Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 6, 2013 at 05:05 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 March 2, 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 5. Solar wind speed at SOHO ranged between 271 and 311 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 134.4 (increasing 18.2 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: 2.4). Three hour interval K indices: 00000011 (planetary), 01001222 (Boulder).

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

At midnight UTC the visible solar disk had 11 spotted active regions (in 2K resolution SDO images).

Region 11708 [N11W36] decayed slowly and quietly.
Region 11710 [S22W42] decayed slowly and quietly.
Region 11711 [S18W02] was quiet. New penumbra spots formed to the southeast of the single large spot.
Region 11713 [N09W20] developed slowly and quietly.
Region 11714 [N12E28] was quiet and stable.
Region 11715 [N17W27] was quiet and stable.
New region 11716 [S20E34] rotated into view on April 1 and was numbered by SWPC 4 days later.
New region 11717 [S12E67] emerged with several spots.
New region 11718 [N22E46] emerged quickly with several spots. C flares are possible.
New region 11719 [N08E80] rotated into view. While there's only one spot with penumbra, a negative polarity area is sandwiched between 2 positive polarity areas. C5+ flare: M2.2 at 17:48 UTC.

Spotted regions not numbered by SWPC:
S2337 [S07E55] was quiet and stable.

Coronal mass ejections (CMEs)

April 3-5: 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 will likely rotate into 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 6-8. 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
S2314 2013.03.25       S21W57           plage
11708 2013.03.27
2013.03.28
1 3   N13W39 0010 AXX BXO location: N11W36
11707 2013.03.28       S12W84           plage
11710 2013.03.28
2013.03.29
6 6 4 S21W44 0050 DAO BXO location: S22W42
11711 2013.03.29
2013.03.30
6 26 9 S15W02 0530 CKO CHO location: S18W02
11712 2013.03.30
2013.03.31
      N02W35           plage
11716 2013.04.01
2013.04.05
2 6 2 S19E32 0010 AXX BXO  
11714 2013.04.01
2013.04.02
1 4 1 N12E28 0050 HSX CSO  
S2330 2013.04.01       N24E08           plage
11713 2013.04.01
2013.04.02
19 26 14 N10W19 0070 DAI DAI beta-gamma

area: 0120

S2332 2013.04.01       S14W35         plage
11715 2013.04.02
2013.04.04
5 9 4 N17W28 0030 CAO CRO  
S2336 2013.04.03       S10E12           plage
S2337 2013.04.04   1   S07E55 0002   AXX  
S2338 2013.04.04       N10E24         plage
S2339 2013.04.04       N10W18         plage
S2340 2013.04.04       S27W43         plage
11717 2013.04.05 3 4 1 S10E66 0010 AXX CRO   location: S12E67

area: 0025

11718 2013.04.05 2 12 7 N23E45 0010 AXX DRI   area: 0050
11719 2013.04.05 1 2 1 N08E78 0090 HSX CSO    
Total spot count: 46 99 43  
Sunspot number: 146 209 133  (total spot count + 10 * number of spotted regions)
Weighted SN: 81 133 77  (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): 88 73 73 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) 9.86
2013.04 126.2 (1) 18.7 (2A) / 112.2 (2B) / 55.3 (2C) (51.0 projected, -1.2) (3.48)

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.