Solar Terrestrial Activity Report

Last major update issued on September 17, 2011 at 05:55 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 15, 2011]
Annotated geomagnetic activity charts - Carrington rotation 2112 [July 2011] -  2113 [July-August 2011]
[Solar polar fields vs solar cycles - updated June 27, 2011]

Recent activity

The geomagnetic field was very quiet on September 16. Solar wind speed ranged between 347 and 453 km/s. A solar wind shock was observed at ACE near 03h UTC on September 17. This was the arrival of the CME observed on Sept.13/14.

Solar flux measured at 20h UTC on 2.8 GHz was 143.1 (increasing 42.6 over the last solar rotation). The planetary A index was 2 (STAR Ap - based on the mean of three hour interval ap indices: 2.1). Three hour interval K indices: 10001101 (planetary), 11012221 (Boulder).

The background x-ray flux is at the class C1 level.

At midnight UTC the visible solar disk had 13 spotted regions (in 2K resolution SDO images).

Region 11289 [N23W52] was mostly unchanged. Flare: C2.6 long duration event peaking at 23:51 UTC. This event was associated with a CME which is likely not going to become geoeffective.
Region 11290 [S12W68] developed slowly and could produce further C flares. Flares: C9.3 at 11:36, C2.0/1F at 15:08, C1.4 at 22:13 UTC
Region 11291 [N22W82] developed further and could produce a C flare as it rotates over the northwest limb.
Region 11292 [N10W04] was quiet and stable.
Region 11293 [N17W63] decayed quietly retaining only 2 spots.
Region 11294 [S17W30] decayed slowly and quietly.
Region 11295 [N22E18] decayed losing quite a few spots. There's still polarity intermixing and C and M flares are possible.  Flare: C4.5 at 02:57 UTC.
Region 11296 [N26E34] decayed but could produce C flares. Flare: C2.2 at 17:21 UTC.
Region 11297 [S18W79] decayed further as it rotated to the southwest limb. Flares: C7.8/1F at 00:19, C4.7/1F at 04:39, C2.2 at 08:46, C1.5 at 19:31 UTC.
Region 11298 [N16E24] decayed slowly and quietly.
New region 11299 [S19E12] emerged in the southeast quadrant on September 14 and received an SWPC number 2 days later.

Spotted regions not numbered by NOAA/SWPC:
[S1214] reemerged with a single tiny spot. Location at midnight: S25W31
[S1218] emerged in the northwest quadrant on September 16. Location at midnight: N24W16

Coronal mass ejections (CMEs)

September 15-16: No obviously Earth directed CMEs observed.
September 13-14: A bright CME was observed following an eruption in region 11289 late on September 13.

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

No obvious coronal holes are currently in or near potentially geoeffective positions.

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 poor to fair.

Forecast

The geomagnetic field is expected to be quiet to active on September 17 due to CME effects. Quiet conditions are likely on September 18-19.

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
11289 2011.09.05
2011.09.06
5 9 N22W51 0310 CKO CHO

location: N23W52

11290 2011.09.07
2011.09.09
3 11 S13W69 0010 BXO CAI

location: S12W68

area: 0050

11291 2011.09.09
2011.09.10
3 7 N24W82 0090 DAO DSO area: 0150

location: N22W82

11294 2011.09.10
2011.09.12
1 4 S16W31 0020 CRO BXO area: 0010

location: S17W30

S1203 2011.09.10     N07W15           plage
11292 2011.09.11 1 6 N10W04 0020 HRX BXO  
11295 2011.09.11
2011.09.12
23 39 N22E17 0240 DAI DAI beta-gamma
S1206 2011.09.11     N15W52           plage
11293 2011.09.11
2011.09.12
2 2 N17W65 0010 BXO BXO location: N17W63
11296 2011.09.12
2011.09.13
8 23 N26E31 0130 DAO CAO beta-gamma

location: N26E34

S1212 2011.09.12     N38W34           plage
S1213 2011.09.13     S18W40           plage
S1214 2011.09.13   1 S26W31 0000   AXX    
11297 2011.09.13
2011.09.14
2 9 S18W77 0060 DAO CAO location: S18W79
11299 2011.09.14
2011.09.16
8 19 S21E11 0030 CRO CRO location: S19E12
11298 2011.09.14 7 13 N15E23 0070 DSO CSO beta-gamma
S1218 2011.09.16   2 N24W16 0000   BXO    
Total spot count: 63 145  
Sunspot number: 173 275  (total spot count + 10 * number of spotted regions)
Classification adjusted SN: 107 188  (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): 104 91  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
2011.09 121.7 (1) 57.1 (2A) /  107.0 (2B) (56.7 predicted, +2.3) (11.38)

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.