Solar Terrestrial Activity Report

Last major update issued on May 24, 2015 at 06:05 UT. Updates may be late and incomplete until May 25.

Recent activity

The geomagnetic field was very quiet on May 23. Solar wind speed at SOHO ranged between 277 and 391 km/s.

Solar flux at 20h UTC on 2.8 GHz was 97.7 (decreasing 20.7 over the last solar rotation). The 90 day 10.7 flux at 1 AU was 127.3. The Potsdam WDC planetary A index was 3 (STAR Ap - based on the mean of three hour interval ap indices: 2.6). Three hour interval K indices: 01111011 (planetary), 11112212 (Boulder).

The background x-ray flux is at the class B2 level.

At the time of counting spots (see image time), spots were observed in 7 active regions using 2K resolution (SN: 133) and 7 active regions using 1K resolution (SN: 104) SDO images on the visible solar disk.

Region 12348 [S10W58] decayed slowly and quietly.
Region 12349 [S19W36] developed slowly and produced a few low level flares.
Region 12351 [N22E04] decayed slowly and quietly.
Region 12352 [N07E01] decayed slowly and quietly.
Region 12353 [N08W17] developed a small magnetic delta in a central penumbra and produced a few low level flares.
New region 12354 [S20W16] emerged on May 22 and was numbered by SWPC the next day.

Spotted regions not numbered (or interpreted differently) by SWPC:
New region S4495 [S09E56] emerged with several spots. C flares are possible.

C2+ flares:

Flare activity according to SDO/EVE/ESP XRS-B proxy

Coronal mass ejections (CMEs)

May 23: No obviously Earth directed CMEs were observed.
May 21-22: A partial halo CME was observed late on May 21 and early on May 22. It is uncertain if the CME source was backsided or on the visible disk. A filament eruption in the central northern hemisphere starting near 20h UT may have been the source, in that case the CME could have Earth directed components.

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 (CH669) will rotate into an Earth facing position on May 23-25, while a northern hemisphere coronal hole (CH670) will rotate across the central meridian on May 24-26.

Propagation

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

Forecast

The geomagnetic field is expected to be quiet on May 24. Late on May 24 and on May 25 there is a chance of a CME arrival if the CME observed on May 21/22 was caused by an observed filament eruption. In that case unsettled to active conditions will be possible. On May 26-28 unsettled to minor storm conditions will be possible due to effects from high speed streams associated with CH669 and CH670.

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 overlays		Comment
		SWPC	Magnetic (SDO)				SWPC	STAR	Current	Previous
			2K	1K
12348	2015.05.12 2015.05.14	1	1	1	S12W59	0040	HSX	HAX
12349	2015.05.17 2015.05.18	5	16	10	S21W36	0040	CAO	DAI			area: 0140
12350	2015.05.17 2015.05.18				S15W49
12351	2015.05.17 2015.05.19		11	2	N22W09	0020		BXO
S4478	2015.05.17				N13W42
12352	2015.05.20 2015.05.22	4	5	1	N05W03	0010	BXO	AXX
S4485	2015.05.20				S08E19
S4486	2015.05.20				N16E09
12353	2015.05.21 2015.05.22	7	16	11	N07W18	0050	DAO	DAI			beta-delta area: 0150
S4489	2015.05.21				N19E19
S4490	2015.05.21				S11W16
S4491	2015.05.22				N08W11
12354	2015.05.22 2015.05.23	2	3	3	S21W15	0010	CRO	CRO
S4493	2015.05.22				S10E37
S4494	2015.05.22				N17W16
S4495	2015.05.23		11	6	S09E56	0050		DRI
Total spot count:		19	63	34
Sunspot number:		69	133	104	(total spot count + 10 * number of spotted regions)
Weighted SN:		37	84	55	(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):		41	47	57	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.