Solar Terrestrial Activity Report

Last major update issued on September 12, 2011 at 04:30 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)
[Solar cycles 21-24 (last update September 1, 2011)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22, 23 and 24 (last update September 1, 2011)]
[Graphical comparison of cycles 10, 12, 13, 14, 16 and 24 (last update September 1, 2011)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports since January 2003 (last update September 1, 2011)]

[POES auroral activity level since October 2009 - updated September 8, 2011]
Annotated geomagnetic activity charts - Carrington rotation 2112 [July 2011] -  2113 [July-August 2011] NEW
[Solar polar fields vs solar cycles - updated June 27, 2011]

Recent activity

The geomagnetic field was quiet to unsettled on September 11. Solar wind speed ranged between 539 and 608 km/s under the influence of a high speed stream from CH475.

Solar flux measured at 20h UTC on 2.8 GHz was 121.3 (increasing 30.9 over the last solar rotation). The planetary A index was 9 (STAR Ap - based on the mean of three hour interval ap indices: 9.4). Three hour interval K indices: 32113213 (planetary), 32213313 (Boulder).

The background x-ray flux is at the class B7 level.

At midnight UTC the visible solar disk had 12 spotted regions (in 2K resolution SDO images).

Region 11283 rotated to the northwest limb. Flares: C6.6 at 08:51, C1.9 at 13:26, C1.7 at 19:49, C1.1 at 21:25 UTC
Region 11287 was quiet and stable.
Region 11289 decayed slightly losing the penumbra which had been located to the southwest of the large penumbra.
Region 11290 developed slowly and has minor polarity intermixing. C flares are possible.
New region 11292 emerged in the northeast quadrant on September 11.

Spotted regions not numbered by NOAA/SWPC:
[S1196] reemerged with several spots on September 11. Location at midnight: S21W53
[S1201] emerged in the southeast quadrant on September 10. Location at midnight: S17E43
[S1205] rotated into view at the northeast limb on September 11. Location at midnight: N22E83
[S1206] emerged in the northeast quadrant on September 11. Location at midnight: N15E11
[S1207] emerged in the northeast quadrant on September 11. Location at midnight: N17E04
[S1208] emerged in the northwest quadrant on September 11. Location at midnight: N16W58
[S1209] emerged in the northwest quadrant on September 11. Location at midnight: N21W42

Coronal mass ejections (CMEs)

September 9: No obviously Earth directed CMEs were observed. There was a CME after the M2 event in region 11283 but its path makes any terrestrial effects unlikely. Several backsided CMEs were noted.
September 10: A large filament eruption in the northwest quadrant early in the day was associated with at least a partial halo CME. A filament eruption starting at 07h UTC to the south of region 11289 may have been associated with a potentially Earth directed CME.
September 11: No obviously Earth directed CMEs observed.

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 recurrent trans equatorial coronal hole (CH475) was in an Earth facing position on September 8-10. Another and smaller trans equatorial coronal hole (CH476) was Earth facing on September 11 as it decayed and closed.

The above coronal hole map is based on a new method where coronal holes are detected automatically. The method may need some fine tuning, however, it has significant advantages over detecting coronal holes manually. The main improvement is the ability to detect coronal holes at and just beyond the solar limbs. Early results using this method for SDO images over a span of several weeks indicate a good match between coronal holes observed over the visible disk and their extent and position at the east and west limbs. Note that the polar coronal holes are easily detected using the new method, the extent and intensity of both holes are consistent with other data sources.

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 active on September 12-13 due to effects from CH475. CME impacts are possible on September 13 and could cause an increase in disturbance levels. Quiet to unsettled conditions are likely on September 14.

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
11283 2011.08.29
2011.08.30
2 4 N14W87 0140 DSO DSO

 

11287 2011.09.02
2011.09.03
2 7 S28W42 0060 HSX CSO location: S28W40
11288 2011.09.03
2011.09.04
    N19W49           plage
S1196 2011.09.04   5 S21W53 0010   BXO    
11289 2011.09.05
2011.09.06
16 17 N22E12 0430 DKO CHO beta-gamma

location: N23E13

11290 2011.09.07
2011.09.09
10 26 S15E03 0070 DSO DRI

beta-gamma

location: S14E04

11291 2011.09.09
2011.09.10
2   N23W15 0010 BXO     plage
S1201 2011.09.10   3 S17E43 0010   HRX  
S1202 2011.09.10     N11W16         plage
11292 2011.09.11 2 7 N08E66 0040 BXO CRO   formerly region S1203
S1205 2011.09.11   3 N22E83 0050   CAO    
S1206 2011.09.11   1 N15E11 0010   AXX    
S1207 2011.09.11   5 N17E04 0010   BXO    
S1208 2011.09.11   5 N16W58 0020   BXO    
S1209 2011.09.11   2 N21W42 0000   AXX    
Total spot count: 34 85  
Sunspot number: 94 205  (total spot count + 10 * number of spotted regions)
Classification adjusted SN: 59 119  (Sum of total spot count + classification adjustment for each AR. Classification adjustment: X=0, R=3, A/S=5, H/K=10)
Relative sunspot number (Wolf number): 56 68  k * (sunspot number). k = 0.6 for SWPC. k = 0.33 for STAR SDO

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
2010.06 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 23.2 (+3.6) 6.07 / 6.27
2010.11 82.5 21.5 26.5 (+3.3) 4.80 / 5.50
2010.12 84.2 14.4 28.8 (+2.3) 3.41 / 4.35
2011.01 83.6 19.1 31.0 (+2.2) 4.32 / 5.51
2011.02 94.6 29.4 33.4 (+2.4) 5.41 / 6.44
2011.03 115.0 56.2 (36.2 predicted, +2.8) 7.79 / 8.18
2011.04 112.6 54.4 (39.1 predicted, +2.9) 9.71 / 8.83
2011.05 95.8 41.6 (42.4 predicted, +3.3) 9.18 / 8.94
2011.06 95.8 37.0 (46.1 predicted, +3.7) 8.96
2011.07 94.2 43.9 (50.3 predicted, +4.2) 9.14
2011.08 101.7 50.6 (54.4 predicted, +4.1) 8.16
2011.09 115.2 (1) 33.8 (2A) /  92.1 (2B) (56.7 predicted, +2.3) (11.52)

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.