Solar Terrestrial Activity Report

Last major update issued on April 11, 2012 at 04:20 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 9, 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 active on April 10. Solar wind speed at SOHO ranged between 294 and 354 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 93.3 (decreasing 25.5 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: 11.8). Three hour interval K indices: 43222223 (planetary), 33212213 (Boulder).

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

At midnight UTC the visible solar disk had 7 spotted active regions (in 2K resolution SDO images).

New region 11454 [S13E68] rotated into view at the southeast limb on April 9 and was assigned a number by SWPC the next day.

Spotted active regions not numbered by NOAA/SWPC:
S1571 [N15E01] was quiet and stable.
New region S1575 [S28E59] emerged in the southeast quadrant.
New region S1576 [N07E23] emerged with an east-west inversion line.
New region S1577 [S27E14] emerged in the southeast quadrant.
New region S1578 [S41E22] emerged at a high latitude in the southeast quadrant.
New region S1579 [S17W26] emerged in the southwest quadrant near the central part of CH512.

Coronal mass ejections (CMEs)

April 9: A full halo CME became visible near noon after a C3 LDE in spotless AR 11451.
April 8 and 10: 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 coronal hole (CH513) in the southern hemisphere could rotate into an Earth facing position on April 12.

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 active on April 11 and unsettled to minor storm on April 12-13 due to effects from CH512. The CME observed on April 9 could reach Earth on April 12, however, in the presence of what could be a strong high speed stream from CH512, what would likely have been a weak flanking impact will probably not be noticed.

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
11451	2012.03.30 2012.03.31				N17W87						plage
11452	2012.03.31 2012.04.02	2			N18W65	0005	AXX				spotless
S1567	2012.04.05				S26W39						plage
S1570	2012.04.07				N10E27						plage
S1571	2012.04.08		1		N15E01	0000		AXX
S1572	2012.04.08				S34W55						plage
S1573	2012.04.09				N23W01						plage
11454	2012.04.09 2012.04.10	2	3	2	S13E70	0010	CRO	BXO
S1575	2012.04.10		2		S28E59	0000		BXO
S1576	2012.04.10		4	3	N07E23	0010		CRO
S1577	2012.04.10		3	1	S27E14	0000		BXO
S1578	2012.04.10		3	1	S41E22	0000		BXO
S1579	2012.04.10		1	1	S17W26	0000		AXX
Total spot count:		4	17	8
Sunspot number:		24	87	58	(total spot count + 10 * number of spotted regions)
Weighted penumbral SN:		7	20	11	(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):		14	30	32	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.