The geomagnetic field was quiet to active on April 28, early in the day under the influence of effects from CH1216. The high latitude magnetometer at Andenes recorded quiet to minor storm levels. The above 10 MeV proton flux was at background levels at the end of the day.
Solar flux density measured at 20h UT on 2.8 GHz was 140.1 - increasing 19.7 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 158.67. In comparison SC24 peaked on June 28, 2014 at 145.50. Current SC25 peak: 158.71 on October 28, 2023). The Potsdam WDC planetary A index was 6 (STAR Ap - based on the mean of three hour interval ap indices: 6.3). Three hour interval K indices: 42100001 (planetary), 42222211 (Boulder), 54111113 (Andenes).
The background x-ray flux is at the class C1 level (GOES 16).
At the time of counting spots (see image time), spots were observed in 14 active regions using 2K resolution (SN: 249) and in 13 active regions using 1K resolution (SN: 184) SDO/HMI images.
Region 13646 [N22W73] decayed slowly and
quietly.
Region 13652 [N14W70] was quiet and stable.
Region 13654 [S07W34] developed slowly and has a strong magnetic
delta in the central spot section. The region produced many C flares on
April 28 and 2 M flares early on April 29. A major flare is possible. C1
flares: C1.8 @ 11:13, C1.7 @ 11:27, C1.8 @ 18:22, C1.8 @ 18:28 UT
Region 13655 [S26W31] was quiet and stable.
Region 13656 [S13W20] decayed slowly and quietly.
Region 13660 [N10E52] was quiet and stable.
Spotted regions not observed (or interpreted
differently) by SWPC/USAF:
S9600 [N14W80] decayed slowly and was mostly quiet. C1 flares: C1.4 @
10:18 UT
S9635 [S23W81] decayed slowly and quietly. SWPC consider these
spots to be part of AR 13658.
S9637 [S09E20] was quiet and stable.
S9641 [N04W00] was quiet and stable.
S9646 [S12E00] was quiet and stable.
S9647 [N30E38] was quiet and stable.
New region S9650 [N23E78] rotated into view with a mature spot.
New region S9651 [N06E22] emerged with tiny spots.
C2+ flares
| Magnitude | Peak time (UT) | Location | Source | Recorded by | Comment |
| C2.8 | 00:38 | northwest limb | 13648 | GOES16 | |
| C2.3 | 01:15 | S9635 | GOES16 | ||
| C2.1 | 12:04 | 13654 | GOES16 | ||
| C7.8 | 12:35 | S06W28 | 13654 | GOES16 | |
| C4.5 | 13:10 | 13654 | GOES16 | ||
| C2.8 | 14:30 | 13654 | GOES16 | ||
| C2.4 | 15:01 | 13654 | GOES16 | ||
| C3.5 | 15:30 | 13654 | GOES16 | ||
| C6.3 | 16:01 | 13654 | GOES16 | ||
| C3.7 | 16:40 | 13654 | GOES16 | ||
| C2.1 | 19:07 | 13654 | GOES16 | ||
| C2.5 | 19:31 | 13654 | GOES16 | ||
| C8.4 | 20:20 | S06W35 | 13654 | GOES16 | |
| C2.4 | 21:20 | 13654 | GOES16 | ||
| C2.6 | 21:30 | S06W34 | 13654 | GOES16 | |
| C2.1 | 21:59 | 13654 | GOES16 | ||
| C2.6 | 22:18 | S22W77 | S9635 | GOES16 | |
| C7.7 | 23:06 | S08W31 | 13654 | GOES16 | |
| C2.2 | 23:59 | 13654 | GOES16 |
April 25-27: No obviously Earth directed CMEs were observed.
[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 (CH1217) rotated across the central meridian on April 27-28 and decayed slowly.
Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over upper middle and high latitudes is poor. Propagation on long distance northeast-southwest paths is poor.
The geomagnetic field is expected to be quiet to unsettled on April 29. Quiet to minor storm conditions are possible on April 30 - May 1 due to effects from CH1217.
| 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 |
Magnetic (SDO) |
SWPC | STAR | Current | Previous | ||||||
| 2K | 1K | ||||||||||
| 13644 | 2024.04.16 2024.04.16 |
2 | N13W83 | 0010 | BXO |
 |
location: N12W85 spotless |
||||
| 13646 | 2024.04.16 2024.04.17 |
1 | 2 | 1 | N22W74 | 0010 | AXX | AXX |
 |
 |
locaton: N22W73 |
| S9600 | 2024.04.16 | 2 | 1 | N14W80 | 0005 | AXX |
 |
 |
|||
| S9612 | 2024.04.19 | S20W47 | |||||||||
| 13657 | 2024.04.19 2024.04.21 |
1 | S14W46 | 0010 | AXX |
location: S15W42 spotless |
|||||
| 13652 | 2024.04.19 2024.04.20 |
2 | 2 | 2 | N14W70 | 0050 | HSX | HSX |
 |
 |
area: 0070 |
| 13654 | 2024.04.20 2024.04.21 |
25 | 51 | 27 | S07W36 | 0310 | EKC | EKC |
 |
 |
beta-gamma-delta location: S07W34 area: 0840 |
| 13653 | 2024.04.20 2024.04.21 |
N03W45 | location: N02W38 | ||||||||
| 13655 | 2024.04.21 | 1 | 9 | 4 | S26W33 | 0060 | HSX | CSO |
 |
 |
location: S26W31 |
| 13656 | 2024.04.21 2024.04.21 |
3 | 2 | S12W21 | 0008 | BXO |
 |
 |
location: S13W20 | ||
| 13658 | 2024.04.22 2024.04.24 |
4 | S22W84 | 0050 | CAO |
 |
location: S21W89 spotless SWPC includes spots from AR S9635 |
||||
| S9622 | 2024.04.22 | S20W59 | |||||||||
| S9626 | 2024.04.23 | S00W22 | |||||||||
| S9627 | 2024.04.23 | S15W45 |
 |
||||||||
| S9628 | 2024.04.23 | N19W47 | |||||||||
| 13659 | 2024.04.24 2024.04.25 |
S13W08 | |||||||||
| S9635 | 2024.04.25 | 6 | 5 | S23W81 | 0030 | CRO |
 |
 |
|||
| S9637 | 2024.04.25 | 7 | 2 | S09E20 | 0015 | BXO |
 |
 |
|||
| S9638 | 2024.04.25 | N04E04 | |||||||||
| S9639 | 2024.04.25 | N05E23 | |||||||||
| S9640 | 2024.04.25 | N11W48 | |||||||||
| S9641 | 2024.04.26 | 11 | 3 | N04W00 | 0020 | BXO |
 |
 |
|||
| S9642 | 2024.04.26 | S08W52 | |||||||||
| 13660 | 2024.04.26 2024.04.27 |
3 | 5 | 3 | N10E50 | 0010 | BXO | HRX |
 |
 |
location: N10E52
|
| S9644 | 2024.04.26 | S16W25 | |||||||||
| S9646 | 2024.04.27 | 5 | S12E08 | 0008 | AXX |
 |
 |
||||
| S9647 | 2024.04.27 | 2 | 2 | N30E38 | 0006 | BXO |
 |
 |
|||
| S9648 | 2024.04.27 | S09W54 |
 |
||||||||
| S9649 | 2024.04.27 | N04W11 |
 |
||||||||
| S9650 | 2024.04.28 | 1 | 1 | N23E78 | 0060 | HSX |
 |
||||
| S9651 | 2024.04.28 | 3 | 1 | N06E22 | 0007 | AXX |
 |
||||
| Total spot count: | 39 | 109 | 54 | ||||||||
| Sunspot number: | 119 | 249 | 184 | (total spot count + 10 * number of spotted regions) | |||||||
| Weighted SN: | 64 | 140 | 85 | (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): | 131 | 137 | 147 | ||||||||
| 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 |
| 2022.09 | 135.1 | 136.5 | 96.0 | 96.5 (+3.9) | 12.18 |
| 2022.10 | 133.5 | 132.7 | 95.5 | 98.9 (+2.4) | 11.16 |
| 2022.11 | 123.4 | 120.7 | 80.5 | 101.2 (+2.3) | 9.33 |
| 2022.12 | 147.9 | 143.4 | 112.8 | 106.7 (+5.5) | 10.99 |
| 2023.01 | 182.4 | 176.6 | 144.4 | 113.3 (+6.6) | 8.73 |
| 2023.02 | 167.2 | 163.2 | 111.3 | 117.8 (+3.5) | 14.48 (current SC25 peak) |
| 2023.03 | 157.2 | 155.6 | 123.3 | 121.1 (+3.3) | 14.42 |
| 2023.04 | 145.4 | 146.4 | 97.6 | 122.9 (+1.8) | 13.40 |
| 2023.05 | 155.6 | 159.2 | 137.4 | 124.1 (+1.2) | 10.67 |
| 2023.06 | 161.7 | 166.8 | 160.5 | 125.2 (+1.1) (SC25 solar max candidate) |
8.95 |
| 2023.07 | 176.4 | 182.2 | 160.0 | 124.3 (-0.9) | 8.15 |
| 2023.08 | 153.7 | 157.6 | 114.8 | 124.0 (-0.3) | 7.19 |
| 2023.09 | 154.4 | 156.0 | 134.2 | 123.8 (-0.2) | 14.26 |
| 2023.10 | 142.8 | 141.9 | 99.4 | (123.8 projected, 0.0) | 8.16 |
| 2023.11 | 153.5 | 150.2 | 105.4 | (123.5 projected, -0.3) | 12.20 |
| 2023.12 | 151.1 | 146.4 | 114.2 | (120.1 projected, -3.4) | 9.60 |
| 2024.01 | 164.6 | 159.3 | 123.0 | (116.8 projected, -3.3) | 5.46 |
| 2024.02 | 172.5 | 168.3 | 124.6 | (116.0 projected, -0.8) | 5.31 |
| 2024.03 | 154.4 | 152.9 | 104.9 | (115.4 projected, -0.6) | 11.03 |
| 2024.04 | 163.3 (1) | 135.8 (2A) / 145.5 (2B) / 160.2 (2C) | (115.4 projected, -0.0) | (9.3) | |
| 2024.05 | (116.6 projected, +1.2) | ||||
| 2024.06 | (115.8 projected, -0.8) | ||||
| 2024.07 | (114.1 projected, -1.7) | ||||
| 2024.08 | (112.1 projected, -2.0) | ||||
| 2024.09 | (110.9 projected, -1.2) | ||||
| 2024.10 | (110.3 projected, -0.6) | ||||
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 30 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
The big increase in sunspot counts during the April 14-27 interval caused a major uptick in the smoothed SNs and solar flux. It's not yet clear when the next peak will be, anytime between October 28 and December 20, 2023 looks possible. The 365d smoothed solar flux exceeded the June 27 peak on October 28, while the 365d smoothed ISN and NOAA SN both exceeded the June 2023 peak in late October 2023.
--------------------------------------------------------------------------------------
This report has been prepared by Jan Alvestad. It is based on the analysis of data from whatever 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.
