Solar Terrestrial Activity Report

Activity chart

Last major update issued on September 21, 2023 at 03:45 UT.

Charts (* = updated daily) Data and archive
  Solar wind (*) Solar and geomagnetic data - last month (*)
  Electron fluence (*) Archived daily reports and monthly data since 2003.01 (September 3, 2023)
Solar cycle Solar cycles 23-25 (September 1, 2023) Historical solar and geomagnetic data charts 1954-2006 (April 5, 2007)
  Cycle 24-25 progress (September 1, 2023) Noon SDO sunspot count 1K image / 4K (*)
  Solar cycles 1-24 (July 1, 2020) POES auroral activity level [October 2009 - December 2012]
  Comparison of cycles 21-25 (September 1, 2023) 3rd SSN Workshop, Tucson, 2013
  Comparison of cycles 12-14, 16, 24-25 (September 1, 2023) 4th SSN Workshop, Locarno, 2014
  Solar polar fields vs. solar cycles (July 10, 2023) Cycle 25 spots (final update December 25, 2019)
  Solar cycles 24-25 transition using 365d smoothing Research: Solar Cycle 25 Started on November 17, 2019 with 365 Days Smoothing

Recent activity

The geomagnetic field was quiet to active on September 20 under the weakening combined influence of CME effects and a coronal high speed stream. Solar wind speed at SOHO ranged between 448 and 657 km/sec. The high latitude magnetometer at Andenes recorded quiet to major storm levels.

Solar flux density measured at 20h UT on 2.8 GHz was 155.5 - increasing 11.4 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 154.30. In comparison SC24 peaked on June 28, 2014 at 145.50). The Potsdam WDC planetary A index was 16 (STAR Ap - based on the mean of three hour interval ap indices: 15.8). Three hour interval K indices: 43432233 (planetary), 33443323 (Boulder), 65323265 (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 16 active regions using 2K resolution (SN: 310) and in 14 active regions using 1K resolution (SN: 214) SDO/HMI images.

Region 13429 [N12W79] was mostly quiet and stable.
Region 13433 [N28W40] was quiet and stable.
Region 13435 [N09E30] decayed in the southern part of the large penumbra. The magnetic delta weakened after the major M8 flare. M class flaring is still likely.
Region 13436 [N20W64] decayed and was mostly quiet.
Region 13437 [S17W42] was mostly quiet and stable.
Region 13438 [N11E22] gained spots while the main penumbra decayed. C flares are likely and there's a chance of M class flaring. C1 flares: C1.7 @ 02:17 UT
Region 13439 [S24E32] was quiet and stable.
Region 13440 [N18E48] was quiet and stable.
Region 13441 [N09W02] displayed no significant changes and was quiet.
New region 13442 [S10E58] rotated into view on September 18 with SWPC numbering the region 2 days later. The region was somewhat unstable and further C class flaring is likely. The spot group could be 2 regions. C1 flares: C1.2 @ 13:21 UT

Spotted regions not observed (or interpreted differently) by SWPC/USAF:
S8968 [N16W32] was quiet and stable.
S8975 [N28W12] developed slowly and was mostly quiet. C1 flares: C1.5 @ 10:30 UT
S8979 [N24E59] developed slowly and quietly.
New region S8981 [N05W01] emerged before noon with tiny spots.
New region S8982 [S15E09] was observed with tiny spots in an old plage area.
New region S8983 [S08W79] emerged with a tiny spot.

A C1.3 flare was recorded at 20:38 UT from a source behind the northeast limb.

C2+ flares:

Magnitude Peak time (UT) Location Source Recorded by Comment
C3.0 04:37   13442 GOES18  
C2.3 06:52   13429 GOES16  
C2.2 08:01   13442 GOES16  
C2.6 08:27   13442 GOES16  
C3.1 08:54   13437 GOES16  
C3.1 09:10   13435 GOES16 SWPC attributes this to weak simultaneous flare in AR 13437
C3.4 12:12   13438 GOES16  
M8.2 14:19   13435 GOES16 weak type II radio sweep, faint halo CME
C2.3 15:00   13441 GOES16  
C2.2 16:04   13438 GOES16  
C4.2 18:02 S10E67 13442 GOES16  
C5.5 18:40   13438 GOES16  
C4.7 21:38   13442 GOES16  
C2.0 22:09   13442 GOES16  
C2.4 23:21 behind northeast limb   GOES16  

Coronal mass ejections (CMEs)

September 18-19: No obviously Earth directed CMEs were observed.
September 20: A very faint halo CME was observed in LASCO C2 imagery after the impulsive M8 flare in AR 13435. This CME could reach Earth on September 22.

Coronal holes

[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]

Positive polarity coronal hole CH1174 formed in the northern hemisphere on September 16 and rotated across the central meridian on September 16-17. A negative polarity trans equatorial coronal hole (CH1174) was Earth facing on September 19.

Propagation

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 to fair.

Forecast

The geomagnetic field is expected to be quiet to unsettled on September 21. On September 22 a high speed stream from CH1175 will likely arrive and cause quiet to active conditions. The September 20 CME could cause unsettled to minor storm conditions on September 22-23.

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.

Active solar regions


(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
13425 2023.09.05
2023.09.06
1     N24W99 0060 HSX      

not sure what SWPC observed

the original AR 13425 rotated out of view on September 18

location: N24W113

13429 2023.09.09
2023.09.10
3 3 1 N12W81 0100 CAO CAO

location: N12W79

13434 2023.09.09
2023.09.15
      N08W70           location: N09W66
13431 2023.09.09
2023.09.10
      S14W80          

location: S10W69

13433 2023.09.10
2023.09.12
1 1 1 N28W41 0090 HSX HSX area: 0130

location: N28W40

S8966 2023.09.15       S07E06          
13435 2023.09.16
2023.09.16
4 22 10 N09E29 0300 DKI DKC beta-delta

area: 0480

location: N09E30

S8968 2023.09.16   4 1 N16W32 0008   BXO  
13436 2023.09.17
2023.09.17
6 12 6 N21W64 0220 DAI EAO  
13439 2023.09.17
2023.09.18
2 6 2 S25E32 0030 CAO CSO area: 0070
13437 2023.09.17
2023.09.18
11 15 11 S18W43 0190 DAI ESI

location: S17W42

13440 2023.09.17
2023.09.18
1 3 1 N17E46 0060 CSO CSO location: N18E48

area: 0130

13438 2023.09.18 11 23 13 N10E20 0070 CAI DAI beta-gamma-delta

location: N11E22

area: 0110

13442 2023.09.18
2023.09.20
5 13 9 S10E58 0050 CSI CSI two regions?

area: 0080

S8975 2023.09.18   15 7 N28W12 0050   DRI  
S8976 2023.09.18       N24E28            
13441 2023.09.19
2023.09.19
4 10 5 N08W03 0020 CRO DRO

area: 0060

S8978 2023.09.19       S17E15          
S8979 2023.09.19   9 4 N24E50 0030   CRO  
S8980 2023.09.19       S05W07          
S8981 2023.09.20   4   N05W01 0008   BXO    
S8982 2023.09.20   9 2 S15E05 0015   BXO    
S8983 2023.09.20   1   S08W79 0001   AXX    
Total spot count: 49 150 74  
Sunspot number: 159 310 214  (total spot count + 10 * number of spotted regions)
Weighted SN: 107 209 133  (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): 175 171 171  

Monthly solar cycle data

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
2022.02 109.1 106.5 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 92.6 (+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 80.5 101.1 (+2.2) 9.33
2022.12 147.9 143.4 112.8 106.7 (+5.6) 10.99
2023.01 182.4 176.6 144.4 113.4 (+6.7) 8.73
2023.02 167.2 163.2 111.3 117.9 (+3.5) 14.48
(current
SC25 peak)
2023.03 157.2 155.6 123.3 (121.0 projected, +3.1) 14.42
2023.04 145.4 146.4 96.4 (126.3 projected, +5.3) 13.40
2023.05 155.6 159.2 137.9 (131.9 projected, +5.6) 10.67
2023.06 161.7 166.8 163.4 (135.1 projected, +3.2) 8.95
2023.07  176.4 182.2 159.1 (135.5 projected, +0.4) 8.15
2023.08  153.7 157.6 114.9 (137.3 projected, +1.8) 7.19
2023.09  149.4 (1)   79.6 (2A) / 119.4 (2B) / 120.7 (2C) (140.7 projected, +3.4) (14.8)
2023.10       (142.5 projected, +1.8)  
2023.11       (145.1 projected max SC25, +2.6)  
2023.12       (144.2 projected, -0.9)  
2024.01       (141.4 projected, -2.8)  
2024.02       (141.2 projected, -0.2)  
2024.03       (140.8 projected, -0.4)  

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: WDC-SILSO, Royal Observatory Of Belgium, Brussels

Solar cycles 24-25

Smoothed SF and sunspot numbers

Update on the progress of solar cycle 25 as of August 20, 2023

Looking back 6 months, the 365d smoothed values for solar flux and all sunspot numbers with the exception of NOAA's, are all above their solar cycle 24 peak. The first peak of solar cycle 25 is forecast to be between July 7 and 10, 2023 (solar flux on July 7, ISN and STAR 1K and 2K all have that peak on July 9, while NOAA peaks on July 10). This is unlikely to be the final peak of SC25, however, there is a small probability that it is the actual sunspot and solar flux maximum.

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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.