Solar Terrestrial Activity Report

Last major update issued on April 24, 2004 at 03:40 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 18, 2004)]

Recent activity

The geomagnetic field was quiet to minor storm on April 23. Solar wind speed ranged between 402 and 481 km/sec under the influence of a high speed stream from coronal hole CH91.

Solar flux measured at 20h UTC on 2.8 GHz was 115.3. The planetary A index was 20 (STAR Ap - based on the mean of three hour interval ap indices: 20.9).
Three hour interval K indices: 23445423 (planetary), 23444323 (Boulder).

The background x-ray flux is at the class B7 level.

At midnight there were 2 spotted regions on the visible disk. The solar flare activity level was moderate. A total of 19 C and 2 M class events was recorded during the day.

Region 10596 decayed slowly and was quiet.
Region 10597 rotated out of view at the southwest limb but continued to be very active. Further M class flares from behind the southwest limb are possible today and early tomorrow. Flares: C1.6 at 00:16, C1.1 at 01:19, C1.9 at 04:56, C1.8 at 06:50, C1.2 at 07:19, C6.1 at 07:56, C4.4 at 09:30, C3.0 at 09:47, C4.0 at 10:44, M1.5 at 11:50, C5.1 at 12:03, C1.4 at 14:37, C3.9 at 16:05, C4.8 at 17:31, C1.6 at 19:06, M1.1 at 21:12, C2.8 at 21:26, C1.8 at 22:16, C2.2 at 22:41, C2.5 at 22:54 and C2.9 at 23:37 UTC.

Spotted regions not numbered or numbered incorrectly by NOAA/SEC:
[S391] This region emerged to the north of region 10595 late on April 16 and developed moderately quickly on April 17. Further development was observed on April 18, while the region decayed slowly on April 19 and lost several small spots. The region decayed further on April 20, 21 and 22 and was stable on April 23. Location at midnight: S06W26.

Coronal mass ejections (CMEs)

April 21: No fully or partly Earth directed CME observed. There's no new LASCO data available as SOHO is currently recovering from a failure.

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

The northernmost extensions of a coronal hole (CH91) in the southern hemisphere were in a geoeffective position on April 19-20. A recurrent coronal hole (CH92) in the northern hemisphere will probably rotate into a geoeffective position on April 23-24.

Processed SOHO/EIT 284 image at 01:05 UTC on April 22. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to unsettled on April 24 and most of April 25. Late on April 25 or early on April 26 a high speed stream from coronal hole CH92 is likely to arrive and cause unsettled to minor storm conditions until April 28.

Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is poor to very poor, slow improvement is expected until the arrival of the next coronal hole flow. 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). CPN Radio was heard weakly at times. Only two stations from North America were noted, VOWR on 800 and CJYQ on 930 kHz, both with decent signals].

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.