The geomagnetic field was at unsettled to minor storm levels on April 18 under the influence of effects related to CH1358. Solar wind speed at SOHO ranged between 379 and 593 km/sec, averaging 489 km/sec (+150 km/sec compared to the previous day). The high latitude magnetometer at Andenes was at unsettled 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 105.1 - decreasing 15.0 over the previous solar rotation.
The 365 day average solar flux at 1 AU was 141.80 (183 days ago). The 81 day average solar flux at 1 AU was 126.8 (41 days ago, this is 36.5% 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 32 (STAR Ap - based on the average of three hour interval ap indices: 31.9). Three hour interval K indices: 35554335 (planetary), 34644433 (Boulder), 55643345 (Andenes).
The background x-ray flux is at the class B2 level (GOES 19).
At the time of counting spots (see image time), spots were observed in 5 active regions using 2K resolution (SN: 90) and in 3 active regions using 1K resolution (SN: 50) SDO/HMI images.
AR 14415 [S18W58] was quiet and stable.
AR 14419 [N14E01] gained a few spots and appears to have developed a small
magnetic delta configuration in the northern part of the trailing spot
section. C and minor M class flaring is possible.
Spotted regions not observed (or interpreted
differently) by SWPC/USAF:
AR S11995 [S16E00] reemerged with tiny spots.
AR S11996 [N02E31] was quiet and stable.
AR S11998 [S16E34] was quiet and stable.
AR 14416 produced the only C flare of the day while at the northwest limb, a C1.6 event peaking at 07:03 UT.
C2+ flares
| Magnitude | Peak time (UT) | Location | Source | Recorded by | Comment |
April 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 large recurrent negative polarity trans equatorial coronal hole (CH1358) rotate across the central meridian on April 15-18. A recurrent positive polarity northern hemisphere coronal hole (CH1359) will likely become Earth facing on April 22-23.
The geomagnetic field is expected to be at quiet to minor storm levels on April 19-21 due to effects associated with CH1358.
| 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 | ||||||||||
| 14416 | 2026.04.06 2026.04.10 |
1 | N22W91 | 0090 | HAX |
 |
was AR S11976 location: N20W92 rotated out of view |
||||
| 14414 | 2026.04.07 2026.04.07 |
N15W73 |
location: N18W65 |
||||||||
| 14415 | 2026.04.07 2026.04.08 |
1 | 1 | 1 | S18W61 | 0060 | HSX | HSX |
 |
 |
was AR S11978 area: 0100 location: S18W58 |
| 14418 | 2026.04.12 2026.04.13 |
S11W63 |
was AR S11987 location: S12W45 |
||||||||
| 14419 | 2026.04.12 2026.04.13 |
12 | 32 | 18 | N13E01 | 0270 | EHO | EKI |
 |
 |
beta-gamma-delta was AR S11991 area: 0510 location: N14E01 |
| S11993 | 2026.04.15 | S20W34 | |||||||||
| S11994 | 2026.04.15 | S13W22 | |||||||||
| S11995 | 2026.04.16 | 2 | S16E00 | 0002 | AXX |
 |
|||||
| S11996 | 2026.04.17 | 3 | 1 | N02E31 | 0006 | AXX |
 |
 |
|||
| S11997 | 2026.04.17 | S30W45 |
 |
||||||||
| S11998 | 2026.04.17 | 2 | S16E34 | 0002 | AXX |
 |
 |
||||
| Total spot count: | 14 | 40 | 20 | ||||||||
| Sunspot number: | 44 | 90 | 50 | (total spot count + 10 * number of spotted regions) | |||||||
| Weighted SN: | 34 | 55 | 35 | (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): | 48 | 50 | 40 | ||||||||
| 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 |
| 2024.10 | 221.0 | 219.6 | 165.8 | 160.9 (+1.5) (SC25 solar max) | 18.99 |
| 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 | 128.6 (-4.7) | 17.26 |
| 2025.06 | 131.3 | 135.4 | 114.6 | 124.7 (-3.9) | 21.43 |
| 2025.07 | 137.8 | 142.3 | 125.9 | 122.4 (-2.3) | 11.80 |
| 2025.08 | 154.9 | 158.7 | 133.7 | 118.2 (-4.2) | 9.97 |
| 2025.09 | 154.4 | 156.0 | 129.7 | 112.9 (-5.3) | 14.02 |
| 2025.10 | 139.5 | 138.6 | 114.6 | (108.9 projected, -4.0) | 15.64 |
| 2025.11 | 140.3 | 137.3 | 91.7 | (106.9 projected, -2.0) | 21.01 |
| 2025.12 | 160.8 | 155.8 | 124.0 | (105.4 projected, -1.5) | 13.35 |
| 2026.01 | 148.7 | 144.0 | 112.6 | (101.5 projected, -3.9) | 22.47 |
| 2026.02 | 136.4 | 133.1 | 78.2 | (97.3 projected, -4.2) | 12.88 |
| 2026.03 | 131.0 | 129.7 | 85.9 | (92.7 projected, -4.6) | 15.44 |
| 2026.04 | 111.4 (1) | 49.8 (2A) / 82.9 (2B) / 90.6 (2C) | (88.7 projected, -4.0) | (13.2) | |
| 2026.05 | (87.5 projected, -1.2) | ||||
| 2026.06 | (85.4 projected, -2.1) | ||||
| 2026.07 | (81.0 projected, -4.4) | ||||
| 2026.08 | (78.8 projected, -2.2) | ||||
| 2026.09 | (77.9 projected, -0.9) | ||||
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
Solar activity appears to have exited the solar max phase as of February
2026 with a strong decrease in the number of sunspots observed. The northern
polar field has weakened considerably over the last months, and although
there is a chance the the field could recover over the next 1-2 years, there
is an increasing chance that solar cycle 26 will be very weak. The southern
polar field is not impressive either, however, a southern polar coronal hole
has formed early in 2026 and appears to be growing.
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.
