Solar Terrestrial Activity Report

Last major update issued on April 12, 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 unsettled on April 11. Solar wind speed ranged between 386 and 464 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 89.6. The planetary A index was 8 (STAR Ap - based on the mean of three hour interval ap indices: 9.9).
Three hour interval K indices: 32322222 (planetary), 32312323 (Boulder).

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

At midnight there were 4 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.

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 10. During the afternoon of April 9 new positive and negative polarity flux emerged in the trailing part of the region while the leading spot lost its penumbra. The trailing penumbra is growing quickly and has a magnetic delta structure. Flares: C9.6/1F long duration event peaking at 04:19 (associated with an erupting filament and a full halo CME. This was a small proton event as well), C1.2 at 22:24 and C1.5 at 23:08 UTC.
[S385] This region emerged in the southwest quadrant after noon on April 11. Location at midnight: S17W30.
[S386] A new region emerged quickly in the southeast quadrant after noon on April 11. Location at midnight: S15E12.

Coronal mass ejections (CMEs)

April 9:  A partial halo CME was observed following a long duration C3 event in region S380.
April 10: No fully or partly Earth directed CME observed.
April 11: A full halo CME was observed after a C9 event in region S380. This CME is likely to impact Earth on April 14.

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 small coronal hole (CH89) in the southern hemisphere could rotate into a geoeffective position on April 12 and 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 11. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to unsettled on April 12-13 and quiet to minor storm on April 14.

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 to fair. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: Radio Vibración (Venezuela). Otherwise 590 VOCM and 930 CJYQ were back after some days' absence while WWZN on 1510 kHz had a weak signal. An interesting Spanish speaking station was noted on 1420 kHz at 03h UTC above the usually dominant Venezuela station Marabina 1420].

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.