Solar Terrestrial Activity Report

Activity chart

Last major update issued on April 29, 2012 at 05:20 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 27, 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 28. Solar wind speed at SOHO ranged between 409 and 512 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 121.1 (increasing 13.8 over the last solar rotation). The Potsdam WDC planetary A index was 9 (STAR Ap - based on the mean of three hour interval ap indices: 8.8). Three hour interval K indices: 21132323 (planetary), 10121212 (Boulder).

The background x-ray flux is at the class B4 level.

At midnight UTC the visible solar disk had 8 spotted active regions (in 2K resolution SDO images).

Region 11465 [S18W66] decayed quickly losing all penumbra on the trailing spots and most of the penumbra on the leader spots.
Region 11466 [N12W53] developed as new negative polarity flux emerged in the leading spot section.
Region 11467 [N12E19] decayed slowly and quietly.
Region 11468 [N10W43] decayed slowly and quietly.
Region 11469 [S20E13] developed slowly and was mostly quiet.
New region 11470 [S17E63] rotated into view at the southeast limb on April 27 and got an SWPC number the next day. Slow development was observed on April 28.
New region 11471 [S22E70] rotated into view at the southeast limb on April 27 and was assigned a number by SWPC the following day. This is an interesting region as there is a magnetic delta structure in the central eastern part of the leading penumbra. An M flare is possible.

Spotted active regions not numbered by NOAA/SWPC:
New region S1618 [N21E53] emerged with a few spots

An apparant chain of filament eruptions was observed during the day. A filament in the southwest quadrant erupted just after noon and may have triggered an eruption of a high latitude southern hemisphere filament across the central meridian near 18h UTC. The apparent chain reaction of events moved northwards and ended with the eruption of a filament between AR 11467 and AR 11469 near 22h UTC. The latter event is associated with a CME which may have Earth directed components.

Coronal mass ejections (CMEs)

April 26-27: No obviously Earth directed CMEs were observed in LASCO and STEREO imagery.
April 28: A filament eruption late in the day may have been associated with a partially Earth directed CME.

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 in the northern hemisphere rotated across the central meridian on April 26-27 but was probably too far to the north to cause a geomagnetic 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 to fair. Propagation on long distance northeast-southwest paths is poor to fair.

Forecast

The geomagnetic field is expected to be quiet to unsettled on April 29 - 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: 0-20% 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
11465 2012.04.19
2012.04.20
12 7 3 S18W66 0130 DAI CAO area: 0050
11468 2012.04.20
2012.04.24
6 6 3 N10W42 0070 DSO DSO area: 0040
11466 2012.04.21
2012.04.22
6 15 8 N12W51 0070 CSO DAO location: N12W53

area: 0190

11469 2012.04.23
2012.04.24
13 16 8 S19E14 0090 DSI DAO location: S20E13
S1609 2012.04.23       S25W27         plage
11467 2012.04.24 6 8 4 N12E18 0060 CSO BXO area: 0010
S1611 2012.04.25       S26E17         plage
S1612 2012.04.26       N27W22           plage
11471 2012.04.27
2012.04.28
2 7 3 S23E70 0120 HSX EKO beta-gamma-delta

area: 0290

11470 2012.04.27
2012.04.28
3 8 3 S17E61 0040 CSO DRO location: S17E63
S1616 2012.04.27       N04W04         plage
S1617 2012.04.27       N30W15         plage
S1618 2012.04.28   3 3 N21E53 0020   CRO    
Total spot count: 48 70 35  
Sunspot number: 118 150 115  (total spot count + 10 * number of spotted regions)
Weighted penumbral SN: 83 106 71  (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): 71 53 63 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
2012.04 112.9 (1) 76.8 (2A) / 82.3 (2B) (74.9 projected, +1.0) (12.16)

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.