Solar Terrestrial Activity Report

Last update issued on April 20, 2003 at 03:20 UTC.

[Solar and geomagnetic data - last 4 weeks (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update April 2, 2003)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update April 2, 2003)]
[Graphical comparison of cycles 10, 13, 17, 20 and 23 (last update April 2, 2003)]
[Historical solar and geomagnetic data charts 1954-2003 (last update April 13, 2003)]
[Archived reports (last update April 14, 2003)]

Recent activity

The geomagnetic field was quiet to unsettled on April 19. Solar wind speed ranged between 531 and 681 km/sec under the decreasing influence of a high speed stream from coronal hole CH32.

Solar flux measured at 20h UTC on 2.8 GHz was 112.1. The planetary A index is estimated at 12 - estimated because SEC/NOAA reported an out of range value of 18 - the range of 3 hour ap values for the day was 4-17 - (STAR Ap - based on the mean of three hour interval ap indices: 12.0).
Three hour interval K indices: 33313323 (planetary), 33323323 (Boulder).

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

At midnight there were 6 spotted regions on the visible disk. Solar flare activity was very low.

Region 10334 decayed slowly and quietly.
Region 10336 was mostly quiet and unchanged.
Region 10337 had the main penumbra partly split into two penumbrae, otherwise the region did not change much, There is a magnetic delta structure in the southern part of the leading spots. There is still a chance of minor M class flares.
New region 10338 emerged in the northeast quadrant just west of leading positive polarity field of region S139. If both regions continue to develop they could merge.

Spotted regions not yet numbered by SEC/NOAA:
[S139] A new region emerged in the northeast quadrant on April 16, then became spotless before reemerging on April 18. The region is located between regions 10336 and 10338 with the leader spot near the trailing spot of region 10338. Location at midnight: N17E30.
[S142] A new region emerged late on April 19 in the northwest quadrant. Location at midnight: N15W29.

Coronal mass ejections (CMEs)

April 17-19: No obviously geoeffective CMEs 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 small coronal hole (CH33) in the southern hemisphere was in a geoeffective position on April 18. A recurrent coronal hole (CH34) in the northern hemisphere was in a geoeffective position on April 18-19. A recurrent coronal hole (CH35) in the southern hemisphere is likely to rotate to a geoeffective position on April 21-22.

Processed SOHO EIT 284 image at 19:06 UTC on April 18. [With SOHO EIT in CCD bakeout mode until April 21, the next processed EIT 284 image will likely not be posted until April 22.] Any black areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to active on April 20 while high speed coronal hole streams from CH33 and CH34 will cause unsettled to active conditions on April 21-22. Long distance medium wave (AM) band propagation along east-west paths over high and upper middle latitudes is likely to remain very poor until at least April 23. Propagation along north-south paths is poor to fair and is likely to vary between poor and fair until at least April 22. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: Radio Cristal del Uruguay.]

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.
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 SEC/NOAA. 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.

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 (SEC/NOAA) sunspot number. The official international sunspot number is typically 25-45% less.

This report has been prepared by Jan Alvestad. It is based partly on my own observations and interpretations, and partly on data from sources noted in solar links. All time references are to the UTC day. Comments and suggestions are always welcome.