Solar Terrestrial Activity Report

Last major update issued on April 27, 2005 at 04:10 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 26. Solar wind speed ranged between 376 and 466 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 90.9. The planetary A index was 5 (STAR Ap - based on the mean of three hour interval ap indices: 4.6).
Three hour interval K indices: 10112221 (planetary), 11012121 (Boulder).

The background x-ray flux is at the class B1 level.

At midnight there were 2 spotted regions on the visible solar disk. The solar flare activity level was low. A total of 4 C class events was recorded during the day.

Region 10756 developed moderately quickly adding spots and penumbral area. The region remains complex with both polarities present within the single large penumbra. The region is capable of producing M class flares. Flares: C1.2 at 02:25, C5.3 at 04:41, C1.8 at 05:33 and C1.8 at 20:05 UTC.

Spotted regions not numbered by NOAA/SEC:
[S538] This region emerged in the northwest quadrant on April 26. Location at midnight: N08W46.

Coronal mass ejections (CMEs)

April 24-26: No obvious fully or partly Earth directed CMEs were observed. A partial halo CME was observed early in the day, most of the observed material was distributed rather symmetrically off the southern limbs. The absence of activity in the central southern hemisphere late on April 25 and early on April 26 indicates that the source of this CME was backsided.

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 (CH162) in the northern hemisphere will rotate to an Earth facing position on April 28-29.

Processed SOHO/EIT 284 image at 19:06 UTC on April 26. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected be quiet to unsettled on April 27-29 becoming unsettled to major storm on April 30 or May 1 due to a high speed stream from CH162.

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 poor. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant station tonight: Radio Cristal del Uruguay after 23:15 UTC. Earlier several stations from Brazil had occasional strong peaks, one of them was Rádio Rural AM do Parelhas. On other frequencies stations from Uruguay, Argentina and Brazil could be heard with weak signals. WWZN Boston on 1510 kHz had fair peaks after 02h UTC.

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.