Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 7, 2013 at 07:05 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 Spril 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 6. Solar wind speed at SOHO ranged between 271 and 352 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 137.0 (increasing 17.8 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: 4.0). Three hour interval K indices: 11111111 (planetary), 11111111 (Boulder).

The background x-ray flux was at the class B5 level.

At midnight UTC the visible solar disk had 14 spotted active regions (in 2K resolution SDO images).

Region 11710 [S24W54] decayed further and had a single barely visible spot left by the end of the day.
Region 11711 [S18W14] was quiet and stable losing several penumbra spots.
Region 11713 [N08W37] decayed slowly and quietly.
Region 11714 [N13E15] developed slowly and was quiet.
Region 11715 [N18W38] decayed slowly and was mostly quiet.
Region 11716 [S20E23] developed slowly and quietly.
Region 11717 [S12E51] decayed slowly and was mostly quiet.
Region 11718 [N21E33] developed slowly and has polarity intermixing. The region produced several low level C flares.
Region 11719 [N08E68] developed and has polarity intermixing. C flares are likely and there's a possibility of another minor M class event.

Spotted regions not numbered by SWPC:
S2330 [N19W02] reemerged with several penumbra spots.
S2337
[S08E42] decayed and had a single barely visible penumbra spot by the end of the day.
S2338 [N09E07] reemerged with several spots.
New region S2341 [N03E38] emerged at a low latitude.
New region S2342 [N11W16] emerged with several penumbra spots in an old plage area.

Coronal mass ejections (CMEs)

April 4-6: 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 coronal hole (CH564) in the northern hemisphere was in an Earth facing position on April 6.

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 7-8. Quiet to unsettled is likely on April 9-10 due to effects from CH564.

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
11708 2013.03.27
2013.03.28
      N13W53         plage
11710 2013.03.28
2013.03.29
  1   S23W55 0002   AXX location: S24W53
11711 2013.03.29
2013.03.30
5 26 3 S17W16 0440 DHO CHO location: S18W14

area: 0540

11712 2013.03.30
2013.03.31
      N02W50           plage
11716 2013.04.01
2013.04.05
  12 3 S19E18 0020   BXO  
11714 2013.04.01
2013.04.02
6 8 4 N13E14 0080 CSO CSO  
S2330 2013.04.01   3   N19W02 0006       plage
11713 2013.04.01
2013.04.02
16 20 10 N10W33 0130 DAI DSI  
S2332 2013.04.01       S14W48           plage
11715 2013.04.02
2013.04.04
4 2 1 N18W39 0010 BXO HRX  
S2336 2013.04.03       S10W01           plage
S2337 2013.04.04   1   S08E42 0002   AXX  
S2338 2013.04.04   6 5 N09E07 0045   DRO    
S2339 2013.04.04       N10W31           plage
S2340 2013.04.04       S27W56           plage
11717 2013.04.05 2 2 1 S12E51 0010 BXO HRX

area: 0015

11718 2013.04.05 10 15 9 N22E33 0130 DSI DSI beta-gamma

area: 0200

11719 2013.04.05 4 11 6 N08E66 0080 CSO DSO beta-gamma

location: N08E68

area: 0130

S2341 2013.04.06   2 1 N03E38 0009   CRO    
S2342 2013.04.06   4 2 N11W16 0014   AXX    
Total spot count: 47 113 45  
Sunspot number: 117 243 155  (total spot count + 10 * number of spotted regions)
Weighted SN: 77 155 87  (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): 70 85 85 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
2013.04 128.0 (1) 22.6 (2A) / 113.0 (2B) / 56.1 (2C) (51.0 projected, -1.2) (3.56)

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.