Solar Terrestrial Activity Report

Last update issued on May 31, 2003 at 04:20 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 unsettled to very severe storm on May 30. Solar wind speed ranged between 558 and 782 km/sec. A solar wind shock was observed at SOHO at 16:02 UTC with an abrupt increase in solar wind speed from 610 to 770 km/sec. This shock was likely the arrival of the full halo CME observed early on May 29 after an X1.2 flare in region S169. The interplanetary magnetic field, having been mostly northwards since 02h UTC, swung strongly southwards at first, then became northwards again and weakened towards the end of the day. 

Solar flux measured at 20h UTC on 2.8 GHz was 117.2. The planetary A index was 49 (STAR Ap - based on the mean of three hour interval ap indices: 51.1).
Three hour interval K indices: 84434545 (planetary), 74334544 (Boulder).

The background x-ray flux is at the class B4 level.

At midnight there were 4 spotted regions on the visible disk. Solar flare activity was low. A total of 5 C class events was recorded during the day.

Region 10368 decayed slowly and quietly.
Region 10373 decayed slowly losing penumbral area. Flare: C4.9 long duration event peaking at 09:19 UTC.

Spotted regions not numbered or misnumbered by NOAA/SEC:
[S169] This 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 25-28. On May 29-30 the region decayed slowly losing some of its penumbral area and quite a few small spots.  Major flares are still possible as there is a magnetic delta structure in the trailing part of the region. Location at midnight: S07W59. Flares: C1.0 at 05:57, C8.6/1N at 06:50 and C1.7 at 17:24 UTC. At 02:24 UTC on May 31 region S169 produced an X1.0 flare. Proton fluxes at Earth are currently increasing and a proton event will likely begin soon.
[S174] A new region emerged in the northeast quadrant near the central meridian on May 30. Location at midnight: N18W01.

Coronal mass ejections (CMEs)

May 30: 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 large recurrent coronal hole (CH42) in the southern hemisphere will rotate into a geoeffective position on May 29-June 5. This coronal hole has a narrow leading extension into the northern hemisphere.

Processed SOHO EIT 284 image at 19:06 UTC on May 30. Any black areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be unsettled to minor storm until June 8, at first due to CME effects, then due to a high speed stream from coronal hole CH42 arriving on June 1.

Long distance medium wave (AM) band propagation along east-west paths over high and upper middle latitudes is useless and will likely be very poor to useless until at least June 10. Propagation along north-south paths is very poor. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: none, only a weak unidentified signal heard.]

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 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.

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 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.