Solar Terrestrial Activity Report

Last major update issued on August 21, 2005 at 05:40 UTC. Minor update posted at 07:02 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update August 2, 2005)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update August 2, 2005)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update August 2, 2005)]
[Historical solar and geomagnetic data charts 1954-2004 (last update February 1, 2005)]
[Archived reports (last update August 13, 2005)]

Recent activity

The geomagnetic field was quiet on August 20. Solar wind speed ranged between 380 and 463 (all day average 437) km/sec, slowly decreasing all day.

Solar flux measured at 20h UTC on 2.8 GHz was 98.1. The planetary A index was 5 (STAR Ap - based on the mean of three hour interval ap indices: 5.0).
Three hour interval K indices: 21102222 (planetary), 21112212 (Boulder).

The background x-ray flux is at the class B3 level.

At midnight there were 4 spotted regions on the visible solar disk. The solar flare activity level was very low. No C class events were recorded during the day.

Region 10797 decayed slowly and was quiet.
Region 10798 decayed further and has only a single small spot left. Note that SEC has included region S583 in this region even though they are two separate bipolar regions.
Region 10800 developed slowly and quietly.

Spotted regions not numbered by NOAA/SEC:
[S583] This is a complex reversed polarity region just west southwest of region 10798. The first signs of the region were noted late on August 17. Rapid development was observed on August 18 and 19. On August 20 the region became complex as a magnetic delta structure formed in the central part. An M class flare is possible. Location at midnight: S10W36

Comment added at 07:02 UTC on August 21: Another possible cycle 24 duopole has been emerging slowly today and was located at N26E36 at 05:30 UTC. This has recently become visible as a small bright area to the north northeast of region 10800 in GOES SXI images. 

Coronal mass ejections (CMEs)

August 18-19: No obvious partly or fully Earth directed CMEs were observed.
August 20: A faint full halo CME was observed in LASCO C3 images beginning at 18:45 UTC. There was no associated frontside activity so this CME likely had a backsided source.

Coronal holes

Coronal hole history (since late October 2002)
Compare today's report with the situation one solar rotation ago: 28 days ago 27 days ago 26 days ago

A recurrent coronal hole (CH182) in the southern hemisphere was in an Earth facing position on August 17-18. While this coronal hole didn't produce any disturbance during the previous rotation, it has extended somewhat in a northerly direction. A recurrent coronal hole (CH183) in the southern hemisphere will likely rotate to an Earth facing position on August 21-22.

Processed SOHO/EIT 284 image at 01:06 UTC on August 21. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to unsettled on August 21-22 with a chance of a few active intervals due to effects from CH182. Quiet conditions are likely on August 23 with unsettled to minor storm expected for August 24-25 due to a high speed stream from CH183.

Coronal holes (1) Coronal mass ejections (2) M and X class flares (3)
Coronal hole indicator CME indicator M and X class flare indicator

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) Material from a CME is likely to impact Earth within 96 hours.
3) There is a possibility of either M or X class flares within the next 48 hours.

Green: 0-20% probability, Yellow: 20-60% probability, Red: 60-100% probability.


Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is poor to fair. Propagation on long distance northeast-southwest paths is poor to fair. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant stations tonight: Radio Vibración (Venezuela) and Radio Cristal del Uruguay. Propagation was best towards the easternmost parts of the USA and Canada before LSR, after LSR most of the stations audible were from Argentina. The New York stations on 660, 880, 1050, 1130, 1190 and 1560 all had good signals, as had 1080 WTIC, 1510 WWZN and 1500 WTOP.

Active solar regions (Recent map)

Compare to the previous day's image.

Data for all numbered solar regions according to the Solar Region Summary provided by NOAA/SEC. 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 SEC or where SEC has observed no spots. SEC active region numbers in the table below and in the active region map above are the historic SEC/USAF numbers.

Active region Date numbered SEC
Location at midnight Area Classification Comment
10797 2005.08.11 1 1 S13W66 0070 HSX  
10798 2005.08.14 12 1 S11W33 0510 EKI classification was AXX at midnight, area 0010
SEC has included region S583 in this region
location: S09W29
10799 2005.08.18 2   S09W82 0030   spotless
10800 2005.08.19 8 13 N16E33 0050 DSO classification was DSI at midnight, location: N17W31
10801 2005.08.20 1   N06E54 0020 HSX formerly region S585
S583 2005.08.18   25 S10W36 0600 DKC beta-delta
reversed polarity region
Total spot count: 24 40  
SSN: 74 80  

Monthly solar cycle data

Month Average solar
flux at Earth
International sunspot number Smoothed sunspot number
2000.04 184.2 125.5 120.8
cycle 23 sunspot max.
2000.07 202.3 170.1 119.8
2001.12 235.1 132.2 114.6 (-0.9)
2004.06 97.4 43.2 41.6 (-2.2)
2004.07 119.1 51.1 40.2 (-1.4)
2004.08 109.6 40.9 39.2 (-1.0)
2004.09 103.1 27.7 37.5 (-1.7)
2004.10 105.9 48.0 35.9 (-1.6)
2004.11 113.2 43.5 35.3 (-0.6)
2004.12 94.5 17.9 35.2 (-0.1)
2005.01 102.2 31.3 34.6 (-0.6)
2005.02 97.2 29.2 (33.5 predicted, -1.1)
2005.03 89.9 24.5 (32.1 predicted, -1.4)
2005.04 86.0 24.4 (30.2 predicted, -1.9)
2005.05 99.3 42.6 (27.6 predicted, -2.6)
2005.06 93.7 39.6 (26.1 predicted, -1.5)
2005.07 96.4 39.9 (25.1 predicted, -1.0)
2005.08 88.5 (1) 38.8 (2) (23.2 predicted, -1.9)

1) Running average based on the daily 20:00 UTC observed solar flux value at 2800 MHz.
2) Unofficial, accumulated value based on the Boulder (NOAA/SEC) sunspot number. The official international sunspot number is typically 30-50% lower.

This report has been prepared by Jan Alvestad. It is based partly on my own observations and analysis, and partly on data from some of these solar data sources. All time references are to the UTC day. Comments and suggestions are always welcome.

[DX-Listeners' Club]