Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 21, 2023 at 06:15 UT. Minor update posted at 20:55 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, 2023)
Solar cycle Solar cycles 23-25 (April 1, 2023) Historical solar and geomagnetic data charts 1954-2006 (April 5, 2007)
  Cycle 24-25 progress (April 1, 2023) 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, 2023) 3rd SSN Workshop, Tucson, 2013
  Comparison of cycles 12-14, 16, 24-25 (April 1, 2023) 4th SSN Workshop, Locarno, 2014
  Solar polar fields vs. solar cycles (April 5, 2023) 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

Recent activity

The geomagnetic field was quiet on April 20. Solar wind speed at SOHO ranged between 385 and 476 km/sec. The high latitude magnetometer at Andenes recorded quiet to minor storm levels.

Solar flux density measured at 20h UT on 2.8 GHz was 147.0 - decreasing 4.1 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 139.94. In comparison SC24 peaked on June 28, 2014 at 145.50). The Potsdam WDC planetary A index was 10 (STAR Ap - based on the mean of three hour interval ap indices: 9.5). Three hour interval K indices: 21134211 (planetary), 31244322 (Boulder), 00011211 (Andenes).

The background x-ray flux is at the class B7 level (GOES 16).

At the time of counting spots (see image time), spots were observed in 12 active regions using 2K resolution (SN: 281) and in 11 active regions using 1K resolution (SN: 191) SDO/HMI images.

Region 13276 [S22W57] decayed slowly and quietly.
Region 13279 [S21W37] decayed slowly and quietly.
Region 13281 [S22W22] decayed slowly and produced several C flares. C1 flares: C1.8 @ 07:25 UT
Region 13282 [N11W31] gained spots in the leading and intermediate spot sections. The region has polarity intermixing and an M class flare is possible. C1 flares: C1.5 @ 06:41, C1.3 @ 11:47, C1.4 @ 13:12 UT
Region 13283 [S22W03] developed as new flux emerged gaining spots and area. C1 flares: C1.8 @ 03:12, C1.4 @ 14:26, C1.4 @ 19:44, C1.2 @ 21:01 UT
Region 13284 [S09E28] decayed slowly and quietly.

Spotted regions not observed (or interpreted differently) by SWPC:
S8473 [S31E18] was quiet and stable.
S8475 [N22E24] was quiet and stable.
New region S8478 [N12W66] emerged with a few spots.
New region S8479 [N06E37] emerged with tiny spots.
New region S8480 [S18E80] rotated into view and could produce C and M class flares. C1 flares: C1.1 @ 02:18, C1.3 @ 04:47, C1.6 @ 15:21, C1.7 @ 15:50, C1.3 @ 17:59, C1.2 @ 23:27 UT
New region S8481 [S12W00] was observed with tiny spots in an old plage area.

AR 13272 behind the southwest limb produced a C1.6 flare at 08:53 UT

Minor update added at 20:55 UT on April 21: AR 13283 produced a long duration M1.6 flare peaking at 18:11 UT. The flare involved filaments to the east and west of the region across the central meridian. An EIT wave was observed over large parts of both the southern and northern hemisphere. A relatively fast asymmetrical full halo CME was observed beginning at 18:12 UT in LASCO C2 imagery. Earth could receive an impact on April 23, active to severe storm conditions are possible.

C2+ flares:

Magnitude Peak time (UT) Location Source Recorded by Comment
C2.2 01:19 behind NW limb   GOES16  
C2.2 03:23   13281 GOES16 incorrectly attributed to AR 13284 by SWPC
C2.0 05:15 behind SW limb 13272 GOES16  
C2.6 07:43   13281 GOES16  
C2.0 09:07   13281 GOES16  
C2.3 09:12   13281 GOES16  
C3.6 09:22   13281 GOES16  
C2.4 10:55   13281 GOES16  
C2.3 12:24 S21E02 13283 GOES16  
C3.3 16:23   13282 GOES16 simultaneous flare in AR S8480
C2.3 22:30 S24W19 13281 GOES16  

Coronal mass ejections (CMEs)

April 18-20: 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 trans equatorial coronal hole (CH1141) rotated across the central meridian on April 19 and closed. A large recurrent trans equatorial coronal hole will likely become Earth facing on April 23-25.

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

Quiet geomagnetic conditions are likely on April 21. Expect quiet to unsettled conditions on April 22-23 due to effects from CH1141, isolated active intervals are possible.

Coronal holes (1) Coronal mass ejection (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
13275 2023.04.09
2023.04.10
      N18W72          

location: N19W68

13276 2023.04.10
2023.04.10
1 1   S21W33 0010 AXX AXX real position: S22W57

area: 0001

SWPC inexplicably moved this region 43 degrees eastwards on April 19 to the position of the trailing spots of AR 13281. On April 20 the region was repositioned once again, now 33 degrees longitude westwards. It is unclear what the USAF observer is seeing and reporting.

13279 2023.04.10
2023.04.12
1 19 6 S19W39 0010 HAX CRO

location: S21W37

13281 2023.04.12
2023.04.13
6 29 15 S22W22 0060 BXO CAI  
13282 2023.04.13
2023.04.13
23 55 30 N12W28 0380 FHI FKI

area: 0710

S8463 2023.04.13       N20W21            
S8464 2023.04.13       S13W54            
13283 2023.04.13
2023.04.16
4 32 19 S20W01 0050 BXO DRI area: 0080

location: S22W03

S8466 2023.04.13       S19W07            
S8467 2023.04.14       N08W52            
S8468 2023.04.14       N39W50            
13284 2023.04.17
2023.04.17
2 5 2 S08E30 0010 AXX CRO

location: S09E28

area: 0020

S8472 2023.04.17       N20W49          
S8473 2023.04.19   5 2 S31E18 0010   BXO  
S8474 2023.04.19       N19E05          
S8475 2023.04.19   4 1 N22E24 0008   BXO  
S8476 2023.04.19       N16W53          
S8477 2023.04.19       S22W23          
S8478 2023.04.20   4 2 N12W66 0016   DRO    
S8479 2023.04.20   2 1 N06E37 0004   BXO    
S8480 2023.04.20   2 2 S18E80 0280   HKX    
S8481 2023.04.20   3 1 S12W00 0007   AXX    
Total spot count: 37 161 81  
Sunspot number: 97 281 191  (total spot count + 10 * number of spotted regions)
Weighted SN: 52 198 118  (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): 107 155 153  

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
2021.09 87.0 88.2 51.3 40.2 (+4.8) 6.33
2021.10 88.9 88.3 37.4 45.2 (+5.0) 7.38
2021.11 86.2 84.4 34.8 50.8 (+5.6) 9.83
2021.12 103.0 99.8 67.5 55.9 (+5.1) 6.40
2022.01 103.8 100.5 55.3 60.1 (+4.2) 8.92
2022.02 109.1 106.5 60.9 64.7 (+4.6) 10.46
2022.03 117.0 115.8 78.6 68.7 (+4.0) 10.20
2022.04 130.8 131.7 84.0 73.0 (+4.3) 11.79
2022.05 133.8 136.8 96.5 77.4 (+4.4) 7.48
2022.06 116.1 119.8 70.3 81.1 (+3.7) 8.20
2022.07 125.4 129.5 91.4 86.7 (+5.6) 9.51
2022.08 114.2 117.1 74.6 92.5 (+5.8) 10.92
2022.09 135.1 136.5 96.0 96.4 (+3.9) 12.18
2022.10 133.5 132.7 95.5 (99.0 projected, +2.6) 11.16
2022.11 123.4 120.7 80.5 (102.0 projected, +3.0) 9.33
2022.12 147.9 143.4 112.8 (106.8 projected, +4.8) 10.99
2023.01 182.4 176.6 143.6 (112.9 projected, +6.1) 8.73
2023.02 167.2 163.2 110.9 (117.9 projected, +5.0) 14.48
(current
SC25 peak)
2023.03 157.2 155.6 122.6 (121.0 projected, +3.1) 14.42
2023.04 147.2 (1)   60.4 (2A) / 90.7 (2B) / 144.1 (2C) (126.4 projected, +5.4) (8.1)
2023.05       (132.1 projected, +5.7)  
2023.06       (135.2 projected, +3.1)  
2023.07       (134.7 projected, -0.5)  
2023.08       (135.7 projected, +1.0)  
2023.09       (139.2 projected, +3.5)  
2023.11       (142.5 projected max SC25)  

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: SIDC-SILSO.

Solar cycles 24-25

Smoothed SF and sunspot numbers

 

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.