Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 19, 2021 at 04:45 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, 2021)
Solar cycle Solar cycles 23-25 (April 1, 2021) Historical solar and geomagnetic data charts 1954-2006 (April 5, 2007)
  Cycle 24-25 progress (April 1, 2021) Noon SDO sunspot count 1K image / 4K (*)
  Solar cycles 1-24 (June 1, 2020) POES auroral activity level October 2009 - December 2012]
  Comparison of cycles 21-25 (April 1, 2021) 3rd SSN Workshop, Tucson, 2013
  Comparison of cycles 12-14, 16, 24-25 (April 1, 2021) 4th SSN Workshop, Locarno, 2014
  Solar polar fields vs. solar cycles (January 7, 2021) Cycle 25 spots (final update December 25, 2019)
  Solar cycles 24-25 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 18 under the influence of a high speed stream associated with CH1007. The high latitude magnetometer at Andenes recorded unsettled to severe storm conditions.

Solar flux density measured at 20h UT on 2.8 GHz was 78.1 - increasing 1.0 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 74.92). The Potsdam WDC planetary A index was 17 (STAR Ap - based on the mean of three hour interval ap indices: 17.3). Three hour interval K indices: 43343234 (planetary), 34442233 (Boulder), 75443366 (Andenes).

The background x-ray flux is at the class A8 level (GOES 16).

At the time of counting spots (see image time), spots were observed in 5 active regions using 2K resolution (SN: 90) and in 3 active regions using 1K resolution (SN: 55) SDO/HMI images.

Region 12815 [S21W46] was quiet and stable.
Region 12816 [S25E36] developed as new flux emerged in the eastern section of the region. C flares are possible.

Spotted regions not observed (or interpreted differently) by SWPC:
S6823 [N20E17] decayed slowly and quietly.
New region S6824 [N15W19] was observed with a tiny spot.
New region S6825 [N18W32] emerged with several spots.

C2+ flares:

Magnitude Peak time (UT) Location AR Recorded by Comment
           

Coronal mass ejections (CMEs)

April 16-18: No obviously Earth directed CMEs were observed in available LASCO imagery.

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 southern hemisphere coronal hole (CH1007) - an extension of the southern polar coronal hole - was Earth facing on April 14-17. Another recurrent southern hemisphere coronal hole (CH1008) will rotate across the central meridian on April 19-20.

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 fair.

Forecast

The geomagnetic field is expected to be unsettled to minor storm on April 19-20 due to effects from CH1007, major storm intervals are possible. Quiet to unsettled is likely on April 21 becoming quiet to active on April 22 due to effects from CH1008.

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 red colored.

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
12814 2021.04.08
2021.04.12
      S22W73          
S6817 2021.04.14       S31E03            
12816 2021.04.15
2021.04.16
5 28 19 S25E34 0050 CAO DRI area: 0120
12815 2021.04.15
2021.04.16
  2 1 S21W49 0004   AXX

location: S21W46

S6820 2021.04.15       S30W28            
S6822 2021.04.16       N21W11          
S6823 2021.04.17   1   N20E17 0002   AXX  
S6824 2021.04.18   1   N15W19 0002   AXX    
S6825 2021.04.18   8 5 N18W32 0025   CRO  
S6826 2021.04.19       S18E84 @ 12:00 UT          
Total spot count: 5 40 25  
Sunspot number: 15 90 55  (total spot count + 10 * number of spotted regions)
Weighted SN: 10 46 31  (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): 17 50 44 k * (sunspot number)
As of May 7, 2016: k = 1.1 for SWPC, k = 0.55 for MSN 2K, k = 0.80 for MSN 1K (MSN=Magnetic Sunspot Number)

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 (cycle peak) 110.5 10.70
2014.04 143.9 144.8 112.5 116.4 (solar max) 7.88
2017.09 91.3 92.3 43.6 18.2 (-1.3) 18.22 (cycle peak)
2019.09 67.9 68.7 1.1 3.1 (-0.3) 9.81
2019.10 67.4 67.0 0.4 2.6 (-0.5) 7.53
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
2020.01 72.2 69.9 6.4 2.2 (+0.4) 4.39
2020.02 71.0 69.3 0.4 2.8 (+0.6) 6.16
2020.03 70.2 69.5 1.5 3.0 (+0.2) 5.63
2020.04 69.5 70.0 5.4 3.6 (+0.6) 5.32
2020.05 69.0 70.6 0.2 5.6 (+2.0) 3.80
2020.06 69.5 71.7 5.8 7.8 (+2.2) 3.75
2020.07 69.5 71.8 6.3 8.8 (+1.0) 4.28
2020.08 71.6 73.4 7.6 9.3 (+0.5) 5.68
2020.09 70.7 71.4 0.7 10.5 (+1.2) 8.59
2020.10 74.6 74.2 14.6 (11.6 projected, +1.1) 6.13
2020.11 89.9 88.0 34.5 (13.2 projected, +1.6) 4.77
2020.12 86.9 84.2 23.1 (16.3 projected, +3.1) 4.72
2021.01 76.0 73.6 10.4 (20.0 projected, +3.7) 4.39
2021.02 74.3 72.4 8.3 (23.3 projected, +3.3) 9.50
2021.03 76.0 75.2 17.3 (27.5 projected, +4.2) 10.17
2021.04 73.9 (1)   6.4 (2A) / 10.6 (2B) / 23.5 (2C) (32.6 projected, +5.1) (7.5)
2021.05       (35.6 projected, +3.0)  
2021.06       (38.8 projected, +3.2)  
2021.07       (43.4 projected, +4.6)  
2021.08       (48.0 projected, +4.6)  
2021.09       (53.7 projected, +5.7)  

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 transition

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.