Solar Terrestrial Activity Report

Activity chart

Last major update issued on September 17, 2012 at 05:20 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 quiet to active on September 16. Solar wind speed at SOHO ranged between 353 and 422 km/s, slowly increasing after 08h UTC, likely under the influence of a low speed stream from CH535.

Solar flux measured at 20h UTC on 2.8 GHz was 97.3 (increasing 1.1 over the last solar rotation). The Potsdam WDC planetary A index was 9 (STAR Ap - based on the mean of three hour interval ap indices: 9.0). Three hour interval K indices: 23121142 (planetary), 22122232 (Boulder).

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

At midnight UTC the visible solar disk had 5 spotted active regions (in 2K resolution SDO images).

Region 11569 [S12W15] decayed slowly and quietly.
Region 11571 [S13E06] decayed slowly and quietly.
New region 11573 [N17E65] rotated into view on September 15 and was numbered the next day by SWPC.
New region 11574 [S25W16] emerged early in the day and could become an interesting region as it currently has reversed polarities.

Spotted regions not numbered by NOAA/SWPC:
New region S1922 [N15E13] emerged with a tiny spot.

Coronal mass ejections (CMEs)

September 14-16: 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 coronal hole (CH535) in the southern hemisphere was Earth facing position on September 13. A trans equatorial coronal hole (CH536) will likely rotate into an Earth facing position on September 17-19.

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 poor to fair. Propagation on long distance northeast-southwest paths is poor to fair.

Forecast

The geomagnetic field is expected to be quiet to unsettled on September 17 due to weak coronal hole effects. Quiet conditions are likely on September 18-19. A high speed stream from CH536 could cause quiet to active conditions on September 20-22.

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
11566 2012.09.03 1     N23W89 0010 HRX    

rotated out of view

11567 2012.09.07       N17W71           plage
11569 2012.09.09
2012.09.10
6 8 4 S12W13 0120 CSO CSO

area: 0240

11571 2012.09.10
2012.09.12
6 12 4 S13E06 0090 CSO CSO area: 0130
S1911 2012.09.11       S16W39           plage
S1912 2012.09.12       N14E24         plage
S1913 2012.09.12       N13W08           plage
S1914 2012.09.13       N20E31           plage
S1915 2012.09.13       N23E11           plage
S1916 2012.09.13       S20W38           plage
S1917 2012.09.14       S25W30           plage
11572 2012.09.14
2012.09.15
1     N16W83 0010 AXX     spotless
S1919 2012.09.14       N31W55           plage
S1920 2012.09.14       S04W25           plage
11573 2012.09.15
2012.09.16
1 3 2 N17E62 0010 AXX AXX  
11574 2012.09.16 2 8 4 S25W17 0000 BXO DRO   reversed polarities
S1922 2012.09.16   1   N15E13 0000   AXX    
Total spot count: 17 32 14  
Sunspot number: 77 82 54  (total spot count + 10 * number of spotted regions)
Weighted SN: 30 45 27  (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): 46 29 30 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) 7.96
2012.09 120.4 (1)  48.0 (2A)/ 89.9 (2B) (70.0 projected, +2.8) (11.66)

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.