Solar Terrestrial Activity Report

Last major update issued on April 10, 2004 at 03:45 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 minor storm on April 9. Solar wind speed ranged between 414 and 546 km/sec. A solar wind shock was observed at SOHO at 01:47 UTC on April 9 with a sudden increase in wind speed from 447 to 515 km/sec. This was likely the arrival of a full halo CME observed on April 6. The geomagnetic disturbance lasted only a few hours.

Solar flux measured at 20h UTC on 2.8 GHz was 90.0. The planetary A index was 16 (STAR Ap - based on the mean of three hour interval ap indices: 16.9).
Three hour interval K indices: 35432222 (planetary), 35432232 (Boulder).

The background x-ray flux is at the class A7 level.

At midnight there were 2 spotted regions on the visible disk. The solar flare activity level was low. A total of 1 C class event was recorded during the day.

Region 10588 was quiet and stable.

Spotted regions not numbered by NOAA/SEC:
[S380] This region emerged on April 3 just south of region 10588. The region developed moderately quickly on April 4 and slowly on April 5. Slow decay was observed on April 6 after an M2 flare. Late on April 7 new positive polarity flux emerged and a magnetic delta structure formed. Quick decay was observed on April 8 after a long duration C class event. The region decayed further on April 9 and could soon become spotless if the current rate of decay is sustained. Location at midnight: S17W27. Flare: C3.0 long duration event peaking at 20:38 UTC. As I write this there are no LASCO images available from the hours after this event, however, the event was fairly similar to the C7 event one day earlier and may have been associated with a full halo CME.

At about noon a new region emerged at N06W25, however, the spots were visible only for a few hours.

Coronal mass ejections (CMEs)

April 7: No fully or partly Earth directed CME observed.
April 8: A full halo CME was observed after a long duration C7 event in region S380. This CME will likely reach Earth late on April 10 and cause unsettled to minor storm conditions.
April 9:  No fully or partly Earth directed CME observed. An interesting long duration event in region S380 late in the day may have been associated with a CME (no relevant LASCO imagery available yet).

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

An elongated, recurrent trans equatorial coronal hole (CH88) was in a geoeffective position on April 1-7. This coronal hole is best defined in the easternmost part, however, the overall size of the coronal hole is much smaller than one rotation ago.

Processed SOHO/EIT 284 image at 19:06 UTC on April 9. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to minor storm on April 10-11 as a CME is expected to arrive during the latter half of April 10.

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 poor to fair. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: Radio Vibración].

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.