Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 10, 2012 at 03:50 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)
[Solar cycles 21-24 (last update April 1, 2012)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22, 23 and 24 (last update April 1, 2012)]
[Graphical comparison of cycles 10, 12, 13, 14, 16 and 24 (last update April 1, 2012)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports since January 2003 (last update April 1, 2012)]

[POES auroral activity level since October 2009 - updated April 9, 2012]
Annotated geomagnetic activity charts - Carrington rotation 2118 [December 2011 - January 2012] - 2119 [January-February 2012]
[Solar polar fields vs solar cycles - updated June 27, 2011]

Recent activity

The geomagnetic field was quiet to unsettled on April 9. Solar wind speed at SOHO ranged between 288 and 340 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 94.5 (decreasing 32.0 over the last solar rotation). The Potsdam WDC planetary A index was 5 (STAR Ap - based on the mean of three hour interval ap indices: 5.4). Three hour interval K indices: 11111023 (planetary), 12112222 (Boulder).

The background x-ray flux is at the class B1 level.

At midnight UTC the visible solar disk had 4 spotted active regions (in 2K resolution SDO images).

Region 11452 [N17W51] decayed slowly and quietly.

Spotted active regions not numbered by NOAA/SWPC:
[N15E17] was quiet and stable.
New region S1573 [N23E12] emerged with two spots.
New region S1574 [S13E82] rotated into view at the southeast limb.

Spotless region 11451 was the source of the most significant activity observed during the day, a long duration C3.9 event peaking at 12:44 UTC. This event was associated with a wide CME. While most of the ejected material was observed off the west limbs, this appears to have been a full halo CME. Like the event on April 7 STEREO-A displays the CME over the east limb. STEREO-A, like LASCO, appears to display a full halo CME.

Coronal mass ejections (CMEs)

April 9: A CME with an origin in AR 11451 just after noon appears to have been a full halo CME.
April 8
: No obviously Earth directed CMEs were observed in LASCO and STEREO imagery.
April 7: A filament eruption across AR 11451 was associated with a long duration B class event and a CME which may have been partially Earth directed.

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 trans equatorial coronal hole (CH512) will be in an Earth facing position on April 8-10.

Coronal hole map

The above coronal hole map is based on a method where coronal holes are detected automatically. While the method may need some fine tuning, it has significant advantages over detecting coronal holes manually. The main improvement is the ability to detect coronal holes at and just beyond the solar limbs. Early results using this method for SDO images over a span of several weeks indicate a good match between coronal holes observed over the visible disk and their extent and position at the east and west limbs. Note that the polar coronal holes are easily detected using this method, the extent and intensity of both CHs are consistent with other data sources.


Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over high and upper middle latitudes is poor. Propagation on long distance northeast-southwest paths is poor to fair.


The geomagnetic field is expected to be quiet to unsettled on April 10. A high speed stream associated with CH512 could cause unsettled to minor storm conditions on April 11-13. The CME observed on April 9 could reach Earth on April 12, however, in the presence of what could be a strong high speed stream from CH512, what would likely have been a weak flanking impact will probably not be noticed.

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 higher resolution image) Compare to the previous day's image

When available the active region map has a coronal hole polarity overlay where red (pink) is negative and blue (blue-green) 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
Spot count Location at midnight Area Classification SDO / HMI 4K continuum
image with magnetic polarity overlay
2K 1K
11450 2012.03.30
1     N15W90 0120 HSX    

rotated out of view

11451 2012.03.30


11452 2012.03.31
3 5 2 N18W51 0010 BXO BXO  
S1565 2012.04.04       N23E12           plage
S1567 2012.04.05       S26W26           plage
S1568 2012.04.05       S16W54           plage
S1569 2012.04.05       N22W59           plage
S1570 2012.04.07       N10E40           plage
S1571 2012.04.08   2   N15E17 0000   AXX  
S1572 2012.04.08       S34W42         plage
S1573 2012.04.09   2 1 N23E12 0000   AXX    
S1574 2012.04.09   2 1 S13E82 0000   AXX    
Total spot count: 4 11 4  
Sunspot number: 24 51 34  (total spot count + 10 * number of spotted regions)
Weighted penumbral SN: 9 11 4  (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): 14 18 19 k * (sunspot number). k = 0.6 for SWPC, k = 0.35 (changed from 0.45 on March 1, 2011) 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
2008.07 65.7 (SF minimum) 0.5 2.8 (-0.4)  
2008.12 69.2 0.8 1.7 (-)
sunspot minimum
2011.01 83.6 19.1 31.0 (+2.2) 5.51
2011.02 94.6 29.4 33.4 (+2.4)  6.44
2011.03 115.0 56.2 36.9 (+3.5) 8.18
2011.04 112.6 54.4 41.8 (+4.9) 8.83
2011.05 95.8 41.6 47.6 (+5.8) 8.94
2011.06 95.8 37.0 53.2 (+5.6) 8.06
2011.07 94.2 43.9 57.2 (+4.0) 8.16
2011.08 101.7 50.6 59.0 (+1.8) 7.26
2011.09 133.8 78.0 59.5 (+0.5) 12.27
2011.10 137.3 88.0 (60.1 projected, +0.6) 8.28
2011.11 153.5 96.7 (61.6 projected, +1.5) 5.55
2011.12 141.3 73.0 (64.3 projected, +2.7) 3.78
2012.01 132.5 58.3 (67.8 projected, +3.5) 7.15
2012.02 106.5 33.1 (71.8 projected, +4.0) 8.81
2012.03 114.7 64.2 (73.9 projected, +2.1) 16.08
2012.04 100.1 (1) 13.5 (2A) / 44.9 (2B) (74.9 projected, +1.0) (9.21)

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) Month average to date.
3) Running average based on the quicklook 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.