Solar Terrestrial Activity Report

Last major update issued on May 25, 2011 at 03:15 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)
[Solar cycles 21-24 (last update May 1, 2011)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22, 23 and 24 (last update May 1, 2011)]
[Graphical comparison of cycles 10, 12, 13, 14, 16 and 24 (last update May 1, 2011)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports since January 2003 (last update May 1, 2011)]

[POES auroral activity level charts since October 2009 - updated May 23, 2011]
Annotated geomagnetic activity charts - Carrington rotation 2108 [March-April 2011] - 2109 [April-May 2011] NEW

Recent activity

The geomagnetic field was quiet on May 24. Solar wind speed ranged between 349 and 414 km/s under the influence of a weak coronal hole stream.

Solar flux measured at 20h UTC on 2.8 GHz was 81.7 (decreasing 26.2 over the last solar rotation). The planetary A index was 6 (STAR Ap - based on the mean of three hour interval ap indices: 6.0). Three hour interval K indices: 21112212 (planetary), 31122222 (Boulder).

The background x-ray flux is at the class A9 level.

At midnight UTC the visible solar disk had 6 spotted regions.

Region 11216 was quiet and stable.
Region 11218 was quiet and stable.
Region 11219 was quiet and stable.

Spotted regions not numbered by NOAA/SWPC:
[S1019] emerged in the northeast quadrant on May 20, became spotless on May 21 and reemerged on May 24. Location at midnight: N14W09
[S1024] emerged in the northeast quadrant on May 24. Location at midnight: N29E28
[S1025] emerged in the northwest quadrant on May 24. Location at midnight: N25W18

Coronal mass ejections (CMEs)

May 22-24: No obviously Earth directed CMEs were observed in LASCO and STEREO imagery.

Coronal holes

Coronal hole history (since late October 2002)
Compare today's report to the situation one solar rotation ago: 28 days ago 27 days ago 26 days ago

A recurrent trans equatorial coronal hole (CH450) was in an Earth facing position on May 24-25. A small coronal hole (CH451) in the northern hemisphere will likely rotate into an Earth facing position on May 27.

The darkest areas on the solar disk are likely coronal holes.

Propagation

Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over high and upper middle latitudes is poor. Propagation on long distance northeast-southwest paths is fair.

Forecast

The geomagnetic field is expected to be quiet on May 25-26 and quiet to minor storm on May 27-28 due to effects from CH450.

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.

Active solar regions

(Click on image for higher resolution image) Compare to the previous day's image

When available the active region map has a coronal hole polarity overlay where red (pink) is negative and blue (blue-green) is positive.

Data for all numbered solar regions according to the Solar Region Summary provided by NOAA/SWPC. 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 SWPC or where SWPC has observed no spots. SWPC active region numbers in the table below and in the active region map above are the historic SWPC/USAF numbers.

Active region Date numbered
detected
Spot count Location at midnight Area Classification SDO / HMI 4K continuum
image with polarity overlay
Comment
SWPC STAR SDO SWPC STAR Current Previous
11216 2011.05.15
2011.05.16
1 2 S15W38 0090 HSX CSO location: S16W36
S1010 2011.05.15     S18W58         plage
11218 2011.05.17
2011.05.18
  3 S16W14 0000   BXO

location: S17W08

S1018 2011.05.19     N17W35         plage
S1019 2011.05.20   1 N14W09 0000   AXX    
11219 2011.05.21   1 N15E29 0000   AXX location: N13E27
S1021 2011.05.21     S13E42           plage
11220 2011.05.21
2011.05.22
2   N12W94 0010 BXO     rotated out of view
11221 2011.05.22
2011.05.23
    S18W83           plage
S1024 2011.05.24   1 N29E28 0000   AXX    
S1025 2011.05.24   1 N25W18 0000   AXX    
Total spot count: 3 9  
Sunspot number: 23 69  

Monthly solar cycle data

Month Average measured solar flux International sunspot number (SIDC) Smoothed sunspot number Average ap
(3)
2008.07 65.7 (SF minimum) 0.5 2.8 (-0.4)  
2008.12 69.2 0.8 1.7 (-)
sunspot minimum
3.25
2010.02 84.7 18.8 10.6 (+1.3) 4.15 / 4.61
2010.03 83.4 15.4 12.3 (+1.7) 4.58 / 4.65
2010.04 75.9 8.0 14.0 (+1.7) 10.22 / 10.24
2010.05 73.8 8.7 15.5 (+1.5) 9.18 / 8.15
2010.06 72.5 13.6 16.4 (+0.9) 8.17 / 6.85
2010.07 79.8 16.1 16.7 (+0.3) 6.31 / 5.15
2010.08 79.2 19.6 17.4 (+0.7) 8.49 / 7.77
2010.09 81.1 25.2 19.6 (+2.2) 5.33 / 5.45
2010.10 81.6 23.5 23.2 (+3.6) 6.07 / 6.27
2010.11 82.5 21.5 (26.9 predicted, +3.7) 4.80 / 5.50
2010.12 84.2 14.4 (30.1 predicted, +3.2) 3.41 / 4.35
2011.01 83.6 19.1 (33.1 predicted, +3.0) 4.32 / 5.51
2011.02 94.6 29.4 (35.6 predicted, +2.5) 5.41 / 6.44
2011.03 115.0 56.2 (37.9 predicted, +2.3) 7.79
2011.04 112.6 54.4 (40.8 predicted, +2.9) 9.71
2011.05 95.1 (1) 43.9 (2A) / 56.7 (2B) (44.1 predicted, +3.3) (7.01)

1) Running average based on the daily 20:00 UTC observed solar flux value at 2800 MHz.
2A) Current impact on the monthly sunspot number based on the Boulder (NOAA/SWPC) sunspot number (accumulated daily sunspots / month days). The official SIDC international sunspot number is typically 30-50% lower. 2B) Month average to date.
3) Running average based on the preliminary daily SWPC ap indices. Values in red are based on the official NGDC ap indices.

This report has been prepared by Jan Alvestad. It is based on analysis of data from whatever sources are available at the time the report is prepared. All time references are to the UTC day. Comments and suggestions are always welcome.

SDO images are courtesy of NASA/SDO and the AIA, EVE, and HMI science teams.