Solar Terrestrial Activity Report

Last major update issued on April 22, 2011 at 05:50 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 on April 21. Solar wind speed ranged between 407 and 457 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 113.0 (increasing 0.4 over the last solar rotation). The planetary A index was 5 (STAR Ap - based on the mean of three hour interval ap indices: 4.8). Three hour interval K indices: 12111212 (planetary), 12111222 (Boulder).

The background x-ray flux is at the class B8 level.

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

Region 11191 decayed further and could become spotless today.
Region 11193 decayed losing spots and penumbral area.
Region 11195 developed slowly during the first half of the day, then more quickly during the latter half. Early on April 22 the region has developed rapidly and could soon become capable of producing a major flare. Flares: C1.0 at 08:38, C8.5/1N at 09:48, C4.9 at 14:51 and C4.5 at 22:00 UTC.
Region 11196 was quiet and stable.
New region 11197 rotated into view at the southeast limb on April 19 and was numbered by NOAA/SWPC two days later. Slow decay was observed on April 21.
New region  11198 was first observed with spots on April 19, then became spotless on April 20 before reemerging with several spots on April 21.

Spotted regions not numbered by NOAA/SWPC:
[S965] emerged in the southeast quadrant on April 20. Location at midnight: S18E21

Coronal mass ejections (CMEs)

April 19-21: 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

No obvious coronal holes are currently in or near Earth facing positions.

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 22-24.

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
11191 2011.04.11
2011.04.12
1 3 N08W52 0010 HRX BXO

location: N09W48

area: 0000

11193 2011.04.12
2011.04.13
20 21 N16W32 0300 EHI EHI  
S950 2011.04.13     S15W49         plage
S951 2011.04.13     N28W61           plage
S953 2011.04.14     N21W65           plage
S957 2011.04.17     N08W59           plage
11195 2011.04.18
2011.04.19
10 31 S17E43 0240 DAI DAC

beta-gamma

S960 2011.04.18     N10W08           plage
11196 2011.04.19
2011.04.20
4 15 S26E63 0040 CSO CAO

location: S26E65

11197 2011.04.19
2011.04.21
1 2 S16E57 0010 AXX AXX formerly region S962

area: 0000

S963 2011.04.19     S18E01           plage
11198 2011.04.19
2011.04.21
4 4 S26W38 0010 BXO BXO   formerly region S964
S965 2011.04.20   6 S18E21 0000   AXX  
S966 2011.04.20     S32W38         plage
Total spot count: 40 82  
Sunspot number: 100 152  

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) 60.2 (2A) / 86.0 (2B) (39.6 predicted, +2.9) (10.61)

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.