Solar Terrestrial Activity Report

Last major update issued on September 7, 2017 at 05:00 UT.

Recent activity

The geomagnetic field was quiet to unsettled on September 6. Solar wind speed at SOHO ranged between 349 and 621 km/s. A moderate solar wind shock was observed at SOHO at 23:13 UT, the arrival of the September 4 CME. The interplanetary magnetic field has initially been mostly northwards resulting in only a weak increase in geomagnetic activity.

Solar flux at 23h UTC on 2.8 GHz was 127.3 (increasing 52.7 over the previous solar rotation). The average 90 day 10.7 flux at 1 AU was 81.5. The Potsdam WDC planetary A index was 7 (STAR Ap - based on the mean of three hour interval ap indices: 7.3). Three hour interval K indices: 11122213 (planetary), 12234314 (Boulder)

The background x-ray flux is at the class C1 level.

At the time of counting spots (see image time), spots were observed in 6 active regions using 2K resolution (SN: 191) and in 6 active regions using 1K resolution (SN: 126) SDO images on the visible solar disk.

Region 12673 [S09W42] produced 2 X class events, the largest an X9.3 flare at 12:02 UT, the most intense flare of solar cycle 24. While a large and fast asymmetrical CME was observed with this event, it is uncertain if Earth will be hit by the core CME or just the outer edges. The region still has a very strong magnetic delta and could produce further X class flares.
Region 12674 [N13W28] decayed slowly and quietly.
Region 12677 [N17E26] was quiet and stable.
Region 12678 [N10E33] was quiet and stable.

Spotted regions not numbered (or interpreted differently) by SWPC:
S5790 [N15W12] developed slowly and quietly.
New region S5791 [S09E02] emerged with a few spots.

C2+ flares:

Coronal mass ejections (CMEs)

September 6: A large and fast CME was observed after the X9 event in AR 12673. The arrival time of this CME at Earth is uncertain as it depends on whether or not Earth is in the path of the core of CME. The most likely time is during the latter half of September 8, but could even occur early in the day.
September 5: No obviously Earth directed CMEs were observed in available LASCO imagery.
September 4: A full halo CME was observed starting at 20:06 UT in LASCO C3 imagery. This CME reached SOHO at 23:13 UT on September 6.

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 southern hemisphere coronal hole (CH823) was in an Earth facing position on September 4-5.

Propagation

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

Forecast

The geomagnetic field is expected to be unsettled to major storm on September 7-9 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: 0-30% probability, Yellow: 30-70% probability, Red: 70-100% probability.

Active solar regions

(Click on image for 2K resolution). 4K 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 overlays		Comment
		SWPC	Magnetic (SDO)				SWPC	STAR	Current	Previous
			2K	1K
12673	2017.08.28 2017.08.29	24	47	25	S09W45	0960	EKC	DKC			location: S09W42 beta-gamma-delta
12674	2017.08.28 2017.08.29	10	43	24	N14W28	0680	FHI	FKI			beta-gamma
12677	2017.09.02 2017.09.03	1	15	4	N18E25	0010	AXX	CRO			area: 0025
S5788	2017.09.02				S10E04
12678	2017.09.04 2017.09.05	4	11	6	N11E31	0040	CSO	DAO			area: 0060
S5790	2017.09.05		10	5	N15W12	0030		DRO
S5791	2017.09.06		5	2	S09E02	0015		CRO
Total spot count:		39	131	66
Sunspot number:		79	191	126	(total spot count + 10 * number of spotted regions)
Weighted SN:		64	165	100	(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):		87	105	101	k * (sunspot number) As of May 7, 2016: k = 1.1 for SWPC, k = 0.55 for MSN 2K, k = 0.80 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).
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.
4) Updated to new data set from WDC-SILSO on July 1, 2015

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 Universal Time. Comments and suggestions are always welcome.

SDO images are courtesy of NASA/SDO and the AIA, EVE, and HMI science teams.