Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 17, 2013 at 04:45 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 16. Solar wind speed at SOHO ranged between 345 and 412 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 113.3 (increasing 5.7 over the last solar rotation). The Potsdam WDC planetary A index was 2 (STAR Ap - based on the mean of three hour interval ap indices: 2.5). Three hour interval K indices: 10000112 (planetary), 20001211 (Boulder).

The background x-ray flux was at the class B4 level.

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

Region 11719 [N09W63] developed and became more complex magnetically with significant polarity intermixing. Further C class flaring is likely
Region 11721 [S19W47] decayed slowly and quietly. The easternmost spot section could be viewed as a separate region.
Region 11722 [S20W33] developed further and was quiet. The northernmost spot could be a separate region.
Region 11723 [S18E08] developed further and has polarity intermixing. Further C class flaring is likely.
Region 11724 [S26E33] decayed slowly and quietly.

Spotted regions not numbered by SWPC:
S2354 [N09W08] was quiet and stable.
S2356 [S13E13] decayed slowly and quietly.
New region S2357 [S26E14] emerged to the southeast of AR 11723.

Coronal mass ejections (CMEs)

April 14-16: 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.

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

Forecast

The geomagnetic field is expected to be quiet on April 17-19 possibly becoming quiet to unsettled 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
11717 2013.04.05       S12W85          

plage

11719 2013.04.05 3 12 5 N09W64 0060 CSO DSI beta-gamma

area: 0100

11721 2013.04.09
2013.04.10
6 12 5 S18W47 0110 DAO DAO  
11722 2013.04.09
2013.04.10
8 21 9 S20W33 0040 CAO DAI  
S2350 2013.04.11       S24E07           plage
11724 2013.04.12
2013.04.13
7 10 6 S26E31 0070 DAO CRO location: S26E33
11723 2013.04.12
2013.04.13
23 43 18 S17E09 0180 DAI DAC area: 0300
S2353 2013.04.12       N17W31           plage
S2354 2013.04.13   1   N09W08 0003   AXX  
S2355 2013.04.14       S05W42           plage
S2356 2013.04.15   1   S13E13 0003   AXX  
S2357 2013.04.16   4 1 S26E14 0014   CRO    
Total spot count: 47 104 44  
Sunspot number: 97 184 104  (total spot count + 10 * number of spotted regions)
Weighted SN: 72 130 70  (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): 58 64 57 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
2013.04 130.2 (1) 65.6 (2A) / 122.9 (2B) / 57.3 (2C) (51.0 projected, -1.2) (3.91)

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.