Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 13, 2024 at 06:30 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 12. 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 151.5 - increasing 6.6 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 156.82. 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: 22110011 (planetary), 12112222 (Boulder), 22111100 (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 13 active regions using 2K resolution (SN: 245) and in 11 active regions using 1K resolution (SN: 165) SDO/HMI images.

Region 13628 [N07W50] decayed slowly and quietly.
Region 13633 [S08W11] developed slowly and quietly.
Region 13634 [N26W03] developed slowly and produced several C flares.
Region 13635 [N20E27] decayed slowly and was mostly quiet.
Region 13636 [S20E59] was mostly quiet and stable. C1 flares: C1.6 @ 10:00 UT

Spotted regions not observed (or interpreted differently) by SWPC/USAF:
S9562 [N20W58] reemerged with a tiny spot.
S9570 [S15W40] was quiet and stable.
S9576 [N10W01] was quiet and stable.
S9577 [S19W08] was quiet and stable.
S9280 [N18E08] reemerged with a tiny spot.
New region S9583 [S12E81] rotated into view with a few spots. The region appears to be unstable and could produce M flares. C1 flare: C1.9 @ 13:32 UT
New region S9584 [S17E83] rotated into view with a mature spot.
New region S9585 [S25E05] emerged with tiny spots.

C2+ flares

Magnitude Peak time (UT) Location Source Recorded by Comment
C5.5 03:27 N28E07 13634 GOES16  
C2.7 05:43   13635 GOES16  
C2.4 06:13   13636 GOES16  
C2.3 07:36   13636 GOES16  
C3.1 11:22 N18E64 (SDO/AIA) spotless plage GOES16  
C2.0 12:27 S12E90 (SDO/AIA) S9583 GOES16  
C3.6 13:32 N27E03 13634 GOES16  
C2.7 14:12   13634 GOES16  
C2.4 14:31 S12E90 (SDO/AIA) S9583 GOES16  
C2.1 14:50 S12E90 (SDO/AIA) S9583 GOES16  
C4.0 15:52 S12E87 (SDO/AIA) S9583 GOES16  
C8.9 17:55 S12E88 (SDO/AIA) S9583 GOES16  
C2.0 18:22 S12E87 (SDO/AIA) S9583 GOES16  
C3.1 23:14 S12E85 (SDO/AIA) S9583 GOES16  

Coronal mass ejections (CMEs)

April 10: No obviously Earth directed CMEs were observed.
April 11: A CME was observed after a filament eruption in the northeast quadrant near the central meridian. The eruption began at 05:27 UT in SDO/AIA imagery and peaked near 06h UT. The CME could reach Earth on April 14.
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.

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 negative polarity southern hemisphere coronal hole (CH1213) rotated across the central meridian on April 9-10.

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 unsettled on April 13 due to effects from CH1213. The April 11 CME could reach Earth on April 14 and cause unsettled to active conditions. The April 12 CME could extend unsettled to active conditions into April 15.

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
13627 2024.04.01
2024.04.02
      N09W80          

location: N09W75

S9562 2024.04.02   1 1 N20W58 0003   AXX    
13628 2024.04.02
2024.04.03
3 4 3 N07W51 0240 HAX CHO

area: 0320

location: N07W50

13632 2024.04.03
2024.04.05
      N26W51           location: N26W45
13633 2024.04.05
2024.04.06
6 22 12 S08W10 0110 CSO DSO location: S08W11

area: 0180

S9570 2024.04.05   2 2 S15W40 0007   BXO  
13634 2024.04.07
2024.04.08
13 35 16 N26W03 0120 DSI DAI

area: 0270

S9575 2024.04.07       S03W35          
S9576 2024.04.08   3   N10W01 0005   AXX  
S9577 2024.04.08   8 2 S19W08 0020   BXO  
13635 2024.04.08
2024.04.10
9 23 10 N21E26 0050 CSI DAI area: 0080

location: N20E27

S9579 2024.04.09       S15W01            
S9580 2024.04.10       N19E07            
13636 2024.04.10
2024.04.11
2 6 4 S21E58 0050 HSX CSO location: S20E59

area: 0180

S9583 2024.04.12   6 3 S12E81 0050   DRO    
S9584 2024.04.12   1 1 S17E83 0050   HAX    
S9585 2024.04.12   4 1 S25E05 0009   CRO    
Total spot count: 33 115 55  
Sunspot number: 83 245 165  (total spot count + 10 * number of spotted regions)
Weighted SN: 58 156 96  (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): 91 135 132  

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
2024.04 125.2 (1)   25.6 (2A) / 64.1 (2B) / 117.5 (2C) (115.4 projected, -0.0) (7.7)
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.