Solar Terrestrial Activity Report

Last major update issued on April 29, 2011 at 04:20 UTC.

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

[POES auroral activity level charts since October 2009 - updated April 19, 2011]
Annotated geomagnetic activity charts - Carrington rotation 2107 [Feb.-March 2011] - 2108 [March-April 2011] NEW

Recent activity

The geomagnetic field was quiet on April 28. Solar wind speed ranged between 326 and 381 km/s. The interplanetary magnetic field at ACE has been southwards since 15h UTC.

Solar flux measured at 20h UTC on 2.8 GHz was 110.4 (increasing 1.5 over the last solar rotation). The planetary A index was 3 (STAR Ap - based on the mean of three hour interval ap indices: 3.1). Three hour interval K indices: 00011221 (planetary), 00001111 (Boulder).

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

At midnight UTC the visible solar disk had 12 spotted regions.

Region 11195 decayed slowly and quietly.
Region 11196 was mostly quiet. Flare: C1.0 at 02:40 UTC.
Region 11199 became more complex again with minor polarity intermixing observed. Flare: C2.4 at 11:58 UTC.
Region 11200 was quiet and stable.
Region 11201 displayed no significant changes and was quiet.
New region 11202 emerged in the northeast quadrant on April 24 and was numbered by NOAA/SWPC 4 days later.
New region 11203 rotated partially into view at the northeast limb on April 28.

Spotted regions not numbered by NOAA/SWPC:
[S973] reemerged with a single tiny spot on April 28. Location at midnight: N32W47
[S976] emerged in the northeast quadrant on April 28. Location at midnight: N07E45
[S977] emerged in the northeast quadrant on April 28. Location at midnight: N05E29
[S978] emerged near the southwest limb on April 28. Location at midnight: S20W82
[S979] emerged with a tiny spot in an old plage area in the northeast quadrant on April 28. Location at midnight: N28E07

Coronal mass ejections (CMEs)

April 26-28: 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 trans equatorial coronal hole (CH446) was in an Earth facing position on April 26-28.

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 to active on April 29 - May 1 due to effects from CH446, minor storm intervals are possible on April 29-30.

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
11195 2011.04.18
2011.04.19
6 10 S18W52 0220 DHO DHO

 

11196 2011.04.19
2011.04.20
2 8 S23W32 0010 BXO BXO

location: S26W26

11197 2011.04.19
2011.04.21
    S16W41           plage

location: S17W35

S967 2011.04.22     S15W23         plage
11201 2011.04.24
2011.04.27
  4 N16E26 0000   AXX location: N13E27
11202 2011.04.24
2011.04.28
2 6 N15W38 0010 BXO BXO formerly region S969
11199 2011.04.25
2011.04.26
10 17 N18W48 0170 DHI DSI beta-gamma

location: N20W49

11200 2011.04.25
2011.04.26
  3 S17E14 0000   BXO location: S17E17
S973 2011.04.26   1 N32W47 0000   AXX    
S974 2011.04.27     S37E40         plage
S975 2011.04.27     N17E01         plage
11203 2011.04.28 1 1 N19E77 0040 HSX HSX   location: N18E75

area: 0080

S976 2011.04.28   2 N07E45 0000   AXX    
S977 2011.04.28   3 N05E29 0000   AXX    
S978 2011.04.28   3 S20W82 0010   AXX    
S979 2011.04.28   1 N28E07 0000   AXX    
Total spot count: 21 59  
Sunspot number: 71 179  

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 (22.6 predicted, +3.0) 6.07 / 6.27
2010.11 82.5 21.5 (25.7 predicted, +3.1) 4.80 / 5.50
2010.12 84.2 14.4 (28.9 predicted, +3.2) 3.41 / 4.35
2011.01 83.6 19.1 (31.9 predicted, +3.0) 4.32 / 5.51
2011.02 94.6 29.4 (34.4 predicted, +2.5) 5.41 / 6.44
2011.03 115.0 56.2 (36.7 predicted, +2.3) 7.79
2011.04 112.8 (1) 76.7 (2A) / 82.2 (2B) (39.6 predicted, +2.9) (9.11)

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.