Solar Terrestrial Activity Report

Activity chart

Last major update issued on May 31, 2021 at 03:50 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 (May 1, 2021)
Solar cycle Solar cycles 23-25 (May 1, 2021) Historical solar and geomagnetic data charts 1954-2006 (April 5, 2007)
  Cycle 24-25 progress (May 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 (May 1, 2021) 3rd SSN Workshop, Tucson, 2013
  Comparison of cycles 12-14, 16, 24-25 (May 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 on May 30. The high latitude magnetometer at Andenes recorded quiet to unsettled conditions.

Solar flux density measured at 20h UT on 2.8 GHz was 74.4 - increasing 2.8 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 75.76). The Potsdam WDC planetary A index was 5 (STAR Ap - based on the mean of three hour interval ap indices: 4.6). Three hour interval K indices: 11111112 (planetary), 21122223 (Boulder), 00211113 (Andenes).

The background x-ray flux is at the class B1 level (GOES 16).

At the time of counting spots (see image time), spots were observed in 2 active regions using 2K resolution (SN: 46) and in 2 active regions using 1K resolution (SN: 37) SDO/HMI images.

Region 12827 [N11E29] developed slowly and quietly.
New region 12828 [S32E33] emerged on May 29 and was numbered by SWPC the next day. The region decayed slowly after noon.

C2+ flares:

Magnitude Peak time (UT) Location AR Recorded by Comment
           

Coronal mass ejections (CMEs)

May 29-30: No obviously Earth directed CMEs were observed in available LASCO imagery.
May 28: The long duration C9.4 proton event in AR 12824 late in the day was associated with a partial halo CME. While the main part of the ejecta was headed west of the Earth-Sun line as observed in LASCO C3 imagery, it is likely that a component of this CME will reach Earth either late on May 31 or on June 1.

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]

No obvious coronal holes are currently in or near Earth facing positions.

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 to fair.

Forecast

The geomagnetic field is expected to be quiet on May 31 and June 3. Late on May 31 or on June 1 the CME observed after the C9 flare on May 28 could reach Earth and cause unsettled to minor storm conditions.

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
12825 2021.05.21
2021.05.23
      N17W45         location: N17W39
S6876 2021.05.25       S21W51            
S6877 2021.05.26       N49W46            
S6880 2021.05.27       N25W22            
S6882 2021.05.27       S02W18           SC24
S6883 2021.05.27       N36W40            
S6884 2021.05.28       S06W25           SC24
S6885 2021.05.28       S03E14           SC24
S6886 2021.05.28       S30W08            
12827 2021.05.29
2021.05.29
5 23 15 N11E29 0060 CRO DRI

area: 0100

12828 2021.05.29
2021.05.30
2 3 2 S32E33 0010 AXX AXX  
S6890 2021.05.30       S28E16          
Total spot count: 7 26 17  
Sunspot number: 27 46 37  (total spot count + 10 * number of spotted regions)
Weighted SN: 10 29 20  (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): 30 25 30 k * (sunspot number)
As of May 7, 2016: k = 1.1 for SWPC, k = 0.55 for STAR 2K, k = 0.80 for STAR 1K

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)
2019.10 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 2.7 (+0.5) 6.16
2020.03 70.2 69.5 1.5 3.0 (+0.3) 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 7.9 (+2.3) 3.75
2020.07 69.5 71.8 6.3 9.0 (+1.1) 4.28
2020.08 71.6 73.4 7.6 9.5 (+0.5) 5.68
2020.09 70.7 71.4 0.7 10.5 (+1.0) 8.59
2020.10 74.6 74.2 14.6 11.9 (+1.4) 6.13
2020.11 89.9 88.0 34.5 (13.8 projected, +1.9) 4.77
2020.12 86.9 84.2 23.1 (16.2 projected, +2.4) 4.72
2021.01 76.0 73.6 10.4 (19.5 projected, +3.3) 4.39
2021.02 74.3 72.4 8.3 (22.8 projected, +3.3) 9.50
2021.03 76.0 75.2 17.3 (26.2 projected, +3.4) 10.17
2021.04 75.9 76.4 24.5 (30.3 projected, +4.1) 8.40
2021.05 75.1 (1)   19.0 (2A) / 19.7 (2B) / 29.4 (2C) (33.0 projected, +2.7) (6.7)
2021.06       (36.2 projected, +3.2)  
2021.07       (40.8 projected, +4.6)  
2021.08       (45.5 projected, +4.7)  
2021.09       (51.2 projected, +5.7)  
2021.10       (55.6 projected, +4.4)  

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.