Solar Terrestrial Activity Report

Last major update issued on February 27, 2006 at 04:25 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update February 4, 2006)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update February 4, 2006)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update February 4, 2006)]
[Historical solar and geomagnetic data charts 1954-2004 (last update February 1, 2005)]
[Archived reports (last update February 7, 2006)]

Recent activity

The geomagnetic field was inactive to quiet on February 26. Solar wind speed ranged between 330 and 392 (all day average 350) km/sec. The interplanetary magnetic field was southwards most of the day after 09h UTC.

Solar flux measured at 20h UTC on 2.8 GHz was 76.5. The planetary A index was 5 (STAR Ap - based on the mean of three hour interval ap indices: 4.8).
Three hour interval K indices: 02101212 (planetary), 03111212 (Boulder).

The background x-ray flux is at the class A1 level.

At midnight there was 1 spotted region on the visible solar disk. The solar flare activity level was very low. No C class events were recorded during the day.

Spotted regions not numbered by NOAA/SEC:
[S627] This region rotated into view at the southeast limb during the latter half of the day. This region has brightened the southeast limb in the last days' solar images and appears to be in the decay phase. Location at midnight: S09E78.

Coronal mass ejections (CMEs)

February 24-26: No obviously fully or partly Earth directed CMEs were observed.

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 (CH214) in the southern hemisphere was in an Earth facing position on February 24-25.

Processed SOHO/EIT 284 image at 01:06 UTC on February 27. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to unsettled on February 27-28 due to weak coronal hole effects and quiet on March 1-2.

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) 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: 0-20% 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 poor. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant station tonight: WLAM Lewiston ME. On other frequencies propagation to North America was significantly better than one day ago with stations audible on at least double the number of frequencies.

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
S627 2006.02.26   1 S09E78 0010 HSX  
Total spot count: 0 1  
SSN: 0 11  

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)
2004.12 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 31.6 (-1.9)
2005.05 99.3 42.6 28.9 (-2.7)
2005.06 93.7 39.6 28.8 (-0.1)
2005.07 96.4 39.9 29.1 (+0.3)
2005.08 90.5 36.4 (27.6 predicted, -1.5)
2005.09 91.1 22.1 (25.8 predicted, -1.8)
2005.10 77.0 8.5 (24.0 predicted, -1.8)
2005.11 86.3 18.0 (21.6 predicted, -2.4)
2005.12 90.7 41.2 (18.7 predicted, -2.9)
2006.01 83.4 15.4 (15.6 predicted, -3.1)
2006.02 76.5 (1) 4.0 (2) (12.5 predicted, -3.1)

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]