The geomagnetic field was quiet to active on December 20 under the influence of effects from CH1193. Solar wind speed at SOHO ranged between 412 and 632 km/sec. The high latitude magnetometer at Andenes recorded quiet to active levels.
Solar flux density measured at 20h UT on 2.8 GHz was 195.3 - increasing 1.1 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 158.09. In comparison SC24 peaked on June 28, 2014 at 145.50. Current SC25 peak: 158.42 on June 4, 2023). The Potsdam WDC planetary A index was 10 (STAR Ap - based on the mean of three hour interval ap indices: 10.3). Three hour interval K indices: 43222211 (planetary), 43232221 (Boulder), 44323433 (Andenes).
The background x-ray flux is at the class C1 level (GOES 16).
At the time of counting spots (see image time), spots were observed in 14 active regions using 2K resolution (SN: 358) and in 14 active regions using 1K resolution (SN: 266) SDO/HMI images.
Region 13519 [S09W58] developed slowly as the
positive polarity penumbra to the north of the main spot gained area. That
patch of positive polarity is largely within the leading negative polarity
area. The region was the source of an M4.2 flare at 05:38 UT on December 21.
Region 13521 [N12E07] developed further and could produce a minor M
class flare. C1 flares: C1.8 @ 02:34, C1.9 @ 07:55 UT
Region 13524 [N27E17] developed slowly and was mostly quiet.
Region 13525 [S08W06] decayed slowly and quietly.
Region 13526 [N14E31] developed slowly and could produce a minor M
class flare.
Region 13528 [N08W13] developed slowly and has M class flare
potential.
Region 13529 [S20E27] gained area as the main spots enlarged. The
region is currently not very complex, but there is still a small chance of a
major flare.
Region 13530 [N08E50] decayed and has only rudimentary penumbra on
both leading and trialing spots.
New region 13531 [S20E69] rotated into view on December 19 and was
numbered the next day by SWPC. C1 flares: C1.9 @ 23:38 UT
Spotted regions not observed (or interpreted
differently) by SWPC/USAF:
S9251 [S14W29] was quiet and stable.
S9253 [N21E30] was quiet and stable.
S9255 [N14E70] was quiet and stable.
New region S9256 [N30E32] emerged with tiny spots.
New region S9257 [S20W56] emerged with a tiny spot.
C2+ flares:
| Magnitude | Peak time (UT) | Location | Source | Recorded by | Comment |
| C2.8 | 04:46 | 13521 | GOES16 | ||
| C7.9 | 06:03 | N10E17 | 13521 | GOES16 | |
| C2.4 | 06:33 | 13521 | GOES16 | ||
| C2.3 | 08.35 | 13521 | GOES16 | ||
| C8.3 | 08:54 | N10E15 | 13521 | GOES16 | |
| C7.9 | 09:36 | S10W50 | 13519 | GOES16 | |
| C2.3 | 11:39 | 13521 | GOES16 | ||
| C3.7 | 13:45 | 13519 | GOES16 | ||
| C3.2 | 14:10 | 13526 | GOES16 | ||
| C3.8 | 14:36 | N08E54 | 13530 | GOES16 | |
| C2.3 | 15:54 | 13529 | GOES16 | ||
| C2.5 | 16:28 | 13530 | GOES16 | attributed to AR 13526 by SWPC | |
| C3.3 | 16:34 | 13529 | GOES16 | ||
| C2.5 | 17:00 | 13530 | GOES16 | ||
| C6.8 | 17:27 | 13519 | GOES16 | attributed by SWPC to weaker, simultaneous flare in AR 13531 | |
| C7.2 | 18:43 | 13521 | GOES16 | ||
| C3.8 | 18:53 | 13531 | GOES16 | ||
| C2.5 | 19:15 | 13529 | GOES16 | ||
| C2.4 | 19:33 | 13531 | GOES16 | ||
| C3.4 | 20:17 | 13531 | GOES16 | simultaneous flare in AR 13529. Incorrectly attributed to AR 13524 by SWPC | |
| C4.4 | 21:01 | 13529 | GOES16 | incorrectly attributed to AR 13524 by SWPC | |
| C6.6 | 21:54 | 13519 | GOES16 | ||
| C3.3 | 22:29 | 13529 | GOES16 | ||
| C2.5 | 22:59 | 13526 | GOES16 |
December 18-20: No obviously Earth directed CME observed.
[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 negative polarity southern hemisphere coronal hole (CH1194) was Earth facing on December 18-19, but is likely too far to the south to cause a geomagnetic disturbance.
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.
The geomagnetic field is expected to be quiet to unsettled on December 21 due to lingering effects from CH1193. There's a slight chance of unsettled intervals on December 22-23 should effects from CH1194 reach Earth.
| Coronal holes (1) | Coronal mass ejections (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 | ||||||||||
| 13516 | 2023.12.08 2023.12.08 |
S18W82 |
location: S17W78 |
||||||||
| 13518 | 2023.12.12 2023.12.12 |
N13W35 |
 |
location: N14W31 |
|||||||
| 13519 | 2023.12.12 2023.12.13 |
9 | 23 | 14 | S11W58 | 0140 | ESO | DSI |
 |
 |
location: S09W58 |
| 13521 | 2023.12.14 2023.12.15 |
4 | 34 | 21 | N11E03 | 0080 | DSO | DAI |
 |
 |
area: 0240 location: N12E07 |
| S9238 | 2023.12.14 | N30W27 | |||||||||
| 13523 | 2023.12.15 2023.12.16 |
2 | N25E10 | 0010 | BXO | merged with AR 13524 | |||||
| 13525 | 2023.12.15 2023.12.16 |
5 | 2 | S05W12 | 0010 | BXO |
 |
 |
location: S08W06 |
||
| 13522 | 2023.12.15 2023.12.16 |
S03W32 |
 |
location: S02W26 | |||||||
| 13524 | 2023.12.15 2023.12.16 |
23 | 12 | N26E08 | 0060 | DRO |
 |
 |
location: N27E17 | ||
| 13526 | 2023.12.16 2023.12.17 |
6 | 29 | 17 | N15E30 | 0200 | CAO | DAC |
 |
 |
location: N14E31 |
| 13528 | 2023.12.16 2023.12.18 |
9 | 35 | 19 | N09W14 | 0140 | DAI | DAI |
 |
 |
area: 0370 location: N08W13 |
| 13529 | 2023.12.16 2023.12.18 |
6 | 35 | 23 | S19E27 | 0450 | DKI | EKO |
 |
 |
beta-gamma area: 0810 location: S20E27 |
| 13527 | 2023.12.17 | 2 | S01W83 | 0025 | CAO |
 |
location: S01W85 rotated out of view |
||||
| S9247 | 2023.12.17 | N14E15 | |||||||||
| S9248 | 2023.12.17 | S21E06 | |||||||||
| S9249 | 2023.12.17 | N21W58 | |||||||||
| 13530 | 2023.12.18 2023.12.19 |
4 | 17 | 9 | N08E49 | 0180 | DAO | ERI |
 |
 |
beta-gamma location: N08E50 area: 0090 |
| S9251 | 2023.12.18 | 5 | 2 | S14W29 | 0010 | BXO |
 |
 |
|||
| S9252 | 2023.12.19 | S19E01 |
 |
||||||||
| S9253 | 2023.12.19 | 4 | 1 | N21E30 | 0010 | BXO |
 |
 |
|||
| 13531 | 2023.12.19 2023.12.20 |
1 | 2 | 2 | S20E68 | 0060 | HAX | HSX |
 |
 |
area: 0240 |
| S9255 | 2023.12.19 | 5 | 1 | N14E70 | 0012 | BXO |
 |
 |
|||
| S9256 | 2023.12.20 | 2 | 2 | N30E32 | 0005 | BXO |
 |
||||
| S9257 | 2023.12.20 | 1 | 1 | S20W56 | 0002 | AXX |
 |
||||
| Total spot count: | 43 | 218 | 126 | ||||||||
| Sunspot number: | 133 | 358 | 266 | (total spot count + 10 * number of spotted regions) | |||||||
| Weighted SN: | 83 | 259 | 167 | (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 | 197 | 213 | ||||||||
| 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 |
| 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 | 92.6 (+5.9) | 10.92 |
| 2022.09 | 135.1 | 136.5 | 96.0 | 96.5 (+3.9) | 12.18 |
| 2022.10 | 133.5 | 132.7 | 95.5 | 98.9 (+2.4) | 11.16 |
| 2022.11 | 123.4 | 120.7 | 80.5 | 101.2 (+2.3) | 9.33 |
| 2022.12 | 147.9 | 143.4 | 112.8 | 106.7 (+5.5) | 10.99 |
| 2023.01 | 182.4 | 176.6 | 144.4 | 113.3 (+6.6) | 8.73 |
| 2023.02 | 167.2 | 163.2 | 111.3 | 117.8 (+3.5) | 14.48 (current SC25 peak) |
| 2023.03 | 157.2 | 155.6 | 123.3 | 121.0 (+3.2) | 14.42 |
| 2023.04 | 145.4 | 146.4 | 97.6 | 122.7 (+1.7) | 13.40 |
| 2023.05 | 155.6 | 159.2 | 137.4 | 123.9 (+1.2) | 10.67 |
| 2023.06 | 161.7 | 166.8 | 160.5 | (126.3 projected, +2.4) | 8.95 |
| 2023.07 | 176.4 | 182.2 | 159.1 | (127.1 projected, +0.8) | 8.15 |
| 2023.08 | 153.7 | 157.6 | 114.8 | (128.2 projected, +1.1) | 7.19 |
| 2023.09 | 154.4 | 156.0 | 133.6 | (130.4 projected, +2.2) | 14.26 |
| 2023.10 | 142.8 | 141.9 | 99.4 | (132.2 projected, +1.8) | 8.16 |
| 2023.11 | 153.5 | 150.2 | 105.4 | (134.1 projected max SC25, +1.9) | 12.20 |
| 2023.12 | 145.0 (1) | 78.9 (2A) / 122.3 (2B) / 154.4 (2C) | (132.7 projected, -1.4) | (12.7) | |
| 2024.01 | (130.0 projected, -2.7) | ||||
| 2024.02 | (129.9 projected, -0.1) | ||||
| 2024.03 | (129.3 projected, -0.6) | ||||
| 2024.04 | (130.1 projected, +0.8) | ||||
| 2024.05 | (132.2 projected, +2.1) | ||||
| 2024.06 | (131.5 projected, -0.7) | ||||
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: WDC-SILSO, Royal Observatory
Of Belgium, Brussels
Due to relatively low solar activity over the last couple of months, the possibility that solar cycle 25 has already peaked has increased significantly. Whether the first peak (and maybe solar max) will be in June or July depends on solar activity in December and early January 2024. If the average solar flux is less than 150 during this period, the first peak of solar cycle 25 using 365 day smoothing will likely be sometime between June 2 and July 9. Should the average solar flux instead become 140 then the peak date will be in early June (June 4 for solar flux, June 6 for STAR 2K SN, and June 7 for all the other sunspot numbers in the graph above). We won't know for a while yet when the final peak will be, however, it is interesting that the peak of SC25 could be as early as June 2023. The next update will likely be posted here in January 2024.
--------------------------------------------------------------------------------------
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.
