Solar Terrestrial Activity Report

Last update issued on April 25, 2003 at 04:30 UTC. Minor update posted at 10:37 UTC.

[Solar and geomagnetic data - last 4 weeks (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update April 2, 2003)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update April 2, 2003)]
[Graphical comparison of cycles 10, 13, 17, 20 and 23 (last update April 2, 2003)]
[Historical solar and geomagnetic data charts 1954-2003 (last update April 13, 2003)]
[Archived reports (last update April 21, 2003)]

Recent activity

The geomagnetic field was unsettled to minor storm on April 24. Solar wind speed ranged between 432 and 585 km/sec under the influence of a high speed stream from coronal hole CH35. This stream dominated the solar wind after about 04h UTC.

Solar flux measured at 20h UTC on 2.8 GHz was 128.3. The planetary A index was 24 (STAR Ap - based on the mean of three hour interval ap indices: 25.8).
Three hour interval K indices: 33454444 (planetary), 33343444 (Boulder).

The background x-ray flux is at the class B5 level.

At midnight there were 8 spotted regions on the visible disk. Solar flare activity was moderate. A total of 9 C and 1 M class events was recorded during the day. Region 10339 behind the northwest limb was very active and produced a C1.0 flare at 02:47, a C7.1 flare at 04:56, a C1.0 flare at 06:37, a C1.4 flare at 08:16, a C8.2 flare at 15:53 and a C1.2 flare at 23:07 UTC.

Region 10336 decayed quickly and could become spotless today.
Region 10337 decayed slowly and was mostly quiet. There is a small positive polarity field with spots southwest of the main (negative polarity) penumbra, otherwise the region has a magnetically simple layout. Flare: C4.5 at 05:38 UTC.
Region 10338 decayed both in the leading in trailing spot sections, however, interesting development was observed in the central section. While the magnetic delta in the leader spots has disappeared a new delta could be forming in the emerging flux in the central part of the region. There is still a delta in the main trailing penumbra. Further minor M class flares are possible. Flares: C1.2 at 02:10, M3.3/1N (associated with a moderate type II and a weak type IV radio sweep) at 12:53 and C1.3 at 22:33 UTC.
Region 10342 decayed slowly and could soon become spotless.
Region 10343 emerged near the northeast limb and is developing slowly.
New region 10344 emerged quickly in the northeast quadrant.
New region 10345 rotated into view at the southeast limb.
New region 10346 rotated into view at the northeast limb.

Comment added at 10:37 UTC on April 25: Changes to spotted groups noted so far today: Region 10345 has been developing quickly and further development could soon create a magnetic delta structure. A delta could be forming near the the eastern edge of the leading penumbra in region 10344 as well. This region is currently developing very quickly and has already doubled its penumbral area to approximately 200 mills. M class flares are now possible from both regions 10344 and 10345. Another development of interest is in region 10342. A new positive polarity field has emerged inside the previously dominant negative polarity field. Several spots have emerged and this region will have to watched closely for further development. Region 10338 is quickly losing its leader spots while gaining spots and penumbral area in the northern central part. Spots could be emerging in a new region at a high latitude at the southeast limb.

Otherwise the geomagnetic field continues to be at minor storm levels with the planetary a index reaching 47 and 49 during the 03-06 and 06-09h UTC intervals respectively.

Coronal mass ejections (CMEs)

April 22 and 24: No obviously geoeffective CMEs observed.

April 23: A partial halo CME was observed in LASCO images after the M5.1 flare in region 10338 early in the day. The major part of the ejected material was observed off of the northwest limb. While Earth will be outside of the reaches of the main body of the CME, there is a possibility of a minor impact from the southern CME flank on April 25.

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 decaying, recurrent coronal hole (CH35) in the southern hemisphere was in a geoeffective position on April 21-22. A recurrent trans equatorial coronal hole (CH36) was in a geoeffective position on April 23-24.

Processed SOHO EIT 284 image at 01:06 UTC on April 25. Any black areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be unsettled to minor storm on April 25 due to a high speed stream from coronal hole CH35. A high speed stream from coronal hole CH36 will likely arrive on April 26 and cause unsettled to minor storm conditions that day with unsettled to active on April 27. Long distance medium wave (AM) band propagation along east-west paths over high and upper middle latitudes is very poor, a condition which is likely to persist until at least April 28. Propagation along north-south paths is poor to fair and will likely be poor to fair until at least April 28. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: Cadena Peruana de Noticias (strong 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.
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 SEC/NOAA. 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.

Solar region Date numbered SEC
Location at midnight Area Classification Comment
10335 2003.04.10     S24W82     plage
10336 2003.04.17 8 3 N14W16 0030 CSO classification was AXX
at midnight, area 0010
10337 2003.04.18 22 20 S14E00 0280 DKO beta-gamma
10338 2003.04.19 25 25 N18W45 0200 EAI beta-gamma-delta
10340 2003.04.21 2   S07E13 0010 AXX spotless
10341 2003.04.21     S10E37     plage
10342 2003.04.22 6 3 N17W35 0020 BXO  
10343 2003.04.23 6 7 N06E45 0040 DSO  
10344 2003.04.24 7 18 N16E39 0030 DSO classification was DAO
at midnight, area 0100
10345 2003.04.24 4 5 S17E74 0030 CSO classification was CAO
at midnight, area 0080
10346 2003.04.24 1 1 N16E74 0050 HSX  
S140 emerged on
    N07W83     plage
S143 emerged on
    N04W41     now spotless
Total spot count: 81 82
SSN: 171 162

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)
2002.03 179.5 98.4 113.3 (-1.3)
2002.04 189.8 120.7 110.5 (-2.9)
2002.05 178.4 120.8 108.8 (-1.7)
2002.06 148.7 88.3 106.2 (-2.6)
2002.07 173.5 99.6 102.7 (-3.5)
2002.08 183.6 116.4 98.7 (-4.0)
2002.09 175.8 109.6 94.6 (-4.1)
2002.10 167.0 97.5 (91.0 predicted, -3.6)
2002.11 168.7 95.0 (85.7 predicted, -5.3)
2002.12 157.2 81.6 (81.3 predicted, -4.4)
2003.01 144.0 79.5 (78.3 predicted, -3.0)
2003.02 124.5 46.2 (73.3 predicted, -5.0)
2003.03 131.4 61.5 (67.6 predicted, -5.7)
2003.04 120.4 (1) 76.8 (2) (62.7 predicted, -4.9)

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 (SEC/NOAA) sunspot number. The official international sunspot number is typically 25-45% less.

This report has been prepared by Jan Alvestad. It is based partly on my own observations and interpretations, and partly on data from sources noted in solar links. All time references are to the UTC day. Comments and suggestions are always welcome.

[DX-Listeners' Club]