Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 27, 2015 at 05:10 UT

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 23-24 (last update April 1, 2015)] [Cycle 24 progress (last update April 1, 2015) ]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22, 23 and 24 (last update April 1, 2015)]
[Graphical comparison of cycles 10, 12, 13, 14, 16 and 24 (last update April 1, 2015)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports since January 2003 (last update April 1, 2015)]

[Noon SDO sunspot count 1K Reference: 4K (large file) (updated daily)]

[POES auroral activity level October 2009 - December 2012]
[Solar polar fields vs solar cycles - updated April 10, 2015]
[Presentations: 3rd SSN Workshop, Tucson, 2013 (pdf) / 4th SSN Workshop, Locarno, 2014]

Recent activity

The geomagnetic field was very quiet on April 26. Solar wind speed at SOHO ranged between 271 and 371 km/s.

Solar flux at 20h UTC on 2.8 GHz was 118.5 (decreasing 15.1 over the last solar rotation). The 90 day 10.7 flux at 1 AU was 129.2. The Potsdam WDC planetary A index was 2 (STAR Ap - based on the mean of three hour interval ap indices: 1.6). Three hour interval K indices: 00001001 (planetary), 10012212 (Boulder).

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

At the time of counting spots (see image time), spots were observed in 10 active regions using 2K resolution (SN: 149) and 8 active regions using 1K resolution (SN: 108) SDO images on the visible solar disk.

Region 12327 [S08W49] decayed slowly and quietly.
Region 12331 [S09W60] was mostly quiet and stable.
Region 12333 [N21E13] was quiet and has weak polarity intermixing.

Spotted regions not numbered (or interpreted differently) by SWPC:
S4389 [S18W42] was quiet and stable
S4404 [N11E01] decayed slowly and quietly.
S4413 [S21W30] decayed slowly and quietly.
New region S4414 [S18E27] emerged with penumbra spots.
New region S4415 [N02E25] was observed with a penubra spot.
New region S4416 [S12W49] emerged with penumbra spots.
New region S4417 [N15W19] was observed with a penumbra spot.

C2+ flares:

Magnitude Peak time (UTC) Location AR Recorded by Comment
           

Flare activity according to SDO/EVE/ESP XRS-B proxy

Coronal mass ejections (CMEs)

April 24-26: No obviously Earth directed CMEs were observed.

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 recurrent southern hemisphere coronal hole (CH665) will rotate into an Earth facing position on April 27-28.

Propagation

Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over 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 27-29. Effects from CH665 could cause some unsettled and active intervals on April 30-May 1.

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: 0-30% probability, Yellow: 30-70% probability, Red: 70-100% 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 Magnetic
(SDO)
SWPC STAR Current Previous
2K 1K
12325 2015.04.13
2015.04.14
1     N04W94 0220 HSX     rotated out of view
12327 2015.04.16
2015.04.17
3 5 3 S08W49 0060 CSO CAO  
S4389 2015.04.17   1    S18W42        
12331 2015.04.17
2015.04.21
9 15 8  S10W59 0240 DAI DKI area: 0370
12332 2015.04.18
2015.04.21
       S13W84            
12330 2015.04.19
2015.04.20
       N15W51            
S4400 2015.04.20        N07W35          
S4404 2015.04.21   7 4  N11E01 0020   BXO images/AR_S4404_20150426_2345.png images/AR_S4404_20150424_2345.png  
12333 2015.04.21
2015.04.22
2 8 6  N20E12 0010 HRX DRO beta-gamma
S4407 2015.04.22        N20W07          
S4409 2015.04.22        S02W12          
S4410 2015.04.22        N23W39            
S4411 2015.04.24        S17E21            
S4412 2015.04.24        N27W41            
S4413 2015.04.25   2 1 S21W30 0010   HRX  
S4414 2015.04.26   4 2 S18E27 0010   AXX    
S4415 2015.04.26   1 1 N02E25 0003   AXX    
S4416 2015.04.26   5 3 S12W49 0020   CRO    
S4417 2015.04.26   1   N15W19 0003   AXX    
Total spot count: 15 49 28  
Sunspot number: 55 149 108  (total spot count + 10 * number of spotted regions)
Weighted SN: 33 73 52  (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): 33 52 59 k * (sunspot number). k = 0.6 for SWPC, k = 0.35 for MSN 2K, k = 0.55 for MSN 1K (MSN=Magnetic Sunspot Number)

Monthly solar cycle data

Month Average solar flux International sunspot number
(WDC-SILSO)
Smoothed sunspot number Average ap
(3)
Measured 1 AU
2013.11  148.3 145.1 77.6 75.4 (+0.4) 5.68
2013.12 147.7 143.1 90.3 76.0 (+0.6) 4.68
2014.01 157.4 152.4 81.8 77.3 (+1.3) 5.44
2014.02 170.3
(cycle peak)
166.3 102.3 (cycle peak) 78.4 (+1.1) 10.70
2014.03 149.9 148.5 91.9 80.8 (+2.4) 4.88
2014.04 143.9 144.8 84.7 81.9 (+1.1)
(likely solar max)
7.88
2014.05 129.7 132.9 75.2 80.5 (-1.4) 5.75
2014.06 122.0 125.8 71.0 79.7 (-0.8) 6.72
2014.07 137.4 141.8 72.5 78.6 (-1.1) 4.50
2014.08 124.7 127.9 74.7 75.6 (-3.0) 7.71
2014.09 146.6 148.1 87.6 70.9 (-4.7) 9.78
2014.10 153.4 152.9 60.6 (67.3 projected, -3.6) 8.96
2014.11 154.8 151.4 70.1 (64.7 projected, -2.6) 9.33
2014.12 158.7 153.8 78.0 (62.4 projected, -2.3) 11.24
2015.01 141.9 137.3 67.0 (60.2 projected, -2.2) 9.46
2015.02 129.1 126.0 44.8 (58.4 projected, -1.8) 9.92
2015.03 125.9 124.6 38.4 (56.1 projected, -2.3) 16.14
2015.04 (132.4)   68.2 (2A) / 78.7 (2B) / 83.3 (2C) (53.4 projected, -2.7) (11.3)

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 WDC-SILSO 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 GFZ Potsdam WDC ap indices.

This report has been prepared by Jan Alvestad. It is based on the 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.