Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 25, 2024 at 03:30 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 (April 1, 2024)
Solar cycle Solar cycles 23-25 (April 1, 2024) Historical solar and geomagnetic data charts 1954-2006 (April 5, 2007)
  Cycle 24-25 progress (April 1, 2024) 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 (April 1, 2024) 3rd SSN Workshop, Tucson, 2013
  Comparison of cycles 12-14, 16, 24-25 (April 1, 2024) 4th SSN Workshop, Locarno, 2014
  Solar polar fields vs. solar cycles (March 3, 2024) 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
Calculating the Strength of Solar Cycle 25 Using 365-day Smoothing

Recent activity

The geomagnetic field was very quiet on April 24. The high latitude magnetometer at Andenes recorded quiet levels. The above 10 MeV proton flux was at background levels at the end of the day.

Solar flux density measured at 20h UT on 2.8 GHz was 199.1 - increasing 26.4 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 158.59. In comparison SC24 peaked on June 28, 2014 at 145.50. Current SC25 peak: 158.71 on June 27, 2023). The Potsdam WDC planetary A index was 2 (STAR Ap - based on the mean of three hour interval ap indices: 2.0). Three hour interval K indices: 11000001 (planetary), 10012312 (Boulder), 22011001 (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 21 active regions using 2K resolution (SN: 411) and in 19 active regions using 1K resolution (SN: 290) SDO/HMI images.

Region 13638 [S18W75] decayed slowly and produced several C and M flares.
Region 13639 [N29W63] decayed quickly and quietly.
Region 13643 [S11W65] decayed slightly and was mostly quiet.
Region 13644 [N12W32] was quiet and stable.
Region 13645 [S08W78] decayed further and produced several flares.
Region 13646 [N22W22] decayed slowly and produced a few C flares before noon.
Region 13647 [S13W72] decayed slowly and quietly.
Region 13648 [N18W29] merged with AR S9631 forming a magnetic delta structure where the leader spot of AR 13648 and easternmost spot of AR S9631 are now within one penumbra.
Region 13652 [N14W14] decayed slowly and quietly.
Region 13653 [N02E16] was quiet and stable.
Region 13654 [S07E15] matured. The southern spot sections were split off into AR S9630.
Region 13655 [S27E21] decayed in the trailing spot section and was mostly quiet.
Region 13656 [S12E34] was quiet and stable.
Region 13657 [S13E02] was mostly quiet and stable.
New region 13658 [S21W32] emerged on April 22 and was numbered by SWPC 2 days later.

Spotted regions not observed (or interpreted differently) by SWPC/USAF:
S9600 [N15W26] was quiet and stable.
S9627 [S15E09] was mostly quiet and stable.
New region S9630 [S09E23] was split off from AR 13654.
New region S9632 [S13E49] emerged with tiny spots.
New region S9633 [S08E77] rotated into view with tiny spots.
New region S9634 [N33W08] emerged with a tiny spot.

C2+ flares

Magnitude Peak time (UT) Location Source Recorded by Comment
M1.7/2F 00:29   13645 GOES16  
M1.6 00:42   13638 GOES16  
C5.6 01:55   13646 GOES16  
M1.8 02:39   13638 GOES16  
C4.7 03:38   13654 GOES16  
C6.2 04:13   13650 GOES16  
C7.4 04:40   13646 GOES16  
C3.0 05:49   13638 GOES16 simultaneous flare in AR 13645
C4.2 06.38 S17W65 13638 GOES16  
C3.4 07:22   13648 GOES16  
C3.5 07:33   13643 GOES16  
C6.9 07:41 S06W64 13645 GOES16  
C3.5 08:12   13648 GOES16  
C2.9 08:36   13645 GOES16  
C3.3 08:55   13646 GOES16  
C5.0 09:43   13648 GOES16  
C5.1 10:31   S9627 GOES16  
C5.7 10:35   13648 GOES16 simultaneous flare in AR 13643
C2.9 10:59   13646 GOES16  
C3.6 11:47   13648 GOES16  
M1.4 12:14   13645 GOES16  
M1.0 12:27   13648 GOES16  
C3.4 13:48   13658 GOES16  
C9.4/1F 14:10   13638 GOES16 strong type II and moderate type IV radio sweep
C4.1 15:04   13648 GOES16 strong type II and moderate type IV radio sweep
C3.5 15:43   13638 GOES16  
C2.7 16:32   13654 GOES16  
C2.7 17:48   13654 GOES16  
C4.0 18:09   13648 GOES16  
C4.0 19:23   13638 GOES16  
C7.9 20:07   13645 GOES16  
C7.4 22:20   S9627 GOES16  
M1.1 22:50   13643 GOES16 incorrectly attributed to AR 13657 by SWPC
M2.0 22:59   13645 GOES16  

Coronal mass ejections (CMEs)

April 22-24: No obviously Earth directed CMEs were observed.
April 21: A faint CME was observed after the M3.4 flare in AR 13638 late in the day. It is uncertain if this CME has any Earth directed components, however, there is a slight chance of CME effects on February 25.

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]

A positive polarity recurrent trans equatorial coronal hole (CH1215) was Earth facing on April 22-23. A positive polarity southern hemisphere coronal hole (CH1216) was Earth facing on April 23-24. A recurrent negative polarity trans equatorial coronal hole (CH1217) will likely rotate across the central meridian on April 27-28.

Propagation

Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over upper middle and high latitudes is fair. Propagation on long distance northeast-southwest paths is poor.

Forecast

The geomagnetic field is expected to be quiet to minor storm on April 25-26 due to effects from CH1215 and quiet to unsettled on April 27.

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
13637 2024.04.12
2024.04.13
      S13W83            
13638 2024.04.12
2024.04.13
6 7 2 S17W74 0030 CAI BXO beta-gamma

location: S18W75

area: 0020

13639 2024.04.13
2024.04.14
4 5 1 N29W66 0080 EAO CRO

location: N29W63

area: 0030

13643 2024.04.15 16 28 13 S12W57 0240 EAC EAC beta-gamma

location: S11W65

13644 2024.04.16
2024.04.16
2 3 1 N13W21 0060 HSX HSX location: N12W32

area: 0040

SWPC position way off

13646 2024.04.16
2024.04.17
12 25 13 N21W20 0230 DAI EAO beta-gamma

locaton: N22W22

S9600 2024.04.16   4 1 N15W26 0040   HAX  
13650 2024.04.16
2024.04.19
2     S11W45 0010 BXO     location: S11W47

spotless

13648 2024.04.17
2024.04.18
11 25 13 N18W38 0070 DAI EAI beta-delta

area: 0100

location: N18W29

13645 2024.04.17
2024.04.17
15 7 4 S08W71 0260 DKC EAO beta-gamma

location: S08W78

13647 2024.04.17
2024.04.18
12 7 4 S14W61 0140 DAI CAO

area: 0170

location: S13W72

13651 2024.04.18
2024.04.19
      N15W45           location: N12W39
S9612 2024.04.19
2024.04.21
      S20E05            
13657 2024.04.19 7 4 1 S12E10 0020 CRO BXO location: S13E02
13652 2024.04.19
2024.04.20
5 7 2 N14W05 0080 CSO CSO area: 0130

locaton: N14W00

S9615 2024.04.19       S33W49            
13654 2024.04.20
2024.04.21
18 12 10 S08E25 0130 DAC EAO

location: S07E15

southern part split off into AR S9630

13653 2024.04.20
2024.04.21
1 4 2 N03E15 0000 AXX BXO location: N02E29

area: 0020

S9618 2024.04.20       N07W49            
13655 2024.04.21 5 15 6 S28E30 0120 ESO EAO location: S27E21
13656 2024.04.21
2024.04.21
5 5 3 S12E42 0020 CRO DRO location: S12E34
13658 2024.04.22
2024.04.24
2 7 4 S21W32 0010 BXO DRO area: 0020
S9622 2024.04.22       S17W11          
S9623 2024.04.22       S44W41          

reversed polarities

S9625 2024.04.23       S43E04           reversed polarities
S9626 2024.04.23       S00E30            
S9627 2024.04.23   16 9 S15E09 0040   DRI beta-gamma
S9628 2024.04.23       N19E05          
S9629 2024.04.23       S04W08          
S9630 2024.04.24   12 7 S09E23 0110   DAO    
S9632 2024.04.24   5 4 S13E49 0015   CRO    
S9633 2024.04.24   2   S08E77 0003   AXX    
S9634 2024.04.24   1   N33W08 0002   AXX    
Total spot count: 123 201 100  
Sunspot number: 283 411 290  (total spot count + 10 * number of spotted regions)
Weighted SN: 189 271 270  (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): 311 226 232  

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
2022.09 135.1 136.5 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)
2023.03 157.2 155.6 123.3 121.1 (+3.3) 14.42
2023.04 145.4 146.4 97.6 122.9 (+1.8) 13.40
2023.05 155.6 159.2 137.4 124.1 (+1.2) 10.67
2023.06 161.7 166.8 160.5 125.2 (+1.1)
(SC25 solar max candidate)
8.95
2023.07  176.4 182.2 160.0 124.3 (-0.9) 8.15
2023.08  153.7 157.6 114.8 124.0 (-0.3) 7.19
2023.09  154.4 156.0 134.2 123.8 (-0.2) 14.26
2023.10  142.8 141.9 99.4 (123.8 projected, 0.0) 8.16
2023.11 153.5 150.2 105.4 (123.5 projected, -0.3) 12.20
2023.12 151.1 146.4 114.2 (120.1 projected, -3.4) 9.60
2024.01 164.6 159.3 123.0 (116.8 projected, -3.3) 5.46
2024.02 172.5 168.3 124.6 (116.0 projected, -0.8) 5.31
2024.03 154.4 152.9 104.9 (115.4 projected, -0.6) 11.03
2024.04 165.1 (1)   115.5 (2A) / 144.4 (2B) / 152.2 (2C) (115.4 projected, -0.0) (9.6)
2024.05       (116.6 projected, +1.2)  
2024.06       (115.8 projected, -0.8)  
2024.07       (114.1 projected, -1.7)  
2024.08       (112.1 projected, -2.0)  
2024.09       (110.9 projected, -1.2)  
2024.10       (110.3 projected, -0.6)  

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 March 10, 2024

Solar activity saw a significant decrease during the latter half of February and the first part of March. While there is still a chance that there could be another and higher peak in October or November 2023, chances that June 2023 was solar max has increased. After November 2023 there is currently no other obvious candidate solar max month. Taking into account the state of the solar polar fields another major peak during SC25 is becoming less likely.

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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.