Solar Terrestrial Activity Report

Last major update issued on April 13, 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 5, 2004)]

Recent activity

The geomagnetic field was quiet to active on April 12. Solar wind speed ranged between 380 and 529 km/sec. A solar wind shock was observed at SOHO at 17:34 UTC. The interplanetary magnetic field was northwards until about 22h UTC and only weakly southwards later on. The arrival of this CME caused a decrease in geomagnetic activity. The CME source was probably a C2.8 long duration event in region S380 on April 9.

Solar flux measured at 20h UTC on 2.8 GHz was 91.3. The planetary A index was 11 (STAR Ap - based on the mean of three hour interval ap indices: 11.9).
Three hour interval K indices: 32432231 (planetary), 42422232 (Boulder).

The background x-ray flux is at the class A8 level.

At midnight there were 5 spotted regions on the visible disk. The solar flare activity level was low. A total of 3 C class events was recorded during the day. All flares had their origin in region S380, which decayed quickly and became spotless during the afternoon. This region produced a C2.3 flare at 02:25, C1.0 at 07:49 and a C1.3 flare at 12:30 UTC.

Region 10588 decayed slightly and is rotating to the southwest limb.
New region 10591 emerged on April 11 and was numbered by SEC the next day. The region decayed slowly on April 12.

Spotted regions not numbered by NOAA/SEC:
[S387] A new region emerged quickly in the southeast quadrant just east of region 10591 on April 12. There is not much separating the leading negative polarity field of this region from the trailing positive polarity area of region 10591. The two regions are clearly two separate bipolar groups. Location at midnight: S15E03.
[S388] This region emerged in the southeast quadrant late on April 12. Location at midnight: S07E55.
[S389] A new region emerged near the southeast limb on April 12. Location at midnight: S11E71.

Coronal mass ejections (CMEs)

April 10, 12: No fully or partly Earth directed CME observed.
April 11: A fast, full halo CME was observed after a C9 event in region S380 early in the day. This CME is likely to impact Earth late on April 13. Another full halo CME was observed near noon, its source was probably a few days behind the northwest limb.

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 very small coronal hole (CH89) in the southern hemisphere was in a possibly geoeffective position on April 12 and could cause a weak geomagnetic disturbance on April 15. A poorly defined coronal hole (CH90) in the northern hemisphere could be in a geoeffective position on April 13-14.

Processed SOHO/EIT 284 image at 19:06 UTC on April 12. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be initially quiet to unsettled on April 13. A likely CME impact during the latter half of the day could cause active intervals that day and early on April 14. Quiet to unsettled is expected after noon on April 14 and on April 15.

Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is poor and slowly improving. Propagation along long distance north-south paths is poor. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: Radio Vibración (Venezuela). Both CPN Radio (Perú) and WLAM Lewiston ME (aka WMTW) were noted at times. East coast US stations were heard on several frequencies, particularly over 1600 kHz].

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.