Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 3, 2024 at 05:55 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 2. The high latitude magnetometer at Andenes recorded quiet to unsettled 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 112.8 - decreasing 23.2 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 157.24. 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 6 (STAR Ap - based on the mean of three hour interval ap indices: 6.0). Three hour interval K indices: 12222221 (planetary), 11142312 (Boulder), 33132221 (Andenes).

The background x-ray flux is at the class B3 level (GOES 16).

At the time of counting spots (see image time), spots were observed in 11 active regions using 2K resolution (SN: 148) and in 9 active regions using 1K resolution (SN: 105) SDO/HMI images.

Region 13624 [N16E12] was quiet and stable.
Region 13626 [N11W47] decayed slowly and quietly.
New region 13627 [N09E59] rotated into view on April 1 with SWPC numbering the region the next day.

Spotted regions not observed (or interpreted differently) by SWPC/USAF:
S9550 [S14E14] reemerged with tiny spots.
S9554 [N10E36] reemerged with tiny spots.
S9555 [N06E15] was quiet and stable.
S9557 [N27E21] was quiet and stable.
New region S9561 [N17W18] emerged with tiny spots.
New region S9562 [N21E76] rotated into view with a small spot.
New region S9563 [N08E82] rotated into view with a large spot.
New region S9564 [S10W33] emerged with a tiny spot.

C2+ flares

Magnitude Peak time (UT) Location Source Recorded by Comment

Coronal mass ejections (CMEs)

March 31 - April 2: 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 northern hemisphere negative polarity coronal hole (CH1210) was Earth facing on March 31. A trans equatorial negative polarity coronal hole (CH1211) rotated across the central meridian on March 31-April 1.

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 to fair. Propagation on long distance northeast-southwest paths is poor.

Forecast

The geomagnetic field is expected to be quiet to minor storm on April 3-4 due to effects from CH1210 and CH1211 and quiet to unsettled on April 5.

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
13620 2024.03.22
2024.03.22
      S08W81          

location: S10W67

13622 2024.03.23
2024.03.24
      N11W68           location: N19W58

SWPC position is way off

S9540 2024.03.24       S11W58            
S9547 2024.03.29       S10W29            
13624 2024.03.30
2024.03.30
  4 2 N15E10 0008   BXO

location: N16E12

13625 2024.03.30
2024.03.31
2     N10W93 0070 DAO     rotated out of view
S9550 2024.03.30   10 3 S14E14 0020   BXO    
13626 2024.03.30
2024.04.01
2 3   N13W48 0001 BXO BXO location: N11W47

area: 0004

S9554 2024.03.31   5 1 N10E36 0010   BXO    
S9555 2024.04.01   7 4 N06E15 0020   CRO  
13627 2024.04.01
2024.04.02
1 2 1 N09E58 0005 AXX HRX area: 0020

location: N09E59

S9557 2024.04.01   2 1 N27E21 0006   AXX  
S9558 2024.04.01       S12W58          
S9560 2024.04.01       S07E32          
S9561 2024.04.02   2 1 N17W18 0008   BXO    
S9562 2024.04.02   1 1 N21E76 0025   HRX    
S9563 2024.04.02   1 1 N08E82 0310   HHX    
S9564 2024.04.02   1   S10W33 0001   AXX    
Total spot count: 5 38 15  
Sunspot number: 35 148 105  (total spot count + 10 * number of spotted regions)
Weighted SN: 10 57 34  (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): 39 81 84  

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) 11.1
2024.04 116.6 (1)   2.8 (2A) / 42.5 (2B) / 119.7 (2C) (115.4 projected, -0.0) (7.9)
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.