Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 25, 2013 at 04:10 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 to minor storm on April 24. Solar wind speed at SOHO ranged between 313 and 515 km/s, most of the day under the influence of a high speed stream from CH566.

Solar flux measured at 20h UTC on 2.8 GHz was 114.7 (increasing 16.0 over the last solar rotation). The Potsdam WDC planetary A index was 20 (STAR Ap - based on the mean of three hour interval ap indices: 20.5). Three hour interval K indices: 33244353 (planetary), 33344333 (Boulder).

The background x-ray flux was at the class B8 level.

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

Region 11726 [N12W62] lost some spots and had no obvious magnetic delta structures by the end of the day. A major flare is possible during the next 2-3 days.
Region 11727 [N24W12] was quiet and stable.
Region 11728 [N20E51] added a few penumbra spots and was quiet.
Region 11729 [S15W22] developed slowly and quietly.
New region 11730 [S19E47] emerged with several spots and has polarity intermixing. C flares are possible.

Spotted regions not numbered by SWPC:
S2368 [S16E20] was quiet and stable.
S2369 [N17E05] was quiet and stable.
S2374 [N16E36] decayed slowly and quietly.
New region S2375 [N08E78] rotated into view with several spots. C and minor M class flares are possible.
New region S2376 [N13W29] emerged with several spots.

Coronal mass ejections (CMEs)

April 22-24: 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) was Earth facing position on April 22-24. CH566 has decayed significantly during its transition of the visible disk.

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

Forecast

The geomagnetic field is expected to be quiet to unsettled on April 25-27 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
      S26W74           plage
S2359 2013.04.17       S15W15           plage
11727 2013.04.18
2013.04.19
3 9 3 N25W11 0030 HAX CAO  
11726 2013.04.19 30 26 15 N13W63 0840 FKC FKC beta-gamma
S2366 2013.04.19       S13W49           plage
S2367 2013.04.19       S06W47           plage
S2368 2013.04.20   14 2 S16E20 0021   BXO  
S2369 2013.04.21   3   N17E05 0007   AXX  
11729 2013.04.21
2013.04.23
6 11 3 S14W22 0010 BXO DRO area: 0050
11728 2013.04.22
2013.04.23
1 7 3 N19E48 0060 HSX CSO location: N20E51
S2373 2013.04.23       N08E30         plage
S2374 2013.04.23   1 1 N16E36 0004   AXX  
11730 2013.04.24 2 14 3 S19E47 0010 BXO DAO   area: 0070
S2375 2013.04.24   8 6 N08E78 0400   DKC    
S2376 2013.04.24   7 5 N13W29 0030   DRO    
Total spot count: 42 100 41  
Sunspot number: 92 200 131  (total spot count + 10 * number of spotted regions)
Weighted SN: 62 141 82  (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): 55 70 72 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
2013.04 122.8 (1) 89.7 (2A) / 112.1 (2B) / 63.9 (2C) (51.0 projected, -1.2) (4.85)

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.