Solar Terrestrial Activity Report

Last major update issued on May 4, 2004 at 04:15 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update May 3, 2004)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update May 3, 2004)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update May 3, 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 on May 3. Solar wind speed ranged between 339 and 374 km/sec. A low speed stream from coronal hole CH94 arrived at ACE at 00:30 UTC on May 4.

Solar flux measured at 20h UTC on 2.8 GHz was 91.3. The planetary A index was 7 (STAR Ap - based on the mean of three hour interval ap indices: 8.3).
Three hour interval K indices: 21222222 (planetary), 12332222 (Boulder).

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

At midnight there were 4 spotted regions on the visible disk. The solar flare activity level was low. A total of 1 C class event was recorded during the day.

Region 10601 decayed quickly and was mostly quiet. Flare: C1.0 at 13:43 UTC.
Region 10603 decayed and had only two tiny spots left at midnight, the region is likely to become spotless today.
New region 10604 emerged near the southeast limb on May 2 and was numbered the next day by SEC. The region developed slowly on May 3.

Spotted regions not numbered by NOAA/SEC:
[S398] This region emerged on May 3 in the southeast quadrant at the southeastern edge of coronal hole CH94. Polarities are intermixed and the region could become interesting if development continues. Location at midnight: S12E13.

Coronal mass ejections (CMEs)

May 1-3: 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 large trans equatorial coronal hole (CH94) - the recurrent eastern part of what was CH88 during the previous rotation - was in a geoeffective position on May 1 - May 4.

Processed SOHO/EIT 284 image at 01:05 UTC on May 4. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to active on May 4-7 due to a high speed stream from coronal hole CH94. Occasional minor storm intervals are possible on May 6-7.

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 to fair. Propagation along long distance north-south paths is fair. Trans Atlantic propagation conditions are monitored every night on 1470 kHz. Dominant stations tonight: Radio Vibración (Venezuela) before 02:30 UTC, then CPN Radio (Perú) with an unusually strong signal. The two other usual Peruvians, Radio Santa Rosa on 1500 and La Peruanisima on 1590 kHz had about the best signals I've ever heard from them. Several North American stations had nice signals prior to 03h UTC, at which time these stations became weaker as the current coronal hole disturbance increased its influence. WWZN 1510, WBBR 1130, CJYQ 930 and CHNS 960 were the strongest stations].

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     N17W80     plage
10601 2004.04.30 14 11 S10W61 0200 DSO classification was DAO
at midnight
10603 2004.05.01 5 2 S16W63 0040 BXO area was 0000
at midnight
10604 2004.05.03 1 7 S19E52 0030 HSX formerly region S397
classification was CAO
at midnight, area 0040
S398 emerged on
  8 S12E13 0030 DRO beta-gamma
Total spot count: 20 28
SSN: 50 68

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)
2003.04 126.4 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 58.1 (-1.4)
2003.11 140.8 67.3 (56.5 predicted, -1.6)
2003.12 114.9 46.5 (53.5 predicted, -3.0)
2004.01 114.1 37.2 (49.1 predicted, -4.4)
2004.02 107.0 46.0 (44.8 predicted, -4.3)
2004.03 112.0 48.9 (42.1 predicted, -2.7)
2004.04 101.2 39.3 (40.0 predicted, -2.1)
2004.05 94.3 (1) 5.0 (2) (36.8 predicted, -3.2)

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]