Solar Terrestrial Activity Report

Last major update issued on April 18, 2012 at 04:25 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 18, 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 17. Solar wind speed at SOHO ranged between 289 and 408 km/s, after 04h UT under the influence of a low speed stream from CH513.

Solar flux measured at 20h UTC on 2.8 GHz was 113.8 (increasing 13.9 over the last solar rotation). The Potsdam WDC planetary A index was 12 (STAR Ap - based on the mean of three hour interval ap indices: 12.0). Three hour interval K indices: 21333333 (planetary), 10323332 (Boulder).

The background x-ray flux is at the class B3 level.

At midnight UTC the visible solar disk had 13 spotted active regions (in 2K resolution SDO images).

Region 11455 [N06W79] decayed slowly and was mostly quiet.
Region 11457 [N22W07] was quiet and stable.
Region 11458 [N08E31] was quiet and stable.
Region 11459 [S16E42] developed slowly adding spots and penumbral area and was mostly quiet. C and minor M class flares are possible. There's minor polarity intermixing.
Region 11460 [N15E27] developed significantly and has minor polarity intermixing. C flares are possible.
New region 11461 [N12E66] rotated into view at the northeast limb on April 16 and was assigned a number by SWPC one day later.
New region 11462 [S24W05] emerged in the southeast quadrant on April 14 and was noticed by SWPC 3 days later.

Spotted active regions not numbered by NOAA/SWPC:
S1581 [N05W21] reemerged with a tiny spot.
S1591 [S27E27] was quiet and stable.
S1593 [N16E03] was quiet and stable.
New region S1595 [S27W02] emerged near AR 11462 with a few spots.
New region S1596 [N08W39] emerged in the northwest quadrant and has potential for further development.
New region S1597 [S27W23] emerged in the southwest quadrant.

Coronal mass ejections (CMEs)

April 15 and 17: No obviously Earth directed CMEs were observed in LASCO and STEREO imagery.
April 16: A partial halo CME was observed after the M1 event in region S1592. There's a chance of a flank CME impact on April 19.

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 will likely rotate into an Earth facing position on April 21.

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 to good.

Forecast

The geomagnetic field is expected to be quiet to active on April 18 due to effects from CH513 and quiet on April 19-20. There's a chance of a weak CME impact on April 19.

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				S12W28						plage
S1575	2012.04.10				S27W32						plage
11455	2012.04.10 2012.04.11	3	6	1	N05W78	0030	CAO	CRO
S1581	2012.04.12		1		N05W21	0000		AXX
11457	2012.04.12 2012.04.13		1		N20W11	0000		AXX			location: N22W07
S1583	2012.04.13				S31W17						plage
S1585	2012.04.13				S21W39						plage
11458	2012.04.14		1		N06E26	0000		AXX			area: 0000 location: N08E31
11459	2012.04.14	11	47	20	S15E40	0150	DAO	EAC			beta-gamma area: 0500
11462	2012.04.14 2012.04.17	7	13	6	S23W07	0030	CAO	DRI			location: S24W05
S1589	2012.04.14				N26W56						plage
11460	2012.04.15 2012.04.16	6	25	8	N16E26	0050	DSO	DAO			beta-gamma area: 0250
S1591	2012.04.16		2	2	S27E27	0010		CRO
11461	2012.04.16 2012.04.17	1	3	1	N13E66	0040	HSX	HSX
S1593	2012.04.16		1		N16E03	0000		AXX
S1594	2012.04.16				S14E04						plage
S1595	2012.04.17		3	1	S27W02	0010		BXO
S1596	2012.04.17		3	2	N08W39	0010		BXO
S1597	2012.04.17		2	1	S27W23	0000		AXX
Total spot count:		28	108	41
Sunspot number:		78	238	131	(total spot count + 10 * number of spotted regions)
Weighted penumbral SN:		53	132	65	(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):		47	83	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 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.