Solar Terrestrial Activity Report

Last major update issued on April 14, 2004 at 03:25 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 1954-2003 (last update January 16, 2004)]
[Archived reports (last update April 5, 2004)]

Recent activity

The geomagnetic field was quiet on April 13. Solar wind speed ranged between 406 and 461 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 93.1. The planetary A index was 6 (STAR Ap - based on the mean of three hour interval ap indices: 7.5).
Three hour interval K indices: 22222222 (planetary), 22223221 (Boulder).

The background x-ray flux is at the class A8 level.

At midnight there were 5 spotted regions on the visible disk. The solar flare activity level was very low. No C class events were recorded during the day.

Region 10588 decayed slowly and will rotate over the southwest limb today.
Region 10591 decayed further and could soon become spotless.
New region 10592 emerged near the southeast limb on April 12 and was numbered by SEC the next day.

Spotted regions not numbered by NOAA/SEC:
[S387] A new region emerged quickly in the southeast quadrant just east of region 10591 on April 12. Moderately quick development was observed on April 13. There is not much separating the leading negative polarity field of this region from the trailing positive polarity area of region 10591. Location at midnight: S16W12.
[S390] This region rotated partly into view at the northeast limb on April 13. Location at midnight: N14E83.

Coronal mass ejections (CMEs)

April 12-13: No fully or partly Earth directed CME observed.
April 11: A fast, full halo CME was observed after a C9 event in region S380 early in the day. This CME is likely to impact Earth on April 14. Another full halo CME was observed near noon, its source was probably a few days behind the northwest limb.

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 very small coronal hole (CH89) in the southern hemisphere was in a possibly geoeffective position on April 12 and could cause a weak geomagnetic disturbance on April 15. A poorly defined coronal hole (CH90) in the northern hemisphere could be in a geoeffective position on April 13-14.

Processed SOHO/EIT 284 image at 19:05 UTC on April 13. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet early on April 14. A likely CME impact during the first half of the day could cause active interval. Quiet to unsettled is likely on April 15 while a weak high speed stream from coronal hole CH90 could arrive on April 16 and cause some unsettled and active intervals that day and on April 17.

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 poor to fair. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: Radio Cristal del Uruguay before 02h UTC, then Radio Vibración (Venezuela) with a fairly strong signal. 590 VOCM and CJYQ on 930 kHz had good signals].

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
10588 2004.04.01 1 1 S13W80 0060 HSX area was 0050
at midnight,
10589 2004.04.05     N11W49     plage
10591 2004.04.12 9 5 S16W13 0050 CAO location was S15W16
at midnight, area 0020,
classification CRO
10592 2004.04.13 1 1 S12E59 0020 HSX formerly region S389
S380 emerged on
    S17W78     plage
S383 emerged on
    S19W72     plage
S385 emerged on
    S17W56     plage
S387 emerged on
  16 S16W12 0110 DAI  
S388 emerged on
    S07E42     plage
S390 visible on
  2 N14E83 0040 CSO  
Total spot count: 11 25
SSN: 41 75

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 99.3 (1) 23.6 (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]