Solar Terrestrial Activity Report

Last major update issued on April 9, 2011 at 05:45 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 8. Solar wind speed ranged between 384 and 453 km/s. A weak solar wind shock was detected by SOHO/MTOF at 18:21 UTC. Since then the interplanetary magnetic field has been southwards resulting in a relatively weak geomagnetic disturbance.

Solar flux estimated at 20h UTC on 2.8 GHz was 108.7 (decreasing 12.0 over the last solar rotation). The planetary A index was 8 (STAR Ap - based on the mean of three hour interval ap indices: 7.6). Three hour interval K indices: 20113233 (planetary), 21112333 (Boulder).

The background x-ray flux is at the class B3 level.

At midnight UTC the visible solar disk had 11 spotted regions.

Region 11184 lost the trailing spots and will rotate to the northwest limb today.
Region 11185 decayed slowly and was quiet.
Region 11186 decayed and was quiet.
Region 11187 was quiet and stable.
New region 11188 emerged in the southeast quadrant on April 5 and was noticed by NOAA/SWPC 3 days later. The region developed slowly on April 8.
New region 11189 emerged in the northeast quadrant on April 6 and was detected by NOAA/SWPC 2 days later. Slow development was observed on April 8.

Spotted regions not numbered by NOAA/SWPC:
[S928] emerged with spots in an old plage field in the northeast quadrant on April 1. Location at midnight: N16W40
[S933] emerged with a few tiny spots in an old plage area in the northeast quadrant on April 4. Location at midnight: N22W12
[S937] emerged in the southeast quadrant near region S936 on April 5. Location at midnight: S18W09.
[S940] emerged in the southeast quadrant on April 6 in an old plage area. Location at midnight: S24E08
[S943] rotated into view at the northeast limb on April 8. Location at midnight: N13E68

Coronal mass ejections (CMEs)

April 6-8: 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 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 fair to good.

Forecast

The geomagnetic field is expected to be quiet to unsettled with a chance of active intervals on April 9 and mostly quiet on April 10-11.

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
11184 2011.03.30
2011.04.01
2 2 N15W68 0170 HSX HSX location: N15W71
S927 2011.03.31     N25W39           plage
S928 2011.04.01   1 N16W40 0000   AXX  
11185 2011.04.03
2011.04.04
14 8 N20E14 0020 CSO CRO location: N22E12
S932 2011.04.04     N13E10           plage
S933 2011.04.04   8 N22W12 0000   BXO  
11186 2011.04.05
2011.04.06
8 17 N22E37 0050 CSO CSI location: N23E33
11188 2011.04.05
2011.04.08
3 6 S25W06 0020 CRO BXO formerly region S936
S937 2011.04.05   3 S18W09 0000   AXX  
11189 2011.04.06
2011.04.08
6 15 N23E11 0020 DSO BXI formerly region S938

location: N17E18

11187 2011.04.06
2011.04.07
4 9 S18E50 0030 CSO CRO

location: S19E52

S940 2011.04.06   3 S24E08 0000   AXX  
S941 2011.04.06     S19W25         plage
S942 2011.04.07     N07W02         plage
S943 2011.04.08   4 N13E68 0010   BXO    
Total spot count: 37 76  
Sunspot number: 97 186  

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
2011.02 94.6 29.4 (34.4 predicted, +2.5) 5.41
2011.03 115.0 56.2 (36.7 predicted, +2.3) 7.79
2011.04 111.3 (1) 18.9 (2A) / 70.9 (2B) (39.6 predicted, +2.9) (12.94)

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.