Solar Terrestrial Activity Report

Last update issued on April 9, 2003 at 02:30 UTC. Minor update posted at 06:24 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 1954-2002 (last update January 27, 2003)]
[Archived reports (last update April 7, 2003)]

Recent activity

The geomagnetic field was quiet to minor storm on April 8. Solar wind speed ranged between 353 and 481 km/sec. A solar wind shock was observed at SOHO at 00:03 UTC. Solar wind speed jumped from 354 to 397 km/sec. The source of this shock is likely a CME observed after an M2 event in region S129 on April 4. The interplanetary magnetic field was moderately southwards after the shock and this caused an increase in geomagnetic disturbance levels to minor storm.

Solar flux measured at 20h UTC on 2.8 GHz was 112.3. The planetary A index was 20 (STAR Ap - based on the mean of three hour interval ap indices: 20.8).
Three hour interval K indices: 23454423 (planetary), 33443423 (Boulder).

The background x-ray flux is at the class B2 level.

At midnight there were 6 spotted regions on the visible disk. Solar flare activity was very low.

Region 10325 decayed slowly and will be rotating out of view today at the northwest limb.
Region 10330 added penumbra to a couple spots east of the dominant penumbra.
Region 10331 decayed slowly and could soon become spotless.
Region 10332 developed slowly and was quiet.

Spotted regions not yet numbered by SEC/NOAA:
[S133] A new region emerged in the southwest quadrant on April 8. The region is developing slowly. Location at midnight: S15W63.
[S134] A new region emerged in the southeast quadrant on April 8. Location at midnight: S18E27.

Comment added at 06:24 UTC on April 9: Region S133 has developed quickly today (currently a DAO region) and has already produced 4 C class events, the latest a C4.7 flare at 06:13 UTC. Minor M class flaring is becoming a possibility. The region is near spotless region 10326 but has emerged southeast of that region.

Coronal mass ejections (CMEs)

April 6-8: 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

The western part of a huge coronal hole (CH31), mainly in the southern hemisphere, was in a geoeffective position on April 6-9. The eastern part of CH31 will rotate to a geoeffective position on April 11-12.

Processed SOHO EIT 284 image at 19:06 UTC on April 8. Any black areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to minor storm on April 9 and unsettled to major storm on April 10-13 when the high speed stream from CH31 dominates the solar wind. Long distance medium wave (AM) band propagation along east-west paths over high and upper middle latitudes is very poor and will likely remain so at least until April 17, propagation along north-south paths is poor but should become fair to good during the next coronal hole related disturbance and remain fairly good until at least April 16. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: none, several stations noted including Radio Cristal del Uruguay and 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.