Last major update issued on April 25, 2012 at 04:50 UTC.
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[POES auroral activity level since October
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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]
The geomagnetic field was unsettled to severe storm on April 24. Solar wind speed at SOHO ranged between 346 and 719 km/s, at first under the influence of a CME, then a high speed stream associated with CH514 became the dominant solar wind source.
Solar flux measured at 20h UTC on 2.8 GHz was 133.6 (increasing 26.6 over the last solar rotation). The Potsdam WDC planetary A index was 51 (STAR Ap - based on the mean of three hour interval ap indices: 51.0). Three hour interval K indices: 76533346 (planetary), 65622335 (Boulder).
The background x-ray flux is at the class B6 level.
At midnight UTC the visible solar disk had 13 spotted active regions (in 2K resolution SDO images).
Region 11459 [S16W52] decayed further losing spots and penumbral
Region 11460 [N15W69] decayed further and has only rudimentary penumbra on the trailing spots.
Region 11461 [N11W23] was mostly quiet and stable.
Region 11465 [S18W13] was quiet in spite of the presence of at least one magnetic delta structure within the large penumbra. A major flare is possible.
Region 11466 [N12E01] was quiet and stable.
New region 11467 [N13E73] rotated into view at the northeast limb. While the region has only small spots it was the source of the only interesting event of the day, a C3.7 flare at 07:45 UTC. This event was associated with a partial halo CME, however, the CME will probably not reach Earth.
New region 11468 [N09E12] emerged in the northeast quadrant on April 20 and was noticed by SWPC 4 days later when it developed quickly.
New region 11469 [S20E70] rotated into view at the southeast limb on April 23 and was numbered the next day by SWPC.
Spotted active regions not numbered by NOAA/SWPC:
S1602 [S32W27] reemerged with a single spot.
S1605 [S12W47] decayed slowly and quietly.
S1609 [S26E15] added a few tiny spots.
New region S1610 [S07W41] emerged with a single spot.
April 22 and 24: No obviously Earth directed CMEs were observed in LASCO and
April 23: Region S1598 (to the west of AR 11461) was the source of a C2 flare at 17:51 UTC. A CME was associated with this event. LASCO images indicate a full halo, however, NASA analysis of all available imagery indicates there were two sources for this apparent full halo CME. The CME associated with the C2 event was observed over most of the southern hemisphere limbs as a partial halo CME. It is uncertain if this CME will reach Earth.
Coronal hole history (since October
Compare today's report to the situation one solar rotation ago: 28 days ago 27 days ago 26 days ago
A coronal hole (CH514) in the northern hemisphere was in an Earth facing position on April 21, however, CH514 closed the same day.
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.
Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over high and upper middle latitudes is very poor. Propagation on long distance northeast-southwest paths is fair to good.
The geomagnetic field is expected to be quiet to major storm on April 24 due to effects from CH514. If the CME observed on April 23 arrives it is likely to do so on April 26 and could cause unsettled to minor storm conditions that day and on April 27. If it fails to arrive we can expect quiet to unsettled conditions.
|Coronal holes (1)||Coronal mass ejection (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 magnetic polarity overlay
|4||S25W95||0300||DHO||rotated out of view|
|Total spot count:||89||126||60|
|Sunspot number:||169||256||170||(total spot count + 10 * number of spotted regions)|
|Weighted penumbral SN:||149||162||96||(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):||101||90||94||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|
|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)|
|2011.10||137.3||88.0||(60.1 projected, +0.6)||8.28|
|2011.11||153.5||96.7||(61.6 projected, +1.5)||5.55|
|2011.12||141.3||73.0||(64.3 projected, +2.7)||3.78|
|2012.01||132.5||58.3||(67.8 projected, +3.5)||7.15|
|2012.02||106.5||33.1||(71.8 projected, +4.0)||8.81|
|2012.03||114.7||64.2||(73.9 projected, +2.1)||16.08|
|2012.04||111.5 (1)||61.1 (2A) / 76.4 (2B)||(74.9 projected, +1.0)||(11.20)|
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 quicklook and definitive 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.