Solar Terrestrial Activity Report

Last major update issued on April 23, 2004 at 03:30 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update April 2, 2004)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update April 2, 2004)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update April 2, 2004)]
[Historical solar and geomagnetic data charts 1954-2003 (last update January 16, 2004)]
[Archived reports (last update April 18, 2004)]

Recent activity

The geomagnetic field was quiet on April 22. Solar wind speed ranged between 363 and 431 km/sec. A weak "high" speed stream from coronal hole CH91 arrived after 05h UTC, however, this did not cause any geomagnetic disturbance even they the interplanetary magnetic field was at times moderately southwards. The geomagnetic influence increased after 02h UTC on April 23.

Solar flux measured at 20h UTC on 2.8 GHz was 117.1. The planetary A index was 4 (STAR Ap - based on the mean of three hour interval ap indices: 5.0).
Three hour interval K indices: 00212211 (planetary), 11213332 (Boulder).

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

At midnight there were 3 spotted regions on the visible disk. The solar flare activity level was moderate. A total of 2 C and 1 M class events was recorded during the day.

Region 10596 decayed slowly. There is only a minor chance of further M class flares. Flare: M1.2/1N at 02:19 UTC.
Region 10597 developed very quickly, particularly after noon. A magnetic delta structure formed and an M class flare is possible while the region is rotating over the southwest limb. Flares: C1.1 at 18:24 and C1.5 at 23:58 UTC.

Spotted regions not numbered or numbered incorrectly by NOAA/SEC:
[S391] This region emerged to the north of region 10595 late on April 16 and developed moderately quickly on April 17. Further development was observed on April 18, while the region decayed slowly on April 19 and lost several small spots. The region decayed further on April 20, 21 and 22 and could soon become spotless. Location at midnight: S06W13.

Coronal mass ejections (CMEs)

April 20-21: No fully or partly Earth directed CME observed. A full halo CME observed on April 20 had a backsided origin. There's no new LASCO data available as SOHO is currently in safe mode.

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

The northernmost extensions of a coronal hole (CH91) in the southern hemisphere were in a geoeffective position on April 19-20. A recurrent coronal hole (CH92) in the northern hemisphere will probably rotate into a geoeffective position on April 23-24.

Processed SOHO/EIT 284 image at 01:05 UTC on April 22. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to unsettled on April 23 due to a weak high speed stream from coronal hole CH91, occasional active intervals are possible. Quiet to unsettled is likely on April 24 becoming unsettled to minor storm on April 25 due to the arrival of a high speed stream from coronal hole CH92.

Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is fair to good and will likely become poorer due to a coronal hole flow. Propagation along long distance north-south paths is poor. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant stations tonight: Radio Vibración (Venezuela) and WLAM Lewsiton ME. Many stations from the easternmost parts of the USA and Canada were noted on other frequencies].

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. When the high speed stream has arrived the color changes to green.
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 NOAA/SEC. 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. SEC active region numbers in the table below and in the active region map above are the historic SEC/USAF numbers.

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 (NOAA/SEC) 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 analysis, and partly on data from some of these solar data sources. All time references are to the UTC day. Comments and suggestions are always welcome.