Solar Terrestrial Activity Report

Last major update issued on April 30, 2004 at 02:50 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 1954-2004 (last update April 28, 2004)]
[Archived reports (last update April 18, 2004)]

Recent activity

The geomagnetic field was quiet on April 29. Solar wind speed ranged between 406 and 535 km/sec. As I write this there are no indications in ACE data of an approaching CME.

Solar flux measured at 20h UTC on 2.8 GHz was 88.5. The planetary A index was 4 (STAR Ap - based on the mean of three hour interval ap indices: 5.6).
Three hour interval K indices: 12112212 (planetary), 12212202 (Boulder).

The background x-ray flux is at the class A5-6 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 10599 decayed quickly with the single penumbra losing about half of its area.

Spotted regions not numbered by NOAA/SEC:
[S395] This region emerged quickly on April 29 in the southwest quadrant. Polarities are mixed and there is a good possibility of a magnetic delta structure forming in the southwestern part. Location at midnight: S15W40.
[S396] A new region emerged in the southwest quadrant near the central meridian on April 29. Location at midnight: S09W08.

Coronal mass ejections (CMEs)

April 29: No fully or partly Earth directed CME observed. A partial halo CME observed late in the day off of the southern limbs and the south pole likely had a backsided origin.
April 27: The C3.1 event in region 10599 at 07:23 UTC was, as observed in GOES SXI images, associated with a CME.

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 (CH93) in the northern hemisphere will in a geoeffective position on April 29 and early on April 30. A trans equatorial coronal hole (CH94) - the recurrent eastern part of what was CH88 during the previous rotation - will be in a geoeffective position on April 30 - May 4.

Processed SOHO/EIT 284 image at 01:05 UTC on April 30. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to unsettled on April 30. A weak CME impact is still possible on April 30 and could cause unsettled to active conditions. A high speed stream from coronal hole CH93 could arrive on May 2 and cause quiet to active conditions while a high speed stream from coronal hole CH94 is likely to arrive on May 3 and cause unsettled to active conditions with occasional minor storm intervals until May 7.

Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is fair to good. Propagation along long distance north-south paths is fair to poor. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: Radio Vibración (Venezuela) before 02h UTC, then CPN Radio (Perú). Occasionally WLAM Lewiston ME was noted as well. On other frequencies stations from Newfoundland, Nova Scotia and the New York area had the best signals of the North American stations].

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
10596 2004.04.18 1   S07W92 0120 HSX rotated out of view
10599 2004.04.24 4 3 N16W26 0080 CAO classification was HAX
at midnight, area 0050
10600 2004.04.26     N18W45     plage
S395 2004.04.29   11 S15W40 0030 DRI beta-gamma
S396 2004.04.29   2 S09W08 0020 HAX  
Total spot count: 5 16
SSN: 25 46

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)
2004.04 101.6 (1) 57.7 (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]