Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 18, 2013 at 03:10 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 very quiet on April 17. Solar wind speed at SOHO ranged between 321 and 352 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 108.1 (increasing 2.0 over the last solar rotation). The Potsdam WDC planetary A index was 3 (STAR Ap - based on the mean of three hour interval ap indices: 2.6). Three hour interval K indices: 11101001 (planetary), 00111211 (Boulder).

The background x-ray flux was at the class B3 level.

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

Region 11719 [N09W77] produced 3 small C flares and appears to be slowly decaying.
Region 11721 [S18W62] decayed slowly and quietly.
Region 11722 [S21W47] was quiet and stable.
Region 11723 [S18W03] decayed slowly and quietly. Two opposite polarity spots in the central trailing spot section are close and could become a magnetic delta structure if they develop further. C flares are possible and there's a small chance of a minor M class event.
Region 11724 [S26E21] decayed slowly and quietly.

Spotted regions not numbered by SWPC:
S2354 [N16W20] was quiet and stable.
New region S2358 [N10E29] emerged with a penumbra spot.
New region S2359 [S14E70] emerged with penumbra spots.

Coronal mass ejections (CMEs)

April 15-17: 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 small trans equatorial coronal hole (CH565) was in an Earth facing position on April 14, CH565 decreased in size on April 13-14 and closed on April 15. A trans equatorial coronal hole (CH566) will likely rotate to an Earth facing position on April 21-22.

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 18-20, possibly with unsettld intervals on April 18 due to weak effects from CH565.

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
11719 2013.04.05 3 6 3 N10W79 0050 CSO CAO

 

11721 2013.04.09
2013.04.10
5 4 3 S17W61 0120 CSO CSO  
11722 2013.04.09
2013.04.10
6 18 9 S19W48 0090 DAO DAI location: S21W47
S2350 2013.04.11       S24W06           plage
11724 2013.04.12
2013.04.13
4 11 4 S26E19 0090 CSO CRO location: S26E21
11723 2013.04.12
2013.04.13
21 35 16 S18W05 0200 DAI DAI beta-gamma
S2353 2013.04.12       N17W44           plage
S2354 2013.04.13   1   N16W20 0002   AXX  
S2355 2013.04.14       S05W55           plage
S2356 2013.04.15       S13W00         plage
S2357 2013.04.16       S26E01         plage
S2358 2013.04.17   1   N10E29 0002   AXX    
S2359 2013.04.17   2   S14E70 0005   AXX    
Total spot count: 39 78 35  
Sunspot number: 89 158 85  (total spot count + 10 * number of spotted regions)
Weighted SN: 64 101 58  (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): 53 55 47 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
2013.04 128.9 (1) 68.5 (2A) / 120.9 (2B) / 56.9 (2C) (51.0 projected, -1.2) (3.92)

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.