Solar Terrestrial Activity Report

Last major update issued on April 3, 2012 at 04:30 UTC.

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

[POES auroral activity level since October 2009 - updated April 1, 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 April 2. Solar wind speed at SOHO ranged between 279 and 354 km/s.

Solar flux measured at 20h UTC on 2.8 GHz was 105.6 (decreasing 32.5 over the last solar rotation). The Potsdam WDC planetary A index was 11 (STAR Ap - based on the mean of three hour interval ap indices: 10.9). Three hour interval K indices: 43223212 (planetary), 33212322 (Boulder).

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

At midnight UTC the visible solar disk had 9 spotted active regions (in 2K resolution SDO images).

Region 11445 [S22W58] was quiet and stable.
Region 11448 [S18W06] could become spotless today.
Region 11449 [S19W74] decayed and was quiet.
Region 11450 [N15E09] developed slowly and is becoming an interesting region. There's weak polarity intermixing. C flares are possible and maybe even an M class flare if there's further development.
Region 11451 [N17E27] was quiet and stable.
New region 11452 [N17E48] emerged near the northeast limb on March 31 and was noticed by SWPC 2 days later.
New region 11453 [S17E03] rotated into view at the southeast limb on March 27 and was numbered by SWPC 6 days later.

Spotted regions not reported by NOAA/SWPC:
[S1558] emerged in the southeast quadrant on March 28. Location at midnight: S30W45
[S1564] emerged near the southwest limb on April 2. Location at midnight: S08W78

Coronal mass ejections (CMEs)

March 31-April 2: 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 coronal hole (CH510) in the northern hemisphere was in an Earth facing position on March 30. A new trans equatorial coronal hole (CH511) emerged near the central meridian on March 31.

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 fair to good.

Forecast

The geomagnetic field is expected to be quiet to unsettled on April 3-4 with occasional active intervals due to weak effects from CH510 and CH511. Quiet conditions are likely on April 5.

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
11443	2012.03.21 2012.03.22				N14W88						plage
11445	2012.03.23	1	2	1	S22W59	0120	HSX	HSX			area: 0200
11448	2012.03.26 2012.03.28		1		S17W13	0000		AXX			location: S18W06
11453	2012.03.27 2012.04.02	4	12	6	S17E02	0020	CSO	BXO
11449	2012.03.28 2012.03.29	3	2	1	S18W74	0040	DSO	AXX
S1558	2012.03.28		1		S30W45	0000		AXX
11450	2012.03.30 2012.03.31	7	26	10	N16E07	0040	DSO	DRI			location: N15E09 beta-gamma
11451	2012.03.30 2012.03.31		3		N17E25	0000		AXX			location: N17E27
11452	2012.03.31 2012.04.02	2	9	4	N19E47	0030	DSO	DSO			location: N17E48
S1563	2012.03.31				N26W09						plage
S1564	2012.04.02		1	1	S08W78	0000		AXX
Total spot count:		17	57	23
Sunspot number:		67	147	83	(total spot count + 10 * number of spotted regions)
Weighted penumbral SN:		42	70	36	(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):		40	51	46	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 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.