Last major update issued on April 20, 2012 at 04:40 UTC.
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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 quiet to unsettled on April 19. Solar wind speed at SOHO ranged between 335 and 423 km/s. A disturbance was observed arriving at ACE near 03h UTC on April 20. Initially the disturbance appears to have a CME origin, maybe the arrival of the CME observed on April 16.
Solar flux measured at 20h UTC on 2.8 GHz was 137.5 (increasing 32.7 over the last solar rotation). The Potsdam WDC planetary A index was 5 (STAR Ap - based on the mean of three hour interval ap indices: 5.3). Three hour interval K indices: 11101123 (planetary), 11002222 (Boulder).
The background x-ray flux is at the class B6 level.
At midnight UTC the visible solar disk had 8 spotted active regions (in 2K resolution SDO images).
Region 11459 [S16E16] decayed losing spots and penumbral area. C and
minor M class flares are possible.
Region 11460 [N15W00] developed further and could soon get a DKC or EKC classification. M flares are possible.
Region 11461 [N12E38] lost penumbral area and gained a few spots.
Region 11462 [S24W33] displayed impressive development and has major flare potential.
Region 11463 [S25W51] decayed and simplified. C flares are possible.
New region 11464 [N23E02] emerged to the north of AR 11460 on April 18 and was numbered by SWPC the next day.
Spotted active regions not numbered by NOAA/SWPC:
S1598 [N11E27] decayed slowly and was quiet.
New region S1603 [S18E54] emerged in the southeast quadrant.
The largest flare of the day was a C7.0 event peaking at 11:26 UTC with a source just behind the northwest limb. The largest CME of the day was observed following a filament eruption in the southeast quadrant after 14h UTC.
April 17 and 19: No obviously Earth directed CMEs were observed in LASCO and
April 18: A small CME associated with a C8 event in region 11463 could have had an Earth directed component.
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 will likely rotate into an Earth facing position on April 21.
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 poor. Propagation on long distance northeast-southwest paths is fair.
The geomagnetic field is expected to be quiet to active on April 20. The CME observed on April 18 could reach Earth on April 21 and cause quiet to active conditions that day and on April 22.
|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
|Total spot count:||62||149||68|
|Sunspot number:||122||229||138||(total spot count + 10 * number of spotted regions)|
|Weighted penumbral SN:||87||185||104||(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):||73||80||76||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||103.2 (1)||36.0 (2A) / 56.8 (2B)||(74.9 projected, +1.0)||(11.65)|
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 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.