Solar Terrestrial Activity Report

Last major update issued on April 21, 2011 at 06:25 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 minor storm on April 20. Solar wind speed ranged between 424 and 543 km/s under the influence of a high speed stream from CH445.

Solar flux measured at 20h UTC on 2.8 GHz was 117.0 (increasing 9.4 over the last solar rotation). The planetary A index was 16 (STAR Ap - based on the mean of three hour interval ap indices: 16.3). Three hour interval K indices: 35433321 (planetary), 33433311 (Boulder).

The background x-ray flux is at the class B4 level.

At midnight UTC the visible solar disk had 8 spotted regions.

Region 11191 decayed with the leader spot fragmenting into several smaller spots and retaining only rudimentary penumbra.
Region 11193 decayed slowly in the trailing spot section and was quiet.
Region 11195 developed slowly and has polarity intermixing. C flares are likely. Flares: C1.0 at 04:31, C4.0 at 19:39 UTC.
New region 11196 rotated partly into view at the southeast limb on April 19 and was numbered the following day by NOAA/SWPC.

Spotted regions not numbered by NOAA/SWPC:
[S950] reemerged on April 15. Location at midnight: S15W36
[S962] rotated into view at the southeast limb late on April 19. Location at midnight: S16E71
[S965] emerged in the southeast quadrant on April 20. Location at midnight: S17E37
[S966] emerged in the southwest quadrant on April 20. Location a midnight: S32W25

Coronal mass ejections (CMEs)

April 18-19: No obviously Earth directed CMEs were observed in LASCO and STEREO imagery.
April 20: A disappearing filament in the southeast quadrant late in the day may have produced a partially Earth directed CME (pending further analysis).

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

No obvious coronal holes are currently in or near Earth facing positions. A large coronal hole will begin rotating into view at the southeast limb within 2-3 days.

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 poor to fair.

Forecast

The geomagnetic field is expected to be mostly quiet on April 21-23.

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
11190 2011.04.08
2011.04.11
2   N14W94 0060 CAO    

rotated out of view

11191 2011.04.11
2011.04.12
1 10 N07W39 0015 HRX CRO

location: N07W36

11193 2011.04.12
2011.04.13
26 35 N16W20 0300 EHI EHI beta-gamma
S950 2011.04.13   4 S15W36 0000   AXX  
S951 2011.04.13     N28W48           plage
S953 2011.04.14     N21W52           plage
S956 2011.04.17     N19E39           plage
S957 2011.04.17     N08W46           plage
11195 2011.04.18
2011.04.19
7 17 S17E55 0100 DAI DAI

beta-gamma

S960 2011.04.18     N10E05         plage
11196 2011.04.19
2011.04.20
4 6 S27E69 0080 DAO CAO formerly region S961

location: S25E77

S962 2011.04.19   1 S16E71 0010   AXX  
S963 2011.04.19     S18E14         plage
S964 2011.04.19     S25W26         plage
S965 2011.04.20   4 S17E37 0000   AXX    
S966 2011.04.20   1 S32W25 0000   AXX    
Total spot count: 40 78  
Sunspot number: 90 158  

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) 56.9 (2A) / 85.3 (2B) (39.6 predicted, +2.9) (10.91)

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.