Solar Terrestrial Activity Report

Last update issued on May 26, 2003 at 02:20 UTC.

[Solar and geomagnetic data - last 4 weeks (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update May 1, 2003)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update May 1, 2003)]
[Graphical comparison of cycles 10, 13, 17, 20 and 23 (last update May 1, 2003)]
[Historical solar and geomagnetic data charts 1954-2003 (last update April 13, 2003)]
[Archived reports (last update May 26, 2003)]

Recent activity

The geomagnetic field was quiet to minor storm on May 25. Solar wind speed ranged between 473 and 631 km/sec, peaking early in the day under the influence of a high speed stream from coronal hole CH40. The coronal hole flow appeared to be ending late on May 25.

Solar flux measured at 20h UTC on 2.8 GHz was 121.1. The planetary A index was 22 (STAR Ap - based on the mean of three hour interval ap indices: 22.6).
Three hour interval K indices: 55432434 (planetary), 55432433 (Boulder).

The background x-ray flux is at the class B2-B3 level.

At midnight there were 4 spotted regions on the visible disk. Solar flare activity was low. A single C class event was recorded during the day.

Region 10367 was quiet and stable.
Region 10368 was mostly quiet and stable. Flare: C3.0 long duration event peaking at 17:54 UTC.
Region 10370 reemerged with a few spots.

Spotted regions not numbered by SEC/NOAA:
[S169] A new region emerged very quickly after noon on May 24 in the southeast quadrant about 11 degrees longitude east of spotless region 10365. The region continued to develop quickly as a compact region on May 25 and has a magnetic delta structure in a leading penumbra. M class flaring is possible. Please note that SEC/NOAA confusingly has recycled spotless region 10365. To complicate the situation further region 10365 actually reemerged with a few spots at noon on May 25 (this is evident in SOHO/MDI images and was noticed by Mt.Wilson as well), only to become spotless once again during the early evening. Location at midnight: S06E08.

Coronal mass ejections (CMEs)

May 23-25: 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 recurrent coronal hole (CH41) in the southern hemisphere was in a geoeffective position on May 24-25. A coronal hole (CH42) in the southern hemisphere will rotate into a geoeffective position on May 30.

Processed SOHO EIT 284 image at 19:06 UTC on May 25. Any black areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to minor storm on May 26. On May 27 a high speed stream from coronal hole CH41 will likely arrive and cause unsettled to minor storm conditions that day and on May 28. Quiet to active is expected for May 29 becoming quiet to unsettled on May 31-June 1.

Long distance medium wave (AM) band propagation along east-west paths over high and upper middle latitudes is very poor and will likely stay very poor until at least May 29. Propagation along north-south paths is good to very good. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: none, strong signals from 4-5 stations from Brazil noted, Radio Cristal del Uruguay only managed to get through a few times.]

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 30-50% 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.