Solar Terrestrial Activity Report

Last update issued on May 21, 2003 at 03:10 UTC.

[Solar and geomagnetic data - last 4 weeks (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update May 1, 2003)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update May 1, 2003)]
[Graphical comparison of cycles 10, 13, 17, 20 and 23 (last update May 1, 2003)]
[Historical solar and geomagnetic data charts 1954-2003 (last update April 13, 2003)]
[Archived reports (last update May 19, 2003)]

Recent activity

The geomagnetic field was quiet to unsettled on May 20. Solar wind speed ranged between 379 and 454 km/sec under the influence of a weak high speed stream from coronal hole CH39.

Solar flux measured at 20h UTC on 2.8 GHz was 117.1. The planetary A index was 12 (STAR Ap - based on the mean of three hour interval ap indices: 13.6).
Three hour interval K indices: 33333233 (planetary), 33332323 (Boulder).

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

At midnight there were 4 spotted regions on the visible disk. Solar flare activity was low. A total of 4 C class events were recorded during the day.

Region 10357 decayed in the trailing spot section. New flux emerged northeast of the leader spot and a few new spots formed.
Region 10362 became more complicated with the emergence of new negative polarity flux at the northern edge of the positive trailing polarity flux. A new penumbra developed in this area and this penumbra has spots of both polarities. While the region has not yet displayed much activity, there is an increasing potential for a minor M class flare. Flare: C1.4 at 19:31 UTC.
Region 10364 decayed substantially, particularly in the leading spot section. Flares: C1.1 at 02:11, C1.0 at 04:57 and C1.0 at 10:45 UTC.
New region 10365 rotated into view on May 19 and was numbered by SEC the next day. The region developed slightly in the northern section during the day.

Coronal mass ejections (CMEs)

May 18 and 20: No obviously geoeffective CMEs observed.

May 19: A filament eruption in the northeast quadrant north of coronal hole CH40 began at approximately 08:20 UTC and peaked two hours later. A partial halo CME was observed later on in LASCO C3 images with most of the ejected material visible above the northeast limb and the north pole. This CME will probably not reach Earth.

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 trans equatorial coronal hole (CH40) was in a geoeffective position on May 19-21.

Processed SOHO EIT 284 image at 19:06 UTC on May 20. Any black areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to active on May 21. A high speed stream from coronal hole CH40 is expected to influence the field from late on May 21 until May 24 and cause unsettled to active conditions with a possibility of occasional minor storm intervals. Long distance medium wave (AM) band propagation along east-west paths over high and upper middle latitudes is very poor and will likely be very poor until at least May 25. Propagation along north-south paths is poor but should improve to fair over the next few days. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: Cadena Peruana de Noticias with a weak 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 30-50% 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.