Solar Terrestrial Activity Report

Last major update issued on October 3, 2011 at 04:00 UTC.

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

[POES auroral activity level since October 2009 - updated September 29, 2011]
Annotated geomagnetic activity charts - Carrington rotation 2113 [July-August 2011] - 2114 [August-September 2011]
[Solar polar fields vs solar cycles - updated June 27, 2011]

Recent activity

The geomagnetic field was quiet to unsettled on October 2. Solar wind speed ranged between 389 and 518 km/s under the influence of a high speed stream from CH477.

Solar flux measured at 23h UTC on 2.8 GHz was 130.9 (increasing 12.2 over the last solar rotation). The planetary A index was 11 (STAR Ap - based on the mean of three hour interval ap indices: 11.1). Three hour interval K indices: 12333323 (planetary), 13242312 (Boulder).

The background x-ray flux is at the class B7 level.

At midnight UTC the visible solar disk had 10 spotted regions (in 2K resolution SDO images).

Region 11302 [N13W60] decayed slowly and becmae less complex. There's still a chance of occasional M class flaring. Flares: C1.5 at 03:49,  C2.4 at 06:34, C2.6 at 15:11, C1.3 at 16:55, M1.3 at 17:23 UTC
Region 11305 [N12W25] decayed slowly losing the penumbra that had developed to the south of the main penumbra. Further M class flares are possible. Flares: M3.9/1N at 00:50, C7.6/1F at 21:49 UTC.
Region 11306 [N15W05] was quiet and stable.
Region 11307 [N15E25] was quiet and stable.
Region 11308 [S26E45] decayed slowly and quietly.
New region 11309 [N23E68] rotated into view at the northeast limb on October 1 and was numbered the next day by SWPC.

Spotted regions not reported by NOAA/SWPC:
[S1245] reemerged on October 2. Location at midnight: S23W12
[S1248] emerged on October 2 in the southeast quadrant. Location at midnight: S33E28
[S1249] emerged in the northeast quadrant on October 2. Location at midnight: N33E31
[S1250] emerged in the northeast quadrant on October 2. Location at midnight: N27E18

Coronal mass ejections (CMEs)

September 30: A small and slow CME was observed after an M1 event in region 11305. This CME could reach Earth on October 3.
October 1: An Earth directed CME was associated with the M1 event in region 11305. The CME will likely reach Earth sometime between late on October 3 and noon on October 4. A large full halo CME was observed later in the day both in STEREO-A and B, its origin an active region a couple of days behind the northeast limb.
October 2: An apparently Earth directed CME was observed in STEREO images early in the day (associated with the M3.9 event in region 11305). This CME could reach Earth sometime between noon and midnight on October 4.

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 (CH477) in the southern hemisphere was in an Earth facing position on September 28-29. A northern hemisphere coronal hole (CH478) will probably rotate into an Earth facing position on October 6.

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 initially quiet on October 3. Several CMEs are likely to arrive, the first one could cause unsettled to active conditions on October 3, the second (and largest) could cause unsettled to major storm conditions starting sometime between late on October 3 and noon on October 4, the third CME could arrive late on October 4 or early on October 5 and prolong the geomagnetic disturbance.

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
11302 2011.09.21
2011.09.22
14 26 N16W55 0410 FKC EHC beta-gamma

location: N13W60

area: 0600

11305 2011.09.24
2011.09.25
9 17 N12W25 0190 DSI CHO area: 0280
11306 2011.09.25
2011.09.26
1 4 N15W06 0020 HSX CSO area: 0050
S1236 2011.09.26     S17W49           plage
11307 2011.09.27
2011.09.28
5 7 N15E22 0030 ERO CRO  
S1239 2011.09.27     S22W33           plage
S1240 2011.09.27     N26W75         plage
11308 2011.09.30
2011.10.01
1 2 S25E43 0030 HRX AXX

location: S26E45

area: 0000

S1242 2011.09.30     N21E17           plage
S1243 2011.09.30     S16W05           plage
S1244 2011.09.30     S27E15           plage
S1245 2011.09.30   1 S23W12 0000   AXX    
11309 2011.10.01
2011.10.02
2 2 N23E67 0080 DSO HSX formerly region S1246

area: 0220

S1247 2011.10.01     N08W35         plage
S1248 2011.10.02   3 S33E26 0000   BXO    
S1249 2011.10.02   1 N33E31 0000   AXX    
S1250 2011.10.02   1 N27E18 0000   AXX    
Total spot count: 32 64  
Sunspot number: 92 164  (total spot count + 10 * number of spotted regions)
Classification adjusted SN: 63 97  (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): 55 54  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
2010.07 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 36.9 (+3.5) 7.79 / 8.18
2011.04 112.6 54.4 (41.1 predicted, +4.2) 9.71 / 8.83
2011.05 95.8 41.6 (45.2 predicted, +4.1) 9.18 / 8.94
2011.06 95.8 37.0 (49.2 predicted, +4.0) 8.96
2011.07 94.2 43.9 (53.1 predicted, +3.9) 9.14
2011.08 101.7 50.6 (57.2 predicted, +4.1) 8.16
2011.09 133.8 78.0 (60.3 predicted, +3.1) 12.80
2011.10 133.9 (1) 5.7 (2A) / 89.0 (2B) (61.8 predicted, +1.5) (10.06)

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.