Solar Terrestrial Activity Report

Last major update issued on October 3, 2005 at 03:10 UTC.

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

Recent activity

The geomagnetic field was quiet to active on October 2. Solar wind speed ranged between 429 and 537 (all day average 470) km/sec under the influence of a high speed stream from CH189. Wind speed decreased gradually after 05h UTC.

Solar flux measured at 20h UTC on 2.8 GHz was 74.9. The planetary A index was 13 (STAR Ap - based on the mean of three hour interval ap indices: 13.1).
Three hour interval K indices: 43422322 (planetary), 43432322 (Boulder).

The background x-ray flux is at the class A6 level.

At midnight there was one spotted region on the visible solar disk. The solar flare activity level was very low. No C class events were recorded during the day. Old region 10808 is just behind the southeast limb. While this region has been mostly quiet while on the back side, it may still possess M class flare potential.

Spotted regions not numbered by NOAA/SEC:
[S596] This region emerged early on October 2 in the southwest quadrant. The region is simple and could soon decay as the opposite polarity areas have drifted slowly apart. Location at midnight: S10W42.

Coronal mass ejections (CMEs)

September 30 - October 2: No obvious fully or partly Earth directed CMEs were observed. Images for October 2 were not available at the time this report was written.

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 small recurrent coronal hole (CH190) in the northern hemisphere could rotate to an Earth facing position on October 2. A recurrent trans equatorial coronal hole (CH191) will likely rotate to an Earth facing position on October 6-8.

Processed SOHO/EIT 284 image at 19:06 UTC on October 1. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be mostly quiet October 3-8, some unsettled intervals are possible on October 5 due to effects from CH190. A high speed stream from CH191 could arrive on October 9 and cause unsettled to active conditions until October 11 becoming quiet to unsettled on October 12.

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 fair. Propagation on long distance northeast-southwest paths is fair. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant stations tonight: Radio Vibración (Venezuela) and Radio Cristal del Uruguay. Several stations from Newfoundland had good to very good signals at 03h UTC and the usual New York and Boston 50 kW stations were heard with fair signals. From South America signals from Colombia (1520 Vida AM Música was very good) and Venezuela dominated as they have done for the last several nights. At LSR on October 2 CPN Radio (Perú) was very strong on 1470 kHz, and stations like 530 Radio Visión Cristiana and 820 Radio Paradise were at near studio quality levels.

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
10812 2005.09.23     S03W46     plage
S595 2005.09.30     N12W41     plage
S596 2005.10.01   6 S10W42 0030 DRI  
Total spot count: 0 6  
SSN: 0 16  

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)
2004.08 109.6 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 33.9 (-0.7)
2005.03 89.9 24.5 33.5 (-0.4)
2005.04 86.0 24.4 (31.9 predicted, -1.6)
2005.05 99.3 42.6 (29.4 predicted, -2.5)
2005.06 93.7 39.6 (28.1 predicted, -1.3)
2005.07 96.4 39.9 (26.9 predicted, -1.2)
2005.08 90.5 36.4 (25.0 predicted, -1.9)
2005.09 91.1 22.1 (23.0 predicted, -2.0)
2005.10 73.5 (1) 0.0 (2) (21.0 predicted, -2.0)

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]