Solar Terrestrial Activity Report

Last major update issued on April 11, 2011 at 04:05 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 7, 2011]
Annotated geomagnetic activity charts - Carrington rotation 2106 [Jan.-Feb.2011] - 2107 [Feb.-March 2011]

Recent activity

The geomagnetic field was quiet to unsettled on April 10. Solar wind speed ranged between 357 and 386 km/s.

Solar flux estimated at 20h UTC on 2.8 GHz was 104.8 (decreasing 2.6 over the last solar rotation). The planetary A index was 5 (STAR Ap - based on the mean of three hour interval ap indices: 5.3). Three hour interval K indices: 20001322 (planetary), 20011111 (Boulder).

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

At midnight UTC the visible solar disk had 6 spotted regions.

Region 11186 was mostly unchanged and quiet.
Region 11187 decayed slowly and quietly.
Region 11188 was quiet and stable.
Region 11189 developed slowly and quietly. [Note that SWPC currently has this region as 11185 while what is actually region 11185 for incomprehensible reasons got the new number 11189]

Spotted regions not numbered by NOAA/SWPC:
[S933] emerged with a few tiny spots in an old plage area in the northeast quadrant on April 4. Since then tiny spots have been coming and going in different parts of the region. Location at midnight: N26W32
[S943] rotated into view at the northeast limb on April 8. Location at midnight: N14E44

Coronal mass ejections (CMEs)

April 8-10: 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. An extension of the southern polar coronal hole is likely too far to the south to cause any geomagnetic 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 to fair.

Forecast

The geomagnetic field is expected to be mostly quiet on April 11-13.

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
11185 2011.04.03
2011.04.04
15   N17W08 0060 DSI     SWPC data is for region 11189
S932 2011.04.04     N13W16           plage
S933 2011.04.04   1 N26W32 0000   AXX  
11186 2011.04.05
2011.04.06
8 21 N23E06 0070 DSO CSI location: N22E08
11188 2011.04.05
2011.04.08
  1 S24W34 0000   AXX location: S26W30
S937 2011.04.05     S18W35           plage
11189 2011.04.06
2011.04.08
  26 N23W16 0060   DRI

location: N17W09

11187 2011.04.06
2011.04.07
3 5 S18E23 0020 BXO BXO

location: S19E25

S940 2011.04.06     S22W23         plage
S941 2011.04.06     S19W51           plage
S942 2011.04.07     N07W28           plage
S943 2011.04.08   1 N14E44 0000   AXX  
S944 2011.04.09     S32E08         plage
S945 2011.04.09     N08W07         plage
Total spot count: 26 55  
Sunspot number: 56 115  

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
2011.04 110.0 (1) 23.6 (2A) / 70.7 (2B) (39.6 predicted, +2.9) (11.84)

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.