Solar Terrestrial Activity Report

Last update issued on October 27, 2003 at 05:15 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update October 4, 2003)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update October 4, 2003)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update October 4, 2003)]
[Historical solar and geomagnetic data charts 1954-2003 (last update October 15, 2003)]
[Archived reports (last update October 22, 2003)]

Recent activity

The geomagnetic field was quiet to unsettled on October 26. Solar wind speed ranged between 356 and 640 km/sec. Two solar wind shocks were recorded during the day. The first was observed at SOHO at 07:49 UTC, probably the arrival of a halo CME associated with a flare on October 23. The interplanetary magnetic field was continuously northwards after the arrival of this CME and therefore the CME did not become geoeffective. The second shock was noted at SOHO at 18:35 UTC. While the IMF was initially northwards, the IMF has become gradually more southwards and a geomagnetic disturbance began late on October 26. The source of the second shock was likely a CME observed after an M7 long duration event on October 24 in region 10486.

Solar flux measured at 23h UTC on 2.8 GHz was 243.4 (the values at both 17 and 20h UTC were strongly influenced by a long duration X class event). The planetary A index was 10 (STAR Ap - based on the mean of three hour interval ap indices: 11.1).
Three hour interval K indices: 22232333 (planetary), 11222344 (Boulder).

The background x-ray flux is at the class C3-C4 level. An above 10 MeV proton event began shortly after the X1 flare in region 10484 and has so far peaked near the 450 pfu level.

At midnight there were 8 spotted regions on the visible disk. Solar flare activity was high. A total of 7 C, 2 M and 2 X class events was recorded during the day. A C3.2 event at 00:50 UTC was associated with an erupting prominence near the west limb. Optically uncorrelated flares: C6.9 at 12:49 and C4.9 at 13:55 UTC.

Region 10484 lost some penumbral area, still the region became more complex. The large opposite polarity umbrae in the leading section are now very close causing strong magnetic shear in this part of the region. Another significant development is an emerging positive polarity area in the northeastern part of the region. Another X class proton flare is likely. Flares: C3.9 at 01:19, M1.0 at 14:20, long duration X1.2/1N proton flare (associated with a moderate type II  radio sweep) peaking at 18:19 and M7.6/2N at 21:40 UTC.
Region 10486 developed further in the central penumbral area. Another X class flare could occur anytime in this highly complex region. Flares: C3.8 at 01:44, C3.1 at 04:56, a long duration X1.2/3B event (associated with strong type II and IV radio sweeps and a large and fast full halo CME) peaking at 06:54 and C3.0 at 16:18 UTC.
Region 10487 lost several spots in the trailing negative polarity area. The magnetic delta structure observed one day earlier disappeared.

Spotted regions not numbered by NOAA/SEC:
[S286] A new region emerged in the southeast quadrant to the northeast of region 10486 on October 24. Slow development was observed on October 25 and 26. Location at midnight: S11E37.
[S288] A new region emerged to the northwest of region 10486 on October 25 and added several small spots on October 26. Location at midnight: S11E19.
[S289] This region emerged in the southeast quadrant on October 26 near the central meridian. Location at midnight: S21W07.
[S290] A new region emerged very quickly in the northeast quadrant on October 26. Some polarity intermixing is evident and it will be interesting to follow the development of this region. It has two bands of negative polarity, one in the south and one in the north. There is a band of positive polarity in the east and a smaller positive polarity area just south of the northern negative polarity band. Location at midnight: N08E21.
[S291] A small region emerged in the northeast quadrant on October 26. Location at midnight: N09E42.

Coronal mass ejections (CMEs)

October 26: A full halo CME was observed after the X1.2 long duration event (peak at 06:54 UTC) in region 10486. This CME will reach Earth sometime between late on October 27 and noon on October 28 and could cause minor to very severe geomagnetic storming. A CME observed off of the west limb prior to this event was associated with a prominence eruption near the west limb.

Another halo CME was likely associated with the X1 proton flare (peak at 18:19 UTC) in region 10484, however, LASCO images covering the hours after this event are not yet available. SOHO/EIT images show a lot of coronal movement in a large area tjust south of region 10484 during the time of the eruption. A slow CME off of the northwest limb and the north pole noted prior to the X class event was likely caused by an erupting filament in the northwest quadrant.

October 25: No obviously geoeffective CMEs observed.

October 24: A full halo CME was observed following an M7 event in region 10486 early in the day. The core of the CME is not heading towards the Earth, however, a minor part of this CME could reach Earth late on October 25 or early on October 26.

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 in the northern hemisphere (CH64) may have been in a geoeffective position on October 25-26. During the previous solar rotation this coronal hole did not cause a geomagnetic disturbance.

Processed SOHO/EIT 284 image at 01:06 UTC on October 27 (image quality is low because of high energy protons). The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be unsettled to active on October 27 until the possible arrival late in the day or on October 28 of a fast CME observed early on October 26. When this CME arrives severe geomagnetic storming is likely for 12-18 hours. Another CME impact could occur on October 28 after the expected arrival of a CME associated with an X1 long duration proton flare in region 10484 on October 26.

Long distance low frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is useless. Propagation along north-south paths is poor. [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 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.