Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 19, 2024 at 05:00 UT. Flare data and active region table to be updated

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 on April 18. 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 226.9 - increasing 29.3 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 157.33. 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 3 (STAR Ap - based on the mean of three hour interval ap indices: 3.0). Three hour interval K indices: 10011102 (planetary), 21112312 (Boulder), 10001210 (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 22 active regions using 2K resolution (SN: 512) and in 21 active regions using 1K resolution (SN: 363) SDO/HMI images.

Region 13634 [N26W83] was mostly quiet and stable.
Region 13635 [N22W58] gained a few spots and was quiet.
Region 13636 [S22W17] was quiet and stable.
Region 13637 [S13W01] decayed losing penumbra on all spots.
Region 13638 [S18E06] displayed signs of decay and produced a few flares.
Region 13639 [N28E10] decayed further and was mostly quiet.
Region 13641 [N09W45] decayed slowly and quietly.
Region 13642 [N16W51] decayed slowly and quietly.
Region 13643 [S13E23] displayed no significant changes and could produce further M flares.
Region 13644 [N10E47] was quiet and stable.
Region 13645 [S10E08] is a compact spot group capable of M class flaring.
Region 13646 [N20E51] was quiet and stable.
New region 13647 [S13E12] formed on April 17 and was numbered the next day by SWPC.
New region 13648 [N18E38] emerged on April 17 and received its NOAA number the next day the region began to decay.

Spotted regions not observed (or interpreted differently) by SWPC/USAF:
S9588 [N17W25] was quiet and stable.
S9593 [S21W32] was quiet and stable.
S9600 [N14E52] was quiet and stable.
S9601 [S12E34] developed slowly and quietly.
S9604 [S18W02] decayed slowly and quietly.
New region S9609 [N16W10] emerged with tiny spots.
New region S9610 [N12E39] emerged with a tiny spot.
New region S9611 [S24E03] emerged with a tiny spot.

C2+ flares

Magnitude Peak time (UT) Location Source Recorded by Comment

Coronal mass ejections (CMEs)

April 16-18: 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 fair. Propagation on long distance northeast-southwest paths is poor.

Forecast

The geomagnetic field is expected to be quiet to active on April 19-21 due to CME and coronal hole effects.

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
13633 2024.04.05
2024.04.06
3 1 1 S07W78 0080 CSO HSX

area: 0140

location: S08W78

13634 2024.04.07
2024.04.08
8 9 6 N27W70 0290 DKI DKO

area: 0380

location: N26W69

13635 2024.04.08
2024.04.10
3 9 4 N22W42 0010 AXX BXO

location: N21W43

area: 0016

13636 2024.04.10
2024.04.11
4 13 4 S20W05 0070 CSO CAO location: S21W04

area: 0190

13637 2024.04.12
2024.04.13
4 10 4 S13E13 0020 CRO DRO

split into several ARs on 2024.04.17

area: 0040

13638 2024.04.12
2024.04.13
5 21 10 S17E15 0030 CRI DAC beta-gamma-delta

area: 0130

location: S18E18

13639 2024.04.13
2024.04.14
16 61 26 N29E22 0320 EKI EAI beta-gamma

location: N29E37

13641 2024.04.13
2024.04.14
3 9 3 N12W28 0060 DAO CAO location: N09W31

area: 0050

S9588 2024.04.13   6 3 N17W14 0015   BXO  
13640 2024.04.14       N21E17            
S9590 2024.04.14       S08W43            
13642 2024.04.14
2024.04.15
  2 1 N18W39 0004   AXX

location: N16W35

S9592 2024.04.14       S04W40            
S9593 2024.04.14   1 1 S22W17 0003   AXX    
13643 2024.04.15 20 43 26 S13E34 0130 FAI DAI   location: S12E35

area: 0300

S9595 2024.04.15       S18W52          
S9597 2024.04.16   4 2 S05W79 0020   CRO  
13644 2024.04.16
2024.04.16
2 1 1 N12E60 0080 DSO HSX location: N10E60

area: 0100

13646 2024.04.16
2024.04.17
3 7 4 N21E59 0030 CSO DAO area: 0080
S9600 2024.04.16   1 1 N13E65 0100   HSX  
S9601 2024.04.16   4 1 S11E48 0006   BXO  
S9602 2024.04.16       S42E20          
S9603 2024.04.17   3 2 N19E53 0010   CRO    
S9604 2024.04.17   7 5 S17E11 0020   CRO   split off from AR 13638
13645 2024.04.17
2024.04.17
8 41 26 S10E24 0030 CAI DAI   beta-gamma

split off from AR 13637
was AR S9605

location: S09E22

area: 0280

S9606 2024.04.17   27 17 S12E28 0300   DAC   beta-gamma-delta

split off from AR 13637

S9607 2024.04.17   2   S06W17 0002   BXO    
S9608 2024.04.17   1   S35W15 0001   AXX    
Total spot count: 79 283 148  
Sunspot number: 199 513 358  (total spot count + 10 * number of spotted regions)
Weighted SN: 140 360 225  (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): 219 282 286  

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
2024.04 144.1 (1)   53.5 (2A) / 94.4 (2B) / 127.7 (2C) (115.4 projected, -0.0) (8.5)
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.