Solar Terrestrial Activity Report

Last major update issued on April 8, 2004 at 03:55 UTC. Minor update posted at 13:28 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 7. Solar wind speed ranged between 444 and 558 km/sec, weakly under the influence of a high speed stream from coronal hole CH88.

Solar flux measured at 20h UTC on 2.8 GHz was 98.1. The planetary A index was 10 (STAR Ap - based on the mean of three hour interval ap indices: 10.4).
Three hour interval K indices: 33322223 (planetary), 33322333 (Boulder).

The background x-ray flux is at the class B1 level.

At midnight there were 3 spotted regions on the visible disk. The solar flare activity level was very low. No C class events were recorded during the day.

Region 10587 decayed quickly and had only a few small penumbraless spots left at the end of the day.
Region 10588 was quiet and stable (this region has been virtually unchanged since it rotated into view and has not changed even if the hot region just south of it has changed a lot).

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. A minor M class flare is possible. Location at midnight: S17W01.

Comment added at 13:28 UTC on April 8: Region S380 produced a long duration C7.4 event peaking at 10:16 UTC. This event was associated with a full halo CME in LASCO C3 images. The CME will impact Earth, most likely on April 10.

The geomagnetic field has been mostly active today as the high speed stream from the eastern (and well defined) part of coronal hole CH88 is dominating the solar wind. Recent ACE EPAM data indicates that a solar wind shock is likely within 2-3 hours.

Coronal mass ejections (CMEs)

April 5: A partial halo CME was observed after 06h UTC in LASCO images. The main ejecta was off of the southeast limb, however, a faint front was seen around most of the visible disk. A weak solar wind shock is possible on April 8.
April 6: A full halo CME was observed in LASCO images after an M2.4 event in region S380 peaking at 13:28 UTC. This CME is likely to reach Earth near noon on April 8.
April 7: 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

An elongated, recurrent trans equatorial coronal hole (CH88) was in a geoeffective position on April 1-7. This coronal hole is best defined in the easternmost part, however, the overall size of the coronal hole is much smaller than one rotation ago.

Processed SOHO/EIT 284 image at 19:06 UTC on April 7. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to major storm on April 8 and unsettled to minor storm on April 9 becoming quiet to active on April 10. The likely arrival of a CME on April 8 will probably cause unsettled to major storm conditions after the impact and early on April 9. The high speed stream from coronal hole CH88 is expected to resume sometime on April 9.

Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is poor to 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 and CPN Radio (Perú). CJYQ on 930 kHz had the best signal of only a few stations from North America].

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
10587 2004.03.28 5 3 S13W59 0030 CAO classification was AXX
at midnight, area 0010
10588 2004.04.01 9 1 S13E00
0150 DAO SEC spot count,
area and classification
include region S380
10589 2004.04.05 1   N11E29 0010 AXX spotless
10590 2004.04.07 2   S09W71 0020 BXO formerly region S384
S380 emerged on
  22 S17W01 0120 DAI beta-delta
split off from region
S383 emerged on
    S19E06     plage
Total spot count: 17 26
SSN: 57 56

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)
2004.04 106.5 (1) 18.1 (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]