Solar Terrestrial Activity Report

Last major update issued on April 30, 2012 at 04:00 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 29. Solar wind speed at SOHO ranged between 348 and 436 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 116.0 (increasing 10.1 over the last solar rotation). The Potsdam WDC planetary A index was 7 (STAR Ap - based on the mean of three hour interval ap indices: 7.0). Three hour interval K indices: 33111121 (planetary), 22111210 (Boulder).

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

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

Region 11465 [S18W80] decayed further as it rotated to the southwest limb.
Region 11466 [N12W67] decayed slowly and was mostly quiet.
Region 11467 [N13E09] decayed slowly and quietly.
Region 11468 [N10W57] decayed slowly and quietly.
Region 11469 [S21E01] developed slowly and was mostly quiet.
Region 11470 [S16E48] decayed slowly and quietly.
Region 11471 [S22E58] was quiet and stable.
New region 11472 [S28E41] emerged quickly initially and seemed to be decaying slowly by the end of the day.

Spotted active regions not numbered by NOAA/SWPC:
S1611 [S27E07] reemerged with many spots.
New region S1619 [S13E19] emerged with a tiny spot.
New region S1620 [S34W28] emerged with a tiny spot.

Coronal mass ejections (CMEs)

April 27 and 29: 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.

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

Forecast

The geomagnetic field is expected to be quiet to unsettled on April 30 - May 2. There's a chance of effects from a CME observed late on April 28 arriving on May 2. If that happens some active intervals will be likely.

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	4	4	1	S18W80	0090	CSO	BXO			area: 0010
11468	2012.04.20 2012.04.24	2	2	1	N11W55	0010	BXO	CRO			location: N10W57
11466	2012.04.21 2012.04.22	6	6	4	N13W65	0140	DSO	DAO			location: N12W67 area: 0190
11469	2012.04.23 2012.04.24	10	31	14	S19W01	0090	DSO	DSI			location: S21E01
S1609	2012.04.23				S25W40						plage
11467	2012.04.24	1	5	3	N12E04	0020	HRX	BXO			area: 0010
S1611	2012.04.25		15	10	S27E04	0050		DRI
S1612	2012.04.26				N27W35						plage
11471	2012.04.27 2012.04.28	5	10	6	S23E57	0260	CHO	EHO			area: 0330
11470	2012.04.27 2012.04.28	3	8	3	S16E47	0040	CSO	BXO			area: 0010
S1616	2012.04.27				N04W17						plage
S1617	2012.04.27				N30W28						plage
S1618	2012.04.28				N21E40						plage
11472	2012.04.29	3	20	9	S29E40	0010	BXO	DRI
S1619	2012.04.29		1		S13E19	0000		AXX
S1620	2012.04.29		1		S34W28	0000		AXX
Total spot count:		34	103	51
Sunspot number:		114	213	141	(total spot count + 10 * number of spotted regions)
Weighted penumbral SN:		69	132	80	(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):		68	75	78	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

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.