Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 19, 2024 at 05:00 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 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] decayed slowly and quietly.
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] decayed in the northern spot section.
Region 13644 [N10E47] was quiet and stable.
Region 13645 [S10E08] is a compact spot group capable of M class flaring.
Region 13646 [N20E51] decayed slowly and was mostly quiet.
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 as 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 [S29E03] emerged with a tiny spot.

C2+ flares

Magnitude Peak time (UT) Location Source Recorded by Comment
C5.0 00:50   13645 GOES16  
C6.4 01:19   13645 GOES16  
C4.7 02:03   13645 GOES16 simultaneous flare in AR 13646
C5.8 02:19   13647 GOES16  
M2.2 02:48 S19E17 (SDO/AIA) 13638 GOES16 simultaneous smaller flares in AR 13643 and 13645
C6.9 03:17   13645 GOES16  
C5.4 04:20   13645 GOES16  
C5.3 05:02   13647 GOES16  
C7.3 06:09 S09E19 13645 GOES16  
C3.7 06:59   13638 GOES16  
C3.4 07:10   13646 GOES16  
M1.3 07:37 S12E23 13647 GOES16  
C7.2 08:26   13645 GOES16  
C4.5 09:08   13645 GOES16  
C4.5 09:29   13645 GOES16  
C4.5 10:08   13645 GOES16  
C4.4 11:02   13645 GOES16  
C8.9 11:51   13645 GOES16  
C5.5 12:24   13645 GOES16  
C3.9 12:59   13638 GOES16  
C3.1 13:25   13645 GOES16  
C3.6 13:45   13645 GOES16  
C3.6 13:54   13645 GOES16  
C3.3 14:34   13645 GOES16  
C3.7 15:04   13645 GOES16  
C3.3 15:14   13645 GOES16  
C2.6 15:56   13645 GOES16  
C2.9 16:21   13647 GOES16  
C9.8/1N 16:46 S10E12 13645 GOES16  
C3.2 17:34   13647 GOES16  
C2.9 18:26   13633 GOES16  
C3.5 19:19   13647 GOES16  
M1.6 20:16   13647 GOES16  
C4.6 22:56   13638 GOES16  

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     S08W92 0080 CSO     rotated out of view
13634 2024.04.07
2024.04.08
6 4 2 N28W83 0220 DSO CKO

area: 0330

location: N26W83

13635 2024.04.08
2024.04.10
3 5 4 N22W56 0020 CRO CRO

location: N22W58

area: 0030

13636 2024.04.10
2024.04.11
4 13 8 S21W18 0060 CAO CAO location: S22W17

area: 0120

13637 2024.04.12
2024.04.13
6 9 2 S14E01 0010 BXO AXX

location: S13W01

area: 0020

13638 2024.04.12
2024.04.13
5 18 10 S18E03 0030 CRI DRI beta-delta

area: 0120

location: S18E06

13639 2024.04.13
2024.04.14
16 51 26 N29E11 0290 EAI EAI

location: N28E10

area: 0360

13641 2024.04.13
2024.04.14
1 8 2 N09W45 0030 HSX CAO

 

S9588 2024.04.13   6 1 N17W25 0012   BXO  
13640 2024.04.14       N21E02            
S9590 2024.04.14       S08W56            
13642 2024.04.14
2024.04.15
  2 1 N18W53 0005   BXO

location: N16W51

S9592 2024.04.14       S04W53            
S9593 2024.04.14   3 1 S22W17 0006   BXO  
13643 2024.04.15 29 48 28 S12E17 0160 DAI EAI location: S13E23

area: 0220

13644 2024.04.16
2024.04.16
2 1 1 N12E49 0120 DSO HSX location: N10E47

area: 0140

13646 2024.04.16
2024.04.17
8 13 7 N21E50 0070 CRO DRO area: 0050

location: N20E51

S9600 2024.04.16   3 1 N14E52 0130   HSX  
S9601 2024.04.16   11 5 S12E34 0025   CRO  
S9602 2024.04.16       S42E07            
13648 2024.04.17
2024.04.18
2 3 1 N19E39 0010 BXO BXO  
S9604 2024.04.17   5 3 S18W02 0010   CRO  
13645 2024.04.17
2024.04.17
12 45 25 S09E10 0140 DAI DAC beta-gamma

location: S10E08

area: 0600

13647 2024.04.17
2024.04.18
10 26 15 S10E12 0140 DAC DKC beta-delta

area: 0340

location: S13E12

S9607 2024.04.17       S06W30          
S9608 2024.04.17       S35W28          
S9609 2024.04.18   15 9 N16W10 0050   DRI    
S9610 2024.04.18   2 1 N12E39 0007   AXX    
S9611 2024.04.18   1   S29E03 0002   AXX    
Total spot count: 107 292 153  
Sunspot number: 247 512 363  (total spot count + 10 * number of spotted regions)
Weighted SN: 161 355 226  (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): 274 282 290  

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
2024.04 148.7 (1)   61.7 (2A) / 102.8 (2B) / 132.7 (2C) (115.4 projected, -0.0) (8.2)
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.

--------------------------------------------------------------------------------------

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.