The geomagnetic field was very quiet on April 21. Solar wind speed at SOHO ranged between 323 and 353 km/sec.
Solar flux at 20h UTC on 2.8 GHz was 69.3 (decreasing 1.9 over the previous solar rotation). The average 90 day 10.7 flux at 1 AU was 71.1 (The centered average 90 day SF at 1 AU hit a low of 67.77 on December 9, 2018. The centered average 1 year SF at 1 AU reached a minimum of 69.88 on August 18, 2018. The current average 1 year SF is 70.52). The Potsdam WDC planetary A index was 3 (STAR Ap - based on the mean of three hour interval ap indices: 2.6). Three hour interval K indices: 11110000 (planetary), 11312221 (Boulder)
The background x-ray flux is at the class A7 level (note that on April 18, 2019 NOAA adjusted the reference GOES15 x-ray flux to match that of GOES14. This adjustment seems questionable as it caused a nearly 10 fold artificial increase in the background x-ray flux)
At the time of counting spots (see image time), spots were observed in 1 active region using 2K resolution (SN: 11) and in 0 active regions using 1K resolution (SN: 0) SDO/HMI images.
Spotted regions not numbered (or interpreted
differently) by SWPC:
New region S6158 [S33E14] emerged with a tiny spot.
C2+ flares:
| Magnitude | Peak time (UT) | Location | AR | Recorded by | Comment |
April 19-21: 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 poorly defined southern hemisphere coronal hole (CH915) was Earth facing on April 19-21.
Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over upper middle latitudes is good. Propagation on long distance northeast-southwest paths is poor.
The geomagnetic field is expected to be quiet on April 22-24. Occasional unsettled intervals are possible on April 23-25 due to weak coronal hole effects.
| 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 numbered solar regions according to the Solar Region Summary provided by NOAA/SWPC. 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.
| Active region | Date numbered detected |
Spot count | Location at midnight | Area | Classification | SDO / HMI 4K continuum image with magnetic polarity overlays |
Comment | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| SWPC | Magnetic (SDO) |
SWPC | STAR | Current | Previous | ||||||
| 2K | 1K | ||||||||||
| 12739 | 2019.04.17 | N06W80 |
 |
||||||||
| S6158 | 2019.04.21 | 1 | S33E14 | 0002 | AXX |
 |
|
||||
| Total spot count: | 0 | 1 | 0 | ||||||||
| Sunspot number: | 0 | 11 | 0 | (total spot count + 10 * number of spotted regions) | |||||||
| Weighted SN: | 0 | 1 | 0 | (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): | 0 | 6 | 0 | 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) |
| 2017.11 | 72.2 | 70.6 | 5.7 | 15.4 (-1.2) | 10.06 |
| 2017.12 | 71.6 | 69.3 | 8.2 | 15.1 (-0.3) | 7.33 |
| 2018.01 | 69.9 | 67.7 | 6.7 | 14.3 (-0.8) | 5.53 |
| 2018.02 | 72.0 | 70.2 | 10.6 | 12.6 (-1.7) | 6.40 |
| 2018.03 | 68.3 | 67.6 | 2.5 | 9.9 (-2.7) | 7.91 |
| 2018.04 | 70.0 | 70.5 | 8.9 | 7.9 (-2.0) | 6.80 |
| 2018.05 | 70.8 | 72.4 | 13.2 | 7.5 (-0.4) | 7.16 |
| 2018.06 | 72.5 | 74.7 | 15.9 | 7.3 (-0.2) | 6.83 |
| 2018.07 | 69.6 | 72.3 | 1.6 | 7.1 (-0.2) | 5.38 |
| 2018.08 | 69.1 | 70.8 | 8.8 | 6.8 (-0.3) | 8.98 |
| 2018.09 | 68.2 | 69.0 | 3.3 | 6.6 (-0.2) | 8.91 |
| 2018.10 | 69.6 | 69.1 | 4.9 | (6.9 projected, +0.3) | 6.49 |
| 2018.11 | 68.9 | 67.4 | 5.9 | (6.8 projected, -0.1) | 5.78 |
| 2018.12 | 70.0 | 67.8 | 3.1 | (6.5 projected, -0.3) | 6.10 |
| 2019.01 | 71.5 | 69.2 | 7.8 | (6.5 projected, 0.0) | 5.89 |
| 2019.02 | 70.6 | 68.9 | 0.8 | (6.9 projected, +0.4) | 6.88 |
| 2019.03 | 71.6 | 70.8 | 9.5 | (7.7 projected, +0.8) | 6.12 |
| 2019.04 | (74.3) | 8.5 (2A) / 12.1 (2B) / 9.4 (2C) | (8.5 projected, +0.8) | (6.7) | |
| 2019.05 | (9.1 projected, +0.6) | ||||
| 2019.06 | (10.0 projected, +0.9) | ||||
| 2019.07 | (10.7 projected, +0.7) | ||||
| 2019.08 | (11.6 projected, +0.9) | ||||
| 2019.09 | (12.8 projected, +1.2) | ||||
1) Running average based on the daily 20:00 UTC observed solar flux value at 2800 MHz.
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.
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.
