The geomagnetic field was very quiet on May 18. Solar wind speed at SOHO ranged between 318 and 397 km/sec. The high latitude magnetometer at Andenes recorded very quiet levels.
Solar flux density measured at 20h UT on 2.8 GHz was 150.6 - increasing 9.9 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 140.75. In comparison SC24 peaked on June 28, 2014 at 145.50). The Potsdam WDC planetary A index was 2 (STAR Ap - based on the mean of three hour interval ap indices: 2.1). Three hour interval K indices: 11000010 (planetary), 1201121* (Boulder), 11011100 (Andenes).
The background x-ray flux is at the class C2 level (GOES 16).
At the time of counting spots (see image time), spots were observed in 10 active regions using 2K resolution (SN: 248) and in 10 active regions using 1K resolution (SN: 181) SDO/HMI images.
Region 13301 [N14W49] decayed slowly and
quietly.
Region 13302 [N17W44] decayed slowly and quietly.
Region 13305 [N11W42] developed in the northern spot section and a
weak magnetic delta formed in the central spots. Further
development will increase the chances of M class flaring.
Region 13307 [S10W05] was quiet and stable.
Region 13308 [N11W27] developed further with poor separation between
opposite polarity spots in the central spots. M class flaring is becoming
possible.
Region 13309 [S18W63] developed again late in the day. Although the
region only has tiny spots, an area of positive polarity is squeezed between
two area of negative polarity flux. This development could make the region
more unstable.
Region 13310 [S21E61] matured with a large leading penumbra and
otherwise only small spots. There is still a chance of isolated M class
flares.
New region 13311 [N18E73] rotated partly into view on May 17 and was
numbered the next day by SWPC. The region was very active producing many M
and C flares. The activity is likely caused by a small and very tight
magnetic delta in a trailing penumbra.
Spotted regions not observed (or interpreted
differently) by SWPC:
S8569 [S30E17] decayed slowly and quietly.
New region S8571 [S24E82] rotated into view and appears to be a
compact region. M class flaring is possible. C1 flares: C1.9 @ 01:41 UT
C2+ flares:
| Magnitude | Peak time (UT) | Location | Source | Recorded by | Comment |
| C8.6 | 03:21 | GOES16 | |||
| C4.5 | 03:49 | S8571 | GOES16 | ||
| C3.8 | 04:12 | GOES16 | |||
| C2.2 | 04:57 | GOES16 | |||
| M1.0 | 06:26 | 13311 | GOES16 | ||
| M1.2 | 06:55 | 13311 | GOES16 | ||
| C2.4 | 08:25 | 13311 | GOES16 | ||
| C2.5 | 08:31 | 13311 | GOES16 | ||
| C5.2 | 10:11 | 13311 | GOES16 | ||
| C9.6 | 10:20 | 13311 | GOES16 | ||
| C4.2 | 11:05 | 13311 | GOES16 | ||
| C5.2 | 11:24 | 13311 | GOES16 | ||
| M2.2 | 11:47 | 13311 | GOES16 | ||
| M1.9 | 12:13 | 13311 | GOES16 | ||
| M1.6 | 12:49 | 13311 | GOES16 | ||
| C7.0 | 13:34 | 13311 | GOES16 | ||
| C8.5 | 13:55 | 13311 | GOES16 | ||
| C2.9 | 15:09 | 13311 | GOES16 | ||
| C4.0 | 15:55 | 13311 | GOES16 | ||
| C2.7 | 16:39 | 13309 | GOES16 | ||
| C2.3 | 16:54 | 13311 | GOES16 | simultaneous flare in AR S8571 | |
| C2.5 | 17:30 | 13311 | GOES16 | ||
| M1.1 | 17:50 | 13311 | GOES16 | ||
| C2.3 | 18:55 | 13311 | GOES16 | ||
| C2.4 | 19:06 | 13305 | GOES16 | ||
| C2.1 | 19:51 | 13311 | GOES16 | ||
| M3.8 | 20:23 | 13311 | GOES16 | ||
| M3.6 | 20:33 | 13311 | GOES16 | ||
| M4.5 | 21:05 | 13311 | GOES16 | ||
| M2.4 | 21:28 | 13311 | GOES16 | ||
| C9.4 | 22:15 | 13311 | GOES16 | ||
| C7.9 | 22:31 | 13311 | GOES16 | ||
| C4.0 | 23:20 | 13311 | GOES16 | ||
| C3.8 | 23:40 | S8571 | GOES16 |
May 16, 18: No obviously Earth directed CMEs were
observed.
May 17: A filament eruption associated with a C4 flare in AR 13309
was the source of a CME that may have Earth directed components. If that's
the case weak effects could reach Earth on May 20 or 21.
[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 trans equatorial coronal hole (CH1148) was Earth facing on May 16-17. A southern hemisphere coronal hole (CH1149) will likely rotate across the central meridian on May 20-22.
Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over upper middle and high latitudes is fair to good. Propagation on long distance northeast-southwest paths is poor.
Quiet to active geomagnetic conditions are possible on May 19-20 due to effects from CH1148, there's a chance of minor storm intervals. Quiet conditions are likely on May 21.
| 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 | ||||||||||
| 13303 | 2023.05.07 2023.05.09 |
S10W69 | location: S12W61 | ||||||||
| 13301 | 2023.05.08 2023.05.09 |
3 | 3 | 3 | N14W51 | 0005 | AXX | AXX |
 |
 |
location: N14W49 area: 0008 |
| 13304 | 2023.05.08 2023.05.11 |
N20W75 | |||||||||
| 13302 | 2023.05.08 2023.05.09 |
1 | 2 | 2 | N18W47 | 0030 | HSX | HSX |
 |
 |
area: 0110 location: N17W44 |
| S8549 | 2023.05.09 | S21W48 | |||||||||
| 13305 | 2023.05.12 | 12 | 46 | 27 | N12W43 | 0100 | DSI | DAI |
 |
 |
beta-delta location: N11W42 area: 0280 |
| S8558 | 2023.05.13 | S37W33 | |||||||||
| S8560 | 2023.05.14 | S28W41 | |||||||||
| 13308 | 2023.05.14 2023.05.16 |
8 | 29 | 17 | N12W28 | 0060 | CAO | DAI |
 |
 |
beta-gamma location: N11W27 area: 0190 |
| 13307 | 2023.05.14 2023.05.15 |
5 | 11 | 4 | S08W10 | 0010 | BXO | BXO |
 |
 |
location: S10W05 area: 0020 |
| S8565 | 2023.05.14 | S21W22 |
 |
||||||||
| S8566 | 2023.05.15 | N21E02 | |||||||||
| 13309 | 2023.05.16 2023.05.17 |
1 | 12 | 4 | S19W64 | 0010 | AXX | CRI |
 |
 |
area: 0030 location: S18W63 |
| 13310 | 2023.05.16 2023.05.17 |
5 | 16 | 9 | S20E59 | 0250 | DHO | CKO |
 |
 |
location: S21E61 area: 0560 |
| S8569 | 2023.05.16 | 3 | 1 | S30E17 | 0007 | BXO |
 |
 |
|||
| 13311 | 2023.05.17 2023.05.18 |
6 | 20 | 10 | N18E76 | 0110 | DAO | EAC |
 |
 |
beta-delta location: N18E73 area: 0390 |
| S8571 | 2023.05.18 | 6 | 4 | S24E82 | 0180 | DAC |
 |
||||
| Total spot count: | 41 | 148 | 81 | ||||||||
| Sunspot number: | 121 | 248 | 181 | (total spot count + 10 * number of spotted regions) | |||||||
| Weighted SN: | 71 | 186 | 119 | (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): | 133 | 136 | 145 | ||||||||
| 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 | 98.7 (+2.3) | 11.16 |
| 2022.11 | 123.4 | 120.7 | 80.5 | (100.4 projected, +1.7) | 9.33 |
| 2022.12 | 147.9 | 143.4 | 112.8 | (104.1 projected, +3.7) | 10.99 |
| 2023.01 | 182.4 | 176.6 | 143.6 | (110.1 projected, +6.0) | 8.73 |
| 2023.02 | 167.2 | 163.2 | 110.9 | (115.2 projected, +5.1) | 14.48 (current SC25 peak) |
| 2023.03 | 157.2 | 155.6 | 122.6 | (118.3 projected, +3.1) | 14.42 |
| 2023.04 | 145.4 | 146.4 | 96.4 | (123.7 projected, +5.4) | 13.40 |
| 2023.05 | 153.5 (1) | 69.3 (2A) / 119.3 (2B) / 146.9 (2C) | (129.3 projected, +5.6) | (10.2) | |
| 2023.06 | (132.5 projected, +3.2) | ||||
| 2023.07 | (132.0 projected, -0.5) | ||||
| 2023.08 | (133.0 projected, +1.0) | ||||
| 2023.09 | (136.4 projected, +3.4) | ||||
| 2023.10 | (138.3 projected, +1.9) | ||||
| 2023.11 | (141.4 projected, +3.1) | ||||
| 2023.12 | (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.
