Solar Terrestrial Activity Report

Last update issued on September 17, 2003 at 04:10 UTC. 

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update September 1, 2003)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update September 1, 2003)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update September 1, 2003)]
[Historical solar and geomagnetic data charts 1954-2003 (last update July 23, 2003)]
[Archived reports (last update September 16, 2003)]

Recent activity

The geomagnetic field was quiet to major storm on September 16. Solar wind speed ranged between 349 and 562 km/sec. The disturbance which began after 18h UTC on September 15 intensified as the interplanetary magnetic field at times was strongly southwards. Towards the end of the day high speed streams from coronal holes CH56 and CH58 began to dominate the solar wind.

Solar flux measured at 20h UTC on 2.8 GHz was 99.3. The planetary A index was 37 (STAR Ap - based on the mean of three hour interval ap indices: 39.3).
Three hour interval K indices: 43556542 (planetary), 54555532 (Boulder).

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

At midnight there were 5 spotted regions on the visible disk. Solar flare activity was moderate. A total of 4 C and 1 M class events was recorded during the day. A C1.4 flare at 05:25 and a long duration M1.3 event peaking at 22:24 UTC appears to have had its origin just behind the southwest limb.

Region 10459 developed slowly and was mostly quiet. Flare: C1.8 at 08:58 UTC.
Region 10460 added a trailing spot and was quiet.
New region 10461 emerged in the northwest quadrant on September 14 and was finally noticed by NOAA/SEC two days later. The region developed quickly on September 16 and there is not much separating the positive and negative polarity areas.
New region 10462 emerged in the southwest quadrant on September 15 and was numbered by SEC the next day. The region developed slowly on September 16.

Spotted region not numbered by NOAA/SEC:
[S257] A new region rotated into view at the northeast limb on September 16. Location at midnight: N09E80.

Coronal mass ejections (CMEs)

September 14-16: No potentially 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

Small coronal holes (CH56 and CH58) near the equator were in geoeffective positions on September 13 and appeared to close on September 14. A large recurrent trans equatorial coronal hole (CH57) will rotate into a geoeffective position on September 14-17. CH57 decreased substantially in size on September 16, particularly in the northern and western sections. A small coronal hole (CH59) in the southern hemisphere could rotate into a geoeffective position on September 18-19.

Processed SOHO/EIT 284 image from 01:06 UTC on September 17. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be unsettled to minor storm until September 20 with a possibility of occasional major storm intervals on September 17 and 18 when the most intense part of a high speed stream from coronal hole CH57 will dominate the solar wind.

Long distance low frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is very poor. Propagation along north-south paths is fair. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant stations tonight: Radio Vibración (Venezuela) and Radio Cristal del Uruguay. At sunrise on September 15 WWNN Boca Raton, Florida was heard with an exceptionally good signal].

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 analysis, and partly on data from sources noted in solar links. All time references are to the UTC day. Comments and suggestions are always welcome.