Solar Terrestrial Activity Report

Last major update issued on April 1, 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 April 1, 2006)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update April 1, 2006)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update April 1, 2006)]
[Historical solar and geomagnetic data charts 1954-2005 (last update March 3, 2006)]
[Archived reports (last update March 2, 2006)]

Recent activity

The geomagnetic field was inactive to quiet on March 31. Solar wind speed ranged between 337 and 391 (all day average 365) km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 86.3. The planetary A index was 4 (STAR Ap - based on the mean of three hour interval ap indices: 4.3).
Three hour interval K indices: 10122121 (planetary), 20122211 (Boulder).

The background x-ray flux is at the class A8 level.

At midnight there were 3 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 10865 developed slowly in the trailing and intermediate spot sections while the leading penumbra matured and became symmetric. Small patched of negative polarity flux emerged inside the trailing positive flux area. C flares are possible.
Region 10866 was quiet and stable.

Spotted regions not numbered by NOAA/SEC:
[S638] A single small spot emerged in this region on March 31. The region is located due south of region 10866. Location at midnight: S16E43.

Coronal mass ejections (CMEs)

March 29-31: No partly or fully Earth directed CMEs were observed in LASCO imagery.

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 coronal hole (CH218) in the northern hemisphere will likely rotate to an Earth facing position on April 2. On March 31 CH218 decayed significantly and could disappear before rotating to a geoeffective position.

Processed SOHO/EIT 284 image at 01:06 UTC on April 1. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to unsettled on April 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

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: Radio Vibración (Venezuela). On other frequencies quite a few stations from the east coast of North America were audible at fair levels. 1290 Radio Puerto Cabello and 1390 Radio Fé y Alegria had the best signals.

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
10865 2006.03.28 18 21 S13E20 0210 EAI classification was ESI at midnight, area 0170
10866 2006.03.29 1 1 S07E42 0120 HSX classification was HAX at midnight, area 0080
S638 2006.03.31   1 S16E43 0000 AXX  
Total spot count: 19 23  
SSN: 39 53  

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)
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 24.2 31.6 (-1.9)
2005.05 99.3 42.7 28.9 (-2.7)
2005.06 93.7 39.3 28.8 (-0.1)
2005.07 96.4 40.1 29.1 (+0.3)
2005.08 90.5 36.4 27.4 (-1.7)
2005.09 91.1 21.9 25.8 (-1.6)
2005.10 77.0 8.5 (24.8 predicted, -1.0)
2005.11 86.3 18.0 (22.7 predicted, -2.1)
2005.12 90.7 41.2 (19.8 predicted, -2.9)
2006.01 83.4 15.4 (16.7 predicted, -3.1)
2006.02 76.5 4.7 (13.6 predicted, -3.1)
2006.03 75.4 10.8 (11.4 predicted, -2.2)
2006.04  (1) (2) (10.7 predicted, -0.7)

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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