Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 16, 2024 at 05:20 UT.

Charts (* = updated daily) 3Data 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 unsettled on April 15. A disturbance was observed reaching DSCOVR at 17:28 UT, likely the arrival of the April 12 CME. There was a minor sudden increase in solar wind speed and density as well as the total field of the IMF. The high latitude magnetometer at Andenes recorded quiet to minor storm 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 191.9 - increasing 23.0 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 156.84. 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 6 (STAR Ap - based on the mean of three hour interval ap indices: 5.8). Three hour interval K indices: 21110123 (planetary), 12012423 (Boulder), 31112455 (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 15 active regions using 2K resolution (SN: 307) and in 11 active regions using 1K resolution (SN: 190) SDO/HMI images.

Region 13633 [S08W51] was quiet and stable.
Region 13634 [N27W42] decayed in the trailing spot section and lost the magnetic delta structure.
Region 13635 [N20W15] decayed slowly and quietly.
Region 13636 [S21E22] was mostly quiet and stable.
Region 13637 [S13E55] developed in the trailing spot section (SWPC split the new spots off into AR 13643). A magnetic delta structure is still present in a leading spot section penumbra. The spot group extends more than 30 degrees longitudinally. Further M class flaring is possible.
Region 13638 [S17E45] was mostly quiet and stable.
Region 13639 [N29E50] developed a magnetic delta structure in a trailing penumbra. The region produced many C and M class flares.
Region 13641 [N11W00] was mostly quiet and stable.
New region 13642 [N17W10] emerged on April 14 and was numbered the next day by SWPC.

Spotted regions not observed (or interpreted differently) by SWPC/USAF:
S9576 [N10W51] reemerged with a tiny spot.
S9588 [N18E14] was quiet and stable.
S9590 [S08W17] was quiet and stable.
New region S9594 [S23W63] emerged with tiny spots before noon, then decayed slowly.
New region S9595 [S21W28] was observed with tiny spots in an old plage area.
New region S9596 [S15E54] emerged with tiny spots.

C2+ flares

Magnitude Peak time (UT) Location Source Recorded by Comment
C4.7 00:09   13639 GOES16  
M1.7 01:18 N28E63 (SDO/AIA) 13639 GOES16  
C3.5 01:55   13639 GOES16  
C2.9 02:18   13634 GOES16  
C3.1 02:29   13639 GOES16  
C4.5 03:09   13637 GOES16  
C4.2 03:15   13639 GOES16  
C6.3 03:33   13639 GOES16 simultaneous flare in AR 13634
C5.3 04:17   13639 GOES16  
C5.5 04:46 N28W30 13634 GOES16  
C4.1 05:01   13637 GOES16 simultaneous flare in AR 13639
C7.9 05:37 N29W28 13634 GOES16  
C5.6 05:59   13637 GOES16  
C3.8 06:22   13639 GOES16  
C7.9 07:11   13639 GOES16  
M1.0/1F 07:32 N30E57 13639 GOES16  
C5.1 08:25   13639 GOES16  
M2.3/1B 08:42 N27W29 13634 GOES16  
C4.6 08:58   13639 GOES16  
M1.2 09:32   13639 GOES16  
C6.2 09:46   13639 GOES16  
C2.2 10:34   13639 GOES16  
C3.5 11:42   13639 GOES16  
C2.0 13:22   13637 GOES16  
M1.1/1F 13:58 N28E56 13639 GOES16 simultaneous flare in AR 13638
M1.4 14:04 N26W33 13634 GOES16  
M2.2 14:16   13639 GOES16  
C2.5 16:42   13639 GOES16  
C5.0 17:05   13639 GOES16  
C2.5 17:54   13639 GOES16  
C2.6 18:38   13639 GOES16  
C4.2/1N 19:12   13634 GOES16  
M4.0/1N 19:32   13639 GOES16  
C2.9 20:08   13634 GOES16  
C2.5 20:16   13642 GOES16  
C2.1 20:31   13638 GOES16  
C4.4 20:57 N26E55 (SDO/AIA) 13639 GOES16  
C5.2 21:43   13638 GOES16  
C2.8 22:22   13634 GOES16  
C3.9 23:55   13638 GOES16  

Coronal mass ejections (CMEs)

April 14: A faint CME was observed before noon, mainly off the northeast limb. There's a chance this CME could have an Earth directed component which could reach Earth on April 17.
April 13, 15: 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) will likely rotate across the central meridian on April 17.

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 16 due to weak CME effects. Weak effects from another faint CME could reachg Earth on April 17 and cause some unsettled intervals that day and on April 18. Quiet conditions are likely on April 19. Quiet to active conditions will be possible on April 20-21 due to effects from CH1214.

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
13628 2024.04.02
2024.04.03
1     N05W91 0060 HSX    

area: 0300

rotated out of view

13633 2024.04.05
2024.04.06
1 4 2 S10W51 0080 HSX CSO

area: 0160

location: S08W51

13634 2024.04.07
2024.04.08
23 18 9 N25W42 0300 EHI DKO

area: 0400

location: N27W42

S9576 2024.04.08   1   N10W51 0001   AXX    
S9577 2024.04.08       S18W45            
13635 2024.04.08
2024.04.10
3 13 5 N22W14 0010 BXO CRO area: 0020

location: N20W15

S9579 2024.04.09       S15W40            
S9580 2024.04.10       N19W32            
13636 2024.04.10
2024.04.11
3 13 6 S18E20 0090 CSO DAO location: S21E22

area: 0220

13637 2024.04.12
2024.04.13
2 34 16 S12E39 0010 BXO FAI beta-gamma-delta

location: S13E55

SWPC has split off the easternmost spot section into AR 13643

13638 2024.04.12
2024.04.13
4 13 9 S17E44 0080 CAO DAO area: 0100

location: S17E45

S9585 2024.04.12       S25W34            
13639 2024.04.13
2024.04.14
14 26 16 N30E48 0240 EAI DAI beta-delta

location: N29E50

area: 0320

13641 2024.04.13
2024.04.14
19 11 7 N11W01 0090 DAO DAO location: N11W00

area: 0210

S9588 2024.04.13   8 2 N18E14 0013   BXO  
13640 2024.04.14       N21E44            
S9590 2024.04.14   1 1 S08W17 0005   AXX  
13642 2024.04.14
2024.04.15
5 10 7 N18W11 0010 BXO CRO area: 0025

location: N17W10

S9592 2024.04.14       S04W14          
S9593 2024.04.14       S20E11          
13643 2024.04.15 8     S10E63 0100 DAI       currently part of AR 13637
S9594 2024.04.15   1   S23W63 0001   AXX    
S9595 2024.04.15   2   S21W28 0003   AXX    
S9596 2024.04.15   2   S15W54 0003   BXO    
Total spot count: 83 157 80  
Sunspot number: 193 307 190  (total spot count + 10 * number of spotted regions)
Weighted SN: 128 203 126  (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): 212 169 152  

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
2024.04 135.6 (1)   41.0 (2A) / 81.9 (2B) / 121.5 (2C) (115.4 projected, -0.0) (7.1)
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.