|Charts (* = updated daily)||Data and archive|
|Solar wind (*)||Solar and geomagnetic data - last month (*)|
|Electron fluence (*)||Archived daily reports and monthly data since 2003.01 (April 1, 2021)|
|Solar cycle||Solar cycles 23-25 (April 1, 2021)||Historical solar and geomagnetic data charts 1954-2006 (April 5, 2007)|
|Cycle 24-25 progress (April 1, 2021)||Noon SDO sunspot count 1K image / 4K (*)|
|Solar cycles 1-24 (June 1, 2020)||POES auroral activity level October 2009 - December 2012]|
|Comparison of cycles 21-25 (April 1, 2021)||3rd SSN Workshop, Tucson, 2013|
|Comparison of cycles 12-14, 16, 24-25 (April 1, 2021)||4th SSN Workshop, Locarno, 2014|
|Solar polar fields vs. solar cycles (January 7, 2021)||Cycle 25 spots (final update December 25, 2019)|
|Solar cycles 24-25 using 365d smoothing||Research: Solar Cycle 25 Started on November 17, 2019 with 365 Days Smoothing|
The geomagnetic field was quiet on April 21. The high latitude magnetometer at Andenes recorded quiet to active conditions.
Solar flux density measured at 20h UT on 2.8 GHz was 78.0 - decreasing 0.8 over the previous solar rotation. (Centered 1 year average SF at 1 AU - 183 days ago: 75.03). The Potsdam WDC planetary A index was 6 (STAR Ap - based on the mean of three hour interval ap indices: 6.0). Three hour interval K indices: 22222111 (planetary), 23332111 (Boulder), 42322113 (Andenes).
The background x-ray flux is at the class B3 level (GOES 16).
At the time of counting spots (see image time), spots were observed in 4 active regions using 2K resolution (SN: 91) and in 4 active regions using 1K resolution (SN: 67) SDO/HMI images.
Region 12816 [S25W03]
developed polarity intermixing during the latter half of the day as patches
of positive polarity emerged within the leading polarity area. A long
duration C3.9 event was recorded peaking at 04:35 UT on April 22.
Significant coronal dimming was observed in all directions in SDO/AIA
imagery after this event, and it is very likely that a full halo CME was
produced. LASCO imagery covering the hours after the LDE are not available
at the time this is written.
Region 12817 [N19W74] decayed slightly losing area as it rotated to the northwest limb. A C1.5 flare was recorded at 01:29 UT.
Region 12818 [S17E52] was quiet and stable.
Spotted regions not observed (or interpreted
differently) by SWPC:
New region S6829 [S18W57] emerged with tiny spots in a reversed polarities configuration.
|Magnitude||Peak time (UT)||Location||AR||Recorded by||Comment|
April 19-21: No obviously Earth directed CMEs were observed in available LASCO imagery.
While a small CME was associated with the M1.1 flare on April 19, no Earth
directed components were observed.
April 22: SDO/AIA imagery indicate that a full halo CME was produced by the LDE in AR 12816 peaking at 04:35 UT. A confirmation of this awaits the availability of LASCO 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 recurrent southern hemisphere coronal hole (CH1008) rotated across the central meridian on April 19-20.
Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over upper middle and high latitudes is poor. Propagation on long distance northeast-southwest paths is poor to fair.
The geomagnetic field is expected to be quiet to active on April 22-23 due to effects from CH1008 and quiet on April 24. A CME could arrive on April 25 and cause unsettled to minor storm conditions.
|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 officially numbered solar regions according to the Solar Region Summary provided by NOAA/SWPC, all other regions are numbered sequentially as they emerge using the STAR spot number. 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. SWPC data considered to be not sufficiently precise (location, area, classification) are red colored.
|Active region||SWPC date numbered
|Spot count||Location at midnight||Area||Classification||SDO / HMI 4K continuum
image with magnetic polarity overlays
|Total spot count:||17||51||27|
|Sunspot number:||47||91||67||(total spot count + 10 * number of spotted regions)|
|Weighted SN:||32||66||42||(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):||52||50||54||k * (sunspot number)
As of May 7, 2016: k = 1.1 for SWPC, k = 0.55 for MSN 2K, k = 0.80 for MSN 1K (MSN=Magnetic Sunspot Number)
|Month||Average solar flux||International sunspot number
|Smoothed sunspot number (4)||Average ap
|166.3||146.1 (cycle peak)||110.5||10.70|
|2014.04||143.9||144.8||112.5||116.4 (solar max)||7.88|
|2017.09||91.3||92.3||43.6||18.2 (-1.3)||18.22 (cycle peak)|
(Solar minimum using 365d smoothing:
November 17, 2019)
(ISN 13 months smoothed
|2020.10||74.6||74.2||14.6||(11.6 projected, +1.1)||6.13|
|2020.11||89.9||88.0||34.5||(13.2 projected, +1.6)||4.77|
|2020.12||86.9||84.2||23.1||(16.3 projected, +3.1)||4.72|
|2021.01||76.0||73.6||10.4||(20.0 projected, +3.7)||4.39|
|2021.02||74.3||72.4||8.3||(23.3 projected, +3.3)||9.50|
|2021.03||76.0||75.2||17.3||(27.5 projected, +4.2)||10.17|
|2021.04||75.0 (1)||10.9 (2A) / 15.6 (2B) / 25.9 (2C)||(32.6 projected, +5.1)||(8.7)|
|2021.05||(35.6 projected, +3.0)|
|2021.06||(38.8 projected, +3.2)|
|2021.07||(43.4 projected, +4.6)|
|2021.08||(48.0 projected, +4.6)|
|2021.09||(53.7 projected, +5.7)|
1) Running average based on the daily 20:00 UTC observed solar flux value at 2800 MHz
and any corrections applied to that measurement.
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) Source: SIDC-SILSO.
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.