Solar Terrestrial Activity Report

Last major update issued on May 31, 2006 at 04:20 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update April 1, 2006)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update April 1, 2006)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update April 1, 2006)]
[Historical solar and geomagnetic data charts 1954-2005 (last update March 3, 2006)]
[Archived reports (last update May 3, 2006)]

Recent activity

The geomagnetic field was inactive to unsettled on May 30. Solar wind speed ranged between 275 and 350 (all day average 310) km/sec, mot of the day under the influence of a low speed, high density disturbance.

Solar flux measured at 20h UTC on 2.8 GHz was 80.0. The planetary A index was 9 (STAR Ap - based on the mean of three hour interval ap indices: 8.9).
Three hour interval K indices: 22023232 (planetary), 22035332 (Boulder).

The background x-ray flux is at the class A2 level.

At midnight there were 5 spotted regions on the visible solar disk. The solar flare activity level was very low. No C class events were recorded during the day.

Region 10886 decayed slowly and quietly.
Region 10887 decayed and was quiet.
Region 10890 decayed further and is likely to become spotless today.
New region 10891 emerged in the southeast quadrant on May 29 and was numbered the following day by SEC.

Spotted regions not numbered by NOAA/SEC:
[S659] A new region emerged in the northwest quadrant on May 30, only a tiny spot was visible at the end of the day. Location at midnight: N04W14

Coronal mass ejections (CMEs)

May 28-30: No partly or fully Earth directed CMEs were observed in limited LASCO imagery.

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 trans equatorial coronal hole (CH226) was in an Earth facing position on May 29-30.

Processed SOHO/EIT 284 image at 19:06 UTC on May 26. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to unsettled on May 31, perhaps with active intervals during the latter half of the day when a high speed stream from CH226 is likely to arrive. Quiet to active conditions are likely on June 1-3.

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. When the high speed stream has arrived the color changes to green.
2) Effects from a CME are likely to be observed at 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.

Propagation

Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is fair to poor. Propagation on long distance northeast-southwest paths is fair to poor. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Radio Cristal del Uruguay was the dominant station tonight. On other frequencies signals were generally poorer than a day ago with most of the observed signals from Uruguay and Argentina. From North America 1510 WWZN, 1660 WWRU and 1700 KVNS were all heard just before LSR.

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. SEC active region numbers in the table below and in the active region map above are the historic SEC/USAF numbers.

Active region Date numbered SEC
spot
count
STAR
spot
count
Location at midnight Area Classification Comment
10886 2006.05.23 3 2 N08W53 0020 CRO area was 0020 at midnight
10887 2006.05.26 2 3 S12E10 0030 HRX classification was CSO at midnight, area 0020
10889 2006.05.27     S01W33     plage
10890 2006.05.28 2 1 S15W59 0030 CRO classification was AXX at midnight, area 0000
10891 2006.05.30 4 2 S13E19 0030 CSO formerly region S658
classification was HSX at midnight, area 0020
S659 2006.05.31   1 N04W14 0000 AXX  
Total spot count: 11 9  
SSN: 51 59  

Monthly solar cycle data

Month Average solar
flux at Earth
International sunspot number Smoothed sunspot number
2000.04 184.2 125.5 120.8
cycle 23 sunspot max.
2000.07 202.3 170.1 119.8
2001.12 235.1 132.2 114.6 (-0.9)
2005.02 97.2 29.2 33.9 (-0.7)
2005.03 89.9 24.5 33.5 (-0.4)
2005.04 86.0 24.2 31.6 (-1.9)
2005.05 99.3 42.7 28.9 (-2.7)
2005.06 93.7 39.3 28.8 (-0.1)
2005.07 96.4 40.1 29.1 (+0.3)
2005.08 90.5 36.4 27.4 (-1.7)
2005.09 91.1 21.9 25.8 (-1.6)
2005.10 77.0 8.5 25.5 (-0.3)
2005.11 86.3 18.0 (24.5 predicted, -1.0)
2005.12 90.7 41.2 (21.8 predicted, -2.7)
2006.01 83.4 15.4 (18.7 predicted, -3.1)
2006.02 76.5 4.7 (15.6 predicted, -3.1)
2006.03 75.4 10.8 (13.4 predicted, -2.2)
2006.04 89.0 30.2 (12.7 predicted, -0.7)
2006.05 81.0 (1) 38.1 (2) (12.2 predicted, -0.5)

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% lower.

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


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