Solar Terrestrial Activity Report

Last major update issued on April 18, 2014 at 05:20 UTC. Minor update posted at 14:45 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, 2014)] [Cycle 24 progress (last update April 1, 2014) ]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22, 23 and 24 (last update April 1, 2014)]
[Graphical comparison of cycles 10, 12, 13, 14, 16 and 24 (last update April 1, 2014)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports since January 2003 (last update April 2, 2014)]

[POES auroral activity level October 2009 - December 2012]
[Solar polar fields vs solar cycles - updated April 17, 2014]
[Presentation 3rd SSN Workshop, Tucson, 2013 (pdf)]

Recent activity

The geomagnetic field was quiet to unsettled on April 17. Solar wind speed at SOHO ranged between 343 and 445 km/s under the influence of a low speed coronal hole stream.

Solar flux at 20h UTC on 2.8 GHz was 178.9 (increasing 26.3 over the last solar rotation). The 90 day 10.7 flux at 1 AU was 151.9. The Potsdam WDC planetary A index was 10 (STAR Ap - based on the mean of three hour interval ap indices: 9.9). Three hour interval K indices: 33212321 (planetary), 33213422 (Boulder).

The background x-ray flux is at the class B9 level.

At the time of counting spots (see image time), spots were observed in 15 active regions in 2K resolution (SN: 403) and 12 active regions in 1K resolution (SN: 247) SDO images on the visible solar disk.

Region 12032 [N11W56] was quiet and stable.
Region 12033 [N12W43] was quiet and stable.
Region 12034 [N04W25] developed further and has major flare potential.
Region 12035 [S16W03] decayed early in the day, then displayed explosive growth during the latter half of the day with new flux emerging in the central sections. A major flare is possible.
Region 12036 [S17W26] decayed slowly and quietly.  
Region 12037 [S09W28] decayed slowly and was quiet. As there is polarity intermixing there is still a chance of a minor M class flare.
Region 12038 [S13E38] developed and is close to forming a magnetic delta structure. A minor M class flare is possible.
Region 12039 [N24W16] redeveloped umbra on both polarities.
Region 12040 [N15W01] developed slowly and was quiet.
Region 12042 [N18E53] developed slowly and quietly. A minor M class flare is possible.
New region 12043 [S11W16] emerged on April 17 and decayed the next day as it was numbered by SWPC.

Spotted regions not numbered (or interpreted differently) by SWPC:
S3323 [S16E21] was quiet and stable.
S3330 [N13E33] gained trailing penumbra spots.
New region S3333 [S07W09] emerged early in the day with penumbra spots, then decayed and had only a penumbra spot left by the end of the day.
New region S3334 [S34W35] emerged with a penumbra spot.

An interesting region is approaching the southeast limb and has displayed frequent flaring over the last day.

Update added at 14:45 UTC: AR 12036 produced a major M7.3 flare (as recorded by GOES-15, SDO/EVE had the flare peaking at M8.0) peaking at 13:03 UTC. This event was associated with an increase in proton levels at Earth and a halo CME (as observed by STEREO). The CME could reach Earth on April 20.

Coronal mass ejections (CMEs)

April 15-17: 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 small trans equatorial coronal hole (CH612) rotated across the central meridian on April 16.

Propagation

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

Forecast

The geomagnetic field is expected to be mostly quiet on April 18-20. Weak effects from CH612 could cause unsettled intervals on April 19.

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: 0-30% probability, Yellow: 30-70% probability, Red: 70-100% 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	Magnetic (SDO)				SWPC	STAR	Current	Previous
			2K	1K
12032	2014.04.07 2014.04.08	1	1	1	N13W57	0110	HAX	HSX			area: 0180 location: N11W56
12033	2014.04.09	1	8	1	N13W45	0080	HSX	HSX			area: 0120 location: N12W43
12034	2014.04.10	40	46	29	N05W26	0280	DHC	EKC			area: 0710 location: N04W25
12035	2014.04.10 2014.04.11	40	53	28	S14W04	0240	FSC	EKC			beta-gamma-delta area: 0470 location: S16W03
12037	2014.04.12 2014.04.13	24	23	13	S09W27	0110	DAI	DAI			beta-gamma area: 0180
12036	2014.04.12 2014.04.13	34	54	27	S15W28	0510	DHC	DAC			beta-gamma area: 0460 location: S17W26
S3317	2014.04.13				S09E24						plage
12040	2014.04.13 2014.04.15	14	11	6	N16W02	0010	BXO	CRO			area: 0025 location: N15W01
12038	2014.04.14 2014.04.15	6	17	7	S13E37	0050	CSO	DSC			beta-gamma area: 0150
S3323	2014.04.14		7		S16E21	0015		BXO
S3324	2014.04.14				N14W25						plage
12039	2014.04.15	5	5	3	N25W17	0010	BXO	DRO			area: 0025 location: N24W16
12041	2014.04.15 2014.04.16	5			S19W43	0010	BXO				spotless
12042	2014.04.16	4	20	9	N18E54	0240	DSO	DKO			area: 0350
S3330	2014.04.16		4		N13E38	0008		BXO
12043	2014.04.16 2014.04.17	2	2	2	S11W17	0010	BXO	BXO			area: 0008
S3333	2014.04.17		1		S07W09	0002		AXX
S3334	2014.04.17		1	1	S34W35	0005		AXX
Total spot count:		176	253	127
Sunspot number:		296	403	247	(total spot count + 10 * number of spotted regions)
Weighted SN:		226	314	183	(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):		178	141	136	k * (sunspot number). k = 0.6 for SWPC, k = 0.35 for MSN 2K, k = 0.55 for MSN 1K (MSN=Magnetic Sunspot Number)

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 WDC-SILSO 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 GFZ Potsdam WDC ap indices.

This report has been prepared by Jan Alvestad. It is based on the 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.