Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 17, 2012 at 04:40 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 14, 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 on April 16. Solar wind speed at SOHO ranged between 313 and 450 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 107.9 (increasing 8.3 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: 11112222 (planetary), 22012222 (Boulder).

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

At midnight UTC the visible solar disk had 10 spotted active regions (in 2K resolution SDO images).

Region 11455 [N06W63] decayed further early in the day, then new positive polarity flux began to emerge in the central part.
Region 11457 [N23E07] decayed slowly and quietly.
Region 11458 [N07E44] decayed and could become spotless today.
Region 11459 [S16E56] developed slowly and quietly. C and minor M class flares are possible.
New region 11460 [N16E42] emerged in the northeast quadrant on April 15 and got an SWPC number the next day.

Spotted active regions not numbered by NOAA/SWPC:
S1586
[S23E11] was quiet and stable.
New region S1591 [S26E38] emerged with a few small spots.
New region S1592 [N12E80] rotated into view at the northeast limb. This appears to be the region which has generated most of the flares observed over the last few days. Flares: C1.8 at 00:46, M1.7 at 17:46 UTC. The M1 event was associated with a fast and wide partial halo CME.
New region S1593 [N18E17] emerged in the northeast quadrant.
New region S1594 [S14E17] emerged with a tiny spot.

Coronal mass ejections (CMEs)

April 14-15: No obviously Earth directed CMEs were observed in LASCO and STEREO imagery.
April 16: A partial halo CME was observed after the M1 event in region S1592. There's a chance of a flank CME impact on April 19.

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 and poorly defined trans equatorial coronal hole (CH513) was in an Earth facing position on April 12-13.

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.

Propagation

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

Forecast

The geomagnetic field is expected to be quiet on April 17-19.

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
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
S1570 2012.04.07       N10W51           plage
11454 2012.04.09
2012.04.10
      S12W14         plage
S1575 2012.04.10       S27W19           plage
11455 2012.04.10
2012.04.11
16 17 5 N06W59 0200 FSI DRI area: 0030

location: N06W63

SWPC area and classification far removed from reality

S1578 2012.04.10       S40W54           plage
11456 2012.04.11
2012.04.12
      S20W75           plage

location: S19W69

S1581 2012.04.12       N04W08         plage
11457 2012.04.12
2012.04.13
1 1   N20E03 0010 AXX AXX area: 0000

location: N23E07

S1583 2012.04.13       S31W04         plage
S1585 2012.04.13       S21W26           plage
11458 2012.04.14 2 1   N06E41 0010 BXO AXX area: 0000

location: N07E44

11459 2012.04.14 12 26 11 S15E56 0260 FHI EAC beta-gamma

area: 0400

strange SWPC classification, region is 10 degrees longitudinally

S1586 2012.04.14   3   S23E11 0000   AXX  
S1587 2012.04.14       S25W53           plage
S1589 2012.04.14       N26W43           plage
11460 2012.04.15
2012.04.16
5 10 4 N15E40 0020 CRO DRO  
S1591 2012.04.16   2   S26E38 0000   AXX    
S1592 2012.04.16   1 1 N12E80 0080   HSX    
S1593 2012.04.16   1 1 N18E17 0000   AXX    
S1594 2012.04.16   1   S14E17 0000   AXX    
Total spot count: 36 63 22  
Sunspot number: 86 163 72  (total spot count + 10 * number of spotted regions)
Weighted penumbral SN: 54 79 38  (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): 52 57 40 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
(3)
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 99.3 (1) 26.1 (2A) / 49.0 (2B) (74.9 projected, +1.0) (11.84)

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.