Solar Terrestrial Activity Report

Last update issued on April 29, 2003 at 02:20 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 28, 2003)]

Recent activity

The geomagnetic field was quiet to minor storm on April 28. Solar wind speed ranged between 400 and 546 km/sec under the influence of a high speed stream from coronal hole CH36 for the first half of the day. A solar wind disturbance was observed at SOHO at 18:40 UTC with a sudden increase in solar wind speed from 414 to 456 km/sec and a sudden increase in the total field of the interplanetary magnetic field. This disturbance may have been associated with the arrival of the leading edge of the full halo CME observed on April 25 from an origin near the northeast limb.

Solar flux measured at 20h UTC on 2.8 GHz was 152.2. The planetary A index was 20 (STAR Ap - based on the mean of three hour interval ap indices: 20.6).
Three hour interval K indices: 35453322 (planetary), 35342212 (Boulder).

The background x-ray flux is at the class B5 level.

At midnight there were 9 spotted regions on the visible disk. Solar flare activity was low. A total of 8 C class events was recorded during the day. Region 10338 behind the northwest limb produced a C1.1 flare at 00:53, a C1.5 flare at 10:17, a C1.3 flare at 14:17, a C2.0 flare at 17:19 and a C1.8 flare at 21:30 UTC.

Region 10337 decayed slowly and was mostly quiet. Flares: C4.4 (long duration event peaking) at 04:36 and C2.1 at 15:46 UTC.
Region 10344 decayed slowly with most of the decay occurring in the trailing penumbra. The region is simply structured with no intermixing of polarities. Flare: C3.3 at 18:18 UTC.
Region 10345 developed slowly adding a few spots. The opposite polarity fields are not as well separated as they were a day ago and the flare potential is increasing slowly.
Region 10346 added a couple of small spots and was otherwise quiet and stable.
Region 10348 did not change much apart from elongating slowly.
Region 10349 developed quickly and currently has the largest penumbral coverage of all visible regions. The region still has a fairly simple magnetic layout and at this time appears unlikely to produce M class flares.

Spotted regions not yet numbered by SEC/NOAA:
[S145] A new region emerged on April 26 south of region 10337 and developed slowly on April 27. Location at midnight: S20W53.
[S146] A new region emerged early in the day on April 28 in the southwest quadrant. The region has developed quickly but is so far simply structured. Location at midnight: S12W29.
[S147] A new region emerged in the southwest quadrant near the central meridian on April 28. Location at midnight: S17W06.

Coronal mass ejections (CMEs)

April 26-28: 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 recurrent coronal hole (CH37) in the southern hemisphere was probably in a geoeffective position on April 26-27. A recurrent coronal hole (CH38) in the southern hemisphere will likely rotate into a geoeffective position on May 2-3.

Processed SOHO EIT 284 image at 19:06 UTC on April 28. Any black areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to active April 29 - May 1. 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 May 1. Propagation along north-south paths is fair to poor and is likely to remain that way until May 1. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: Radio Cristal del Uruguay, an unidentified station from Brazil was observed as well.]

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.