Solar Terrestrial Activity Report

Last major update issued on April 27, 2012 at 05:10 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 minor storm on April 26. Solar wind speed at SOHO ranged between 548 and 751 km/s under the decreasing influence of a high speed coronal hole stream..

Solar flux measured at 20h UTC on 2.8 GHz was 119.2 (increasing 8.6 over the last solar rotation). The Potsdam WDC planetary A index was 21 (STAR Ap - based on the mean of three hour interval ap indices: 20.6). Three hour interval K indices: 55323233 (planetary), 65322222 (Boulder).

The background x-ray flux is at the class B5 level.

At midnight UTC the visible solar disk had 10 spotted active regions (in 2K resolution SDO images).

Region 11459 [S15W79] decayed quickly losing spots and nearly all penumbra.
Region 11465 [S18W40] decayed slowly and was mostly quiet.
Region 11466 [N12W25] was mostly quiet and stable.
Region 11467 [N12E47] decayed early on, then new positive polarity flux emerged in the southern part and the region became slightly more complex.
Region 11468 [N09W15] was quiet and stable.
Region 11469 [S19E39] decayed slowly and was quiet. Apparantly SWPC has chosen to add S1611 to this region, that decision is difficult to understand.

Spotted active regions not numbered by NOAA/SWPC:
S1609 [S27W14] reemerged with a few tiny spots.
S1611 [S26E41] was quiet and stable.
New region S1612 [N27E04] emerged inside a coronal hole and has reversed polarities.
New region S1613 [S23W62] emerged with two spots.

Coronal mass ejections (CMEs)

April 24-26: 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 will rotate across the central meridian on April 26-27 but is 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 fair.

Forecast

The geomagnetic field is expected to be quiet to unsettled on April 27-29.

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	10	8	3	S16W78	0070	DSI	CRO			area: 0030
11460	2012.04.15 2012.04.16	1			N15W93	0060	CSO				rotated out of view
11461	2012.04.16 2012.04.17				N10W61						plage location: N11W49
S1598	2012.04.18				N14W59						plage
S1602	2012.04.18				S32W53						plage
11465	2012.04.19 2012.04.20	11	15	7	S18W39	0200	DSI	DKO
11468	2012.04.20 2012.04.24	12	13	8	N08W17	0090	DSO	DSO			location: N09W15
11466	2012.04.21 2012.04.22	9	17	11	N12W26	0090	CSI	DSI
S1607	2012.04.22				S13W57						plage
11469	2012.04.23 2012.04.24	3	6	2	S24E41	0020	CSO	BXO			location: S19E39
S1609	2012.04.23		3		S27W14
11467	2012.04.24	1	6	5	N14E45	0010	CSO	DRO			location: N12E47 SWPC again thinks 1 spot is enough for a CSO classification area: 0040
S1611	2012.04.25		2	2	S26E41	0010		BXO
S1612	2012.04.26		1	1	N27E04	0000		AXX
S1613	2012.04.26		2	2	S23W62	0010		BXO
Total spot count:		47	73	41
Sunspot number:		117	173	131	(total spot count + 10 * number of spotted regions)
Weighted penumbral SN:		82	99	67	(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):		70	61	72	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.