Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 24, 2012 at 04:20 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 22, 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 major storm on April 23. Solar wind speed at SOHO ranged between 324 and 413 km/s. A solar wind shock was observed at SOHO at 02:29 UTC, its source was likely one of the CMEs observed on April 19. Initially the disturbance appeared to be weak to moderate, however, after 17h UTC the interplanetary magnetic field has been consistently strongly southwards. This has caused a strong geomagnetic storm. During the 00-03h UTC interval on April 24 the planetary A index reached 156 (Kp 7 - severe storm).

Solar flux measured at 20h UTC on 2.8 GHz was 141.8 (increasing 36.2 over the last solar rotation). The Potsdam WDC planetary A index was 28 (STAR Ap - based on the mean of three hour interval ap indices: 28.4). Three hour interval K indices: 24413456 (planetary), 15522544 (Boulder).

The background x-ray flux is at the class B6 level.

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

Region 11459 [S16W38] decayed further losing spots and penumbral area.
Region 11460 [N15W55] decayed slowly and quietly.
Region 11461 [N11W12] was mostly quiet and stable. A filament eruption was observed to the south of the region from 12:29 UTC. Neither LASCO nor initial investigation of STEREO imagery have revealed any significant CME.
Region 11462 [S25W83] displayed little change and was quiet.
Region 11465 [S18E01] is becoming more complex with nearly all umbrae merging into one large penumbra. While there is a significant magnetic delta structure in this penumbra, the region has been surprisingly quiet. A major flare is possible.
Region 11466 [N12E14] developed slowly and quietly.

Spotted active regions not numbered by NOAA/SWPC:
S1598
[N14W20] was quiet and stable.
S1604 [N10E26] reemerged with a few spots. More spots are visible early on April 24.
S1605 [S12W37] decayed slowly and quietly.
New region S1608 [S18E82] rotated partly into view at the southeast limb on April 23. Early on April 24 more spots are visible in a DRI classification.
New region S1609 [S27E28] emerged in the southeast quadrant.

Early on April 24 a new region is rotating into view at the northeast limb.

Coronal mass ejections (CMEs)

April 21-23: 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 coronal hole (CH514) in the northern hemisphere was in an Earth facing position on April 21, however, CH514 closed the same day and it is uncertain if there will be any associated disturbance.

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 very poor. Propagation on long distance northeast-southwest paths is poor to fair.

Forecast

The geomagnetic field is expected to be quiet to severe storm on April 24 due to CME effects and quiet to unsettled on April 25-26.

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
11458 2012.04.14       N06W64          

plage

location: N08W47

11459 2012.04.14 39 47 27 S14W40 0440 EKI DAC

area: 0300

location: S16W38

11462 2012.04.14
2012.04.17
4 4 2 S25W85 0300 DHO EKO

area: 0500

location: S25W83

11460 2012.04.15
2012.04.16
14 15 6 N16W54 0320 DKO ESO

 

S1591 2012.04.16       S26W53           plage
11461 2012.04.16
2012.04.17
  2 1 N10W19 0000   BXO location: N11W12
S1598 2012.04.18   2   N14W20        
S1599 2012.04.18       S25W40           plage
11464 2012.04.18
2012.04.19
      N23W55           plage
S1601 2012.04.18       N08W57           plage
S1602 2012.04.18       S30W14           plage
11465 2012.04.19
2012.04.20
37 28 18 S18W01 0400 DKI DKC beta-gamma-delta

area: 0600

S1604 2012.04.20   2 2 N10E26 0010   BXO    
S1605 2012.04.20   5 1 S12W37 0010   CRO  
11466 2012.04.21
2012.04.22
14 19 11 N11E14 0120 DAO DSI location: N12E14
S1607 2012.04.22       S13W18         plage
S1608 2012.04.23   2 1 S18E82 0010   BXO    
S1609 2012.04.23   1   S27E28 0000   AXX    
Total spot count: 108 127 59  
Sunspot number: 158 217 149  (total spot count + 10 * number of spotted regions)
Weighted penumbral SN: 153 165 97  (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): 95 76 82 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
2012.04 110.5 (1) 55.5 (2A) / 72.4 (2B) (74.9 projected, +1.0) (9.42)

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 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.