Solar Terrestrial Activity Report

Last major update issued on August 24, 2011 at 04:45 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)
[Solar cycles 21-24 (last update August 2, 2011)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22, 23 and 24 (last update August 2, 2011)]
[Graphical comparison of cycles 10, 12, 13, 14, 16 and 24 (last update August 2, 2011)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports since January 2003 (last update August 2, 2011)]

[POES auroral activity level since October 2009 - updated August 19, 2011]
Annotated geomagnetic activity charts - Carrington rotation 2111 [June-July 2011]  - 2112 [July 2011] NEW
[Solar polar fields vs solar cycles - updated June 27, 2011]

Recent activity

The geomagnetic field was quiet to active on August 23. Solar wind speed ranged between 339 and 529 km/s under the influence of a high speed stream from CH472.

Solar flux measured at 20h UTC on 2.8 GHz was 103.7 (increasing 4.4 over the last solar rotation). The planetary A index was 9 (STAR Ap - based on the mean of three hour interval ap indices: 9.3). Three hour interval K indices: 30112243 (planetary), 20213333 (Boulder).

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

At midnight UTC the visible solar disk had 7 spotted regions (in 2K resolution SDO images).

Region 11271 decayed slightly with loss of penumbral area. There's a weak magnetic delta structure in the western part of the northern penumbra. An M class flare is still possible.
Region 11272 decayed further and was quiet.
Region 11274 lost the trailing spot and was quiet.
Region 11275 was quiet and stable.

Spotted regions not numbered by NOAA/SWPC:
[S1171] reemerged on August 20. Location at midnight: N06W24
[S1178] emerged in the northwest quadrant on August 23. Location at midnight: N17W13
[S1179] emerged in the northwest quadrant on August 23. Location at midnight: N28W24

Coronal mass ejections (CMEs)

August 21-23: No obviously Earth directed CMEs were observed in LASCO or 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 recurrent coronal hole (CH473) in the northern hemisphere could rotate into an Earth facing position on August 24-25.

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.

Forecast

The geomagnetic field is expected to be quiet to unsettled on August 24 due to effects from CH472. Quiet conditions are likely on August 25-26. Quiet to active conditions are possible on August 27-28 due to CH473.

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
11271 2011.08.14
2011.08.15
21 40 N17W29 0270 EKI DAC

beta-gamma-delta

area: 0400

11272 2011.08.15
2011.08.16
6 14 S21W20 0040 DSO CRO

location: S22W22

S1171 2011.08.16   1 N06W24 0000   AXX  
S1173 2011.08.17     N24W40           plage
11274 2011.08.19
2011.08.20
2 6 N19E30 0030 HSX AXX location: N18E32

area: 0010

11275 2011.08.20
2011.08.21
1 5 N08E39 0020 HSX BXO location: N08E46
S1177 2011.08.22     N23W70         plage
S1178 2011.08.23   2 N17W13 0000   AXX    
S1179 2011.08.23   1 N28W24 0000   AXX    
11276 2011.08.23 1   N20E48 0000 AXX       region should be deleted, spot was the trailing spot of region 11274
Total spot count: 31 69  
Sunspot number: 81 139  (total spot count + 10 * number of spotted regions)
Classification adjusted SN: 56 77  (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): 49 46  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
2010.05 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 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 (33.6 predicted, +2.6) 5.41 / 6.44
2011.03 115.0 56.2 (36.6 predicted, +3.0) 7.79 / 8.18
2011.04 112.6 54.4 (39.4 predicted, +2.8) 9.71 / 8.83
2011.05 95.8 41.6 (42.7 predicted, +3.3) 9.18 / 8.94
2011.06 95.8 37.0 (46.5 predicted, +3.8) 8.96
2011.07 94.2 43.9 (50.6 predicted, +4.1) 9.14
2011.08 101.0 (1) 44.7 (2A) / 60.3 (2B) (54.8 predicted, +4.2) (9.28)

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.