Solar Terrestrial Activity Report

Last update issued on April 24, 2003 at 03:10 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 quiet to minor storm on April 23. Solar wind speed ranged between 454 and 565 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 132.8. The planetary A index was 18 (STAR Ap - based on the mean of three hour interval ap indices: 17.9).
Three hour interval K indices: 24543333 (planetary), 14433333 (Boulder).

The background x-ray flux is at the class B4 level.

At midnight there were 6 spotted regions on the visible disk. Solar flare activity was high. A total of 6 C and 2 M class events was recorded during the day. Region 10339 at the northwest limb produced a C2.2 flare at 03:22, a C3.4 flare at 05:36, a C1.1 flare at 09:17 and a C5.8 flare at 12:13 UTC.

Region 10336 decayed slightly in the main penumbral areas. A few new spots emerged.
Region 10337 developed slowly and quietly with the large penumbra adding further to its size. There is a small positive polarity field with spots southwest of the main (negative polarity) penumbra, otherwise the region has a magnetically simple layout.
Region 10338 lost some of its small spots while the general layout of the region did not change much. There are still two magnetic delta structures, the major one being in the largest trailing penumbra. Minor M class flares are possible. Flares: C2.2 at 00:50, M5.1/1N (associated with a moderate type II and a weak type IV radio sweeps) at 01:06, C1.9 at 10:35 and an M2.0/1F at 15:56 UTC.
Region 10342 decayed slightly and could soon become spotless.
New region 10343 emerged near the northeast limb and is developing slowly.

Spotted regions not yet numbered by SEC/NOAA:
[S143] A new region emerged on April 23 in the northwest quadrant south of region 10338. Location at midnight: N04W28.

Coronal mass ejections (CMEs)

April 21: A rather faint partial halo CME was observed in LASCO images after the M2.8 flare in region 10338 at 13:07 UTC. No obvious traces of ejected material were observed below the south pole or off of the southeast limb. The CME could reach Earth on April 23 or 24 and cause active geomagnetic conditions.

April 22: 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 19:06 UTC on April 23. Any black areas on the solar disk are likely coronal holes.


The geomagnetic field is expected to be quiet to active on April 24 and unsettled to active 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 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: Radio Cristal del Uruguay.]

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     S24W69     plage
10336 2003.04.17 6 7 N13W03 0060 CSO  
10337 2003.04.18 19 18 S14E15 0310 DKO beta-gamma
10338 2003.04.19 31 24 N18W32 0170 EAI beta-gamma-delta
10339 2003.04.20 5   N16W84 0060 CSO rotated out of view
10340 2003.04.21 2   S06E30 0010 HSX now spotless
10341 2003.04.21 1   S10E50 0010 AXX now spotless
10342 2003.04.22 4 4 N18W21 0020 AXX  
10343 2003.04.23 4 6 N06E60 0030 CRO classification was DSO
at midnight
S140 emerged on
    N07W70     plage
S143 emerged on
  3 N04W28 0010 BXO  
Total spot count: 72 62
SSN: 152 122

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)
2003.04 120.1 (1) 71.3 (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]