Solar Terrestrial Activity Report

Last major update issued on April 19, 2011 at 03:50 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 active on April 18. Solar wind speed ranged between 311 and 433 km/s. A solar wind shock was observed at SOHO at 06:06 UTC, likely the arrival of the CME observed on April 15.

Solar flux measured at 20h UTC on 2.8 GHz was 111.0 (increasing 11.2 over the last solar rotation). The planetary A index was 10 (STAR Ap - based on the mean of three hour interval ap indices: 9.6). Three hour interval K indices: 10334211 (planetary), 11333321 (Boulder).

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

At midnight UTC the visible solar disk had 7 spotted regions.

Region 11190 decayed further and was mostly quiet. M class flare activity is still possible.
Region 11191 decayed slowly and quietly.
Region 11193 didn't change significantly and could produce a minor M class flare. Flares: C1.8 at 02:43, C1.5 at 19:02 UTC.

Spotted regions not numbered by NOAA/SWPC:
[S950] reemerged on April 15. Location at midnight: S16W07
[S956] rotated into view at the northeast limb late on April 17. Location at midnight: N19E65
[S959] rotated into view at the southeast limb late on April 18. Location at midnight: S17E80
[S960] emerged in the northeast quadrant on April 18. Location at midnight: N10E31

Coronal mass ejections (CMEs)

April 16-18: 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

An extension (CH445) of the southern polar coronal hole was Earth facing on April 16-17 but could be too far to the south to cause a disturbance.

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.

Forecast

The geomagnetic field is expected to be quiet to unsettled on April 19-21. On April 19-20 a high speed coronal hole stream could reach Earth and cause some unsettled and active intervals.

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
8 18 N13W68 0260 DKO DKO

beta-gamma-delta

11191 2011.04.11
2011.04.12
7 13 N08W07 0070 CSO CSO

location: N06W10

11193 2011.04.12
2011.04.13
22 36 N17E05 0350 ESC ESC beta-gamma
S950 2011.04.13   4 S15W07 0000   BXO  
S951 2011.04.13     N28W22           plage
S952 2011.04.14     S19W52           plage
S953 2011.04.14     N21W26           plage
S955 2011.04.16     S37W68           plage
S956 2011.04.17   2 N19E65 0000   AXX  
S957 2011.04.17     N08W20         plage
S958 2011.04.17     N06W46         plage
S959 2011.04.18   3 S17E80 0030   CSO    
S960 2011.04.18   3 N10E31 0000   BXO    
Total spot count: 37 79  
Sunspot number: 67 149  

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
2011.04 112.6 (1) 51.3 (2A) / 85.6 (2B) (39.6 predicted, +2.9) (10.90)

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.