Solar Terrestrial Activity Report

Last major update issued on May 25, 2004 at 03:50 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 May 18, 2004)]

Recent activity

The geomagnetic field was quiet to active on May 24. Solar wind speed ranged between 435 and 539 km/sec under the influence of a high speed stream from coronal hole CH97.

Solar flux measured at 20h UTC on 2.8 GHz was 105.2. The planetary A index was 11 (STAR Ap - based on the mean of three hour interval ap indices: 12.8).
Three hour interval K indices: 32433222 (planetary), 32433332 (Boulder).

The background x-ray flux is at the class B2 level.

At midnight there were 6 spotted regions on the visible disk. The solar flare activity level was low. A total of 2 C class events was recorded during the day.

Region 10613 decayed slowly and quietly, the region will rotate over the southwest limb early on May 26.
Region 10615 decayed slowly. Flare: C1.0 at 22:48 UTC.
Region 10618 developed quickly in the leading spot section while some decay was observed in the trailing spot section. At the end of the day no magnetic delta structures were present, however, in several parts of the region there is only minor separation between the opposite polarities. A minor M class flare is possible. Flare: C4.6 at 11:04 UTC.
Region 10619 decayed slowly and quietly.
Region 10620 decayed slowly and quietly.

Spotted regions not numbered by NOAA/SEC:
[S406] This region emerged just south of region 10618 on May 24. Location at midnight: S16E11.

Coronal mass ejections (CMEs)

May 22-23: No fully or partly Earth directed CME observed.
May 24: A CME was observed off the north pole and northern limbs late in the day following a filament eruption across the central meridian in the northern hemisphere. This eruption was in progress at 20:00 UTC. It is not yet clear if this CME was partially Earth directed or not.

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, poorly defined coronal hole (CH97) in the northern hemisphere was in a geoeffective position on May 19-20. An elongated coronal hole (CH98) in the northern hemisphere will likely be in a geoeffective position on May 25-29.

Processed SOHO/EIT 284 image at 01:05 UTC on May 25. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to unsettled on May 25-27 and quiet to active on May 28-June 1 due to effects from coronal hole CH98.

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 station tonight: Radio Vibración (Venezuela). On other frequencies only a few North American stations were noted with WWZN Boston on 1510 kHz with the best signal. Several stations from Brazil were noted with the strongest signals on 740 and 980 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
10613 2004.05.13 1 1 S09W68 0060 HAX  
10615 2004.05.16 2 2 N17W40 0060 HSX  
10616 2004.05.16     N07W35     plage
10617 2004.05.17     S11W88     plage
10618 2004.05.20 57 52 S10E13 0410 FKI beta-gamma
10619 2004.05.23 3 5 S09W50 0030 CSO  
10620 2004.05.23 5 4 S15E21 0040 CSO classification was HRX
at midnight, area 0020
S406 emerged on
  1 S16E11 0010 AXX  
Total spot count: 68 65
SSN: 118 125

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 99.5 (1) 61.9 (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]