Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 20, 2023 at 04:00 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, 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 to active on April 19 due to CME effects. Solar wind speed at SOHO ranged between 424 and 663 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), 41134521 (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 12 active regions using 2K resolution (SN: 259) and in 8 active regions using 1K resolution (SN: 150) SDO/HMI images.

Region 13276 [S20W43] was quiet and stable.
Region 13279 [S20W26] decayed slowly and was quiet.
Region 13281 [S22W10] decayed slowly and was mostly quiet. C1 flares: C1.2 @ 06:49, C1.4 @ 18:32 UT
Region 13282 [N11W18] gained more intermediate spots and has polarity intermixing. An M class flare is possible.
Region 13283 [S21E08] decayed slowly and was mostly quiet.
Region 13284 [S09E45] decayed slowly and quietly.

Spotted regions not observed (or interpreted differently) by SWPC:
S8472 [N20W36] was quiet and stable.
New region S8473 [S30E30] was observed with tiny spots in an old plage area.
New region S8474 [N19E18] was observed with tiny spots in an old plage area.
New region S8475 [N28E38] was observed with tiny spots in an old plage area.
New region S8476 [N16W40] emerged with tiny spots.
New region S8477 [S09W08] emerged with a tiny spot.

A C1.1 flare was recorded at 07:22 UT from a source behind the northeast limb.
A C1.8 flare at 13:18, a C1.2 flare at 15:04, a C1.7 flare at 20:20, a C1.6 flare 21:29 and a C1.6 flare at 22:21 UT had their origin in a region behind the southeast limb (the C1.8 flare was incorrectly attributed to AR 13282 by SWPC).

C2+ flares:

Magnitude Peak time (UT) Location Source Recorded by Comment
C2.3 04:30   13272 GOES16  
C3.9 08:41 behind SW limb 13280 GOES16 attributed to AR 13272 by SWPC
C2.1 09:37 behind SE limb   GOES16  
C2.1 09:52 behind NE limb   GOES16  
C2.1 11:11 behind SE limb   GOES16  
C2.0 13:35   13282 GOES16  
C2.3 13:47   13282 GOES16  
C2.7 16:08   13282 GOES16  
C3.4 16:38   13282 GOES16  
C2.0 17:24 behind SE limb   GOES16  
C2.6 23:48   13283 GOES16  

Coronal mass ejections (CMEs)

April 17-19: No obviously Earth directed CMEs were observed.
April 15/16: An extensive filament eruption in the northwest quadrant was observed beginning in SDO/AIA imagery at 22:47 UT. A relatively faint partial halo CME was observed early on April 16  and could reach Earth on April 20 and cause unsettled to minor storm conditions. [It is uncertain if the CME arrived earlier than expected, a solar wind shock was observed at 13:08 UT on April 18 at SOHO]

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) will rotate across the central meridian on April 19.

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

Quiet to active conditions are likely on April 20-23 due to CME effects April 20-21 and on April 22-23 due to effects from CH1141.

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
13272 2023.04.05
2023.04.06
2     S24W88 0010 AXX    

rotated out of view

location: S23W89

SWPC position is nearly the same as on the previous day

13275 2023.04.09
2023.04.10
      N18W58        

location: N19W55

13276 2023.04.10
2023.04.10
7 2 1 S21W00 0030 AXX AXX real position: S20W43

area: 0005

SWPC inexplicably moved this region 43 degrees eastwards on April 19 to the position of the trailing spots of AR 13281

13277 2023.04.10
2023.04.11
      N10W86            
13279 2023.04.10
2023.04.12
7 29 13 S19W28 0040 CRO CRO

location: S20W26

13281 2023.04.12
2023.04.13
10 30 19 S21W10 0060 CAO ESI

location: S22W10

area: 0090

13282 2023.04.13
2023.04.13
11 37 22 N12W16 0530 FHO FKI

area: 0630

S8463 2023.04.13       N20W08            
S8464 2023.04.13       S13W41          
13283 2023.04.13
2023.04.16
3 13 4 S21E07 0020 BXO CRO  
S8466 2023.04.13       S19E06            
S8467 2023.04.14       N08W39            
S8468 2023.04.14       N39W37          
13284 2023.04.17
2023.04.17
3 9 7 S08E42 0080 DRO DRO

location: S09E45

area: 0040

S8472 2023.04.17   4 3 N20W36 0015   BXO  
S8473 2023.04.19   2   S30E30 0003   AXX    
S8474 2023.04.19   6 1 N19E18 0010   BXO    
S8475 2023.04.19   3   N28E38 0005   AXX    
S8476 2023.04.19   3   N16W40 0005   BXO    
S8477 2023.04.19   1   S22W10 0002   AXX    
Total spot count: 43 139 70  
Sunspot number: 113 259 150  (total spot count + 10 * number of spotted regions)
Weighted SN: 64 163 94  (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): 124 142 120  

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)   57.2 (2A) / 90.3 (2B) / 142.5 (2C) (126.4 projected, +5.4) (8.3)
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.