Solar Terrestrial Activity Report

Activity chart

Last major update issued on May 1, 2024 at 07:05 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 active on April 30, after noon under the influence of effects from CH1217. 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 high speed stream associated with CH1217 was observed beginning at DSCOVR at 11:32 UT.

Solar flux density measured at 20h UT on 2.8 GHz was 130.2 - increasing 18.5 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 158.58. In comparison SC24 peaked on June 28, 2014 at 145.50. Current SC25 peak: 158.71 on October 28, 2023). The Potsdam WDC planetary A index was 13 (STAR Ap - based on the mean of three hour interval ap indices: 12.6). Three hour interval K indices: 21013344 (planetary), 22113434 (Boulder), 21012446 (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: 260) and in 11 active regions using 1K resolution (SN: 162) SDO/HMI images.

Region 13654 [S07W61] lost most of the magnetic delta configuration and some area after producing 4 M flares, including a major flare. Further M class flares could still occur. C1 flares: C1.2 @ 00:15, C1.3 @ 02:51, C1.4 @ 07:12, C1.8 @ 12:55, C1.4 @ 23:45 UT
Region 13655 [S27W57] was quiet and stable.
Region 13660 [N10E27] decayed slowly and quietly.
Region 13661 [N24E51] was mostly quiet and stable. C1 flares: C1.4 @ 09:42 UT
Region 13662 [N29E11] gained spots and was mostly quiet.
New region 13663 [N27E38] emerged with on April 29 and was numbered by SWPC the next day as the region developed further.

Spotted regions not observed (or interpreted differently) by SWPC/USAF:
S9637 [S12W02] was quiet and stable.
S9641 [N04W28] decayed slowly and quietly.
New region S9655 [S18E82] rotated into view with several spots.
New region S9656 [S04W27] emerged with tiny spots.
New region S9657 [N30W19] emerged with tiny spots.
New region S9658 {N12W02] was observed with tiny spots in an old plage area.
New region S9659 [N20E34] emerged with a tiny spot.
New region S9660 [N07E71] rotated into view with a tiny spot.
New region S9661 [S19E29] was observed with tiny spots in an old plage area.

AR 13652 behind the northwest limb produced a C1.4 flare AT 08:21 UT

C2+ flares

Magnitude Peak time (UT) Location Source Recorded by Comment
M1.6 01:14 S06W50 13654 GOES16  
C2.0 10:04 S06W52 13654 GOES16  
M1.2 15:10 S07W60 13654 GOES16  
M1.3 16:33 S05W60 13654 GOES16  
M9.5/2B 23:46 S05W63 13654 GOES16  

Coronal mass ejections (CMEs)

April 28-30: 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 trans equatorial coronal hole (CH1217) rotated across the central meridian on April 27-28 and decayed slowly. A positive polarity northern hemisphere coronal hole (CH1218) was Earth facing on April 30. A positive polarity northern hemisphere coronal hole (CH1219) will become Earth facing on May 1-2. A positive polarity southern hemisphere coronal hole (CH1220) will rotate into an Earth facing position on May 3.

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 minor storm on May 1 due to effects from CH1217 and quiet on May 2. Effects from CH1218 could cause quiet to unsettled conditions on May 3, while a disturbance related to CH1219 could cause quiet to active conditions on May 4-5. Effects from CH1220 will likely cause quiet to active conditions on May 6.

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
13657 2024.04.19
2024.04.21
      S14W74           location: S15W68
13654 2024.04.20
2024.04.21
20 30 22 S07W63 0550 FKC FKC

beta-delta

location: S07W61

area: 0830

13653 2024.04.20
2024.04.21
      N03W75           location: N02W64
13655 2024.04.21 1 2 1 S26W58 0040 HSX CSO location: S27W57
13656 2024.04.21
2024.04.21
      S12W49           location: S13W46
S9626 2024.04.23       S00W48            
13659 2024.04.24
2024.04.25
      S13W36            
S9637 2024.04.25   10 2 S12W02 0020   BXO  
S9638 2024.04.25       N04W22            
S9639 2024.04.25       N05W03            
S9641 2024.04.26   2   N04W28 0002   AXX  
13660 2024.04.26
2024.04.27
  6   N11E23 0008   BXO location: N10E27
S9646 2024.04.27       S12W18            
13662 2024.04.27
2024.04.29
6 21 9 N30E10 0030 CRO DRI area: 0080

location: N29E11

S9649 2024.04.27       N04W37            
13661 2024.04.28
2024.04.29
1 2 2 N24E50 0040 HSX HSX area: 0060

location: N24E51

S9651 2024.04.28       N06W04            
13663 2024.04.29
2024.04.30
7 15 8 N25E34 0010 BXO DRI location: N27E38

area: 0070

S9653 2024.04.29       S04E14          
S9655 2024.04.30   6 3 S18E82 0170   DAO    
S9656 2024.04.30   2 1 S04W27 0005   AXX    
S9657 2024.04.30   2 1 N30W19 0008   BXO    
S9658 2024.04.30   5 2 N12W02 0010   AXX    
S9659 2024.04.30   1   N20E34 0002   AXX    
S9660 2024.04.30   1   N07E71 0002   AXX    
S9661 2024.04.30   5 1 S19E29 0008   AXX    
Total spot count: 35 110 52  
Sunspot number: 85 260 162  (total spot count + 10 * number of spotted regions)
Weighted SN: 58 141 83  (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): 94 143 130  

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
2024.04 161.3 162.6 141.6 (2A/2B) / 163.2 (2C) (115.4 projected, -0.0) 9.5
2024.05 (1)     (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 April 28, 2024

The big increase in sunspot counts during the April 14-27 interval caused a major uptick in the smoothed SNs and solar flux. It's not yet clear when the next peak will be, anytime between October 28 and December 20, 2023 looks possible. The 365d smoothed solar flux exceeded the June 27 peak on October 28, while the 365d smoothed ISN and NOAA SN both exceeded the June 2023 peak in late October 2023.

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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.