Solar Terrestrial Activity Report

Last major update issued on April 28, 2012 at 05:50 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 27. Solar wind speed at SOHO ranged between 444 and 646 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 117.6 (increasing 7.5 over the last solar rotation). The Potsdam WDC planetary A index was 10 (STAR Ap - based on the mean of three hour interval ap indices: 10.1). Three hour interval K indices: 33312123 (planetary), 32212223 (Boulder).

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

At midnight UTC the visible solar disk had 12 spotted active regions (in 2K resolution SDO images).

Region 11465 [S17W52] decayed slowly with the largest penumbra breaking up into smaller penumbrae. The magnetic layout has simplified. Flare: C2.4 at 11:02 UTC
Region 11466 [N11W40] decayed significantly losing spots and penumbral area. Flare: M1.0/1N at 08:24 UTC
Region 11467 [N11E32] developed early in the day, slow decay was observed late in the day. Flare: C2.0 at 13:22 UTC
Region 11468 [N10W29] decayed slowly and quietly.
Region 11469 [S20E27] developed significantly and was mostly quiet. Flare: C1.0 at 02:02 UTC

Spotted active regions not numbered by NOAA/SWPC:
S1609 [S25W14] lost the leading polarity spots and gained a tiny spot in the trailing polarity area.
S1611 [S26E30] decayed slowly and quietly.
S1613 [S25W73] decayed slowly and quietly.
New region S1614 [S23E83] rotated into view at the southeast limb. While difficult to observe near the limb, there could be a small magnetic delta in the leading penumbra.
New region S1615 [S16E77] rotated into view at the southeast limb with two small spots.
New region S1616 [N04E09] emerged at a low northern latitude near the center of the visible disk.
New region S1617 [N30W02] emerged at a fairly high latitude in the northern hemisphere.

Coronal mass ejections (CMEs)

April 25-27: 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 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 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 28-30.

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
11459	2012.04.14	4			S19W88	0030	CAO				rotated out of view
11461	2012.04.16 2012.04.17				N10W75						plage location: N11W62
11465	2012.04.19 2012.04.20	11	19	9	S17W53	0180	DAI	DAI			area: 0100
11468	2012.04.20 2012.04.24	6	12	6	N09W30	0080	DAO	DSO			location: N10W29
11466	2012.04.21 2012.04.22	8	6	5	N11W38	0090	CSO	CSO			location: N11W40
11469	2012.04.23 2012.04.24	6	14	7	S24E28	0050	DSO	DAO			location: S20E27
S1609	2012.04.23		1		S25W14
11467	2012.04.24	4	12	3	N11E32	0050	DSO	DRO			area: 0030
S1611	2012.04.25		2	1	S26E30	0000		AXX
S1612	2012.04.26				N27W09						plage
S1613	2012.04.26		1	1	S27W73	0000		AXX
S1614	2012.04.27		4	1	S23E83	0160		DSO			beta-gamma-delta?
S1615	2012.04.27		2	1	S16E77	0010		BXO
S1616	2012.04.27		1	1	N04E09	0000		AXX
S1617	2012.04.27		1	1	N30W02	0000		AXX
Total spot count:		39	75	36
Sunspot number:		99	195	146	(total spot count + 10 * number of spotted regions)
Weighted penumbral SN:		69	103	64	(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):		59	68	80	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.