Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 15, 2024 at 05:45 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 on April 14. The high latitude magnetometer at Andenes recorded quiet to active 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 178.4 - increasing 9.5 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 156.80. 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 4 (STAR Ap - based on the mean of three hour interval ap indices: 4.4). Three hour interval K indices: 20111112 (planetary), 11222312 (Boulder), 30112124 (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 14 active regions using 2K resolution (SN: 294) and in 12 active regions using 1K resolution (SN: 194) SDO/HMI images.

Region 13628 [N07W77] was mostly quiet and stable.
Region 13633 [S08W38] decayed slowly and was mostly quiet.
Region 13634 [N27W30] developed in the leading spot section while some loss of spots and area was observed in the trailing spot section. A magnetic delta structure formed in the easternmost part of the trailing spot section. M class flaring is possible.
Region 13635 [N20W02] decayed slowly and quietly.
Region 13636 [S21E34] gained a few tiny spots and produced a few C flares.
Region 13637 [S13E58] displayed no major changes and still has a magnetic delta structure in a leading spot section penumbra. The spot group is very extensive longitudinally. Further M class flaring is possible. C1 flares: C1.8 @ 01:44 UT
Region 13638 [S17E58] was mostly quiet and stable. C1 flares: C1.7 @ 08:54 UT
New region 13639 [N29E63] rotated into view on April 13 and was numbered the next day by SWPC as relatively quick development was observed. An M class flare is possible as there is polarity intermixing.
New region 13641 [N11E14] emerged on April 13 and developed quickly on April 14 when it was numbered by SWPC. C flares are possible.

Spotted regions not observed (or interpreted differently) by SWPC/USAF:
S9588 [N17E26] was quiet and stable.
New region S9590 [S08W03] emerged with a tiny spot.
New region S9591 [N16E03] emerged with several spots to the southeast of AR 13635.
New region S9592 [S04W01] emerged with a tiny spot.
New region S9593 [S20E24] emerged with tiny spots.

C2+ flares

Magnitude Peak time (UT) Location Source Recorded by Comment
C2.9 01:01   13639 GOES16  
M4.3/1F 02:32 S11E67 13637 GOES16  
C2.5 05:29   13639 GOES16  
C3.1 06:24   13628 GOES18 simultaneous flares in ARs 13639 and 13637
C3.3 06:42   13637 GOES18 incorrectly attributed to AR 13638 by SWPC
C2.1 09:22   13639 GOES16  
C2.0 10:11   13639 GOES16  
C5.0 11:01   13636 GOES16  
C4.5 11:35   13637 GOES16 simultaneous flare in AR 13639
C3.5 11:48   13639 GOES16  
C2.9 12:15   13637 GOES16  
C2.9 12:47   13636 GOES16 simultaneous flare in AR 13639
C4.0 13:16 N28E66 13639 GOES16  
C4.6 13:45   13634 GOES16  
C5.3 15:09 N28E66 13639 GOES16  
C2.5 15:50   13639 GOES16  
C8.0 16:29   13639 GOES16  
C2.6 16:54   13639 GOES16  
C2.5 17:13   13639 GOES16  
C3.3 17:46   13639 GOES16  
C2.9 18:17   13639 GOES16  
C4.1 18:23   13639 GOES16  
C7.1 18:30 N31E72 13639 GOES16  
C3.2 19:32   13639 GOES16  
C2.9 19:45   13639 GOES16  
C2.7 21:39   13634 GOES16  
C2.8 22:16   13639 GOES16  
C4.5 23:03   13639 GOES16 simultaneous flare in AR 13637
C4.1 23:53   13639 GOES16  
C3.8 23:57   13639 GOES16  

Coronal mass ejections (CMEs)

April 12: A faint CME was observed after a filament eruption in the southwest quadrant early in the day. The CME could reach Earth early on April 15.
April 13-14: 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 fair. Propagation on long distance northeast-southwest paths is poor.

Forecast

The geomagnetic field is expected to be quiet to active on April 15 due to weak CME effects from the CME observed on April 12. Quiet conditions are likely on April 16-17.

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
2 1 1 N08W77 0120 HAX HHX

area: 0320

location: N07W77

13632 2024.04.03
2024.04.05
      N26W79           location: N26W71
13633 2024.04.05
2024.04.06
2 4 2 S08W38 0080 CSO CSO

area: 0180

13634 2024.04.07
2024.04.08
18 34 16 N26W30 0290 DKI EHC

beta-delta

area: 0430

location: N27W30

S9576 2024.04.08       N08W32          
S9577 2024.04.08       S18W32          
13635 2024.04.08
2024.04.10
5 11 8 N21W00 0020 CSO DRO area: 0030

location: N20W02

S9579 2024.04.09       S15W27            
S9580 2024.04.10       N19W19            
13636 2024.04.10
2024.04.11
4 14 5 S21E33 0080 CSO CSO location: S21E34

area: 0200

13637 2024.04.12
2024.04.13
4 19 9 S12E53 0080 CSO FRO beta-delta

location: S13E58

13638 2024.04.12
2024.04.13
1 4 2 S17E58 0030 HSX CAO area: 0090
S9585 2024.04.12       S25W21            
13639 2024.04.13
2024.04.14
7 19 11 N29E62 0030 CAO DAI beta-gamma

location: N29E63

area: 0220

13641 2024.04.13
2024.04.14
8 23 11 N11E13 0070 DAO DAO location: N11E14

area: 0260

S9588 2024.04.13   6 2 N17E26 0010   BXO  
13640 2024.04.14 1     N21E58 0010 AXX       apparently SWPC thinks the southernmost spot in AR 13639 is a new spot group
S9590 2024.04.14   1 1 S08W03 0005   AXX    
S9591 2024.04.14   13 6 N16E03 0040   DRI    
S9592 2024.04.14   1   S04W01 0001   AXX    
S9593 2024.04.14   4   S20E24 0004   BXO    
Total spot count: 52 154 74  
Sunspot number: 152 294 194  (total spot count + 10 * number of spotted regions)
Weighted SN: 102 208 102  (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): 167 162 155  

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
2024.04 131.6 (1)   34.5 (2A) / 74.0 (2B) / 120.6 (2C) (115.4 projected, -0.0) (7.2)
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.