Solar Terrestrial Activity Report

Last major update issued on May 29, 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 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 unsettled on May 28. Solar wind speed ranged between 331 and 438 km/sec. A fairly weak disturbance began at about 06h UTC and the interplanetary magnetic field has since been mostly weakly to moderately strongly southwards.

Solar flux measured at 20h UTC on 2.8 GHz was 102.4. The planetary A index was 9 (STAR Ap - based on the mean of three hour interval ap indices: 10.0).
Three hour interval K indices: 20123333 (planetary), 21322233 (Boulder).

The background x-ray flux is at the class B3 level.

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

Region 10618 decayed slightly in the easternmost section while new development was observed in the leading spot section. Positive polarity flux has emerged in three patches at the southern edge of the (mainly negative polarity) leading penumbrae. If this development continues the region could produce minor M class flares. Flare: C4.1 at 10:11 (eastern part), C2.2 at 12:13 (eastern part) and C2.1 at 20:45 UTC (western part of region).

Spotted regions not numbered by NOAA/SEC:
[S407] A new region rotated into view at the southeast limb. The opposite polarity areas appear to be narrowly separated. C flares are possible. Location at midnight: S14E74.
[S408] Just over a day after new corona split coronal hole CH98, a new region emerged in the same area. Location at midnight: N13W12.

Coronal mass ejections (CMEs)

May 26-28: 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 recurrent elongated coronal hole (CH98) in the northern hemisphere will likely be in a geoeffective position on May 25-29. A recurrent trans equatorial coronal hole (CH99) will rotate to a geoeffective position on May 30.

Processed SOHO/EIT 284 image at 01:05 UTC on May 29. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to active on May 29-June 2 due to effects from coronal holes CH98 and CH99.

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 good. Trans Atlantic propagation conditions are monitored every night on 1470 kHz. Dominant station tonight: Radio Cristal del Uruguay. At times both Radio Vibración (Venezuela) and CPN Radio (Perú) were noted. Other frequencies offered more unusual stations, particularly after local sunrise. Radio San Nicolas (Argentina) had a nice signal on 1430 kHz and was accompanied by an unidentified Spanish speaking station. On 1480 kHz there was an unidentified station from Uruguay, while 1520 kHz had an unidentified station from either Argentina or Uruguay. On 1590 kHz there were several interesting unidentified Spanish speaking stations. Before local sunrise a few stations from North America could be heard: 1510 kHz had WWZN Boston and an unidentified station which was probably WLAC. Newfoundland station noted on 590, 620, 740, 750, 800 and 930 kHz while Nova Scotia stations made an appearance on 920 and 960 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
10615 2004.05.16 1   N17W90 0060 HAX rotated out of view
10616 2004.05.16     N07W87     plage
10618 2004.05.20 31 24 S10W44 0310 EAC beta-gamma-delta
classification was EAI
at midnight, area 0260
10620 2004.05.23   S15W29     plage
S406 emerged on
    S14W43     plage
S407 visible on
  5 S14E74 0030 CAO  
S408 emerged on
  1 N13W12 0000 AXX  
Total spot count: 32 30
SSN: 52 60

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 99.9 (1) 71.7 (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]