Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 20, 2024 at 07:30 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 quiet to severe storm on April 19. The high latitude magnetometer at Andenes recorded quiet to major storm levels. The above 10 MeV proton flux was at background levels at the end of the day. A CME related disturbance was observed arriving at DSCOVR at 04:54 UT with a sudden increase in solar wind temperature, speed and density as well as in the total field of the interplanetary magnetic field.

Solar flux density measured at 20h UT on 2.8 GHz was 213.4 - increasing 2.7 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 157.51. 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 43 (STAR Ap - based on the mean of three hour interval ap indices: 42.8). Three hour interval K indices: 22445574 (planetary), 22545553 (Boulder), 22365664 (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 20 active regions using 2K resolution (SN: 469) and in 18 active regions using 1K resolution (SN: 314) SDO/HMI images.

Region 13635 [N22W73] decayed slowly and was mostly quiet.
Region 13636 [S21W30] decayed slowly and was mostly quiet.
Region 13637 [S13W15] decayed and became nearly spotless before noon, then new flux emerged and several spots formed.
Region 13638 [S18W08] developed slowly and was mostly quiet.
Region 13639 [N28W02] decayed slowly producing several C flares.
Region 13641 [N09W59] decayed slowly and quietly.
Region 13643 [S13E09] decayed slowly and was mostly quiet.
Region 13644 [N10E34] was quiet and stable.
Region 13645 [S09W05] has large spots and could produce further M class, both on its own and with nearby AR 13647.
Region 13646 [N20E41] was mostly quiet and stable.
Region 13647 [S13W02] still has a magnetic delta structure and produced several flares.
Region 13648 [N17E25] decayed slowly and quietly.
Region 13649 [N16W23] emerged on April 18 and was numbered by SWPC the next day.
New region 13650 [S12E20] emerged on April 18 with SWPC numbering the region the following day.
New region 13651 [N12E26] emerged on April 16 and received its NOAA number 3 days later. Decay was observed after noon.

Spotted regions not observed (or interpreted differently) by SWPC/USAF:
S9600 [N14E38] gained tiny trailing spots and was quiet.
New region S9612 [S21E71] rotated into view with tiny spots.
New region S9613 [S12E74] rotated into view with tiny spots.
New region S9614 [N15E58] was observed with tiny spots in an old plage area.
New region S9615 [S33E16] emerged with a tiny spot.

C2+ flares

Magnitude Peak time (UT) Location Source Recorded by Comment
C3.0 01:11   13639 GOES16  
C3.5 01:27   13647 GOES16 simultaneous flare in AR 13633 behind SW limb
C4.1 01:48   13647 GOES16  
C4.3 02:06   13647 GOES16  
C4.9 02:52   13633 GOES16 incorrectly attributed to AR 13635 by SWPC
C4.5 03:27   13638 GOES16  
C3.0 04:02   13647 GOES16  
C3.4 04:26   13638 GOES16 simultaneous flare in 13634 behind NW limb
M2.1 04:53   13647 GOES16  
C2.7 06:14   13647 GOES16  
C2.7 06:53   13638 GOES16  
C3.0 08:25   13638 GOES16  
C3.3 09:09   13647 GOES16  
C2.7 10:48   13649 GOES16  
C4.9 11:20   13639 GOES16  
C3.2 11:46   13639 GOES16  
C2.9 12:24   13638 GOES16  
M1.0 13:06 S19W00 (SDO/AIA) 13638 GOES16 incorrectly attributed to AR 13647 by SWPC
C9.7 13:14   13638 GOES16  
C3.4 13:45   13639 GOES16  
C4.8 14:06   13636 GOES16  
C4.4 15:04   13639 GOES16  
C3.5 15:35   13645 GOES16  
C2.4 17:27   13639 GOES16  
C4.7 17:43   13638 GOES16  
C3.3 18:03   13638 GOES16  
C2.6 18:50   13638 GOES16  
C3.7 19:03   13639 GOES16 simultaneous flare in 13635
C3.8 19:24 behind southeast limb   GOES16 incorrectly attributed to AR 13639 by SWPC
C3.1 19:52   13647 GOES16  
C3.4 20:16   13638 GOES16  
C3.9 20:51 N17W63 13642 GOES16 simultaneous flare in AR 13637 (location: S17W05)
C3.2 21:25   13645 GOES16  
C3.0 22:21   13638 GOES16  
C3.3 22:25   13638 GOES16  
C3.8 22:32   13638 GOES16  
C3.1 22:53   13638 GOES16  

Coronal mass ejections (CMEs)

April 17-19: No obviously Earth directed CMEs were observed.

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 recurrent negative polarity southern hemisphere coronal hole (CH1214) rotated across the central meridian on April 17. A recurrent trans equatorial coronal hole (CH1215) will likely become Earth facing on April 22.

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.

Forecast

The geomagnetic field is expected to be quiet to active on April 20-21 due to effects from CH1214 and quiet on April 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
13635 2024.04.08
2024.04.10
2 2 1 N22W70 0010 CRO AXX

location: N22W73

area: 0006

13636 2024.04.10
2024.04.11
3 7 3 S21W31 0030 CAO CAO location: S21W30

area: 0040

13637 2024.04.12
2024.04.13
1 15 7 S15W13 0010 AXX DRO

location: S13W15

area: 0060

13638 2024.04.12
2024.04.13
13 25 14 S18W08 0060 CAI DAI beta-gamma

area: 0130

13639 2024.04.13
2024.04.14
19 53 19 N29W02 0300 EKC EAI

location: N28W02

13641 2024.04.13
2024.04.14
1 1 1 N09W59 0010 AXX HAX

area: 0050

S9588 2024.04.13       N17W38          
13640 2024.04.14       N21W12            
13642 2024.04.14
2024.04.15
      N18W67        

location: N16W64

S9593 2024.04.14       S22W30          
13643 2024.04.15 18 32 19 S13E05 0130 DAI DAI location: S13E09
13644 2024.04.16
2024.04.16
2 1 1 N13E37 0120 DSO HSX location: N10E34

area: 0140

13646 2024.04.16
2024.04.17
5 12 4 N21E38 0020 BXO CRO area: 0030

location: N20E41

S9600 2024.04.16   7 2 N14E38 0130   CSO  
13650 2024.04.16
2024.04.19
4 26 11 S11E21 0030 CRO DRI location: S12E20

area: 0100

S9602 2024.04.16       S42W06            
13648 2024.04.17
2024.04.18
  3   N19E25 0005   BXO  
S9604 2024.04.17       S18W15          
13645 2024.04.17
2024.04.17
16 31 21 S09W04 0210 DAC DKI beta-gamma

location: S09W05

area: 0640

13647 2024.04.17
2024.04.18
9 34 19 S13W00 0160 DAC DAC beta-delta

area: 0410

location: S13W02

S9607 2024.04.17       S06W43            
S9608 2024.04.17       S35W41            
13649 2024.04.18
2024.04.19
8 10 7 N16W24 0020 BXI CRI area: 0040

location: N15W23

13651 2024.04.18
2024.04.19
2 3 2 N13E25 0010 BXO BXO  
S9611 2024.04.18       S29W10          
S9612 2024.04.19   2 1 S21E71 0005   BXO    
S9613 2024.04.19   2 1 S12E74 0003   BXO    
S9614 2024.04.19   3 1 N15E58 0005   AXX    
S9615 2024.04.19   1   S33E16 0003   AXX    
Total spot count: 103 269 134  
Sunspot number: 243 469 314  (total spot count + 10 * number of spotted regions)
Weighted SN: 149 331 196  (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): 267 258 251  

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
2024.04 152.1 (1)   69.8 (2A) / 110.2 (2B) / 135.8 (2C) (115.4 projected, -0.0) (10.0)
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.

--------------------------------------------------------------------------------------

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.