Solar Terrestrial Activity Report

Last major update issued on May 1, 2004 at 04:30 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 30, 2004)]

Recent activity

The geomagnetic field was quiet to active on April 30. Solar wind speed ranged between 370 and 463 km/sec. A fairly weak disturbance - source unknown - arrived at ACE at 13h UTC. The interplanetary magnetic field was moderately southwards 19-21h UTC.

Solar flux measured at 20h UTC on 2.8 GHz was 89.5. The planetary A index was 12 (STAR Ap - based on the mean of three hour interval ap indices: 13.3).
Three hour interval K indices: 23312334 (planetary), 33311244 (Boulder).

The background x-ray flux is at the class A6 level.

At midnight there were 3 spotted regions on the visible disk. The solar flare activity level was low. A single C class event was recorded during the day.

Region 10599 decayed further and was quiet.
New region 10601 emerged in the southwest quadrant near the center of the visible disk on April 29 and was numbered by SEC the next day. The region is developing moderately quickly and could produce C flares.
New region 10602 emerged in the southwest quadrant on April 29 and was numbered by SEC the next day. Slow decay was observed late in the day. Flare: C1.7 at 05:47 UTC.

Coronal mass ejections (CMEs)

April 29-30: No fully or partly Earth directed CME observed. A halo CME was observed late on April 29 with ejected material first becoming visible off of the southern limbs and the south pole. This CME most likely had a backsided origin.

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 was 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 May 1. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to unsettled on May 1. 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.

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.


Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is poor. Propagation along long distance north-south paths is fair to poor. Trans Atlantic propagation conditions are monitored every night on 1470 kHz. Dominant stations tonight: Radio Vibración (Venezuela) and CPN Radio (Perú), both with weaker signals compared to the most recent nights. Some of the usual stations from the Caribbean were noted on other frequencies while only a few signals from North America made it across the Atlantic (1510, 1650, 1660 and 1700 kHz)].

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
10599 2004.04.24 2 3 N17W41 0050 CAO area was 0030
at midnight
10600 2004.04.26     N18W58     plage
10601 2004.04.30 7 11 S09W20 0020 BXO formerly region S396
classification was DAO
at midnight, area 0080
10602 2004.04.30 7 6 S14W53 0060 DSO formerly region S395
Total spot count: 16 20
SSN: 46 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)
2004.04 101.2 (1) 59.3 (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]