Solar Terrestrial Activity Report

Last major update issued on April 19, 2013 at 04:55 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 23-24 (last update April 1, 2013)] [Cycle 24 progress (last update April 7, 2013) ]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22, 23 and 24 (last update April 1, 2013)]
[Graphical comparison of cycles 10, 12, 13, 14, 16 and 24 (last update April 1, 2013)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports since January 2003 (last update April 4, 2013)]

[POES auroral activity level since October 2009 - updated January 26, 2013]
[Solar polar fields vs solar cycles - updated March 24, 2013]
[Presentation 3rd SSN Workshop, Tucson, 2013 (pdf)]

Recent activity

The geomagnetic field was very quiet on April 18. Solar wind speed at SOHO ranged between 270 and 344 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 98.4 (the value recorded at 20h UTC was not used as it was flare enhanced) (decreasing 2.5 over the last solar rotation). The Potsdam WDC planetary A index was 2 (STAR Ap - based on the mean of three hour interval ap indices: 1.8). Three hour interval K indices: 10000000 (planetary), 10011111 (Boulder).

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

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

Region 11721 [S19W76] decayed slowly and quietly.
Region 11722 [S21W60] decayed slowly and quietly.
Region 11723 [S18W18] decayed slowly and quietly.
Region 11724 [S26E08] decayed slowly and quietly.

Spotted regions not numbered by SWPC:
S2354 [N09W43] lost the trailing spots and developed new spots in the leading section.
S2357 [S25W13] reemerged with several spots.
New region S2360 [N17W13] emerged with penumbra spots.
New region S2361 [N24E70] emerged with one spot.
New region S2362 [N13E23] emerged with penumbra spots.
New region S2363 [S12W49] emerged with a penumbra spot.

AR 11719 produced a long duration C6.5 event peaking at 18:23 UTC. A wide CME was observed off the west limbs.

Coronal mass ejections (CMEs)

April 16-18: 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 trans equatorial coronal hole (CH566) will likely rotate to an Earth facing position on April 21-23.

Propagation

Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over high and upper middle latitudes is good. Propagation on long distance northeast-southwest paths is poor.

Forecast

The geomagnetic field is expected to be quiet on April 19-22.

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 2K resolution) Compare to the previous day's image. 0.5k image

When available the active region map has a coronal hole polarity overlay where red (pink) is negative and blue 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
11719	2013.04.05	1			N09W91	0050	HSX				rotated out of view
11721	2013.04.09 2013.04.10	2	1	1	S17W75	0100	CSO	HSX
11722	2013.04.09 2013.04.10	10	14	5	S20W62	0090	DAI	DRI
S2350	2013.04.11				S24W19						plage
11724	2013.04.12 2013.04.13	2	6	3	S26E07	0020	CSO	CRO
11723	2013.04.12 2013.04.13	21	25	12	S16W16	0190	DAI	DAI
S2353	2013.04.12				N17W57						plage
S2354	2013.04.13		2		N09W43	0008		BXO
S2356	2013.04.15				S13W13						plage
S2357	2013.04.16		3	2	S25W13	0014		BXO			alternative classification: CRO
S2358	2013.04.17				N10E16						plage
S2359	2013.04.17				S14E57						plage
S2360	2013.04.18		2	1	N17W13	0008		BXO
S2361	2013.04.18		1		N24E70	0002		AXX
S2362	2013.04.18		2		N13E23	0003		BXO
S2363	2013.04.18		1		S12W49	0002		AXX
Total spot count:		36	57	24
Sunspot number:		86	157	84	(total spot count + 10 * number of spotted regions)
Weighted SN:		61	73	40	(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):		52	55	46	k * (sunspot number). k = 0.6 for SWPC, k = 0.35 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) Boulder SN current month average to date. 2C) STAR SDO 1K Wolf number 30 day average.
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.