Solar Terrestrial Activity Report

Last major update issued on May 21, 2012 at 04:45 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)
[Solar cycles 21-24 (last update May 3, 2012)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22, 23 and 24 (last update May 3, 2012)]
[Graphical comparison of cycles 10, 12, 13, 14, 16 and 24 (last update May 3, 2012)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports since January 2003 (last update May 3, 2012)]

[POES auroral activity level since October 2009 - updated May 19, 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 May 20. Solar wind speed at SOHO ranged between 350 and 469 km/s. A weak solar wind shock was observed at SOHO at 01:44 UTC, likely the arrival of the CME observed early on May 17.

Solar flux measured at 20h UTC on 2.8 GHz was 130.8 (decreasing 11.0 over the last solar rotation). The Potsdam WDC planetary A index was 14 (STAR Ap - based on the mean of three hour interval ap indices: 13.5). Three hour interval K indices: 34333111 (planetary), 45312211 (Boulder).

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

At midnight UTC the visible solar disk had 11 spotted active regions (in 2K resolution SDO images).

Region 11478 [S23W75] was quiet and stable.
Region 11479 [N14W53] decayed slowly and quietly.
Region 11482 [N15W43] decayed slowly and quietly.
Region 11483 [S24W42] added a few spots and was quiet.
Region 11484 [N11W14] was quiet but could produce minor M class flares.
Region 11485 [S18W02] decayed slowly and quietly.
Region 11486 [N16E40] decayed slowly and quietly.
New region 11487 [N20W04] emerged early in the day. The current magnetic layout suggests that the southernmost spots could be a separate group. Spots emerged in this area on May 18 and were gone the next day.

Spotted active regions not numbered by NOAA/SWPC:
S1659 [N11E18] decayed slowly and quietly.
New region S1668 [N13W06] emerged to the east of AR 11484.
New region S1669 [N37W48] emerged at a high latitude as a reversed polarities region.

Coronal mass ejections (CMEs)

May 18-20: No obviously Earth directed CMEs were observed in LASCO or 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 (CH517) was in an Earth facing position on May 19-20. A coronal hole (CH518) in the northern hemisphere will be in an Earth facing position on May 21.

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 on May 21. A high speed stream from CH517 could arrive on May 22 and cause quiet to active conditions until May 23. Effects from CH518 could cause some unsettled intervals on May 24-25.

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
11477	2012.05.07 2012.05.08	1			S17W85	0030	HSX				spotless
11478	2012.05.08 2012.05.10	1	2	1	S24W75	0060	HSX	HSX			area: 0080
11479	2012.05.10 2012.05.11	2	4	2	N14W53	0050	HSX	CRO			area: 0030
11482	2012.05.11 2012.05.13	8	14	8	N14W44	0260	DHO	DKO			area: 0330
11483	2012.05.12 2012.05.13	6	17	7	S25W43	0050	DSO	DRO
11481	2012.05.12 2012.05.13				S10W36						plage location: S10W29
11484	2012.05.13	17	39	22	N10W17	0280	DKC	DSC			area: 0370
S1651	2012.05.13				N31W51						plage
S1654	2012.05.14				S25W11						plage
S1655	2012.05.14				S18W39						plage
S1659	2012.05.15		1	1	N11E18	0000		AXX
S1661	2012.05.15				N33W23						plage
11485	2012.05.15		4	2	S20W01	0000		AXX			location: S18W02
11486	2012.05.17 2012.05.18	4	6	3	N16E40	0140	CSO	CSO			area: 0240
S1663	2012.05.17				N12W03						plage
S1664	2012.05.17				N22W46						plage
11487	2012.05.18 2012.05.20	5	10	5	N19W05	0010	BXO	CRO			location: N20W04
S1666	2012.05.18				S19E09						plage
S1667	2012.05.19				N04E42						plage
S1668	2012.05.20		1	1	N13W06	0000		AXX
S1669	2012.05.20		1		N37W48	0000		AXX			reversed polarities
Total spot count:		44	99	52
Sunspot number:		124	209	152	(total spot count + 10 * number of spotted regions)
Weighted penumbral SN:		89	133	76	(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):		74	73	84	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 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.