Solar Terrestrial Activity Report

Last major update issued on May 18, 2013 at 06:35 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 23-24 (last update May 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 May 1, 2013)]
[Graphical comparison of cycles 10, 12, 13, 14, 16 and 24 (last update May 1, 2013)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports since January 2003 (last update May 6, 2013)]

[POES auroral activity level since October 2009 - updated January 26, 2013]
[Solar polar fields vs solar cycles - updated May 12, 2013]
[Presentation 3rd SSN Workshop, Tucson, 2013 (pdf)]

Recent activity

The geomagnetic field was quiet to unsettled on May 17. Solar wind speed at SOHO ranged between 346 and 476 km/s. A CME, probably associated with the X1 event on May 15, was observed arriving at SOHO at 00:23 UTC on May 18. This is causing active to major geomagnetic storm conditions.

Solar flux measured at 20h UTC on 2.8 GHz was 136.4 (increasing 31.5 over the last solar rotation). The Potsdam WDC planetary A index was 7 (STAR Ap - based on the mean of three hour interval ap indices: 6.9). Three hour interval K indices: 22111232 (planetary), 23222322 (Boulder).

The background x-ray flux was at the class B6 level.

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

Region 11743 [N21W53] decayed slowly and quietly.
Region 11744 [N05W38] decayed slowly losing spots and penumbral area. The region still has minor polarity intermixing. C5+ flares: C5.0 at 04:41 UTC.
Region 11745 [N12W12] decayed slowly and quietly.
Region 11746 [S29W12] decayed slowly and was quiet.
Region 11747 [S19W16] decayed slowly and quietly.
Region 11748 [N10E25] has a magnetic delta structure in the leading penumbral structure and could produce further M class events, an X class event may still be possible. The positive polarity area in the leading penumbra is moving slowly southwards as compared to the negative polarity area in the eastern part of the penumbra. If this development continues the delta could disappear within a couple of days. The region has decayed losing both spots and penumbral area. C5+ flares: M3.2/2B at 08:57 UTC. This event was associated with a fast asymmetric full halo CME.
Region 11749 [S23W64] decayed slowly and quietly.
Region 11750 [S10W41] developed slowly and quietly. The region has slight polarity intermixing and C flares are possible.
Region 11751 [S25W00] decayed and could soon become spotless.
Region 11752 [N17W37] added penumbral area with a minor reduction in spot number.

Spotted regions not numbered by SWPC:
S2420 [S13W25] was quiet and stable.
S2424 [S29E14] was quiet and stable.
New region S2425 [S14W14] emerged with one spot.

Coronal mass ejections (CMEs)

May 15: A wide CME was observed after the X1 event in AR 11748.
May 16: No obviously Earth directed CMEs were observed in LASCO and STEREO imagery.
May 17: A halo CME was observed after an M3 event in AR 11748. The CME was fast and will likely reach Earth on May 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

No obvious coronal holes are currently in or near Earth facing positions.

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 unsettled to major storm on May 18-20 due to CME effects.

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
11741	2013.05.05 2013.05.06				S21W85						plage
11742	2013.05.07 2013.05.09				N28W59						plage
11743	2013.05.08 2013.05.09	2	6	2	N22W53	0030	DAO	CRO
11744	2013.05.08 2013.05.09	23	18	7	N06W40	0100	DAO	DAI			beta-gamma
11745	2013.05.10	10	30	10	N13W15	0300	CKO	DAO			location: N12W12
11746	2013.05.10 2013.05.11	7	12	4	S27W14	0160	CSO	CSO			area: 0220 location: S29W12
11747	2013.05.12	10	15	8	S17W17	0080	DAO	DRO			location: S19W16
11751	2013.05.12 2013.05.15	2	2	2	S23W01	0000	AXX	AXX			area: 0008
S2412	2013.05.12				S44W38						plage
11748	2013.05.13	24	30	15	N12E23	0220	DAI	DAO			beta-gamma-delta location: N10E25
S2414	2013.05.13				N20W40						plage
S2415	2013.05.13				S24W39						plage
11749	2013.05.13 2013.05.15	4	3	1	S22W66	0030	CRO	BXO			area: 0010
11750	2013.05.14 2013.05.15	9	18	13	S09W41	0050	CAO	DAI			beta-gamma area: 0030
S2418	2013.05.14				S43W22						plage
S2419	2013.05.14				S17E24						plage
S2420	2013.05.15		1	1	S13W25	0003		AXX
S2421	2013.05.15				S17W29						plage
S2422	2013.05.15				S17W44						plage
11752	2013.05.15 2013.05.16	7	11	6	N18W40	0020	CRO	DRO			location: N17W38
S2424	2013.05.16		2		S29E14	0005		AXX
S2425	2013.05.17		1	1	S14W14	0006		AXX
Total spot count:		98	149	70
Sunspot number:		198	279	190	(total spot count + 10 * number of spotted regions)
Weighted SN:		144	183	104	(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):		119	98	105	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.