Solar Terrestrial Activity Report

Activity chart

Last major update issued on September 18, 2023 at 04:55 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 unsettled on September 17 under the influence of weak CME effects. Solar wind speed at SOHO ranged between 389 and 507 km/sec. The high latitude magnetometer at Andenes recorded quiet to minor storm levels.

Solar flux density measured at 20h UT on 2.8 GHz was 144.6 - decreasing 4.1 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 154.08. In comparison SC24 peaked on June 28, 2014 at 145.50). The Potsdam WDC planetary A index was 15 (STAR Ap - based on the mean of three hour interval ap indices: 14.6). Three hour interval K indices: 33333233 (planetary), 33333333 (Boulder), 45213355 (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 12 active regions using 2K resolution (SN: 208) and in 11 active regions using 1K resolution (SN: 159) SDO/HMI images.

Region 13425 [N24W73] decayed further and had only 2 tiny spots left by the end of the day.
Region 13429 [N11W38] decayed further and was mostly quiet.
Region 13433 [N28W00] was quiet and stable.
Region 13434 [N08W27] was quiet and stable.
Region 13435 [N09E68] has a small magnetic delta structure in the southern part of the largest penumbra. M class flaring is possible. C1 flares: C1.3 @ 06:55, C1.3 @ 10:37, C1.2 @ 23:56 UT
New region 13436 [N19W21] emerged with many small and tiny spots. C flares are possible.

Spotted regions not observed (or interpreted differently) by SWPC/USAF:
S8961 [S13W36] was quiet and stable.
S8964 [N23W67] developed quickly after noon and could produce C flares.
S8968 [N20W00] was quiet and stable.
New region S8971 [S24E72] rotated into view with small spots.
New region S8972 [S18W01] emerged with tiny spots.
New region S8973 [N18E86] rotated partly into view with a mature spot.

AR 13423 behind the northwest limb was the likely source of a C1.2 flare at 12:58 UT

C2+ flares:

Magnitude Peak time (UT) Location Source Recorded by Comment
C3.5 16:04   13435 GOES16 weak type II radio sweep

Coronal mass ejections (CMEs)

September 15, 17: No obviously Earth directed CMEs were observed.
September 16: A CME was observed just after 09h UT due to an extensive filament eruption across the central meridian. The full halo CME will probably reach Earth on September 19.

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]

Several coronal holes formed after the extensive filament eruption on September 16. CH1173 is a positive polarity trans equatorial coronal hole and was Earth facing on September 16. 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) will likely become 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 minor storm on September 18 due to the September 14 CME. Quiet to major storm conditions are possible on September 19-20 when the September 16 CME reaches Earth. Effects from CH1173 and CH1174 are possible on September 20 and could extend into September 21. On September 22 a high speed stream from CH1175 will likely arrive and cause quiet to active conditions.

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
6 2 1 N23W75 0020 CAO AXX

location: N24W73

area: 0003

13427 2023.09.07
2023.09.09
      S27W82           location: S29W76
S8940 2023.09.08       S22W37            
13429 2023.09.09
2023.09.10
13 22 13 N11W36 0060 CAO DAI

area: 0100

13434 2023.09.09
2023.09.15
  3 2 N08W28 0006   BXO  
13431 2023.09.09
2023.09.10
1     S14W38 0000   AXX    

the previous SWPC location was S08W23
they probably counted the spot in AR S8961

location: S10W30

S8945 2023.09.09       N27W52            
13430 2023.09.10
2023.09.10
      S17W88        

 

S8948 2023.09.10       N12W58            
13433 2023.09.10
2023.09.12
3 9 5 N28W04 0090 CAO CSO area: 0120

location: N28W00

S8954 2023.09.11       N15W11            
S8955 2023.09.11       N23W54            
S8958 2023.09.12       S24W56            
S8960 2023.09.13       S13W40          
S8961 2023.09.13   1   S13W36 0001   AXX  
S8963 2023.09.13       N18W41            
S8964 2023.09.14   10 4 N23W67 0190   CAO  
S8965 2023.09.15       S19W48          
S8966 2023.09.15       S07E51          
13435 2023.09.16
2023.09.16
3 7 4 N10E60 0110 DAO DKO beta-delta

area: 0480

location: N09E68

S8968 2023.09.16   7 2 N20W00 0015   AXX  
13436 2023.09.17
2023.09.17
8 17 11 N19W22 0080 CAO DRI   was AR S8970

area: 0120

S8971 2023.09.17   4 2 S24E72 0050   DAO    
S8972 2023.09.17   5 4 S18W01 0015   CRO    
S8973 2023.09.17   1 1 N18E86 0110   HSX    
Total spot count: 34 88 49  
Sunspot number: 94 208 149  (total spot count + 10 * number of spotted regions)
Weighted SN: 59 129 90  (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): 103 114 119  

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  147.8 (1)   64.9 (2A) / 114.5 (2B) / 115.2 (2C) (140.7 projected, +3.4) (12.1)
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.