Solar Terrestrial Activity Report

Last major update issued on April 28, 2011 at 04:10 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 very quiet on April 27. Solar wind speed ranged between 352 and 429 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 107.9 (decreasing 5.4 over the last solar rotation). The planetary A index was 3 (STAR Ap - based on the mean of three hour interval ap indices: 2.8). Three hour interval K indices: 00001111 (planetary), 10011011 (Boulder).

The background x-ray flux is at the class B2 level.

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

Region 11195 decayed slowly and quietly.
Region 11196 has many tiny spots with no significant changes observed over the last days.
Region 11199 matured as the opposite polarity spots increased their spatial separation.
Region 11200 decayed and was quiet.
New region 11201 rotated into view several days ago and was numbered ny SWPC because of flare activity. Flare: C2.0 at 02:33 UTC (associated with a CME off the northeast limb).

Spotted regions not numbered by NOAA/SWPC:
[S967] has a couple of tiny spots and could soon become spotless. Location at midnight: S15W10
[S969] emerged in the northeast quadrant on April 24. Location at midnight: N15W24
[S974] emerged in the southeast quadrant on April 27. Location at midnight: S37E53
[S975] emerged in the northeast quadrant on April 27. Location at midnight: N17E14

Coronal mass ejections (CMEs)

April 25-27: 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 fair. Propagation on long distance northeast-southwest paths is poor.

Forecast

The geomagnetic field is expected to be quiet on April 28. A high speed stream associated with CH446 could cause quiet to active conditions on April 29 - May 1.

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
7 17 S17W38 0230 DHO DHO

area: 0300

11196 2011.04.19
2011.04.20
  12 S28W12 0000   BXO

location: S25W13

11197 2011.04.19
2011.04.21
    S16W27         plage

location: S17W22

S965 2011.04.20     S17W57           plage
S967 2011.04.22   1 S15W10 0000   AXX  
11201 2011.04.24
2011.04.27
  2 N16E40 0000   AXX formerly region S968
S969 2011.04.24   7 N15W24 0010   BXO  
11199 2011.04.25
2011.04.26
12 17 N21W34 0120 DAI DAO  
11200 2011.04.25
2011.04.26
  2 S17E28 0000   AXX location: S18E31
S973 2011.04.26     N33W33         plage
S974 2011.04.27   1 S37E53 0000   AXX    
S975 2011.04.27   2 N17E14 0000   BXO    
Total spot count: 19 61  
Sunspot number: 39 151  

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
2011.04 112.9 (1) 74.3 (2A) / 82.6 (2B) (39.6 predicted, +2.9) (9.33)

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.