Solar Terrestrial Activity Report

Last major update issued on April 11, 2004 at 03:25 UTC. Minor update posted at 11:23 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update April 2, 2004)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update April 2, 2004)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update April 2, 2004)]
[Historical solar and geomagnetic data charts 1954-2003 (last update January 16, 2004)]
[Archived reports (last update April 5, 2004)]

Recent activity

The geomagnetic field was quiet to unsettled on April 10. Solar wind speed ranged between 385 and 545 km/sec. A solar wind shock was observed at SOHO at 19:25 UTC with a sudden increase in wind speed from 423 to 536 km/sec. This was likely the arrival of a full halo CME observed on April 8. The associated geomagnetic disturbance was fairly weak.

Solar flux measured at 20h UTC on 2.8 GHz was 87.7. The planetary A index was 10 (STAR Ap - based on the mean of three hour interval ap indices: 11.6).
Three hour interval K indices: 33322233 (planetary), 33322233 (Boulder).

The background x-ray flux is at the class A7 level.

At midnight there were 2 spotted regions on the visible disk. The solar flare activity level was very low. No C class events were recorded during the day.

Region 10588 decayed slowly and quietly.

Spotted regions not numbered by NOAA/SEC:
[S380] This region emerged on April 3 just south of region 10588. The region developed moderately quickly on April 4 and slowly on April 5. Slow decay was observed on April 6 after an M2 flare. Late on April 7 new positive polarity flux emerged and a magnetic delta structure formed. Quick decay was observed on April 8 after a long duration C class event. The region decayed further on April 9 and 10 and could become spotless before rotating over the southwest limb.

Comment added at 11:23 UTC on April 11: Region S380 and an erupting filament were the sources of a C9.6 event peaking at 04:13 UTC. This was a proton flare and a weak proton event is in progress at Earth. The flare may have been associated with an earth directed CME.

Coronal mass ejections (CMEs)

April 8: A full halo CME was observed after a long duration C7 event in region S380.
April 9:  A partial halo CME was observed following a long duration C3 event in region S380.
April 10: No fully or partly Earth directed CME 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 coronal hole (CH89) in the southern hemisphere could rotate into a geoeffective position on April 12 and cause a weak geomagnetic disturbance on April 15. The southernmost extension of a coronal hole in the northern hemisphere may also be in a geoeffective position on April 12.

Processed SOHO/EIT 284 image at 19:06 UTC on April 10. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to active on April 11 and quiet to unsettled on April 12-13.

Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is very poor. Propagation along long distance north-south paths is poor to fair. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant stations tonight: Radio Vibración (Venezuela) and CPN Radio (Perú)].

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.

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
10588 2004.04.01 10 1 S13W39
0150 CSO SEC spot count,
area and classification
include region S380
classification was HSX
at midnight, area 0050
10589 2004.04.05     N11W10     plage
S380 emerged on
  5 S17W40 0020 CSO reversed polarity
S383 emerged on
    S19W33     plage
Total spot count: 10 6
SSN: 20 26

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)
2003.03 131.4 61.1 74.0 (-4.3)
2003.04 126.4 60.0 70.1 (-3.9)
2003.05 115.7 55.2 67.6 (-2.5)
2003.06 129.3 77.4 65.0 (-2.6)
2003.07 127.7 83.3 61.8 (-3.2)
2003.08 122.1 72.7 60.0 (-1.8)
2003.09 112.2 48.7 59.5 (-0.5)
2003.10 151.7 65.5 (58.0 predicted, -1.5)
2003.11 140.8 67.3 (55.9 predicted, -2.1)
2003.12 114.9 46.5 (53.3 predicted, -2.6)
2004.01 114.1 37.2 (49.1 predicted, -4.2)
2004.02 107.0 46.0 (44.5 predicted, -4.6)
2004.03 112.0 48.9 (41.7 predicted, -2.8)
2004.04 101.7 (1) 20.5 (2) (39.6 predicted, -2.1)

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% less.

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]