Last major update issued on April 20, 2013 at 04:50 UTC.
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The geomagnetic field was very quiet on April 19. Solar wind speed at SOHO ranged between 270 and 285 km/s.
Solar flux measured at 20h UTC on 2.8 GHz was 99.4 (increasing 1.2 over the last solar rotation). The Potsdam WDC planetary A index was 1 (STAR Ap - based on the mean of three hour interval ap indices: 0.8). Three hour interval K indices: 00000001 (planetary), 00012210 (Boulder).
The background x-ray flux was at the class B5 level.
At midnight UTC the visible solar disk had 15 spotted active regions (in 2K resolution SDO images).
Region 11721 [S19W88] was quiet and stable.
Region 11722 [S21W72] decayed slowly and quietly.
Region 11723 [S18W32] decayed slowly and quietly.
Region 11724 [S27W04] decayed slowly and quietly.
New region 11725 [N09W57] emerged with spots on April 13 and was numbered
by SWPC 6 days later as the region developed slowly.
New region 11726 [N12E04] emerged very quickly. The proximity to AR S2362
is likely to increase flare frequency and intensity. C and minor M class flares
are possible.
New region 11727 [N25E58] emerged on April 18 and was numbered by SWPC
the next day. C flares are possible.
Spotted regions not numbered by SWPC:
S2357 [S24W28] was quiet and stable.
S2359 [S15E50] reemerged with a single penumbra spot.
S2360 [N16W32] developed slowly and quietly.
S2362 [N13E08] developed and could merge with AR 11726 if both regions
continue to develop.
New region S2364 [N20W10] emerged with a penumbra spot.
New region S2365 [S14W07] emerged wih a couple of spots.
New region S2366 [S13E16] emerged with a single spot.
New region S2367 [S06E18] emerged with a single spot.
April 17-19: No obviously Earth directed CMEs were observed in LASCO and STEREO imagery.
Coronal hole history (since October
2002)
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 (CH566) will likely rotate to an Earth facing position on April 21-23.
Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over high and upper middle latitudes is good. Propagation on long distance northeast-southwest paths is poor.
The geomagnetic field is expected to be quiet on April 20-22.
| 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
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 2K resolution) Compare to the previous day's image. 0.5k image
When available the active region map has a coronal hole polarity overlay where red (pink) is negative and blue 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 magnetic polarity overlay |
Comment | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| SWPC | STAR SDO | SWPC | STAR | Current | Previous | ||||||
| 2K | 1K | ||||||||||
| 11721 | 2013.04.09 2013.04.10 |
1 | 1 | S18W86 | 0060 | HSX | HSX |
 |
 |
||
| 11722 | 2013.04.09 2013.04.10 |
6 | 6 | 3 | S21W73 | 0040 | CAO | BXO |
 |
 |
|
| S2350 | 2013.04.11 | S24W32 | plage | ||||||||
| 11724 | 2013.04.12 2013.04.13 |
2 | 4 | 1 | S26W05 | 0020 | HRX | BXO |
 |
 |
|
| 11723 | 2013.04.12 2013.04.13 |
14 | 17 | 7 | S18W32 | 0100 | DAI | CSO |
 |
 |
|
| 11725 | 2013.04.13 2013.04.19 |
2 | 4 | 3 | N10W58 | 0020 | CRO | CRO |
 |
 |
|
| S2356 | 2013.04.15 | S13W26 | plage | ||||||||
| S2357 | 2013.04.16 | 3 | 2 | S24W28 | 0010 | BXO |
 |
 |
|||
| S2358 | 2013.04.17 | N10E03 | plage | ||||||||
| S2359 | 2013.04.17 | 1 | 1 | S15E50 | 0006 | AXX |
 |
||||
| S2360 | 2013.04.18 | 3 | 2 | N16W32 | 0020 | BXO |
 |
 |
|||
| 11727 | 2013.04.18 2013.04.19 |
2 | 12 | 5 | N26E57 | 0040 | DAO | DAO |
 |
 |
area: 0090 location: N25E58 |
| S2362 | 2013.04.18 | 14 | 8 | N13E08 | 0060 | DRO |
 |
 |
|||
| 11726 | 2013.04.19 | 4 | 21 | 9 | N13W07 | 0020 | DRO | DAI |
 |
beta-gamma area: 0150 |
|
| S2364 | 2013.04.19 | 1 | 1 | N20W10 | 0006 | AXX |
 |
||||
| S2365 | 2013.04.19 | 2 | 1 | S14W07 | 0010 | CRO |
 |
||||
| S2366 | 2013.04.19 | 1 | S13E16 | 0002 | AXX |
 |
|||||
| S2367 | 2013.04.19 | 1 | S06E18 | 0001 | AXX |
 |
|||||
| Total spot count: | 31 | 91 | 43 | ||||||||
| Sunspot number: | 101 | 241 | 163 | (total spot count + 10 * number of spotted regions) | |||||||
| Weighted SN: | 60 | 120 | 72 | (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): | 61 | 84 | 90 | k * (sunspot number). k = 0.6 for SWPC, k = 0.35 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 (3) |
|---|---|---|---|---|
| 2011.11 | 153.5 (cycle max) | 96.7 (cycle max) | 61.1 (+1.2) | 5.55 |
| 2012.01 | 132.5 | 58.3 | 65.5 (+2.1) | 7.15 |
| 2012.02 | 106.5 | 32.9 | 66.9 (+1.4) possible cycle 24 max |
8.81 |
| 2012.03 | 114.7 | 64.3 | 66.8 (-0.1) | 16.08 |
| 2012.04 | 113.0 | 55.2 | 64.6 (-2.2) | 10.10 |
| 2012.05 | 121.5 | 69.0 | 61.7 (-2.9) | 7.06 |
| 2012.06 | 119.6 | 64.5 | 58.9 (-2.8) | 10.08 |
| 2012.07 | 133.9 | 66.5 | 57.7 (-1.2) | 13.90 |
| 2012.08 | 115.4 | 63.0 | 58.1 (+0.4) | 7.96 |
| 2012.09 | 122.9 | 61.4 | 58.1 (-0.0) | 8.07 |
| 2012.10 | 123.3 | 53.3 | (57.6 projected, -0.5) | 9.97 |
| 2012.11 | 121.3 | 61.8 | (56.9 projected, -0.7) | 7.08 |
| 2012.12 | 108.6 | 40.8 | (55.7 projected, -1.2) | 3.44 |
| 2013.01 | 127.1 | 62.9 | (54.3 projected, -1.4) | 4.69 |
| 2013.02 | 104.3 | 38.0 | (53.3 projected, -1.0) | 6.11 |
| 2013.03 | 111.3 | 57.9 | (52.2 projected, -1.1) | 10.56 |
| 2013.04 | 125.7 (1) | 74.8 (2A) / 118.1 (2B) / 58.4 (2C) | (51.0 projected, -1.2) | (4.16) |
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)
Boulder SN current month
average to date. 2C) STAR SDO 1K Wolf number 30 day average.
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.
