Solar Terrestrial Activity Report

Last update issued on April 22, 2003 at 02:30 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 21. Solar wind speed ranged between 481 and 579 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 125.8. The planetary A index was 21 (STAR Ap - based on the mean of three hour interval ap indices: 21.4).
Three hour interval K indices: 44543333 (planetary), 33443333 (Boulder).

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

At midnight there were 7 spotted regions on the visible disk. Solar flare activity was moderate. A total of 3 C and 1 M class events was recorded during the day.

Region 10335 reemerged early in the day with a few spots, decay was observed during the latter half of the day and the region could soon become spotless again.
Region 10336 was quiet. The single penumbra is about to split into two penumbrae.
Region 10337 developed slowly in the area just south of the main penumbra. A weak magnetic delta structure has redeveloped at the southern edge of that penumbra. Minor M class flares are possible. Flares: C2.3 at 15:59 and C1.8 at 21:47 UTC.
Region 10338 developed significantly in and near the main trailing penumbra. There is a magnetic delta structure in the eastern part of that penumbra, this is where the negative polarity trailing spot is bordering the positive polarity field of region S139. Further minor M class flares are possible. Flare: M2.8/1N at 13:07 UTC. This flare was associated with strong type II and IV radio sweeps and a partial halo CME.
Region 10339 developed slowly with most of the development occurring in and near the southernmost penumbra. This mainly negative polarity penumbra increased its area and had a couple of positive polarity spots emerge at its northern edge. This development has created a weak magnetic delta structure and the region may be capable of producing minor M class flares. Flare: C1.3 at 19:35 UTC.
New region 10340 emerged in the southeast quadrant early in the day and appeared to be decaying late in the day. 
New region 10341 rotated into view at the southeast limb.

Coronal mass ejections (CMEs)

April 19-20: 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 and cause active to minor geomagnetic storm 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 (CH34) in the northern hemisphere was in a geoeffective position on April 18-19. A recurrent coronal hole (CH35) in the southern hemisphere was in a geoeffective position on April 21-22.

Processed SOHO EIT 284 image at 19:06 UTC on April 18. [With SOHO EIT in CCD bakeout mode until April 22, the next processed EIT 284 image will likely not be posted until April 23.] Any black areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be unsettled to active on April 22 due to a high speed stream from coronal hole CH34. 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: none, Radio Vibración (Venezuela) and Radio Cristal del Uruguay were observed at times.]

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.