Solar Terrestrial Activity Report

Last update issued on April 12, 2003 at 01:30 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 1954-2002 (last update January 27, 2003)]
[Archived reports (last update April 7, 2003)]

Recent activity

The geomagnetic field was mostly unsettled on April 11 with a single quiet interval 06-09h UTC. Solar wind speed ranged between 586 and 748 km/sec under the influence of a high speed stream from coronal hole CH31. Wind speed generally decreased throughout the day.

Solar flux measured at 20h UTC on 2.8 GHz was 102.6. The planetary A index was 14 (STAR Ap - based on the mean of three hour interval ap indices: 14.4).
Three hour interval K indices: 33233333 (planetary), 34232333 (Boulder).

The background x-ray flux is at the class B1 level.

At midnight there were 2 spotted regions on the visible disk. Solar flare activity was low. A total of 2 C class events was recorded during the day. A C7.4 flare at 07:30 UTC had its origin behind the southwest limb. A fairly active region at the southeast limb will likely rotate into view today.

Region 10330 developed slowly adding a few spots, some of them with penumbra. The region has become slightly more active and may be capable of producing a minor M class flare. Flare: C1.2 at 04:40 UTC.
Region 10334 developed slowly and has a magnetic delta structure. Despite its complexity this region has been quiet. A minor M class flare is possible.

Coronal mass ejections (CMEs)

April 9-10: No obviously geoeffective CMEs observed.

April 11: A long duration class B3 event beginning just after 13h UTC and peaking near 14h UTC was associated with an erupting filament in the southwest quadrant near the center of the visible disk (and between coronal holes CH31 and CH32). A small CME may have been associated with this event. LASCO C2 and C3 movies are not yet conclusive and will have to investigated further to determine if there was a possibly geoeffective CME.

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 large coronal hole (CH31), mainly in the southern hemisphere, was in a geoeffective position on April 6-9. A huge trans equatorial southern hemisphere coronal hole (CH32) will be in a geoeffective position on April 11-13.

Processed SOHO EIT 284 image at 19:06 UTC on April 11. Any black areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be unsettled to active on April 12-13 when the high speed stream from CH31 dominates the solar wind. A high speed stream from CH32 will likely reach Earth late on April 14 and dominate the solar wind until April 17 resulting in mostly unsettled to minor storm conditions. 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 19, propagation along north-south paths is fair to good, a condition which is likely to persist until at least April 17. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight:  Radio Cristal del Uruguay. Several unidentified stations from Brazil were noted. Brazil provided quite a few stations on other frequencies, like Rádio Farol on 1390 kHz with an unusually good signal.]

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.