Solar Terrestrial Activity Report

Last major update issued on April 17, 2004 at 03:45 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 to active on April 16. Solar wind speed ranged between 387 and 466 km/sec, at first under the influence of a "high speed" stream from coronal hole CH89, then after 10h UTC under the influence of a high speed stream from coronal hole CH90.

Solar flux measured at 20h UTC on 2.8 GHz was 96.9. The planetary A index was 12 (STAR Ap - based on the mean of three hour interval ap indices: 14.0).
Three hour interval K indices: 23432332 (planetary), 24432332 (Boulder).

The background x-ray flux is at the class B1 level.

At midnight there were 6 spotted regions on the visible disk. The solar flare activity level was very low. No C class events were recorded during the day.

Region 10591 decayed slowly and quietly. There is still a weak magnetic delta structure at the western edge of the leading penumbra.
Region 10592 decayed and could soon become spotless.
Region 10594 was quiet, however, the single penumbra became asymmetrical.
New region 10595 emerged near the southeast limb.

Spotted regions not numbered by NOAA/SEC:
[S391] This region emerged to the north of region 10595 late on April 16 and currently has the more interesting magnetic layout of the two regions.
[S392] This region was barely visible at the southeast limb near midnight on April 16. Fairly bright emissions can be observed in various images. Early magnetograms has a positive polarity field in the north. C flares are possible.

Coronal mass ejections (CMEs)

April 14-16: No fully or partly Earth directed CME observed. A near constant stream of ejected material has been observed from a source a few days behind the northeast 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 poorly defined coronal hole (CH90) in the northern hemisphere was in a geoeffective position on April 13-14.

Processed SOHO/EIT 284 image at 19:05 UTC on April 16. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to unsettled on April 17-19 with a chance of a few active intervals on April 17 due to a weak high speed stream from coronal hole CH90.

Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is poor to very poor. Propagation along long distance north-south paths is poor. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant stations tonight: Radio Vibración (Venezuela) and Radio Cristal del Uruguay. 1510 WWZN was there again but only with a very weak signal].

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
10589 2004.04.05     N11W88     plage
10591 2004.04.12 6 7 S16W52 0070 DAO beta-gamma-delta
10592 2004.04.13 1 1 S11E19 0020 HSX  
10593 2004.04.14     S20E18     plage
10594 2004.04.14 2 3 N15E40 0070 HAX  
10595 2004.04.16 4 3 S09E68 0040 CSO classification was CRO
at midnight, area 0020
S388 emerged on
    S07E03     plage
S391 emerged on
  2 S04E68 0020 CRO  
S392 visible on
  1 S08E85 0040 HAX  
Total spot count: 13 17
SSN: 53 77

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 98.7 (1) 29.6 (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]