The geomagnetic field was unsettled to minor storm on April 17 under the influence of high speed streams associated with CH1006 and CH1007. The high latitude magnetometer at Andenes recorded unsettled to major storm conditions.
Solar flux density measured at 20h UT on 2.8 GHz was 75.3 - decreasing 0.6 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 74.90). The Potsdam WDC planetary A index was 30 (STAR Ap - based on the mean of three hour interval ap indices: 29.9). Three hour interval K indices: 55544434 (planetary), 44534433 (Boulder), 66433556 (Andenes).
The background x-ray flux is at the class A7 level (GOES 16).
At the time of counting spots (see image time), spots were observed in 5 active regions using 2K resolution (SN: 71) and in 5 active regions using 1K resolution (SN: 62) SDO/HMI images.
Region 12814 [S22W55]
decayed slowly and quietly.
Region 12815 [S20W36] decayed slowly and quietly.
Region 12816 [S23E47] decayed slowly and quietly, slow growth was
observed early on April 18.
Spotted regions not observed (or interpreted
differently) by SWPC:
S6822 [N21E02] was quiet and stable.
New region S6823 [N20E29] emerged with tiny spots.
An active region behind the southeast limb produced a long duration B9.7 event peaking at 17:17 UT.
C2+ flares:
| Magnitude | Peak time (UT) | Location | AR | Recorded by | Comment |
April 15-17: No obviously Earth directed CMEs were observed in available LASCO 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 recurrent southern hemisphere coronal hole (CH1007) - an extension of the southern polar coronal hole - was Earth facing on April 14-17. CH1007 decayed slightly in the northwestern part on April 15 due to emerging AR S6819. Another recurrent southern hemisphere coronal hole (CH1008) could 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 fair.
The geomagnetic field is expected to be unsettled to minor storm on April 18-20 due to effects from CH1007, major storm intervals are possible. Quiet to unsettled is likely on April 21 becoming quiet to active on April 22 due to effects from CH1008
| 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 red colored.
| 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 | ||||||||||
| 12814 | 2021.04.08 2021.04.12 |
4 | 4 | 1 | S22W59 | 0010 | BXO | BXO |
 |
 |
area: 0005 location: S22W55 |
| S6817 | 2021.04.14 | S31E16 | |||||||||
| 12816 | 2021.04.15 2021.04.16 |
4 | 11 | 6 | S24E46 | 0020 | CAO | DRO |
 |
 |
area: 0050 |
| 12815 | 2021.04.15 2021.04.16 |
2 | 1 | S21W35 | 0005 | AXX |
 |
 |
location: S20W36 |
||
| S6820 | 2021.04.15 | S30W15 | |||||||||
| S6822 | 2021.04.16 | 2 | 2 | N21E02 | 0006 | AXX |
 |
 |
|||
| S6823 | 2021.04.17 | 2 | 2 | N20E29 | 0006 | BXO |
 |
||||
| Total spot count: | 8 | 21 | 12 | ||||||||
| Sunspot number: | 28 | 71 | 62 | (total spot count + 10 * number of spotted regions) | |||||||
| Weighted SN: | 13 | 24 | 15 | (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): | 31 | 39 | 50 | k * (sunspot number) As of May 7, 2016: k = 1.1 for SWPC, k = 0.55 for MSN 2K, k = 0.80 for MSN 1K (MSN=Magnetic Sunspot Number) |
|||||||
| 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 (cycle peak) | 110.5 | 10.70 |
| 2014.04 | 143.9 | 144.8 | 112.5 | 116.4 (solar max) | 7.88 |
| 2017.09 | 91.3 | 92.3 | 43.6 | 18.2 (-1.3) | 18.22 (cycle peak) |
| 2019.09 | 67.9 | 68.7 | 1.1 | 3.1 (-0.3) | 9.81 |
| 2019.10 | 67.4 | 67.0 | 0.4 | 2.6 (-0.5) | 7.53 |
| 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 |
| 2020.01 | 72.2 | 69.9 | 6.4 | 2.2 (+0.4) | 4.39 |
| 2020.02 | 71.0 | 69.3 | 0.4 | 2.8 (+0.6) | 6.16 |
| 2020.03 | 70.2 | 69.5 | 1.5 | 3.0 (+0.2) | 5.63 |
| 2020.04 | 69.5 | 70.0 | 5.4 | 3.6 (+0.6) | 5.32 |
| 2020.05 | 69.0 | 70.6 | 0.2 | 5.6 (+2.0) | 3.80 |
| 2020.06 | 69.5 | 71.7 | 5.8 | 7.8 (+2.2) | 3.75 |
| 2020.07 | 69.5 | 71.8 | 6.3 | 8.8 (+1.0) | 4.28 |
| 2020.08 | 71.6 | 73.4 | 7.6 | 9.3 (+0.5) | 5.68 |
| 2020.09 | 70.7 | 71.4 | 0.7 | 10.5 (+1.2) | 8.59 |
| 2020.10 | 74.6 | 74.2 | 14.6 | (11.6 projected, +1.1) | 6.13 |
| 2020.11 | 89.9 | 88.0 | 34.5 | (13.2 projected, +1.6) | 4.77 |
| 2020.12 | 86.9 | 84.2 | 23.1 | (16.3 projected, +3.1) | 4.72 |
| 2021.01 | 76.0 | 73.6 | 10.4 | (20.0 projected, +3.7) | 4.39 |
| 2021.02 | 74.3 | 72.4 | 8.3 | (23.3 projected, +3.3) | 9.50 |
| 2021.03 | 76.0 | 75.2 | 17.3 | (27.5 projected, +4.2) | 10.17 |
| 2021.04 | 73.7 (1) | 5.9 (2A) / 10.3 (2B) / 22.5 (2C) | (32.6 projected, +5.1) | (7.5) | |
| 2021.05 | (35.6 projected, +3.0) | ||||
| 2021.06 | (38.8 projected, +3.2) | ||||
| 2021.07 | (43.4 projected, +4.6) | ||||
| 2021.08 | (48.0 projected, +4.6) | ||||
| 2021.09 | (53.7 projected, +5.7) | ||||
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.
