Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 23, 2013 at 02:30 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 23-24 (last update April 1, 2013)] [Cycle 24 progress (last update April 7, 2013) ]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22, 23 and 24 (last update April 1, 2013)]
[Graphical comparison of cycles 10, 12, 13, 14, 16 and 24 (last update April 1, 2013)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports since January 2003 (last update April 4, 2013)]

[POES auroral activity level since October 2009 - updated January 26, 2013]
[Solar polar fields vs solar cycles - updated March 24, 2013]
[Presentation 3rd SSN Workshop, Tucson, 2013 (pdf)]

Recent activity

The geomagnetic field was quiet on April 22. Solar wind speed at SOHO ranged between 270 and 277 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 112.9 (increasing 20.5 over the last solar rotation). The Potsdam WDC planetary A index was 4 (STAR Ap - based on the mean of three hour interval ap indices: 3.5). Three hour interval K indices: 12011101 (planetary), 12011222 (Boulder).

The background x-ray flux was at the class B6 level.

At midnight UTC the visible solar disk had 8 spotted active regions (in 2K resolution SDO images).

Region 11723 [S18W74] decayed slowly and quietly.
Region 11726 [N12W36] remained magnetically complex with several deltas in the large trailing penumbral structure. Further M class flares are possible. C5+ flares: M1.0 at 10:29 UTC.
Region 11727 [N25E17] was quiet and stable.

Spotted regions not numbered by SWPC:
S2357 [S23W68] developed slowly and quietly and has minor polarity intermixing.
S2368 [S18E51] added some penumbra spots.
S2369 [N19E32] was quiet and stable.
S2370 [S14E07] was quiet and stable.
New region S2372 [N19E78] rotated into view. This region, or a nearby AR to the east, is capable of C class flaring.

Coronal mass ejections (CMEs)

April 20-22: 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 trans equatorial coronal hole (CH566) will be Earth facing position on April 22-24.

Coronal hole map

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

Forecast

The geomagnetic field is expected to be quiet on April 23. Quiet to minor storm conditions are likely from late on April 24 until April 27 due to effects from CH566.

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 2K resolution) 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 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
11724 2013.04.12
2013.04.13
      S26W46           plage
11723 2013.04.12
2013.04.13
3 3 1 S19W70 0030 CSO BXO location: S18W74

area: 0014

S2357 2013.04.16   9 3 S23W68 0027   BXO  
S2358 2013.04.17       N10W36           plage
S2359 2013.04.17       S15E11           plage
11727 2013.04.18
2013.04.19
8 13 6 N25E18 0070 DAO ESO  
11726 2013.04.19 42 53 27 N13W35 0550 EKC FKC beta-gamma-delta

area: 0730

S2364 2013.04.19       N20W49           plage
S2365 2013.04.19       S14W46           plage
S2366 2013.04.19       S13W23           plage
S2367 2013.04.19       S06W21           plage
S2368 2013.04.20   7 1 S18E51 0019   BXO  
S2369 2013.04.21   3   N19E32 0007   AXX  
S2370 2013.04.21   4 1 S14E07 0012   BXO  
S2371 2013.04.21       N12W48         plage
S2372 2013.04.22   1 1 N19E78 0090   HSX    
Total spot count: 53 93 40  
Sunspot number: 83 173 110  (total spot count + 10 * number of spotted regions)
Weighted SN: 73 113 60  (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): 50 61 61 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)
2011.11 153.5 (cycle max) 96.7 (cycle max) 61.1 (+1.2) 5.55
2012.01 132.5 58.3 65.5 (+2.1) 7.15
2012.02 106.5 32.9 66.9 (+1.4)
possible cycle 24 max
8.81
2012.03 114.7 64.3 66.8 (-0.1) 16.08
2012.04 113.0 55.2 64.6 (-2.2) 10.10
2012.05 121.5 69.0 61.7 (-2.9) 7.06
2012.06 119.6 64.5 58.9 (-2.8) 10.08
2012.07 133.9 66.5 57.7 (-1.2) 13.90
2012.08 115.4 63.0 58.1 (+0.4) 7.96
2012.09 122.9 61.4 58.1 (-0.0) 8.07
2012.10 123.3 53.3 (57.6 projected, -0.5) 9.97
2012.11 121.3 61.8 (56.9 projected, -0.7) 7.08
2012.12 108.6 40.8 (55.7 projected, -1.2) 3.44
2013.01 127.1 62.9 (54.3 projected, -1.4) 4.69
2013.02 104.3 38.0 (53.3 projected, -1.0) 6.11
2013.03 111.3 57.9 (52.2 projected, -1.1) 10.56
2013.04 123.5 (1) 83.4 (2A) / 113.8 (2B) / 61.3 (2C) (51.0 projected, -1.2) (4.11)

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) Boulder SN current month average to date. 2C) STAR SDO 1K Wolf number 30 day average.
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.