Solar Terrestrial Activity Report

Last major update issued on April 7, 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 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 6. Solar wind speed ranged between 451 and 633 km/sec under the influence of a high speed stream from coronal hole CH88. Solar wind speed peaked between 13 and 14h UTC and has since decreased slowly.

Solar flux measured at 20h UTC on 2.8 GHz was 101.4. The planetary A index was 21 (STAR Ap - based on the mean of three hour interval ap indices: 22.0).
Three hour interval K indices: 44444232 (planetary), 54443333 (Boulder).

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

At midnight there were 5 spotted regions on the visible disk. The solar flare activity level was moderate. A total of 1 C and 1 M class events was recorded during the day.

Region 10587 decayed quickly and quietly.
Region 10588 was quiet and stable (this region has been virtually unchanged since it rotated into view and has not changed even if the hot region just south of it has changed a lot).

Spotted regions not numbered by NOAA/SEC:
[S380] This region emerged on April 3 just south of region 10588. The region developed moderately quickly on April 4 and slowly on April 5. Slow decay was observed on April 6 after an M2 flare. The magnetic delta structure disappeared, however, this is a reversed polarity region and the region could quickly become more complex again.. Another minor M class flare is possible. Location at midnight: S16E12. Flares: C1.0 at 05:35 and a M2.4 long duration event peaking at 13:28 UTC. The latter event was associated with a full halo CME.
[S383] This region emerged to the southeast of region S380 on April 5 and developed slowly on April 6. Location at midnight: S19E19.
[S384] A new region emerged to the west of region 10587 on April 6. Location at midnight: S09W58.

Coronal mass ejections (CMEs)

April 4: No fully or partly Earth directed CME observed.
April 5: A partial halo CME was observed after 06h UTC in LASCO images. The main ejecta was off of the southeast limb, however, a faint front was seen around most of the visible disk. A weak solar wind shock is possible on April 8.
April 6: A full halo CME was observed in LASCO images after an M2.4 event in region S380 peaking at 13:28 UTC. This CME is likely to reach Earth near noon on April 8.

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

An elongated, recurrent trans equatorial coronal hole (CH88) was a geoeffective position on April 1-7. This coronal hole is best defined in the easternmost part.

Processed SOHO/EIT 284 image at 01:06 UTC on April 7. The darkest areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to unsettled on April 7. The arrival of at least one CME on April 8 will likely cause unsettled to major storm conditions that day and early on April 9. The high speed stream from coronal hole CH88 is expected to resume after the passage of the CME with unsettled to minor storm likely on April 9 becoming quiet to active on April 10.

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 to fair. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant stations tonight: Radio Vibración with a strong signal before 03h UTC, then CPN Radio (Perú) began to dominate. WWZN Boston on 1510 kHz was heard again, only a few other weak signals from North America were observed].

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
10582 2004.03.25 1   N14W96 0060 HSX rotated out of view
10585 2004.03.27     S15W79     plage
10587 2004.03.28 7 10 S13W45 0070 CAO  
10588 2004.04.01 15 1 S13E13
0130 DAI SEC spot count,
area and classification
include region S380
10589 2004.04.05 3   N10E43 0020 AXX spotless
S380 emerged on
  14 S16E12 0110 DAI split off from region
S382 emerged on
    N15W80     plage
S383 emerged on
  3 S19E19 0010 CRO  
S384 emerged on
  3 S09W58 0020 CRO  
Total spot count: 26 31
SSN: 66 81

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)
2004.04 107.9 (1) 16.2 (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]