Solar Terrestrial Activity Report

Last major update issued on April 23, 2007 at 02:05 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)
[Solar cycles 21-23 (last update April 10, 2007)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update April 10, 2007)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update April 10, 2007)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports (last update April 7, 2007)]

Recent activity

The geomagnetic field was quiet to unsettled on April 22. Solar wind speed ranged between 288 and 449 km/s (average speed was 355 km/s, increasing 58 km/s over the previous day). A generally low speed stream from CH266 arrived early in the day and caused a minor disturbance.

Solar flux measured at 20h UTC on 2.8 GHz was 68.9. The planetary A index was 10 (STAR Ap - based on the mean of three hour interval ap indices: 9.5). Three hour interval K indices: 22222333 (planetary), 22333333 (Boulder).

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

At midnight the visible solar disk was spotless. The solar flare activity level was very low. No C class events were recorded during the day.

Coronal mass ejections (CMEs)

April 20-22: No obvious fully or partially Earth directed CMEs were observed in LASCO imagery.

Coronal holes

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

A recurrent coronal hole (CH267) in the southern hemisphere will likely rotate into an Earth facing position on April 24-26.

Processed SOHO/EIT 195 image at 00:00 UTC on April 23. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to active on April 23 due to effects from CH266. Quiet conditions are likely on April 24-26 becoming unsettled to minor storm on April 27-29 caused by a high speed stream from CH267.

Coronal holes (1) Coronal mass ejections (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: 0-20% probability, Yellow: 20-60% probability, Red: 60-100% probability.

Propagation

Daily monitoring will not resume until a local noise problem (related to construction work on a neighboring property) has been fixed. Occasional monitoring reports will be submitted when propagation is good.

April 8, 2007: Stations from the Canadian Atlantic provinces had strong signals during the night. Some stations from the northeastern USA and from Florida did well too, in particular 1510 WWZN was impressive.

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
spot
count
STAR
spot
count
Location at midnight Area Classification Comment
10951 2007.04.14     S12W70     plage
Total spot count: 0 0  
SSN: 0 0  

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)
2006.01 83.4 15.3 20.8 (-2.2)
2006.02 76.5 4.9 18.6 (-2.2)
2006.03 75.4 10.6 17.4 (-1.2)
2006.04 89.0 30.2 17.1 (-0.3)
2006.05 80.9 22.3 17.3 (+0.2)
2006.06 76.5 13.9 16.3 (-1.0)
2006.07 75.7 12.2 15.3 (-1.0)
2006.08 79.0 12.9 15.6 (+0.3)
2006.09 77.8 14.4 15.6 (+0.0)
2006.10 74.3 10.4 (14.3 predicted, -1.3)
2006.11 86.3 21.5 (12.6 predicted, -1.7)
2006.12 84.5 13.6 (11.6 predicted, -1.0)
2007.01 83.3 16.9 (11.2 predicted, -0.4)
2007.02 77.7 10.6 (11.1 predicted, -0.1)
2007.03 72.2 4.8 (11.3 predicted, +0.2)
2007.04 69.7 (1) 2.7 (2) (11.9 predicted, +0.6)

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.


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