Solar Terrestrial Activity Report

Last major update issued on April 26, 2011 at 05:20 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 to unsettled on April 25. Solar wind speed ranged between 453 and 592 km/s under the influence of what is likely a weak coronal hole stream.

Solar flux measured at 20h UTC on 2.8 GHz was 112.1 (decreasing 4.1 over the last solar rotation). The planetary A index was 6 (STAR Ap - based on the mean of three hour interval ap indices: 5.6). Three hour interval K indices: 23101221 (planetary), 23112211 (Boulder).

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

At midnight UTC the visible solar disk had 9 spotted regions.

Region 11195 decayed in the trailing spot section and the leading penumbra again became the largest. There's still a magnetic delta structure in the southwestern part of the trailing penumbra. An M class flare is possible.
Region 11196 has many tiny spots with no significant changes observed over the last days.
Region 11197 was quiet and stable.

Spotted regions not numbered by NOAA/SWPC:
[S965] emerged in the southeast quadrant on April 20. Location at midnight: S17W31
[S968] was quiet and stable. Location at midnight: N14E64
[S969] emerged in the northeast quadrant on April 24. Location at midnight: N15E03
[S971] emerged in the southeast quadrant on April 25. Location at midnight: S17E57
[S972] emerged near the central meridian in the northern hemisphere on April 25. Location at midnight: N20W08

Coronal mass ejections (CMEs)

April 23-25: 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) will likely rotate into an Earth facing position on April 26-27.

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 to fair. Propagation on long distance northeast-southwest paths is poor to fair.

Forecast

The geomagnetic field is expected to be quiet to unsettled on April 26-29. A high speed stream associated with CH446 could cause quiet to active conditions 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
11193 2011.04.12
2011.04.13
8   N16W84 0270 DSO     rotated out of view
11195 2011.04.18
2011.04.19
25 23 S16W12 0400 EHI EHI

beta-gamma-delta

S960 2011.04.18     N10W60           plage
11196 2011.04.19
2011.04.20
4 24 S26E11 0010 BXO BXI

location: S27E13

11197 2011.04.19
2011.04.21
  4 S16E01 0000   BXO location: S17E07
S963 2011.04.19     S18W51           plage
S965 2011.04.20   5 S17W31 0000   AXX  
S967 2011.04.22   2 S15E18 0000   AXX    
S968 2011.04.24   3 N14E64 0010   AXX  
S969 2011.04.24   4 N15E03 0020   BXO  
S970 2011.04.24     N17W53         plage
S971 2011.04.25   2 S17E57 0020   BXO    
S972 2011.04.25   3 N20W08 0020   BXO    
Total spot count: 37 70  
Sunspot number: 67 160  

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
2011.04 113.2 (1) 71.1 (2A) / 85.4 (2B) (39.6 predicted, +2.9) (9.86)

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.