Solar Terrestrial Activity Report

Last major update issued on April 30, 2011 at 06:55 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 28, 2011]
Annotated geomagnetic activity charts - Carrington rotation 2107 [Feb.-March 2011] - 2108 [March-April 2011] NEW

Recent activity

The geomagnetic field was quiet to active on April 29. Solar wind speed ranged between 334 and 505 km/s. A high speed stream associated with CH446 dominated the solar wind after 17h UTC.

Solar flux measured at 20h UTC on 2.8 GHz was 109.6 (increasing 2.1 over the last solar rotation). The planetary A index was 12 (STAR Ap - based on the mean of three hour interval ap indices: 12.1). Three hour interval K indices: 13112344 (planetary), 13111235 (Boulder).

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

At midnight UTC the visible solar disk had 11 spotted regions.

Region 11195 decayed slowly. Flares: C1.8 at 20:48, C1.5 at 22:55 UTC.
Region 11196 decayed slowly and was quiet.
Region 11197 reemerged with a tiny spot on April 29.
Region 11199 decayed in the leading and intermediate spot section while more penumbra formed on the trailing spots.
Region 11200 developed slowly and was mostly quiet.
Region 11201 added a few tiny spots.
Region 11202 developed slowly and was quiet.
Region 11203 rotated fully into view. Occasional C class flaring is likely. Flare: C3.8 at 00:26 UTC.

Spotted regions not numbered by NOAA/SWPC:
[S975] reemerged with a single tiny spot on April 29. Location at midnight: N22W19
[S980] emerged with a tiny spot on April 29. Location at midnight: N22E37
[S981] emerged with a tiny spot at a high latitude in the southeast quadrant on April 29. Location at midnight: S46E09

Coronal mass ejections (CMEs)

April 27-29: 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 30 - May 1 and quiet to unsettled on May 2 due to effects from CH446, minor storm intervals are possible on April 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
4 5 S15W65 0170 DHO CSO

 

11196 2011.04.19
2011.04.20
2 7 S30W45 0010 BXO BXO

location: S28W39

area: 0000

11197 2011.04.19
2011.04.21
  1 S16W55 0000   AXX  

location: S19W42

S967 2011.04.22     S15W36           plage
11201 2011.04.24
2011.04.27
  7 N16E12 0010   BXO location: N15E17
11202 2011.04.24
2011.04.28
  6 N15W51 0030   CRO  
11199 2011.04.25
2011.04.26
8 14 N18W62 0180 ESI DSI

location: N20W61

11200 2011.04.25
2011.04.26
4 16 S17E05 0030 BXO CRI  
S973 2011.04.26     N32W60         plage
S974 2011.04.27     S37E27           plage
S975 2011.04.27   1 N22W19 0000   AXX    
11203 2011.04.28 2 2 N18E64 0050 CSO ESO location: N18E66

area: 0090

S976 2011.04.28     N07E32         plage
S977 2011.04.28     N05E16         plage
S979 2011.04.28     N28W06         plage
S980 2011.04.29   1 N22E37 0000   AXX    
S981 2011.04.29   1 S46E09 0000   AXX    
Total spot count: 20 61  
Sunspot number: 70 171  

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
2011.04 112.7 (1) 79.0 (2A) / 81.8 (2B) (39.6 predicted, +2.9) (9.22)

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.