Solar Terrestrial Activity Report

Last major update issued on April 30, 2007 at 03:05 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 minor storm on April 29. Solar wind speed ranged between 577 and 716 km/s (average speed was 619 km/s, increasing 46 km/s over the previous day) under the influence of a high speed stream from CH267.

Solar flux measured at 20h UTC on 2.8 GHz was 84.8. The planetary A index was 23 (STAR Ap - based on the mean of three hour interval ap indices: 22.6). Three hour interval K indices: 55542223 (planetary), 54552123 (Boulder).

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

At midnight there were 2 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 10953 lost all spots outside of the area where the large single penumbra is located. There is a weak magnetic delta structure in the eastern part of this penumbra, however, all the positive polarity spots are small. C flares are possible and there is a minor chance of a small M class flare.

Spotted regions not numbered by NOAA/SEC:
[S700] This region emerged to the northeast of region 10953 on April 28 and developed penumbra on both polarities the following day. Location at midnight: S05E42

Coronal mass ejections (CMEs)

April 27-29: 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 was in an Earth facing position on April 24-26.

Processed SOHO/EIT 195 image at 10:00 UTC on April 29. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to minor storm on April 30 due to a high speed stream from CH267 and mostly quiet on May 1-3.

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
10953 2007.04.25 8 16 S10E23 0500 DKI beta-delta
S699 2007.04.27     S10E10     plage
S700 2007.04.28   5 S05E42 0030 DSO  
Total spot count: 8 21  
SSN: 18 41  

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 71.9 (1) 5.6 (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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