Solar Terrestrial Activity Report

Activity chart

Last major update issued on September 12, 2012 at 05:00 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-24 (last update September 8, 2012)] [Cycle 24 progress (last update September 2, 2012) ]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22, 23 and 24 (last update September 8, 2012)]
[Graphical comparison of cycles 10, 12, 13, 14, 16 and 24 (last update September 8, 2012)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports since January 2003 (last update September 3, 2012)]

[POES auroral activity level since October 2009 - updated September 8, 2012]
[Solar polar fields vs solar cycles - updated June 27, 2011]

Recent activity

The geomagnetic field was very quiet on September 11. Solar wind speed at SOHO ranged between 285 and 315 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 105.1 (increasing 4.4 over the last solar rotation). The Potsdam WDC planetary A index was 1 (STAR Ap - based on the mean of three hour interval ap indices: 1.1). Three hour interval K indices: 00100001 (planetary), 11012210 (Boulder).

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

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

Region 11566 [N22W23] was quiet and stable.
Region 11567 [N15W00] decayed slowly and quietly and could soon become spotless.
Region 11568 [S10W55] decayed slowly and quietly.
Region 11569 [S12E54] has minor polarity intermixing and could produce C flares and perhaps a minor M class flare.

Spotted regions not numbered by NOAA/SWPC:
S1907 [S13E76] rotated fully into view.
New region S1910 [S12W18] emerged with a few spots.
New region S1911 [S16E26] emerged with a tiny spot.

Coronal mass ejections (CMEs)

September 9-11: No obviously Earth directed CMEs were observed in LASCO and STEREO imagery.

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 northern hemisphere coronal hole (CH533) was in an Earth facing position on September 8 but may have been too far to the north to become geoeffective. A small coronal hole (CH534) in the southern hemisphere was Earth facing on September 8. A coronal hole (CH535) in the southern hemisphere will likely rotate into an Earth facing position on September 13.

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.

Propagation

Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over high and upper middle latitudes is fair. Propagation on long distance northeast-southwest paths is poor.

Forecast

The geomagnetic field is expected to be quiet on September 12-13 with a chance of unsettled intervals due to weak coronal hole effects. Quiet conditions are likely on September 14-15. Quiet to unsettled conditions are possible on September 16-17 due to effects from CH535.

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. 0.5k 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 magnetic polarity overlay
Comment
SWPC STAR SDO SWPC STAR Current Previous
2K 1K
11564 2012.08.30
2012.08.31
4     S11W82 0110 DAO     spotless, the region decayed rapidly during the day
11565 2012.09.02
2012.09.03
      N11W88            
11566 2012.09.03 3 3 3 N23W25 0040 HSX CSO

area: 0090

11567 2012.09.07 4 7 1 N16W02 0030 DSO BXO area: 0000
S1903 2012.09.07       N05W46           plage
11568 2012.09.08
2012.09.09
4 4 2 S10W55 0050 DSO CRO

area: 0010

S1905 2012.09.08       S21W42           plage
11569 2012.09.09
2012.09.10
8 11 5 S12E53 0160 DAO ESO

 

S1907 2012.09.10   3 2 S13E76 0150   ESO  
S1908 2012.09.10       S12W07         plage
S1909 2012.09.10       S15W42         plage
S1910 2012.09.11   5 3 S12W18 0010   CRO    
S1911 2012.09.11   1   S16E26 0000   AXX    
Total spot count: 23 34 16  
Sunspot number: 73 104 76  (total spot count + 10 * number of spotted regions)
Weighted SN: 48 55 37  (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): 44 36 42 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
(3)
2011.05 95.8 41.5 47.6 (+5.8) 8.94
2011.06 95.8 37.0 53.2 (+5.6) 8.06
2011.07 94.2 43.8 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 66.9 (+1.4) 8.81
2012.03 114.7 64.3 (67.3 projected, +0.4) 16.08
2012.04 113.0 55.2 (66.5 projected, -0.8) 10.10
2012.05 121.5 69.0 (64.4 projected, -2.1) 7.06
2012.06 119.6 64.5 (63.6 projected, -0.8) 10.08
2012.07 133.9 66.5 (64.6 projected, +1.0) 13.90
2012.08 115.4 63.1 (67.2 projected, +2.6) 7.53
2012.09 129.9 (1)  38.4  (2A)/ 104.8 (2B) (70.0 projected, +2.8) (13.70)

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.