Solar Terrestrial Activity Report

Last update issued on April 21, 2003 at 04:05 UTC. Minor update posted at 16:14 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 active on April 20. Solar wind speed ranged between 462 and 563 km/sec. A high speed stream from coronal holes CH33 and CH34 reached ACE at about 21:30 UTC.

Solar flux measured at 20h UTC on 2.8 GHz was 118.5. The planetary A index was 16 (STAR Ap - based on the mean of three hour interval ap indices: 16.1).
Three hour interval K indices: 44423324 (planetary), 34423423 (Boulder).

The background x-ray flux is at the class B3 level.

At midnight there were 6 spotted regions on the visible disk. Solar flare activity was low. A single C class event was recorded during the day.

Region 10334 was quiet and stable.
Region 10336 was mostly quiet and unchanged.
Region 10337 developed slowly in the southern part with a new penumbra forming. Some of the small positive polarity spots observed one day earlier at the southeastern edge of the largest negative penumbra, had disappeared by midnight. 
Region 10338 developed slowly. Magnetograms indicate that a new bipolar region emerged just ahead of 10338 and this region will be split off if the current polarity field layout persists.
New region 10339 emerged in the northwest quadrant on April 19 and was numbered one day later. The region has been developing slowly and has some polarity intermixing. C class flares are possible and, if further development occurs, a minor M class flare may be possible. Flare: C4.4 at 19:23 UTC.

Spotted regions not yet numbered by SEC/NOAA:
[S139] A new region emerged in the northeast quadrant on April 16, then became spotless before reemerging on April 19. All spots disappeared before noon April 20. Then during the last hours of April 20 quite a few spots reemerged, particularly in the trailing negative polarity field. The leading positive polarity field of this region is bordering the trailing negative polarity field of region 10338. Location at midnight: N17E17.

Comment added at 16:14 UTC on April 21, 2003: Region 10338 developed a magnetic delta structure in the southeastern part of the largest penumbra. This development was the likely cause of an M2.8/1N flare at 13:07 UTC. A fast CME was associated with this event, as were strong type II and IV radio sweeps. The CME could likely impact Earth between 09h UTC on April 23 and 04h UTC on April 24 and cause active to minor geomagnetic storm conditions.

Otherwise a small region has rotated into view at the southeast limb while region 10335 has reemerged with a couple of spots. Region 10337 is developing slowly and was the source of a C2.3 flare at 15:59 UTC.

The geomagnetic field has been unsettled to minor storm as the high speed stream from coronal hole CH34 continues to dominate the solar wind.

Coronal mass ejections (CMEs)

April 18-20: No obviously geoeffective CMEs observed.

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 small coronal hole (CH33) in the southern hemisphere was in a geoeffective position on April 18. 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 is likely to rotate to 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 21, the next processed EIT 284 image will likely not be posted until April 22.] Any black areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be unsettled to active conditions on April 21-22 due to a high speed stream from coronal hole CH0034. Long distance medium wave (AM) band propagation along east-west paths over high and upper middle latitudes has improved to poor. Poor to very poor condition are likely over the next few days. Propagation along north-south paths is poor to fair and is likely to vary between poor and fair until at least April 23. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: Radio Vibración (Venezuela).]

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.