13.1). Three hour interval K indices: 33223233 (planetary), 44534433 (Boulder), 54334345 (Andenes).
The background x-ray flux is at the class B8 level (GOES 19).
At the time of counting spots (see image time), spots were observed in 9 active regions using 2K resolution (SN: 238) and in 6 active regions using 1K resolution (SN: 143) SDO/HMI images.
AR 14096 [N07W61] was quiet and stable.
AR 14099 [S13W10] lost the magnetic delta configuration and was
quiet.
AR 14100 [N09E00] changed significantly with decay observed in the
old penumbrae and new penumbrae forming mostly in the northernmost spot sections.
A new magnetic delta configuration formed as well and further M class flares
are likely. C1 flares: C1.7 @ 20:12, C1.7 @ 23:05 UT
AR 14101 [N04W15] decayed slowly and was mostly quiet.
AR 14104 [N07E29] decayed slowly and was mostly quiet.
Spotted regions not observed (or interpreted
differently) by SWPC/USAF:
S11103 [S08W09] reemerged with tiny spots.
S11108 [S09W27] reemerged with tiny spots.
New region S11113 [S09E49] was observed with tiny spots in an
old plage area.
New region S11114 [N11E66] emerged with a tiny spot.
Minor update added at 06:00 UT: A strong solar wind shock was observed at ACE at 05:27 UT, the arrival of the May 30/31 CME after a transit of only 29 hours. The solar wind speed is currently close to 1000 km/sec. K6-K9 geomagnetic storming is likey today. The above 10 MeV proton flux peaked at 146 pfu at 05:45 UT
C2+ flares
| Magnitude | Peak time (UT) | Location | Source | Recorded by | Comment |
| M1.0 | 03:56 | 14100 | GOES18 | ||
| M2.4 | 05:18 | 14100 | GOES18 | ||
| C5.3 | 05:59 | 14100 | GOES18 | ||
| C5.5 | 07:05 | 14100 | GOES18 | ||
| C7.0 | 07:27 | 14100 | GOES18 | ||
| C3.5 | 07:48 | 14100 | GOES18 | ||
| M4.5/1N | 08:18 | N11E05 | 14100 | GOES18 | |
| C3.2 | 10:09 | N10E02 | 14100 | GOES18 | |
| C9.0 | 10:15 | 14100 | GOES18 | ||
| C2.9 | 10:56 | 14100 | GOES18 | ||
| C2.6 | 11:39 | N09E01 | 14100 | GOES18 | |
| C6.5 | 13:28 | N10E00 | 14100 | GOES18 | |
| C3.5 | 13:49 | 14100 | GOES18 | ||
| M2.9/2B | 15:49 | N06E03 | 14100 | GOES18 | moderate type IV radio sweep |
| C5.9 | 16:26 | 14100 | GOES18 | ||
| C2.1 | 17:24 | 14100 | GOES18 | ||
| C2.5 | 18:20 | N10W03 | 14100 | GOES18 | |
| C4.8 | 19:06 | N10W03 | 14100 | GOES18 | |
| C2.2 | 21:58 | N07E06 | 14100 | GOES18 | |
| C2.2 | 22:34 | N10W04 | 14100 | GOES19 |
May 29: No obviously Earth directed CMEs.
May 30/31: An asymmetric full halo CME was observed during and after the long
duration M8.2 event in AR 14100. The CME reached Earth before 06 UT on June
1.
[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 negative polarity trans equatorial coronal hole (CH1298) was Earth facing on May 27-31.
The geomagnetic field is expected to be at active to very severe storm levels June 1 due to CME effects. Quiet to severe storm levels are likely on June 2 becoming quiet to active on June 3.
| 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 | ||||||||||
| 14094 | 2025.05.19 2025.05.21 |
N20W89 |
was AR S11083 location: N20W84 |
||||||||
| 14097 | 2025.05.20 2025.05.22 |
S14W64 |
was AR S11088 |
||||||||
| 14096 | 2025.05.20 2025.05.21 |
1 | 1 | 1 | N07W64 | 0060 | HSX | HSX |
 |
 |
was AR S11089 area: 0090 location: N07W61 |
| 14099 | 2025.05.24 | 13 | 28 | 19 | S14W11 | 0250 | DKC | DHC |
 |
 |
was AR S11093 area: 0450 location: S13W10 |
| 14102 | 2025.05.24 2025.05.27 |
S22W54 |
was AR S11094 location: S20W50 |
||||||||
| 14100 | 2025.05.25 2025.05.26 |
26 | 77 | 45 | N08W00 | 0440 | EKC | FKC |
 |
 |
beta-gamma-delta was AR S11095 location: N09E00 area: 0690 |
| S11097 | 2025.05.25 | S13W42 | |||||||||
| 14101 | 2025.05.26 2025.05.27 |
3 | 14 | 8 | N05W14 | 0030 | DAO | DAO |
 |
 |
was AR S11098 area: 0120 location: N04W15 |
| S11099 | 2025.05.26 | N13W15 | |||||||||
| 14103 | 2025.05.27 2025.05.28 |
S17W44 |
was AR S11101 location: S17W41 |
||||||||
| S11103 | 2025.05.28 | 2 | S08W09 | 0004 | BXO |
 |
|||||
| 14104 | 2025.05.29 2025.05.30 |
3 | 18 | 9 | N06E27 | 0080 | DSO | DAO |
 |
 |
was AR S11107 area: 0180 location: N07E29 |
| S11108 | 2025.05.29 | 5 | 1 | S19W27 | 0008 | AXX |
 |
||||
| S11111 | 2025.05.30 | N15W35 |
 |
||||||||
| S11112 | 2025.05.30 | S23E06 |
 |
||||||||
| S11113 | 2025.05.31 | 2 | S09E49 | 0002 | BXO |
 |
|||||
| S11114 | 2025.05.31 | 1 | N11E66 | 0001 | AXX |
 |
|||||
| Total spot count: | 46 | 148 | 83 | ||||||||
| Sunspot number: | 96 | 238 | 143 | (total spot count + 10 * number of spotted regions) | |||||||
| Weighted SN: | 71 | 183 | 118 | (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): | 106 | 131 | 114 | ||||||||
| Month | Average solar flux | International sunspot number (WDC-SILSO) |
Smoothed sunspot number (4) | Average
ap (3) |
|
|---|---|---|---|---|---|
| Measured | 1 AU | ||||
| 2014.02 | 170.3 (cycle peak) |
166.3 | 146.1 (SC24 peak) | 110.5 | 10.70 |
| 2014.04 | 143.9 | 144.8 | 112.5 | 116.4 (SC24 solar max) | 7.88 |
| 2017.09 | 91.3 | 92.3 | 43.6 | 18.2 (-1.3) | 18.22 (SC24 peak) |
| 2019.11 | 70.2 | 68.7 | 0.5 | 2.0 (-0.6) (Solar minimum using 365d smoothing: November 17, 2019) |
4.19 |
| 2019.12 | 70.8 | 68.6 | 1.6 | 1.8 (-0.2) (ISN 13 months smoothed solar minimum) |
3.22 |
| 2023.12 | 151.1 | 146.4 | 113.5 | 129.5 (+1.6) | 9.60 |
| 2024.01 | 164.6 | 159.3 | 126.0 | 131.2 (+1.7) | 5.46 |
| 2024.02 | 172.5 | 168.3 | 123.0 | 136.9 (+5.7) | 5.31 |
| 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 | 160.8 (+1.4) (SC25 solar max) | 18.99 |
| 2024.11 | 199.6 | 195.3 | 154.1 | 157.0 (-3.8) | 9.33 |
| 2024.12 | 197.3 | 191.2 | 154.6 | (150.7 projected, -6.3) | 8.42 |
| 2025.01 | 190.3 | 184.2 | 137.0 | (144.2 projected, -6.5) | 13.17 |
| 2025.02 | 184.2 | 179.7 | 154.6 | (135.6 projected, -8.6) | 14.42 |
| 2025.03 | 163.7 | 162.1 | 134.2 | (129.2 projected, -6.4) | 15.96 |
| 2025.04 | 162.5 | 163.6 | 140.6 | (124.6 projected, -4.6) | 17.62 |
| 2025.05 | 135.3 | 138.3 | 79.2 | (119.3 projected, -5.3) | 16.9 |
| 2025.06 | (1) | (2A/2B) / 106.4 (2C) | (114.4 projected, -4.9) | () | |
| 2025.07 | (110.2 projected, -4.2) | ||||
| 2025.08 | (105.5 projected, -4.7) | ||||
| 2025.09 | (101.2 projected, -4.3) | ||||
| 2025.10 | (97.3 projected, -3.9) | ||||
| 2025.11 | (95.0 projected, -2.3) | ||||
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 slowly decreasing trend since September
2024 (using the average solar flux over 3 solar rotations as a proxy). The
decline has become more obvious during the first half of May 2025 with solar
flux on May 12 at its lowest level since April 4, 2024. The solar max phase
of solar cycle 25 was considerably shorter than that of the most recent
solar cycles.
All 365 days smoothed sunspot numbers peaked on October 11-12, 2024,
very likely making this the peak of SC25 (STAR 1K 365d peak: 236.1, STAR 2K
365d peak: 364.3, NOAA SN 365d peak: 156.0, ISN 365d peak: 163.6). 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.
