The geomagnetic field was quiet to unsettled on April 17. The high latitude magnetometer at Andenes recorded quiet to active 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 216.5 - increasing 35.2 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 157.10. In comparison SC24 peaked on June 28, 2014 at 145.50. Current SC25 peak: 158.71 on June 27, 2023). The Potsdam WDC planetary A index was 6 (STAR Ap - based on the mean of three hour interval ap indices: 5.6). Three hour interval K indices: 31111212 (planetary), 31122322 (Boulder), 32113421 (Andenes).
The background x-ray flux is at the class C3 level (GOES 16).
At the time of counting spots (see image time), spots were observed in 23 active regions using 2K resolution (SN: 513) and in 21 active regions using 1K resolution (SN: 358) SDO/HMI images.
Region 13633 [S08W78] was mostly quiet and stable.
Region 13634 [N26W69] was mostly quiet and stable.
Region 13635 [N21W43] decayed slowly and quietly.
Region 13636 [S21W04] was quiet and stable.
Region 13637 [S13E13] was split into several spot groups due to
emerging flux in several areas of what used to be the central spot section.
The magnetic delta disappeared during the latter half of the day.
Region 13638 [S18E18] developed significantly and has a magnetic
delta structure. M flares are possible.
Region 13639 [N29E25] decayed losing the magnetic delta structures.
Region 13641 [N09W31] decayed slowly and was mostly quiet.
Region 13642 [N16W35] decayed slowly and quietly.
Region 13643 [S12E35] was mostly quiet and stable.
Region 13644 [N10E60] was quiet and stable.
New region 13645 [S09E22] was split off from AR 13637 and developed
quickly producing the only M flare of the day. A major flare is possible.
New region 13646 [N20E65] rotated into view on April 16 and was
numbered by SWPC the next day.
Spotted regions not observed (or interpreted
differently) by SWPC/USAF:
S9588 [N17W14] was quiet and stable.
S9593 [S22W17] reemerged with a tiny spot.
S9597 [S05W79] was quiet and stable.
S9600 [N13E65] was quiet and stable.
S9601 [S11E48] was quiet and stable.
New region S9603 [N19E53] emerged with a few spots.
New region S9604 [S17E11] was split off from AR 13638.
New region S9606 [S12E28] was split off from AR 13637 as a distinct
bipolar group developed in emerging flux. The region developed quickly and
has a magnetic delta structure. M flares are possible.
New region S9607 [S06W17] emerged with tiny spots.
New region S9608 [S35W15] emerged with a tiny spot.
C2+ flares
| Magnitude | Peak time (UT) | Location | Source | Recorded by | Comment |
| C2.8 | 00:17 | N14W11 | 13641 | GOES16 | |
| C2.9 | 01:02 | 13639 | GOES16 | ||
| C2.2 | 02:22 | 13643 | GOES16 | ||
| C2.4 | 02:29 | 13639 | GOES16 | ||
| C8.1 | 03:28 | N27E37 (SDO/AIA) | 13639 | GOES16 | |
| C2.3 | 04:49 | 13634 | GOES16 | ||
| C2.2 | 05:07 | 13645 | GOES16 | ||
| C2.3 | 05:49 | 13639 | GOES16 | ||
| C8.8 | 07:30 | 13637 | GOES16 | ||
| C2.0 | 08:26 | 13633 | GOES16 | ||
| C2.3 | 08:46 | 13634 | GOES16 | ||
| C3.0 | 08:53 | 13633 | GOES16 | ||
| C2.4 | 10:06 | 13643 | GOES16 | ||
| C3.1 | 10:42 | 13639 | GOES16 | ||
| C2.5 | 12:00 | 13639 | GOES16 | ||
| C3.5 | 13:48 | S09E24 | 13645 | GOES16 | |
| C3.7 | 14:04 | N32E29 (SDO/AIA) | 13639 | GOES16 | |
| C3.3 | 15:11 | 13639 | GOES16 | ||
| C6.6 | 15:48 | 13639 | GOES16 | ||
| C5.2 | 16:48 | S17E22 | 13638 | GOES16 | |
| C2.9 | 17:31 | 13639 | GOES16 | ||
| C3.3 | 18:07 | S9606 | GOES16 | ||
| C4.6 | 18:20 | 13638 | GOES16 | ||
| C2.9 | 18:36 | 13639 | GOES16 | ||
| C2.7 | 19:12 | 13646 | GOES16 | ||
| C2.6 | 19:50 | S9606 | GOES16 | ||
| C9.0/1F | 20:04 | 13638 | GOES16 | incorrectly attributed to AR 13643 by SWPC | |
| C9.7 | 20:08 | 13638 | GOES16 | ||
| C4.3 | 20:21 | 13645 | GOES16 | incorrectly attributed to AR 13639 by SWPC | |
| C4.3 | 21:20 | 13639 | GOES16 | ||
| M1.6/2N | 22:08 | 13645 | GOES16 | incorrectly attributed to AR 13643 by SWPC | |
| C7.8 | 23:25 | 13638 | GOES16 |
April 15-17: 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 southern hemisphere coronal hole (CH1214) rotated across the central meridian on April 17.
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 18-19. Quiet to active conditions will be possible on April 20-21 due to effects from CH1214.
| 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 | ||||||||||
| 13633 | 2024.04.05 2024.04.06 |
3 | 1 | 1 | S07W78 | 0080 | CSO | HSX |
 |
 |
area: 0140 location: S08W78 |
| 13634 | 2024.04.07 2024.04.08 |
8 | 9 | 6 | N27W70 | 0290 | DKI | DKO |
 |
 |
area: 0380 location: N26W69 |
| 13635 | 2024.04.08 2024.04.10 |
3 | 9 | 4 | N22W42 | 0010 | AXX | BXO |
 |
 |
location: N21W43 area: 0016 |
| 13636 | 2024.04.10 2024.04.11 |
4 | 13 | 4 | S20W05 | 0070 | CSO | CAO |
 |
 |
location: S21W04 area: 0190 |
| 13637 | 2024.04.12 2024.04.13 |
4 | 10 | 4 | S13E13 | 0020 | CRO | DRO |
 |
 |
split into several ARs on 2024.04.17 area: 0040 |
| 13638 | 2024.04.12 2024.04.13 |
5 | 21 | 10 | S17E15 | 0030 | CRI | DAC |
 |
 |
beta-gamma-delta area: 0130 location: S18E18 |
| 13639 | 2024.04.13 2024.04.14 |
16 | 61 | 26 | N29E22 | 0320 | EKI | EAI |
 |
 |
beta-gamma location: N29E37 |
| 13641 | 2024.04.13 2024.04.14 |
3 | 9 | 3 | N12W28 | 0060 | DAO | CAO |
 |
 |
location: N09W31 area: 0050 |
| S9588 | 2024.04.13 | 6 | 3 | N17W14 | 0015 | BXO |
 |
 |
|||
| 13640 | 2024.04.14 | N21E17 | |||||||||
| S9590 | 2024.04.14 | S08W43 | |||||||||
| 13642 | 2024.04.14 2024.04.15 |
2 | 1 | N18W39 | 0004 | AXX |
 |
 |
location: N16W35 |
||
| S9592 | 2024.04.14 | S04W40 | |||||||||
| S9593 | 2024.04.14 | 1 | 1 | S22W17 | 0003 | AXX |
 |
||||
| 13643 | 2024.04.15 | 20 | 43 | 26 | S13E34 | 0130 | FAI | DAI |
 |
location: S12E35 area: 0300 |
|
| S9595 | 2024.04.15 | S18W52 |
 |
||||||||
| S9597 | 2024.04.16 | 4 | 2 | S05W79 | 0020 | CRO |
 |
 |
|||
| 13644 | 2024.04.16 2024.04.16 |
2 | 1 | 1 | N12E60 | 0080 | DSO | HSX |
 |
 |
location: N10E60 area: 0100 |
| 13646 | 2024.04.16 2024.04.17 |
3 | 7 | 4 | N21E59 | 0030 | CSO | DAO |
 |
 |
area: 0080 |
| S9600 | 2024.04.16 | 1 | 1 | N13E65 | 0100 | HSX |
 |
 |
|||
| S9601 | 2024.04.16 | 4 | 1 | S11E48 | 0006 | BXO |
 |
 |
|||
| S9602 | 2024.04.16 | S42E20 |
 |
||||||||
| S9603 | 2024.04.17 | 3 | 2 | N19E53 | 0010 | CRO |
 |
||||
| S9604 | 2024.04.17 | 7 | 5 | S17E11 | 0020 | CRO |
 |
split off from AR 13638 | |||
| 13645 | 2024.04.17 2024.04.17 |
8 | 41 | 26 | S10E24 | 0030 | CAI | DAI |
 |
beta-gamma split off from AR 13637 location: S09E22 area: 0280 |
|
| S9606 | 2024.04.17 | 27 | 17 | S12E28 | 0300 | DAC |
 |
beta-gamma-delta split off from AR 13637 |
|||
| S9607 | 2024.04.17 | 2 | S06W17 | 0002 | BXO |
 |
|||||
| S9608 | 2024.04.17 | 1 | S35W15 | 0001 | AXX |
 |
|||||
| Total spot count: | 79 | 283 | 148 | ||||||||
| Sunspot number: | 199 | 513 | 358 | (total spot count + 10 * number of spotted regions) | |||||||
| Weighted SN: | 140 | 360 | 225 | (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): | 219 | 282 | 286 | ||||||||
| 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 | 144.1 (1) | 53.5 (2A) / 94.4 (2B) / 127.7 (2C) | (115.4 projected, -0.0) | (8.5) | |
| 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
Solar activity saw a significant decrease during the latter half of February and the first part of March. While there is still a chance that there could be another and higher peak in October or November 2023, chances that June 2023 was solar max has increased. After November 2023 there is currently no other obvious candidate solar max month. Taking into account the state of the solar polar fields another major peak during SC25 is becoming less likely.
--------------------------------------------------------------------------------------
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.
