Solar Terrestrial Activity Report

Activity chart

Last major update issued on August 18, 2012 at 05:40 UTC.

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[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports since January 2003 (last update August 5, 2012)]

[POES auroral activity level since October 2009 - updated August 5, 2012]
[Solar polar fields vs solar cycles - updated June 27, 2011]

Recent activity

The geomagnetic field was quiet to active on August 17. Solar wind speed at SOHO ranged between 348 and 478 km/s under the influence of mostly weak CME effects.

Solar flux measured at 20h UTC on 2.8 GHz was 95.1 (increasing 5.2 over the last solar rotation). The Potsdam WDC planetary A index was 10 (STAR Ap - based on the mean of three hour interval ap indices: 10.1). Three hour interval K indices: 43311112 (planetary), 43322211 (Boulder).

The background x-ray flux is at the class B4 level.

At midnight UTC the visible solar disk had 6 spotted active regions (in 2K resolution SDO images).

Region 11543 [N23W60] decayed slowly with the single penumbra apparently splitting into two as positive polarity flux emerged between the two largest umbrae.
Region 11546 [N16E60] was quiet and stable.
New region 11547 [N06E22] emerged on August 16 and was numbered by SWPC the next day.

Spotted regions not numbered by SWPC:
S1862 [N14W25] lost a spot and was quiet.
New region S1864 [N19E86] (now AR 11548) rotated partly into view. More spots are visible early on August 18. The region is likely to be complex as it produced 2 M flares during the day and already 2 early on Aug.18. Flares: M2.4 at 13:19, M1.0 at 17:20 UTC. A major M5.5 impulsive flare was recorded at 01:02 on Aug.18.
New region S1865 [S28E17] emerged with a tiny spot.

A large filament eruption was triggered by an event in AR 11543 starting at 22:00 UTC. The eruption produced a wide and bright CME in STEREO imagery, the CME may have Earth directed extensions.

Coronal mass ejections (CMEs)

August 15-16: No obviously Earth directed CMEs were observed in LASCO and STEREO imagery.
August 17: A large filament eruption near AR 11543 starting at 22h UTC was the source of a wide and bright CME. A weak glancing blow is possible on August 20 or 21.

Coronal holes

Coronal hole history (since 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 (CH529) in the southern hemisphere was Earth facing on August 15-16.

Coronal hole map

The above coronal hole map is based on a method where coronal holes are detected automatically. While the method may need some fine tuning, 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 this method, the extent and intensity of both CHs are consistent with other data sources.


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.


The geomagnetic field is expected to be quiet to active on August 18-19 due to effects from CH529. August 20 is likely to see mostly quiet conditions with a chance of weak CME effects late in the day or on August 21.

Coronal holes (1) Coronal mass ejection (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
Spot count Location at midnight Area Classification SDO / HMI 4K continuum
image with magnetic polarity overlay
2K 1K
11542 2012.08.06       S11W76          


11543 2012.08.06
5 9 2 N24W59 0320 CKO CKO

area: 0420

S1856 2012.08.14       N13W10           plage
S1857 2012.08.14       S19W43           plage
11546 2012.08.15
1 1 1 N16E56 0050 HSX HSX location: N16E60
11547 2012.08.16
6 8 5 N05E21 0030 CSO DRO  
S1861 2012.08.16       N23E23         plage
S1862 2012.08.16   1 1 N14W25 0000   AXX  
S1864 2012.08.17   2 1 N19E86 0030   CSO    
S1865 2012.08.17   1   S28E17 0000   AXX    
Total spot count: 12 22 10  
Sunspot number: 42 82 60  (total spot count + 10 * number of spotted regions)
Weighted SN: 32 45 33  (Sum of total spot count + classification weighting for each AR. Classification weighting: X=0, R=3, A/S=5, H/K=10)
Relative sunspot number (Wolf number): 25 29 33 k * (sunspot number). k = 0.6 for SWPC, k = 0.35 for STAR SDO 2K, k = 0.55 for STAR SDO 1K

Monthly solar cycle data

Month Average measured solar flux International sunspot number (SIDC) Smoothed sunspot number Average ap
2011.05 95.8 41.6 47.6 (+5.8) 8.94
2011.06 95.8 37.0 53.2 (+5.6) 8.06
2011.07 94.2 43.9 57.2 (+4.0) 8.16
2011.08 101.7 50.6 59.0 (+1.8) 7.26
2011.09 133.8 78.0 59.5 (+0.5) 12.27
2011.10 137.3 88.0 59.9 (+0.4) 8.28
2011.11 153.5 96.7 61.1 (+1.2) 5.55
2011.12 141.3 73.0 63.4 (+2.3) 3.78
2012.01 132.5 58.3 65.5 (+2.1) 7.15
2012.02 106.5 32.9 (67.4 projected, +1.9) 8.81
2012.03 114.7 64.3 (68.1 projected, +0.7) 16.08
2012.04 113.0 55.2 (67.5 projected, -0.6) 10.10
2012.05 121.5 69.0 (65.8 projected, -1.7) 7.06
2012.06 119.6 64.5 (65.0 projected, -0.8) 10.08
2012.07 133.9 66.5 (66.0 projected, +1.0) 13.90
2012.08 122.4 (1) 51.0 (2A) / 93.1 (2B) (68.6 projected, +2.6) (8.04)

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 quicklook and definitive Potsdam WDC ap indices. Values in red are based on the definitive international Potsdam WDC 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.