Last major update issued on April 21, 2011 at 06:25 UTC.
[Solar and geomagnetic data - last month (updated
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[Solar cycles 21-24 (last update April 1, 2011)]
[Solar cycles 1-20]
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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 minor storm on April 20. Solar wind speed ranged between 424 and 543 km/s under the influence of a high speed stream from CH445.
Solar flux measured at 20h UTC on 2.8 GHz was 117.0 (increasing 9.4 over the last solar rotation). The planetary A index was 16 (STAR Ap - based on the mean of three hour interval ap indices: 16.3). Three hour interval K indices: 35433321 (planetary), 33433311 (Boulder).
The background x-ray flux is at the class B4 level.
At midnight UTC the visible solar disk had 8 spotted regions.
Region 11191 decayed with the leader spot fragmenting into several
smaller spots and retaining only rudimentary penumbra.
Region 11193 decayed slowly in the trailing spot section and was quiet.
Region 11195 developed slowly and has polarity intermixing. C flares are
likely. Flares: C1.0 at 04:31, C4.0 at 19:39
UTC.
New region 11196 rotated partly into view at the southeast limb on April
19 and was numbered the following day by NOAA/SWPC.
Spotted regions not numbered by NOAA/SWPC:
[S950] reemerged on April 15. Location at midnight: S15W36
[S962] rotated into view at the southeast limb late on April 19. Location
at midnight: S16E71
[S965] emerged in the southeast quadrant on April 20. Location at midnight:
S17E37
[S966] emerged in the southwest quadrant on April 20. Location a midnight:
S32W25
April 18-19: No obviously Earth directed CMEs were observed in LASCO
and STEREO imagery.
April 20: A disappearing filament in the southeast quadrant late in
the day may have produced a partially Earth directed CME (pending further
analysis).
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. A large coronal hole will begin rotating into view at the southeast limb within 2-3 days.
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 mostly quiet on April 21-23.
| 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
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.
(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 | |||||
| 11190 | 2011.04.08 2011.04.11 |
2 | N14W94 | 0060 | CAO |
 |
rotated out of view |
|||
| 11191 | 2011.04.11 2011.04.12 |
1 | 10 | N07W39 | 0015 | HRX | CRO |
 |
 |
location: N07W36 |
| 11193 | 2011.04.12 2011.04.13 |
26 | 35 | N16W20 | 0300 | EHI | EHI |
 |
 |
beta-gamma |
| S950 | 2011.04.13 | 4 | S15W36 | 0000 | AXX |
 |
 |
|||
| S951 | 2011.04.13 | N28W48 | plage | |||||||
| S953 | 2011.04.14 | N21W52 | plage | |||||||
| S956 | 2011.04.17 | N19E39 | plage | |||||||
| S957 | 2011.04.17 | N08W46 | plage | |||||||
| 11195 | 2011.04.18 2011.04.19 |
7 | 17 | S17E55 | 0100 | DAI | DAI |
 |
 |
beta-gamma |
| S960 | 2011.04.18 | N10E05 |
 |
plage | ||||||
| 11196 | 2011.04.19 2011.04.20 |
4 | 6 | S27E69 | 0080 | DAO | CAO |
 |
 |
formerly region S961 location: S25E77 |
| S962 | 2011.04.19 | 1 | S16E71 | 0010 | AXX |
 |
 |
|||
| S963 | 2011.04.19 | S18E14 |
 |
plage | ||||||
| S964 | 2011.04.19 | S25W26 |
 |
plage | ||||||
| S965 | 2011.04.20 | 4 | S17E37 | 0000 | AXX |
 |
||||
| S966 | 2011.04.20 | 1 | S32W25 | 0000 | AXX |
 |
||||
| Total spot count: | 40 | 78 | ||||||||
| Sunspot number: | 90 | 158 | ||||||||
| Month | Average measured solar flux | International sunspot number (SIDC) | Smoothed sunspot number | Average ap (3) |
|---|---|---|---|---|
| 2008.07 | 65.7 (SF minimum) | 0.5 | 2.8 (-0.4) | |
| 2008.12 | 69.2 | 0.8 | 1.7 (-) sunspot minimum |
3.25 |
| 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 | 112.7 (1) | 56.9 (2A) / 85.3 (2B) | (39.6 predicted, +2.9) | (10.91) |
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.
