Last major update issued on April 25, 2011 at 05:20 UTC.
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[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
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Annotated geomagnetic activity charts - Carrington rotation 2107 [Feb.-March 2011] - 2108 [March-April 2011] NEW
The geomagnetic field was quiet to unsettled on April 24. Solar wind speed ranged between 370 and 542 km/s under the influence of what is likely a weak coronal hole stream.
Solar flux measured at 20h UTC on 2.8 GHz was 117.2 (increasing 3.5 over the last solar rotation). The planetary A index was 6 (STAR Ap - based on the mean of three hour interval ap indices: 5.8). Three hour interval K indices: 11011213 (planetary), 12111223 (Boulder).
The background x-ray flux is at the class B4 level.
At midnight UTC the visible solar disk had 9 spotted regions.
Region 11193 was quiet. The region has become somewhat more unstable
with both polarity spots currently inside the leading penumbra.
Region 11195 changed significantly in the trailing spot section with most of the spots there merging into a large penumbra, which became the largest penumbra of the region. This penumbra is complex as it has a magnetic delta structure in its southwestern section. Although the region has been quiet, there is again an increasing chance of an M class flare.
Region 11196 has many tiny spots with no significant changes observed over the last day.
Region 11197 reemerged with a couple of tiny spots.
Region 11198 reemerged with spots near the southwest limb.
Spotted regions not numbered by NOAA/SWPC:
[S965] emerged in the southeast quadrant on April 20. Location at midnight: S18W17
[S968] rotated partly into view at the northeast limb on April 24. Location at midnight: N14E78
[S969] emerged in the northeast quadrant on April 24. Location at midnight: N15E16
[S970] emerged in the northwest quadrant on April 24. Location at midnight: N17W40
A C2.4 flare at 19:26 and a C1.7 flare at 20:07 UTC both had their origin at the northeast limb, either in region S968 or in a region trailing S968.
April 22-24: No obviously Earth directed CMEs were observed in LASCO and STEREO imagery.
Coronal hole history (since late October
Compare today's report to the situation one solar rotation ago: 28 days ago 27 days ago 26 days ago
A trans equatorial coronal hole (CH446) will likely rotate into an Earth dacing position on April 26-27.
The darkest areas on the solar disk are likely coronal holes.
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 poor to fair.
The geomagnetic field is expected to be quiet to unsettled on April 25-29. A high speed stream associated with CH446 could cause quiet to active conditions on April 30.
|Coronal holes (1)||Coronal mass ejections (2)||M and X class flares (3)|
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
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.
(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
|Spot count||Location at midnight||Area||Classification||SDO / HMI 4K continuum
image with polarity overlay
|Total spot count:||48||91|
|Month||Average measured solar flux||International sunspot number (SIDC)||Smoothed sunspot number||Average ap
|2008.07||65.7 (SF minimum)||0.5||2.8 (-0.4)|
|2010.02||84.7||18.8||10.6 (+1.3)||4.15 / 4.61|
|2010.03||83.4||15.4||12.3 (+1.7)||4.58 / 4.65|
|2010.04||75.9||8.0||14.0 (+1.7)||10.22 / 10.24|
|2010.05||73.8||8.7||15.5 (+1.5)||9.18 / 8.15|
|2010.06||72.5||13.6||16.4 (+0.9)||8.17 / 6.85|
|2010.07||79.8||16.1||16.7 (+0.3)||6.31 / 5.15|
|2010.08||79.2||19.6||17.4 (+0.7)||8.49 / 7.77|
|2010.09||81.1||25.2||19.6 (+2.2)||5.33 / 5.45|
|2010.10||81.6||23.5||(22.6 predicted, +3.0)||6.07 / 6.27|
|2010.11||82.5||21.5||(25.7 predicted, +3.1)||4.80 / 5.50|
|2010.12||84.2||14.4||(28.9 predicted, +3.2)||3.41 / 4.35|
|2011.01||83.6||19.1||(31.9 predicted, +3.0)||4.32 / 5.51|
|2011.02||94.6||29.4||(34.4 predicted, +2.5)||5.41 / 6.44|
|2011.03||115.0||56.2||(36.7 predicted, +2.3)||7.79|
|2011.04||113.3 (1)||68.9 (2A) / 86.1 (2B)||(39.6 predicted, +2.9)||(10.03)|
1) Running average based on the daily 20:00 UTC observed solar flux value at
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.