Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 22, 2012 at 06:25 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 active on April 21. Solar wind speed at SOHO ranged between 285 and 380 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 149.1 (increasing 47.8 over the last solar rotation). The Potsdam WDC planetary A index was 8 (STAR Ap - based on the mean of three hour interval ap indices: 8.5). Three hour interval K indices: 21110134 (planetary), 21101232 (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 [S16W12] is developing slowly with a significant increase in penumbral area and spots merging. There is polarity intermixing and a chance of C and M class flares.
Region 11460 [N15W27] decayed slowly and quietly. M flares are possible.
Region 11461 [N15E16] decayed slowly and quietly.
Region 11462 [S24W57] developed slowly and currently has a fairly simple magnetic layout. An M class flare is possible.
Region 11463 [S26W80] decayed further and was quiet.
Region 11465 [S17E27] developed slowly and could produce C and M class flares. There's minor polarity intermixing.

Spotted active regions not numbered by NOAA/SWPC:
S1599
[S25W14] was quiet and stable.
S1602 [S30E12] reemerged with a tiny spot.
S1604 [N10E55] lost the leader spot and gained a tiny spot in the trailing polarity area.
S1605 [S12W08] developed slowly and quietly.
New region S1606 [N13E43] emerged fairly quickly in the northeast quadrant.

Coronal mass ejections (CMEs)

April 19-21: 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 poor. Propagation on long distance northeast-southwest paths is poor to fair.

Forecast

The geomagnetic field is expected to be quiet to unsettled on April 22-24.

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
11454 2012.04.09
2012.04.10
      S12W84           plage
11457 2012.04.12
2012.04.13
      N20W67           plage
11458 2012.04.14       N06W34          

plage

location: N08W21

11459 2012.04.14 39 73 35 S15W13 0450 EAC EAC

beta-gamma

area: 0800

11462 2012.04.14
2012.04.17
9 12 8 S24W59 0400 DHO EKO

area: 0700

location: S24W57

11460 2012.04.15
2012.04.16
21 33 23 N16W27 0490 DKC EKI

beta-gamma

area: 0650

S1591 2012.04.16       S26W27           plage
11461 2012.04.16
2012.04.17
2 2 1 N12E08 0010 BXO AXX location: N15E16
S1593 2012.04.16       N16W49           plage
S1594 2012.04.16       S14W48           plage
S1595 2012.04.17       S27W53           plage
11463 2012.04.17
2012.04.18
3 1 1 S26W79 0050 CSO HAX  
S1598 2012.04.18       N12E02         plage
S1599 2012.04.18   3 3 S25W14 0010   BXO  
11464 2012.04.18
2012.04.19
      N23W27         plage
S1601 2012.04.18       N08W31           plage
S1602 2012.04.18   1   S30E12 0000   AXX    
11465 2012.04.19
2012.04.20
13 25 16 S17E27 0230 DSO DSC beta-gamma

area: 0450

S1604 2012.04.20   1   N10E55 0000   AXX  
S1605 2012.04.20   7 4 S12W08 0030   CRO  
S1606 2012.04.21   15 6 N13E43 0030   DRI    
Total spot count: 87 173 97  
Sunspot number: 147 283 187  (total spot count + 10 * number of spotted regions)
Weighted penumbral SN: 122 209 133  (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 99 103 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
2012.04 107.2 (1) 46.3 (2A) / 66.1 (2B) (74.9 projected, +1.0) (8.58)

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.