Last major update issued on April 12, 2011 at 04:30 UTC. Minor update posted at 14:40 UTC.
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The geomagnetic field was quiet to active on April 11. Solar wind speed ranged between 308 and 464 km/s. A high speed stream originating from an extension of the southern polar coronal hole began to influence the geomagnetic field before noon. Apart from southerly swings at 16 and 19h UTC (at ACE) the interplanetary magnetic field has been predominantly northwards. The relatively weak disturbance mainly affected the mid latitudes with polar magnetometers recording quiet conditions.
Solar flux estimated at 20h UTC on 2.8 GHz was 105.8 (increasing 4.3 over the last solar rotation). The planetary A index was 9 (STAR Ap - based on the mean of three hour interval ap indices: 9.3). Three hour interval K indices: 20123432 (planetary), 21223322 (Boulder).
The background x-ray flux is at the class B4 level.
At midnight UTC the visible solar disk had 6 spotted regions.
Region 11185 reemerged with a single tiny spot.
Region 11186 was mostly unchanged and quiet.
Region 11187 decayed slowly and quietly.
Region 11189 decayed slowly and was quiet. [Note that SWPC currently has this region as 11185 with
the real region 11185 having been renumbered 11189]
Region 11190 rotated into view at the northeast limb on April 8 and was
numbered 3 days later by NOAA/SWPC. The region developed fairly quickly on April
11 with mixed polarities observed in the intermediate spot section. Further
development could cause a magnetic delta structure to develop. C flares are
likely and an isolated M class flare is possible.
Flares: C1.2 at 16:02, C1.8 at 20:30 UTC. A C2.5 flare at 23:44 was
attributed to this region as well, however, EVE images suggest the source may
have been region S946.
Spotted regions not numbered by NOAA/SWPC:
[S946] rotated partly into view at the northeast limb on April 11. Location at midnight:
N08E85
Minor update added at 14:40 UTC: The IMF at ACE was moderately southwards for several hours after 05h UTC. This caused active to minor storm conditions. Otherwise new region S947 (located west of region 11190) emerged quickly early today. Region S948 was numbered as well (and should maybe have been numbered for yesterday's spot count, however, at the time it was difficult to be certain it was a region independent of AR 11190), while region S944 has reemerged. The latest high resolution STAR CHARMAP.
April 9-11: No obviously Earth directed CMEs were observed in LASCO and STEREO imagery.
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. An extension (CH444) of the southern polar coronal hole was Earth facing on April 7-8.
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 with a chance of active intervals on April 12 and quiet on April 13-14.
| 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 | |||||
| 11185 | 2011.04.03 2011.04.04 |
17 | 1 | 0060 | DRI |
 |
SWPC data is for region 11189 | |||
| S932 | 2011.04.04 | N13W29 | plage | |||||||
| S933 | 2011.04.04 | N26W45 |
 |
plage | ||||||
| 11186 | 2011.04.05 2011.04.06 |
12 | 21 | N23W07 | 0070 | DSO | CAI |
 |
 |
|
| 11188 | 2011.04.05 2011.04.08 |
S24W48 |
 |
location: S26W43 | ||||||
| S937 | 2011.04.05 | S18W48 | plage | |||||||
| 11189 | 2011.04.06 2011.04.08 |
14 | 0030 | CRI |
 |
 |
location: N16W22 |
|||
| 11187 | 2011.04.06 2011.04.07 |
5 | 6 | S19E11 | 0020 | BXO | BXO |
 |
 |
location: S21E13 area: 0000 |
| S940 | 2011.04.06 | S22W36 | plage | |||||||
| S942 | 2011.04.07 | N07W41 | plage | |||||||
| 11190 | 2011.04.08 2011.04.11 |
6 | 24 | N12E25 | 0040 | CRI | DRI |
 |
 |
formerly region S943 beta-gamma |
| S944 | 2011.04.09 | S32W05 | plage | |||||||
| S945 | 2011.04.09 | N08W20 | plage | |||||||
| S946 | 2011.04.11 | 1 | N08E85 | 0150 | HSX |
 |
||||
| Total spot count: | 40 | 67 | ||||||||
| Sunspot number: | 80 | 127 | ||||||||
| 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 | 109.6 (1) | 26.2 (2A) / 71.5 (2B) | (39.6 predicted, +2.9) | (11.60) |
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.
