The geomagnetic field was quiet to minor storm on April 18. Solar wind speed at SOHO ranged between 344 and 634 km/sec. The high latitude magnetometer at Andenes recorded quiet to active levels. A solar wind shock was observed at SOHO at 13:08 UT. It is uncertain if this is the early arrival of the April 15/16 CME or the arrival of an unexpected CME.
Solar flux density measured at 20h UT on 2.8 GHz was 153.2 - decreasing 5.7 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 139.97. In comparison SC24 peaked on June 28, 2014 at 145.50). The Potsdam WDC planetary A index was 14 (STAR Ap - based on the mean of three hour interval ap indices: 13.6). Three hour interval K indices: 01114543 (planetary), 11114433 (Boulder), 00003444 (Andenes).
The background x-ray flux is at the class B8 level (GOES 16).
At the time of counting spots (see image time), spots were observed in 11 active regions using 2K resolution (SN: 297) and in 10 active regions using 1K resolution (SN: 189) SDO/HMI images.
Region 13272 [S23W76] decayed slowly and
was mostly quiet. C1 flares: C1.7 @ 18:44, C1.9 @ 19:17 UT
Region 13275 [N19W42] decayed slowly and quietly.
Region 13276 [S21W32] decayed slowly and quietly.
Region 13279 [S20W13] decayed slowly and
was mostly quiet. C1 flares: C1.2 @ 07:48 UT
Region 13281 [S23E02] decayed slowly and quietly.
Region 13282 [N11W03] was mostly quiet and stable. There is still a
chance of M class flaring.
Region 13283 [S21E20] continued to be somewhat unstable, probably due
to polarity intermixing.
Region 13284 [S09E61] decayed slowly and quietly.
Spotted regions not observed (or interpreted
differently) by SWPC:
S8464 [S13W28] reemerged with tiny spots.
S8468 [N39W24] reemerged with tiny spots.
New region S8472 [N20W21] emerged with tiny spots before noon.
AR 13280 (now behind the southwest limb) was the most active region during the day. C1 flares: C1.5 @ 04:03, C1.9 @ 09:33, C1.6 @ 11:37, C1.4 @ 21:03 UT
C2+ flares:
| Magnitude | Peak time (UT) | Location | Source | Recorded by | Comment |
| C2.4 | 05:30 | 13280 | GOES16 | ||
| C2.4 | 14:35 | 13280 | GOES16 | ||
| C4.8 | 15:29 | 13280 | GOES16 | ||
| C2.0 | 17:13 | 13283 | GOES16 | ||
| C3.2 | 18:13 | 13283 | GOES16 | simultaneous flares in ARs 13273 and 13280 the most likely source is 13280 due to the flare start time |
|
| C2.9 | 22:56 | 13280 | GOES16 |
April 16-18: No obviously Earth directed CMEs were
observed.
April 15: An extensive filament eruption in the northwest quadrant
was observed beginning in SDO/AIA imagery at 22:47 UT. A relatively faint
partial halo CME was observed early on April 16 and could reach Earth
on April 19 or 20 and cause unsettled to minor storm conditions. [It is
uncertain if the CME arrived earlier than expected due to the solar wind
shock observed at 13:08 UT on April 18]
[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 trans equatorial coronal hole (CH1141) will rotate across the central meridian on April 19.
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.
Quiet to active conditions are likely on April 19-23 due to CME effects April 19-21 and on April 22-23 due to effects from CH1141.
| Coronal holes (1) | Coronal mass ejection (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 | ||||||||||
| 13272 | 2023.04.05 2023.04.06 |
2 | 9 | 5 | S21W88 | 0010 | AXX | BXO |
 |
 |
location: S23W76 SWPC position is way off |
| 13275 | 2023.04.09 2023.04.10 |
1 | 3 | 1 | N18W44 | 0010 | AXX | AXX |
 |
 |
location: N19W42 area: 0007 |
| 13276 | 2023.04.10 2023.04.10 |
3 | 1 | S21W32 | 0010 | AXX | AXX |
 |
 |
area: 0001 | |
| 13277 | 2023.04.10 2023.04.11 |
N10W72 | |||||||||
| 13279 | 2023.04.10 2023.04.12 |
14 | 53 | 21 | S19W16 | 0100 | EAO | ERI |
 |
 |
location: S20W13 |
| 13281 | 2023.04.12 2023.04.13 |
16 | 43 | 19 | S22E03 | 0120 | EAI | EAI |
 |
 |
location: S23E02 |
| 13282 | 2023.04.13 2023.04.13 |
16 | 34 | 19 | N11W03 | 0410 | EKI | FKI |
 |
 |
area: 0610 |
| S8463 | 2023.04.13 | N20E05 |
 |
||||||||
| S8464 | 2023.04.13 | 2 | 1 | S13W28 | 0005 | BXO |
 |
||||
| 13283 | 2023.04.13 2023.04.16 |
5 | 24 | 12 | S21E22 | 0040 | CRO | CRI |
 |
 |
beta-gamma |
| S8466 | 2023.04.13 | S19E19 | |||||||||
| S8467 | 2023.04.14 | N08W26 | |||||||||
| S8468 | 2023.04.14 | 4 | 2 | N39W24 | 0007 | BXO |
 |
||||
| 13284 | 2023.04.17 2023.04.17 |
3 | 9 | 5 | S08E56 | 0060 | DAO | DAO |
 |
 |
location: S09E61 |
| S8472 | 2023.04.17 | 5 | 4 | N20W21 | 0020 | BXO |
 |
||||
| Total spot count: | 60 | 187 | 89 | ||||||||
| Sunspot number: | 140 | 297 | 189 | (total spot count + 10 * number of spotted regions) | |||||||
| Weighted SN: | 88 | 213 | 115 | (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): | 154 | 163 | 151 | ||||||||
| 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 |
| 2021.09 | 87.0 | 88.2 | 51.3 | 40.2 (+4.8) | 6.33 |
| 2021.10 | 88.9 | 88.3 | 37.4 | 45.2 (+5.0) | 7.38 |
| 2021.11 | 86.2 | 84.4 | 34.8 | 50.8 (+5.6) | 9.83 |
| 2021.12 | 103.0 | 99.8 | 67.5 | 55.9 (+5.1) | 6.40 |
| 2022.01 | 103.8 | 100.5 | 55.3 | 60.1 (+4.2) | 8.92 |
| 2022.02 | 109.1 | 106.5 | 60.9 | 64.7 (+4.6) | 10.46 |
| 2022.03 | 117.0 | 115.8 | 78.6 | 68.7 (+4.0) | 10.20 |
| 2022.04 | 130.8 | 131.7 | 84.0 | 73.0 (+4.3) | 11.79 |
| 2022.05 | 133.8 | 136.8 | 96.5 | 77.4 (+4.4) | 7.48 |
| 2022.06 | 116.1 | 119.8 | 70.3 | 81.1 (+3.7) | 8.20 |
| 2022.07 | 125.4 | 129.5 | 91.4 | 86.7 (+5.6) | 9.51 |
| 2022.08 | 114.2 | 117.1 | 74.6 | 92.5 (+5.8) | 10.92 |
| 2022.09 | 135.1 | 136.5 | 96.0 | 96.4 (+3.9) | 12.18 |
| 2022.10 | 133.5 | 132.7 | 95.5 | (99.0 projected, +2.6) | 11.16 |
| 2022.11 | 123.4 | 120.7 | 80.5 | (102.0 projected, +3.0) | 9.33 |
| 2022.12 | 147.9 | 143.4 | 112.8 | (106.8 projected, +4.8) | 10.99 |
| 2023.01 | 182.4 | 176.6 | 143.6 | (112.9 projected, +6.1) | 8.73 |
| 2023.02 | 167.2 | 163.2 | 110.9 | (117.9 projected, +5.0) | 14.48 (current SC25 peak) |
| 2023.03 | 157.2 | 155.6 | 122.6 | (121.0 projected, +3.1) | 14.42 |
| 2023.04 | 147.2 (1) | 53.4 (2A) / 89.1 (2B) / 143.7 (2C) | (126.4 projected, +5.4) | (8.2) | |
| 2023.05 | (132.1 projected, +5.7) | ||||
| 2023.06 | (135.2 projected, +3.1) | ||||
| 2023.07 | (134.7 projected, -0.5) | ||||
| 2023.08 | (135.7 projected, +1.0) | ||||
| 2023.09 | (139.2 projected, +3.5) | ||||
| 2023.11 | (142.5 projected max SC25) | ||||
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: SIDC-SILSO.
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.
