Solar Terrestrial Activity Report

Last major update issued on May 18, 2005 at 03:05 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update May 6, 2005)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update May 6, 2005)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update May 6, 2005)]
[Historical solar and geomagnetic data charts 1954-2004 (last update February 1, 2005)]
[Archived reports (last update May 15, 2005)]

Recent activity

The geomagnetic field was quiet to active on May 17. Solar wind speed ranged between 448 and 729 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 90.0. The planetary A index was 19 (STAR Ap - based on the mean of three hour interval ap indices: 19.1).
Three hour interval K indices: 44433323 (planetary), 44434323 (Boulder).

The background x-ray flux is at the class B1 level.

At midnight there were 3 spotted regions on the visible solar disk. The solar flare activity level was moderate. A total of 3 C and 1 M class events was recorded during the day.

Region 10759 decayed slowly and quietly.
Region 10763 decayed fairly quickly and lost more than half of its penumbral area. The region simplified and no longer has any magnetic delta structures. Flares: M1.8/1B at 02:39 (associated with a weak type IV and a moderate type II radio sweep), C8.4/1N at 04:03, C2.8 at 05:53 and C1.1 at 23:51 UTC.

Spotted regions not numbered by NOAA/SEC:
[S548] This region emerged in the southeast quadrant on May 17 and was decaying slowly late in the day. Location at midnight: S13E12.

Coronal mass ejections (CMEs)

May 15-16: No obviously fully or partly potentially geoeffective CMEs were observed.
May 17: A very faint and slow full halo CME was observed after the M1.8 flare in region 10763 early in the day. This CME could reach Earth early on May 20.

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 (CH166) in the northern hemisphere will likely be in an Earth facing position on May 17. CH166 may be too far to the north to become geoeffective.

Processed SOHO/EIT 284 image at 19:06 UTC on May 17. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected be quiet to unsettled on May 18-19 becoming quiet to active on May 20 due to a weak CME.

Coronal holes (1) Coronal mass ejections (2) M and X class flares (3)
Coronal hole indicator CME indicator M and X class flare indicator

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) 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.

Propagation

Long distance low and medium frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is poor. Propagation along long distance north-south paths is poor. Trans Atlantic propagation conditions are normally monitored every night on 1470 kHz. Dominant stations tonight: Radio Cristal del Uruguay and Radio Rafaela (Argentina), both with poor signals. A few North American stations were noted with audio on frequencies above 1400 kHz after 02h UTC, all US frequencies in the range 1620-1700 kHz had moderate to strong carriers.

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
10759 2005.05.08 1 2 N11W50 0220 HKX classification was CKO at midnight, area 0260
10762 2005.05.10     S12W81     plage
10763 2005.05.12 24 19 S14W10 0140 EAI classification was DAI at midnight, area 0080, location: S16W12
S548 2005.05.17   1 S13E12 0010 AXX  
Total spot count: 25 22  
SSN: 45 52  

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)
2004.03 112.0 49.1 47.1 (-2.2)
2004.04 101.2 39.3 45.5 (-1.6)
2004.05 99.8 41.5 43.8 (-1.7)
2004.06 97.4 43.2 41.6 (-2.2)
2004.07 119.1 51.1 40.2 (-1.4)
2004.08 109.6 40.9 39.2 (-1.0)
2004.09 103.1 27.7 37.5 (-1.7)
2004.10 105.9 48.0 35.9 (-1.6)
2004.11 113.2 43.5 (34.8 predicted, -1.1)
2004.12 94.5 17.9 (33.4 predicted, -1.4)
2005.01 102.2 31.3 (30.9 predicted, -2.5)
2005.02 97.2 29.1 (28.3 predicted, -2.6)
2005.03 89.9 24.8 (26.5 predicted, -1.8)
2005.04 86.0 24.4 (24.6 predicted, -1.9)
2005.05 108.8 (1) 42.6 (2) (22.0 predicted, -2.6)

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 some of these solar data sources. All time references are to the UTC day. Comments and suggestions are always welcome.


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