Solar Terrestrial Activity Report

Last major update issued on February 18, 2005 at 05:00 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update January 2, 2005)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update January 2, 2005)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update January 2, 2005)]
[Historical solar and geomagnetic data charts 1954-2004 (last update February 1, 2005)]
[Archived reports (last update February 16, 2005)]

Recent activity

The geomagnetic field was quiet to unsettled on February 17. Solar wind speed ranged between 351 and 507 km/sec under the influence of a weak stream from CH145. Late in the day, at approximately 2130 UTC at ACE, a more significant disturbance was observed with the interplanetary magnetic field swinging moderately to strongly southwards for several hours.

Solar flux measured at 20h UTC on 2.8 GHz was 111.3. The planetary A index was 6 (STAR Ap - based on the mean of three hour interval ap indices: 6.5).
Three hour interval K indices: 12012223 (planetary), 23011323 (Boulder).

The background x-ray flux is at the class B1-B2 level.

At midnight there were 5 spotted regions on the visible solar disk. The solar flare activity level was low. A total of 1 C class event was recorded during the day.

Spotted regions not numbered by NOAA/SEC:
[S515] A new region emerged in the southeast quadrant on February 17. Location at midnight: S13E48.

Coronal mass ejections (CMEs)

February 17: A full halo CME was observed early in the day and was likely associated with the C4.9 flare in region 10734 at 23:38 on February 16.
February 15-16: 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 (CH145) in the northern hemisphere was in a geoeffective position on February 13-15. A small coronal hole (CH147) in the northern hemisphere will likely rotate to a geoeffective position on February 19-20.

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

Forecast

The geomagnetic field is expected to be unsettled to minor storm on February 18. The CME observed early on February 17 will likely arrive on February 19 and cause unsettled to major storm conditions that day and on February 20.

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 very 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 Cristal del Uruguay. Radio Rafaela (Argentina) was noted occasionally as well. The only North American stations heard were WCNZ on 1660 and WJCC on 1700 kHz, both with weak signals. The best and most stable reception of any trans Atlantic station was of Rádio Metropolitana, Fortaleza on 930 kHz with a near local quality signal from 22:30 UTC on February 17 and several hours into February 18.

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.