Solar Terrestrial Activity Report

Last update issued on April 27, 2003 at 04:10 UTC.

[Solar and geomagnetic data - last 4 weeks (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update 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 26. Solar wind speed ranged between 415 and 483 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 143.7. The planetary A index was 15 (STAR Ap - based on the mean of three hour interval ap indices: 15.6).
Three hour interval K indices: 42433333 (planetary), 32422323 (Boulder).

The background x-ray flux is at the class C1 level.

At midnight there were 10 spotted regions on the visible disk. Solar flare activity was high. A total of 7 C and 4 M class events was recorded during the day.

Region 10337 decayed slowly. The large penumbra appears to be splitting into two penumbrae.
Region 10338 decayed in the trailing spot section and lost all spots there. With polarities thoroughly mixed in the northern central section and a magnetic delta structure in that part of the region, 10338 was very unstable and produced many flares. Flaring is likely to continue until the delta disappears or the region rotates over the northwest limb today and tomorrow. Flares: M2.1 at 00:58, M2.1 at 03:06, major impulsive M7.0 at 08:07, C1.4 at 14:30, C6.0 (with an associated moderate type II radio sweep) at 14:46, C1.3 at 15:43, C5.5 at 16:35, C5.1 at 17:58, C3.8 at 19:41, M2.5 at 23:40 and C1.2 at 23:57 UTC.
Region 10342 developed early in the day, then began to decay. Flare: C6.6/1F at 01:51 UTC.
Region 10344 developed further. The leading positive polarity field extended into the northwestern part of the trailing negative polarity and this caused a magnetic delta structure to develop. While the delta is not yet strong, the flare potential is increasing and M class flares are possible.
Region 10345 decayed slightly but still appears to have a weak delta in the northwestern part of the southern penumbra.
Region 10346 was quiet and stable.
New region 10347 emerged west of region 10345.
New region 10348 emerged in hot plage at a high latitude in the southeast quadrant.
New region 10349 rotated into view on April 25 and was numbered the next day. The region is developing quickly and could soon begin producing flares.

Spotted regions not yet numbered by SEC/NOAA:
[S145] A new region emerged on April 26 south of region 10337. Location at midnight: S20W26.

Coronal mass ejections (CMEs)

April 24: No obviously geoeffective CMEs observed.

April 25: A large CME was observed mainly off of the northeast limb early in the day after an M class event in region 10346. LASCO C3 images indicate that this may have been a full halo CME. In that case a fairly weak impact could be expected on April 28.

April 26: Only limited LASCO data available, no CME analysis possible at this time.

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 (CH36) was in a geoeffective position on April 23-24. A recurrent coronal hole (CH37) in the southern hemisphere could rotate into a geoeffective position on April 26-27, CH37 has decreased in size over the last rotation losing its westernmost extensions. CH37 may be located too far to the south to cause any notable geomagnetic disturbance.

Processed SOHO EIT 284 image at 01:06 UTC on April 27. 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 27 due to a high speed stream from CH36 and quiet to active on April 28-30. 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 poor and will likely become poor to fair April 27-30. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: Radio Vibración (Venezuela) with Cadena Peruana de Noticias observed at times.]

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.