Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 17, 2024 at 04:50 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 unsettled to minor storm on April 16 under the influence of CME effects. The high latitude magnetometer at Andenes recorded unsettled 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 198.7 - increasing 23.2 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 156.93. 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 32 (STAR Ap - based on the mean of three hour interval ap indices: 32.0). Three hour interval K indices: 43433555 (planetary), 43444454 (Boulder), 44443554 (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 17 active regions using 2K resolution (SN: 369) and in 14 active regions using 1K resolution (SN: 233) SDO/HMI images.

Region 13633 [S09W64] was quiet and stable.
Region 13634 [N27W56] was mostly unchanged and quiet.
Region 13635 [N20W29] decayed slowly and quietly.
Region 13636 [S21E09] was quiet and stable.
Region 13637 [S12E44] gained spots and area and remains capable of producing M flares. C1 flares: C1.8 @ 07:15 UT
Region 13638 [S17E29] gained spots and produced a few C flares.
Region 13639 [N29E37] has 2 magnetic delta structures and could produce a major flare. C1 flares: C1.8 @ 04:29, C1.8 @ 21:36 UT
Region 13641 [N10W15] decayed slowly and quietly.
Region 13642 [N16W23] emerged on April 14 and was numbered the next day by SWPC.
New region 13644 [N10E74] rotated into view with a mature spot.

Spotted regions not observed (or interpreted differently) by SWPC/USAF:
S9588 [N17W00] was quiet and stable.
S9595 [S18W34] was quiet and stable.
New region S9597 [S05W65] emerged with tiny spots.
New region S9599 [N20E73] rotated into view with a small spot.
New region S9600 [N13E78] rotated into view with a mature spot.
New region S9601 [S11E60] was observed with tiny spots in an old plage area.
New region S9602 [S42E33] emerged with a tiny spot.

C2+ flares

Magnitude Peak time (UT) Location Source Recorded by Comment
C2.7 01:06   13639 GOES16  
C2.5 01:48   13637 GOES16  
C2.6 01:56   13639 GOES16  
C2.2 02:20   13639 GOES16  
C2.0 02:48   13639 GOES16  
C2.2 03:00   13639 GOES16  
C2.5 09:23   13634 GOES16  
C2.4 09:45   13639 GOES16  
C4.0 10:15   13637 GOES16  
C2.4 10:40   13637 GOES16 simultaneous flare in AR 13639
C2.3 10:51   13639 GOES16  
C2.2 13:41   13639 GOES16  
C4.9 15:34   13639 GOES16  
C3.7 16:14     GOES16  
C2.8 16:33   13639 GOES16  
C5.3 17:29   13639 GOES16  
M1.1/2N 18:02 S10E36 13637 GOES16 simultaneous flare in AR 13639
C2.2 22:26   13641 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 has an Earth directed component which could reach Earth on April 17.
April 15-16: 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 unsettled on April 17 due to lingering effects from the April 12 CME. Weak effects from another faint CME could reach 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
13633 2024.04.05
2024.04.06
3 2 2 S09W65 0080 CSO CSO

area: 0150

location: S09W64

13634 2024.04.07
2024.04.08
9 20 8 N26W56 0310 DHI DKO

area: 0440

location: N27W56

13635 2024.04.08
2024.04.10
3 11 4 N22W28 0010 AXX BXO

location: N20W29

S9579 2024.04.09       S15W53            
S9580 2024.04.10       N19W45            
13636 2024.04.10
2024.04.11
3 7 3 S20E08 0090 CSO CSO location: S21E09

area: 0190

13637 2024.04.12
2024.04.13
2 60 33 S13E27 0020 DRO FAI beta-gamma-delta

location: S12E44

SWPC has split off the easternmost spot section into AR 13643

13638 2024.04.12
2024.04.13
8 11 8 S17E32 0080 CAI DAI area: 0100

location: S17E29

S9585 2024.04.12       S25W47            
13639 2024.04.13
2024.04.14
19 41 16 N29E36 0310 EKI EKC beta-gamma-delta

location: N29E37

area: 0510

13641 2024.04.13
2024.04.14
6 16 8 N12W14 0110 DAO DAO location: N10W15

area: 0210

S9588 2024.04.13   9 2 N17W00 0020   BXO  
13640 2024.04.14       N21E30            
S9590 2024.04.14       S08W30          
13642 2024.04.14
2024.04.15
5 8 2 N18W25 0010 BXO BXO area: 0015

location: N16W23

S9592 2024.04.14       S04W27            
S9593 2024.04.14       S20W02            
13643 2024.04.15 6     S13E48 0100 DAI       currently considered part of AR 13637
S9595 2024.04.15   2   S18W39 0004   BXO  
S9597 2024.04.16   6 4 S05W65 0015   CRO    
13644 2024.04.16
2024.04.16
2 1 1 N12E72 0080 DSO HSX   location: N10E74

area: 0100

S9599 2024.04.16   1 1 N20E73 0050   HAX    
S9600 2024.04.16   1 1 N13E78 0100   HSX    
S9601 2024.04.16   2   S11E60 0002   BXO    
S9602 2024.04.16   1   S42E33 0001   AXX    
Total spot count: 66 199 93  
Sunspot number: 176 369 233  (total spot count + 10 * number of spotted regions)
Weighted SN: 119 262 156  (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): 194 203 186  

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
2024.04 139.6 (1)   46.8 (2A) / 87.8 (2B) / 123.1 (2C) (115.4 projected, -0.0) (8.7)
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.