Solar Terrestrial Activity Report

Last major update issued on April 21, 2013 at 05:05 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 quiet on April 20. Solar wind speed at SOHO ranged between 270 and 349 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 104.9 (increasing 8.9 over the last solar rotation). The Potsdam WDC planetary A index was 4 (STAR Ap - based on the mean of three hour interval ap indices: 3.9). Three hour interval K indices: 10122101 (planetary), 00122210 (Boulder).

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

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

Region 11722 [S21W82] decayed slowly and quietly.
Region 11723 [S18W46] decayed slowly and quietly.
Region 11725 [N09W72] decayed slowly and quietly.
Region 11726 [N12W07] developed very quickly and has become magnetically complex with several small magnetic delta structures forming on the eastern side of the largest penumbral structure. M and X class flares are possible.
Region 11727 [N25E44] matured with the opposite polarity areas drifting apart.

Spotted regions not numbered by SWPC:
S2357 [S23W42] was quiet and stable.
New region S2368 [S16E73] rotated into view with a single penumbra spot.

Coronal mass ejections (CMEs)

April 18-20: 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 fair. Propagation on long distance northeast-southwest paths is poor.

Forecast

The geomagnetic field is expected to be quiet on April 21-23. Quiet to minor storm conditions are likely on April 24-26 due to a high speed stream from CH566.

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
11722	2013.04.09 2013.04.10	4	1		S20W86	0030	CRO	AXX
11724	2013.04.12 2013.04.13	1			S26W19	0010	AXX				spotless
11723	2013.04.12 2013.04.13	9	7	2	S19W44	0060	CAO	CAO			location: S18W46
11725	2013.04.13 2013.04.19	3	3	2	N10W70	0010	BXO	BXO			location: N09W72
S2356	2013.04.15				S13W39						plage
S2357	2013.04.16		4	2	S23W42	0018		CRO
S2358	2013.04.17				N10W10						plage
S2359	2013.04.17				S15E37						plage
S2360	2013.04.18				N16W45						plage
11727	2013.04.18 2013.04.19	9	12	8	N25E44	0050	DAO	DAO			area: 0140 location: N25E58
S2362	2013.04.18										merged with AR 11726
11726	2013.04.19	15	80	40	N13W05	0180	EAI	EKC			beta-gamma-delta area: 0600
S2364	2013.04.19				N20W23						plage
S2365	2013.04.19				S14W20						plage
S2366	2013.04.19				S13E03						plage
S2367	2013.04.19				S06E05						plage
S2368	2013.04.20		1	1	S16E73	0005		AXX
Total spot count:		41	108	55
Sunspot number:		101	178	115	(total spot count + 10 * number of spotted regions)
Weighted SN:		59	131	78	(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):		61	62	63	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.