Solar Terrestrial Activity Report

Activity chart

Last major update issued on May 23, 2021 at 07:35 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 22. The high latitude magnetometer at Andenes recorded quiet to active conditions.

Solar flux density measured at 20h UT on 2.8 GHz was 75.6 - decreasing 3.2 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 75.53). The Potsdam WDC planetary A index was 4 (STAR Ap - based on the mean of three hour interval ap indices: 4.0). Three hour interval K indices: 11111121 (planetary), 11212222 (Boulder), 40012243 (Andenes).

The background x-ray flux is at the class B2 level (GOES 16).

At the time of counting spots (see image time), spots were observed in 3 active regions using 2K resolution (SN: 65) and in 3 active regions using 1K resolution (SN: 49) SDO/HMI images.

Region 12824 [N20E13] produced 2 minor M class flares and 9 C class flares as two weak magnetic deltas formed to the west and south of the major spot. The western delta is small and close to the largest spot while the southern delta is more interesting as a channel of positive polarity is wedged between two areas of negative polarity. The most interesting event of the day was a C1.3 long duration event which peaked at 08:44 UT and was associated with a faint halo CME.

Spotted regions not observed (or interpreted differently) by SWPC:
S6871 [N17E68] was mostly quiet and stable.
S6873 [S24E01] was quiet and stable.

C2+ flares:

Magnitude Peak time (UT) Location AR Recorded by Comment
C6.1/1N 02:56 N17E37 12824 GOES16 moderate type II radio sweep
C6.0/1N 06:17 N17E37 12824 GOES16 weak type II radio sweep
C2.5 11:23 N24E18 12824 GOES16  
C3.2 15:35 N21E17 12824 GOES16  
M1.1/1N 17:11 N17E20 12824 GOES16  
M1.4/1N 21:36 N19E15 12824 GOES16  
C6.8 23:13 N18E16 12824 GOES16  

Coronal mass ejections (CMEs)

May 20-21: No obviously Earth directed CMEs were observed in available LASCO imagery.
May 22: Faint halo CMEs were observed in LASCO imagery following a C1.3 long duration event peaking at 08:44 and an M1.1 flare at 17:11 UT. These CMEs could reach Earth during the latter half of May 25 or the first half of May 26.

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.

Forecast

The geomagnetic field is expected to be quiet on May 23-24 and the first half of May 25. CMEs could reach Earth on May 25 and 26 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
S6863 2021.05.15       S15W25          
S6864 2021.05.16       S15W31            
12824 2021.05.17
2021.05.18
9 29 16 N21E13 0190 CSI DAI beta-gamma-delta

area: 0250

S6866 2021.05.17       S21W08            
S6870 2021.05.20       N08W21            
S6871 2021.05.21   2 1 N17E68 0008   AXX  
S6872 2021.05.21       N20W18          
S6873 2021.05.21   4 2 S24E01 0008   BXO  
Total spot count: 9 35 19  
Sunspot number: 19 65 49  (total spot count + 10 * number of spotted regions)
Weighted SN: 14 40 24  (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): 21 36 39 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 73.6 (1)   11.2 (2A) / 15.7 (2B) / 31.6 (2C) (33.0 projected, +2.7) (7.2)
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.