Solar Terrestrial Activity Report

Last major update issued on April 4, 2011 at 04:25 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, 2011)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22, 23 and 24 (last update April 1, 2011)]
[Graphical comparison of cycles 10, 12, 13, 14, 16 and 24 (last update April 1, 2011)]
[Historical solar and geomagnetic data charts 1954-2006 (last update April 5, 2007)]
[Archived reports since January 2003 (last update April 1, 2011)]

[POES auroral activity level charts since October 2009 - updated April 1, 2011]
Annotated geomagnetic activity charts - Carrington rotation 2106 [Jan.-Feb.2011] - 2107 [Feb.-March 2011]

Recent activity

The geomagnetic field was unsettled to active on April 3. Solar wind speed ranged between 514 and 714 km/s under the influence of a high speed coronal hole stream.

Solar flux estimated at 20h UTC on 2.8 GHz was 114.0 (decreasing 37.9 over the last solar rotation). The planetary A index was 16 (STAR Ap - based on the mean of three hour interval ap indices: 16.4). Three hour interval K indices: 43333343 (planetary), 34333333 (Boulder).

The background x-ray flux is at the class B4 level.

At midnight UTC the visible solar disk had 6 spotted regions.

Region 11176 rotated out of view at the southwest limb. The region was the source of a very long duration B9 event which was associated with a large and slow CME off the southwest limb.
Region 11180 was quiet and stable.
Region 11183 decayed slowly and was mostly quiet. Flare: C1.2 at 05:19 UTC.
Region 11184 developed quickly and became the largest region on the visible disk. The development in this region has caused an increase in the background xray flux. C flares are likely. If the region develops further M class flares will become possible.

Spotted regions not numbered by NOAA/SWPC:
[S928] emerged with spots in an old plage field in the northeast quadrant on April 1. Location at midnight: N08E14
[S929] emerged in the southern hemisphere near the central meridian on April 1.  Location at midnight: S25W28
[S931] rotated into view at the northeast limb on April 3. Location at midnight: N23E79

Coronal mass ejections (CMEs)

April 1-3: No obviously Earth directed CMEs were observed in LASCO and STEREO imagery.

Coronal holes

Coronal hole history (since late October 2002)
Compare today's report to the situation one solar rotation ago: 28 days ago 27 days ago 26 days ago

No obvious coronal holes are currently in or near Earth facing positions.

The darkest areas on the solar disk are likely coronal holes.

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.

Forecast

The geomagnetic field is expected to be quiet to unsettled on April 4 and quiet on April 5-6.

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 polarity overlay		Comment
		SWPC	STAR SDO			SWPC	STAR	Current	Previous
11176	2011.03.21	1		S18W90	0040	HSX				rotated out of view
11178	2011.03.24			S17W64						plage
11181	2011.03.24 2011.03.25			S27W50						plage
11180	2011.03.24 2011.03.25	1	2	N25W50	0030	HSX	CRO			location: N25W45
S920	2011.03.25			S25W64						plage
11183	2011.03.26 2011.03.27	13	18	N17W25	0150	ESO	CAO			location: N15W25
S922	2011.03.26			N24W82						plage
S923	2011.03.27			S26W53						plage
S924	2011.03.29			N36W17						plage
11184	2011.03.30 2011.04.01	15	24	N18E01	0070	DSO	DAI			location: N16E01 area: 0300
S926	2011.03.30			N21W59						plage
S927	2011.03.31			N25E26						plage
S928	2011.04.01		6	N08E15	0000		BXO
S929	2011.04.01		1	S25W28	0000		AXX
S930	2011.04.01			S07W48						plage
S931	2011.04.03		1	N23E79	0000		AXX
Total spot count:		30	52
Sunspot number:		70	112

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 preliminary daily SWPC ap indices. Values in red are based on the official NGDC 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.