Solar Terrestrial Activity Report

Last update issued on April 30, 2003 at 03:20 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 29. Solar wind speed ranged between 358 and 629 km/sec. Following the arrival of a CME based disturbance at 18:40 UTC on April 28, the interplanetary magnetic field continued mostly northwards during the first half of the day. Then from noon until 22h UTC the IMF swung gradually stronger southwards causing an increase in the geomagnetic disturbance level to minor storm. Another disturbance, this time a high speed stream from coronal hole CH37, may have arrived after 19h UTC.

Solar flux measured at 20h UTC on 2.8 GHz was 155.1. The planetary A index was 20 (STAR Ap - based on the mean of three hour interval ap indices: 21.4).
Three hour interval K indices: 23214455 (planetary), 23224544 (Boulder).

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

At midnight there were 8 spotted regions on the visible disk. Solar flare activity was moderate. A total of 13 C and 1 M class events was recorded during the day. Region 10338 behind the northwest limb produced a C1.4 flare at 01:15, a C1.3 flare at 08:59 and a C1.6 flare at 09:48 UTC.

Region 10337 decayed further losing most of its small spots. Flares: C1.0 at 00:25 and M1.1/1F at 04:59 UTC.
Region 10344 decayed slowly losing some penumbral area in the trailing spot section. The region was quiet and is simply structured.
Region 10345 did not change much and was mostly quiet. The proximity of region 10349 could cause activity to increase if region 10349 begins to produce M class flares. Flare: C1.0 at 07:51 UTC.
Region 10346 was quiet and stable.
Region 10348 elongated further and began to decay. The region could soon become spotless.
Region 10349 developed impressively and has major flare potential. While the magnetic field layout still is not very complex, one interesting development is the emergence of a positive polarity field at the southeastern edge of the very strong negative polarity field. Further development in this area will cause a magnetic delta structure to develop. Flares: C1.1 at 06:59, C2.1 at 10:57, C1.7 at 16:59, C1.5 at 19:36, C1.2 at 19:59, C1.7 at 21:19, C1.4 at 22:42 and C3.1 at 23:49 UTC.

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. Slow decay was observed on April 29. Location at midnight: S21W66.
[S146] A new region emerged early in the day on April 28 in the southwest quadrant. The region developed quickly on April 28 and slowly on April 29. Location at midnight: S10W43.

Coronal mass ejections (CMEs)

April 27-29: 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 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 13:06 UTC on April 29. Any black areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be unsettled to minor storm on April 30, possibly with a major storm interval, and quiet to active on May 1-2. 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 2. Propagation along north-south paths is fair to poor and is likely to remain that way until May 2. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: Radio Cristal del Uruguay early on, then Cadena Peruana de Noticias.]

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.