Solar Terrestrial Activity Report

Last major update issued on April 14, 2012 at 06:05 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 14, 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 13. Solar wind speed at SOHO ranged between 530 and 687 km/s under the influence of a high speed stream associated with CH512.

Solar flux measured at 20h UTC on 2.8 GHz was 97.7 (decreasing 4.7 over the last solar rotation). The Potsdam WDC planetary A index was 26 (STAR Ap - based on the mean of three hour interval ap indices: 26.0). Three hour interval K indices: 55442333 (planetary), 45442222 (Boulder).

The background x-ray flux is at the class B1 level.

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

Region 11454 [S13E27] decayed slowly and quietly.
Region 11455 [N07W19] added a few spots and could produce C flares. There's still minor polarity intermixing.
New region 11457 [N22E44] emerged in the northeast quadrant on April 12 and got an SWPC number the next day.

Spotted active regions not numbered by NOAA/SWPC:
S1573 [N27W37] reemerged with a single tiny spot.
S1578 [S40W15] was quiet and stable.
New region S1583 [S27E30] emerged in the southeast quadrant.
New region S1584 [S23W25] emerged in the southwest quadrant with a tiny spot.
New region S1585 [S21E13] emerged in the southeast quadrant.

Coronal mass ejections (CMEs)

April 11-13: 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 recurrent trans equatorial coronal hole (CH512) was in an Earth facing position on April 8-10. A small and poorly defined trans equatorial coronal hole (CH513) was in an Earth facing position on April 12-13.

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 good.

Forecast

The geomagnetic field is expected to be quiet to active on April 14 due to effects from CH512. Quiet to unsettled is possible on April 15-16 due to weak effects from CH513.

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
S1570	2012.04.07				N10W12						plage
S1571	2012.04.08				N15W38						plage
S1573	2012.04.09		1	1	N27W37	0000		AXX
11454	2012.04.09 2012.04.10	1	3	3	S12E26	0010	AXX	AXX
S1575	2012.04.10				S28E20						plage
11455	2012.04.10 2012.04.11	15	30	18	N07W19	0130	DAI	DAI			beta-gamma
S1577	2012.04.10				S28W26						plage
S1578	2012.04.10		1		S40W15	0000		AXX
11456	2012.04.11 2012.04.12				S20W32						plage location: S19W30
S1581	2012.04.12				N05E33						plage
11457	2012.04.12 2012.04.13	4	8	4	N22E41	0010	BXO	CRO
S1583	2012.04.13		2	2	S27E30	0000		AXX
S1584	2012.04.13		1		S23W25	0000		AXX
S1585	2012.04.13		1		S21E13	0000		AXX
Total spot count:		20	47	28
Sunspot number:		50	127	78	(total spot count + 10 * number of spotted regions)
Weighted penumbral SN:		25	55	36	(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):		30	44	43	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.