Solar Terrestrial Activity Report

Last major update issued on April 27, 2004 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 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 18, 2004)]

Recent activity

The geomagnetic field was quiet to unsettled on April 26. Solar wind speed ranged between 437 and 530 km/sec. A weak solar wind shock was observed at ACE at 15:14 UTC with a sudden increase in solar wind speed from 450 to 520 km/sec. The interplanetary magnetic field swung gradually stronger southwards and was moderately southwards just after 18h UTC. After that the IMF swung slowly northwards. The arrival of this shock had little, if any, geomagnetic effect.

Solar flux measured at 20h UTC on 2.8 GHz was 99.6. The planetary A index was 7 (STAR Ap - based on the mean of three hour interval ap indices: 7.6).
Three hour interval K indices: 21312222 (planetary), 21212321 (Boulder).

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

At midnight there were 3 spotted regions on the visible disk. The solar flare activity level was low. A total of 1 Cclass event was recorded during the day.

Region 10596 decayed slowly and quietly.
Region 10599 decayed slowly and is becoming less complex. Occasional C flares are possible. Flare: C2.4 at 02:42 UTC.
New region 10600 emerged in the northern hemisphere near the central meridian. The region appears to be decaying and could soon become spotless.

Coronal mass ejections (CMEs)

April 24-26: No fully or partly Earth directed CME observed due to no new LASCO images.

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 recurrent coronal hole (CH92) in the northern hemisphere was in a geoeffective position on April 23-25.

Processed SOHO/EIT 284 image at 01:05 UTC on April 27. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be mostly quiet to unsettled on April 27-28, some active intervals are possible if  a high speed stream from coronal hole CH92 arrives. Mostly quiet is likely on April 29-30.

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: From 22:30 until 23:10 UTC several weak signals from Brazil were noted, then, surprisingly, CPN Radio (Perú) slowly became the dominant station. Later on Radio Vibración (Venezuela) had the best signal. "La Peruanisima" on 1590 kHz was noted at the same time as CPN].

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
10595 2004.04.16     S08W64     plage
10596 2004.04.18 3 3 S08W52 0240 CAO area was 0160
at midnight
10599 2004.04.24 12 15 N15E14 0200 DAO beta-gamma
10600 2004.04.26 2 2 N18W06 0030 CSO classification was BXO
at midnight, area 0010
Total spot count: 17 20
SSN: 47 50

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)
2004.04 102.9 (1) 54.9 (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]