The geomagnetic field was very quiet on May 23. The high latitude magnetometer at Andenes recorded quiet to unsettled conditions.
Solar flux density measured at 20h UT on 2.8 GHz was 79.0 - decreasing 1.3 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 75.56). The Potsdam WDC planetary A index was 3 (STAR Ap - based on the mean of three hour interval ap indices: 3.1). Three hour interval K indices: 01111011 (planetary), 02121312 (Boulder), 11110023 (Andenes).
The background x-ray flux is at the class A8 level (GOES 16).
At the time of counting spots (see image time), spots were observed in 3 active regions using 2K resolution (SN: 72) and in 3 active regions using 1K resolution (SN: 52) SDO/HMI images.
Region 12824 [N19W00]
simplified magnetically as the small deltas from the previous day
disappeared. Only minor polarity intermixing was observed by the end of the
day. C are still likely, but less frequent than
over the last couple of days. There's a chance of minor M class flaring as
well. The main penumbra became symmetrical and lost area.
New region 12825 [N17E55] rotated into view on May 21 and was
numbered by SWPC 2 days later.
Spotted regions not observed (or interpreted
differently) by SWPC:
S6873 [S26E05] was quiet and stable.
C2+ flares:
| Magnitude | Peak time (UT) | Location | AR | Recorded by | Comment |
| C2.7 | 05:10 | 12824 | GOES16 | ||
| C2.4/1F | 09:22 | N20E07 | 12824 | GOES16 | |
| M1.1/2N | 11:08 | N19E10 | 12824 | GOES16 | halo CME |
| C2.2/1N | 17:05 | N20E01 | 12824 | GOES16 |
May 21: No obviously Earth directed CMEs
were observed in available LASCO imagery.
May 22: Faint halo CMEs were observed in LASCO imagery following a
C1.3 long duration event peaking at 08:44 and an M1.1 flare at 17:11 UT.
These CMEs could reach Earth during the latter half of May 25 or the first
half of May 26.
May 23: Another faint halo CME was observed in LASCO imagery after
the M1.1 flare in AR 12824 at 11:08 UT. This CME could reach Earth on May
26.
[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]
No obvious coronal holes are currently in or near Earth facing positions.
Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over upper middle and high latitudes is poor to fair. Propagation on long distance northeast-southwest paths is poor.
The geomagnetic field is expected to be quiet on May 24 and the first half of May 25. Several CMEs could reach Earth on May 25 and 26 and cause unsettled to major storm conditions.
| 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 | ||||||||||
| S6863 | 2021.05.15 | S15W38 | |||||||||
| S6864 | 2021.05.16 | S15W44 | |||||||||
| 12824 | 2021.05.17 2021.05.18 |
9 | 36 | 18 | N19W00 | 0190 | CSI | DSI |
 |
 |
beta-gamma area: 0240 |
| S6866 | 2021.05.17 | S21W21 | |||||||||
| S6870 | 2021.05.20 | N08W34 | |||||||||
| 12825 | 2021.05.21 2021.05.23 |
1 | 4 | 3 | N16E53 | 0010 | AXX | AXX |
 |
 |
location: N17E55 |
| S6872 | 2021.05.21 | N20W31 | |||||||||
| S6873 | 2021.05.21 | 2 | 1 | S26E05 | 0004 | AXX |
 |
 |
|||
| Total spot count: | 10 | 42 | 22 | ||||||||
| Sunspot number: | 30 | 72 | 52 | (total spot count + 10 * number of spotted regions) | |||||||
| Weighted SN: | 15 | 47 | 27 | (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): | 33 | 40 | 42 | k * (sunspot number) As of May 7, 2016: k = 1.1 for SWPC, k = 0.55 for STAR 2K, k = 0.80 for STAR 1K |
|||||||
| 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) |
| 2019.10 | 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 | 2.7 (+0.5) | 6.16 |
| 2020.03 | 70.2 | 69.5 | 1.5 | 3.0 (+0.3) | 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 | 7.9 (+2.3) | 3.75 |
| 2020.07 | 69.5 | 71.8 | 6.3 | 9.0 (+1.1) | 4.28 |
| 2020.08 | 71.6 | 73.4 | 7.6 | 9.5 (+0.5) | 5.68 |
| 2020.09 | 70.7 | 71.4 | 0.7 | 10.5 (+1.0) | 8.59 |
| 2020.10 | 74.6 | 74.2 | 14.6 | 11.9 (+1.4) | 6.13 |
| 2020.11 | 89.9 | 88.0 | 34.5 | (13.8 projected, +1.9) | 4.77 |
| 2020.12 | 86.9 | 84.2 | 23.1 | (16.2 projected, +2.4) | 4.72 |
| 2021.01 | 76.0 | 73.6 | 10.4 | (19.5 projected, +3.3) | 4.39 |
| 2021.02 | 74.3 | 72.4 | 8.3 | (22.8 projected, +3.3) | 9.50 |
| 2021.03 | 76.0 | 75.2 | 17.3 | (26.2 projected, +3.4) | 10.17 |
| 2021.04 | 75.9 | 76.4 | 24.5 | (30.3 projected, +4.1) | 8.40 |
| 2021.05 | 73.8 (1) | 12.1 (2A) / 16.3 (2B) / 31.2 (2C) | (33.0 projected, +2.7) | (7.2) | |
| 2021.06 | (36.2 projected, +3.2) | ||||
| 2021.07 | (40.8 projected, +4.6) | ||||
| 2021.08 | (45.5 projected, +4.7) | ||||
| 2021.09 | (51.2 projected, +5.7) | ||||
| 2021.10 | (55.6 projected, +4.4) | ||||
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.
