Solar Terrestrial Activity Report

Last major update issued on April 18, 2005 at 04:15 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update April 4, 2005)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update April 4, 2005)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update April 4, 2005)]
[Historical solar and geomagnetic data charts 1954-2004 (last update February 1, 2005)]
[Archived reports (last update April 15, 2005)]

Recent activity

The geomagnetic field was quiet on April 17. Solar wind speed ranged between 355 and 411 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 83.6. The planetary A index was 5 (STAR Ap - based on the mean of three hour interval ap indices: 5.1).
Three hour interval K indices: 12211111 (planetary), 23202321 (Boulder).

The background x-ray flux is at the class A5 level.

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

Region 10752 added a few trailing spots and was mostly quiet. Flare: C1.2 at 12:24 UTC.
Region 10754 decayed early in the day, then new flux emerged in the center of the region and several spots developed.
New region 10755 rotated partly into view at the southeast limb. It is uncertain if this region has trailing spots or if there is another, more active, region trailing it. Flares: C3.3 at 01:44 and C4.6 at 21:07 UTC.

Coronal mass ejections (CMEs)

April 15-17: No obvious fully or partly Earth directed CMEs were 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 (CH158) in the southern hemisphere was in an Earth facing position on April 15-17. A coronal hole (CH159) in the northern hemisphere will likely be in an Earth facing position on April 19.

Processed SOHO/EIT 284 image at 01:06 UTC on April 18. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to become unsettled to active by the end of April 18. These conditions should continue on April 19-20 under the influence of a high speed stream from CH158. Quiet to unsettled is likely on April 21 becoming quiet to active on April 22-23 due to effects from CH159.

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.

Propagation

Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is poor. Propagation along long distance north-south paths is fair. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant station tonight: Radio Vibración (Venezuela). Local sunrise conditions near 04h UTC were good with lots of stations from Venezuela, Colombia and Ecuador audible. From North America the usual Newfoundland stations had the best signals.

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.