The geomagnetic field was quiet on April 18. Solar wind speed at SOHO ranged between 346 and 437 km/s.
Solar flux at 20h UTC on 2.8 GHz was 94.6 (increasing 7.3 over the last solar rotation). The 90 day 10.7 flux at 1 AU was 97.1. The Potsdam WDC planetary A index was 4 (STAR Ap - based on the mean of three hour interval ap indices: 4.1). Three hour interval K indices: 21110011 (planetary), 32221211 (Boulder).
The background x-ray flux is at the class B2 level.
At the time of counting spots (see image time), spots were observed in 4 active regions using 2K resolution (SN: 65) and 3 active regions using 1K resolution (SN: 42) SDO images on the visible solar disk.
Region 12529 [N10W69] lost most trailing and
intermediate spots while the leading umbra fragmented after the major flare
early in the day.
Region 12531 [N17W09] reemerged with a tiny spot.
Region 12532 [N06E40] developed as new flux emerged
in the southern leading polarity section.
Spotted regions not numbered (or interpreted differently) by SWPC:
S5236 [N02W63] reemerged with tiny spots.
C2+ flares:
| Magnitude | Peak time (UT) | Location | AR | Recorded by | Comment |
| M6.7/1F | 00:29 | N12W62 | 12529 | GOES15 | CME |
April 16-18: No obviously Earth directed CMEs were observed in available LASCO imagery. The CME observed early in the day after the M6 event in AR 12529 appears not to have any Earth directed components.
[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 recurrent northern hemisphere coronal hole (CH728) rotated across the central meridian on April 15-16. A recurrent trans equatorial extension of a northern hemisphere coronal hole will likely rotate into an Earth facing position on April 20-21.
Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over upper middle latitudes is poor. Propagation on long distance northeast-southwest paths is poor.
The geomagnetic field is expected to be quiet to active on April 19 as CH728 becomes geoeffective and quiet to unsettled on April 20-21.
| 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: 0-30% probability, Yellow: 30-70% probability, Red: 70-100% probability.
(Click on image for 2K resolution).
4K 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 overlays |
Comment | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| SWPC | Magnetic (SDO) |
SWPC | STAR | Current | Previous | ||||||
| 2K | 1K | ||||||||||
| 12529 | 2016.04.07 | 5 | 10 | 6 | N10W67 | 0610 | CKO | CKO |
 |
 |
location: N10W69 area: 0730 |
| 12531 |
2016.04.12 2016.04.13 |
1 | N13W08 | 0002 | AXX |
 |
|||||
| S5234 | 2016.04.13 | S03W20 | |||||||||
| S5236 | 2016.04.13 | 2 | 1 | N02W63 | 0004 | BXO |
 |
||||
| S5237 | 2016.04.14 | N10E16 | |||||||||
| 12532 |
2016.04.15 2016.04.16 |
3 | 12 | 5 | N06E40 | 0030 | HAX | CAO |
 |
 |
area: 0060 |
| S5241 | 2016.04.15 | S13W59 | |||||||||
| S5242 | 2016.04.16 | S19E01 | |||||||||
| S5243 | 2016.04.17 | N36W00 |
 |
||||||||
| Total spot count: | 8 | 25 | 12 | ||||||||
| Sunspot number: | 28 | 65 | 42 | (total spot count + 10 * number of spotted regions) | |||||||
| Weighted SN: | 23 | 40 | 27 | (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): | 31 | 29 | 34 | k * (sunspot number) As of February 19, 2016: k = 1.1 for SWPC, k = 0.45 for MSN 2K, k = 0.80 for MSN 1K (MSN=Magnetic Sunspot Number) |
|||||||
| Month | Average solar flux | International sunspot number (WDC-SILSO) (4) |
Smoothed sunspot number (4) | Average
ap (3) |
|
|---|---|---|---|---|---|
| Measured | 1 AU | ||||
| 2014.02 | 170.3 (cycle peak) |
166.3 | 146.1 (cycle peak) | 110.5 (+1.2) | 10.70 |
| 2014.04 | 143.9 | 144.8 | 112.5 | 116.4 (+2.1) (solar max) | 7.88 |
| 2015.02 | 129.1 | 126.0 | 66.7 | 86.1 (-3.2) | 9.92 |
| 2015.03 | 125.9 | 124.6 | 54.5 | 82.2 (-3.9) | 16.14 |
| 2015.04 | 128.8 | 129.7 | 75.3 | 78.9 (-3.3) | 10.73 |
| 2015.05 | 120.0 | 122.6 | 88.8 | 76.1 (-2.8) | 8.29 |
| 2015.06 | 122.3 | 126.1 | 66.5 | 72.1 (-4.0) | 13.15 |
| 2015.07 | 107.0 | 110.8 | 66.4 | 68.3 (-3.8) | 8.83 |
| 2015.08 | 105.4 | 108.0 | 64.6 | 66.4 (-1.9) | 14.58 |
| 2015.09 | 101.7 | 102.7 | 78.1 | 66.0 (-0.4) | 15.78 |
| 2015.10 | 104.1 | 103.3 | 61.7 | (64.6 projected, -1.4) | 14.02 |
| 2015.11 | 109.3 | 106.9 | 63.2 | (61.9 projected, -2.7) | 12.09 |
| 2015.12 | 113.1 | 109.5 | 57.7 | (59.9 projected, -2.0) | 14.29 |
| 2016.01 | 103.4 | 100.1 | 56.6 | (58.2 projected, -1.7) | 9.4 |
| 2016.02 | 103.6 | 101.0 | 57.2 | (55.9 projected, -2.3) | 9.9 |
| 2016.03 | 91.5 | 90.6 | 54.9 | (52.9 projected, -3.0) | 10.58 |
| 2016.04 | (98.5) | 19.2 (2A) / 31.9 (2B) / 33.3 (2C) | (50.2 projected, -2.7) | (9.7) | |
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).
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
GFZ Potsdam
WDC
ap indices.
4) Updated to new data set from WDC-SILSO on July 1, 2015
This report has been prepared by Jan Alvestad. It is based on the analysis of data from whatever sources are available at the time the report is prepared. All time references are to Universal Time. Comments and suggestions are always welcome.
SDO images are courtesy of NASA/SDO and the AIA, EVE, and HMI science teams.
