Solar Terrestrial Activity Report

Last update issued on April 23, 2003 at 04:20 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 active on April 22. Solar wind speed ranged between 481 and 627 km/sec under the influence of a high speed stream from coronal hole CH34.

Solar flux measured at 20h UTC on 2.8 GHz was 132.4. The planetary A index was 22 (STAR Ap - based on the mean of three hour interval ap indices: 22.6).
Three hour interval K indices: 44443334 (planetary), 44433333 (Boulder).

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

At midnight there were 7 spotted regions on the visible disk. Solar flare activity was low. A total of 4 C class events was recorded during the day. Region 10338 was the source of a major M5.1 flare at 01:06 UTC on April 23.

Region 10336 was quiet and completed the split into two penumbrae.
Region 10337 decayed with the positive magnetic polarity field weakening. The main penumbra increased its size further but with the region being less complex than a day ago the likelihood of M class flares has decreased.
Region 10338 developed quickly both in  the leading and trailing spot sections. The magnetic delta structure in the trailing penumbra has become stronger and a new delta has developed in a leading penumbra. Major flares are possible. Flares: C1.1 at 08:13, C2.3 at 16:17 and C4.0 at 20:11 UTC.
Region 10339 decayed slowly and will soon be rotating over the northwest limb. Flare: C3.0 at 21:11 UTC.
Region 10340 developed early in the day, then began to decay slowly. 
Region 10341 developed slowly early in the day, then decayed and had only a single small spots left at midnight.
New region 10342 was finally numbered by SEC having first been spotted on April 16 and then become spotless and reemerged several times afterwards. The positive polarity area of this region borders region 10338.

Coronal mass ejections (CMEs)

April 20 and 22: No obviously geoeffective CMEs observed.

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.

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

Processed SOHO EIT 284 image at 22:13 UTC on April 22. Any black areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to active on April 23 and unsettled to active on April 24-25 due to a high speed stream from coronal hole CH35. 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 26. Propagation along north-south paths is poor to fair and should remain poor to fair until at least April 26. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: Radio Vibración (Venezuela) and Radio Cristal del Uruguay.]

Coronal holes (1)	Coronal mass ejections (2)	M and X class flares (3)

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.

Monthly solar cycle data

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.