SB PROP @ ARL $ARLP012
ARLP012 The ARRL Solar Report

ZCZC AP12
QST de W1AW
Propagation Forecast Bulletin 12 ARLP012

From ARRL Headquarters

Newington CT April 4, 2025
To all radio amateurs

SB PROP ARL ARLP012
ARLP012 The ARRL Solar Report

Solar activity is likely to be moderate (R1-R2, Minor-Moderate) with a slight chance for X-class flares through April 5.


The geomagnetic field is expected to be quiet to minor storm levels on April
4 and 5.


NOAA Geomagnetic Activity Probabilities for April 5 and 6 forecast a 15% chance, and then a 1% chance, of a Moderate storm for the reporting period.


The forecast of solar and geomagnetic activity calls for a chance for R1-R2 (Minor-Moderate) effects throughout the outlook period due to multiple
complex regions on the visible disk as well as on the Sun's far side that are likely to return.


A slight chance exists for R3 (Strong) events over the next three days primarily due to the flare potential from complex regions in the Sun's
eastern hemisphere.


Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere - April 3, 2025, by F. K. Janda, OK1HH:


"A harbinger of a somewhat more dramatic development in the Sun-Earth system was the helioseismological observation of a larger active region on the far side of the Sun. This region appeared on the northeastern limb of the solar disk as AR4046. It was followed by the larger, more magnetically complex, growing and eruptively active AR4048. Concurrent with the increase in solar activity, the geomagnetic field remained quiet from March 29 to April 1, a favorable combination for ionospheric evolution.


"The intensified solar wind from the coronal hole margins in the western half of the solar disk was the cause of the geomagnetic disturbances, which caused
a significant decrease in the critical frequencies of the ionospheric F2
layer from 2 April onwards, together with an increase in the attenuation of radio waves, to which the increased concentration of particles in the solar wind - both electrons and especially protons - contributed.


"At the time of writing, the prediction of the onset of the recurrent disturbance on the night of 4/5 April is valid. The cause is the passage of
the Earth through a region of enhanced solar wind in the corotating
interaction region (CIR) structure.


"In the next two weeks, the author of these lines will be in hospital. He
will send his next post after his return."


A greater electron flux at geosynchronous orbit is expected to be at high levels on April 6 to 14 in response to multiple, recurrent, Coronal Hole High-Speed Streams. The remainder of the outlook period is expected to be at normal to moderate levels.


Geomagnetic field activity is expected to range from quiet to G2 (Moderate) geomagnetic storm conditions. G2 conditions are likely on April 5 and 09, G1 (Minor) conditions are likely over April 8 and 10, active conditions are
likely over April 11 and 13, unsettled conditions are likely on April 6 and
7, 12, and April 14 and 15.


All increases in geomagnetic activity are anticipated in response to
multiple, recurrent Coronal Hole High-Speed Streams. The remainder of the outlook period is likely to mostly quiet.


For more information concerning shortwave radio propagation, see www.arrl.org/propagation [ http://www.arrl.org/propagation?utm_source=Informz&utm_medium=Email&utm_campaign=ARRL
] and the ARRL Technical Information Service web page at: www.arrl.org/propagation-of-rf-signals [ http://arrl.org/propagation-of-rf-signals ] . For an explanation of numbers used in this bulletin, see www.arrl.org/the-sun-the-earth-the-ionosphere [ http://arrl.org/the-sun-the-earth-the-ionosphere ] . Information and
tutorials on propagation can be found at: http://k9la.us [ http://k9la.us/ ]
..


Also, check this: "Understanding Solar Indices" from September 2002 QST. https://bit.ly/3Rc8Njt [ https://bit.ly/3Rc8Njt ]

The predicted Planetary A Index for April 5 to 10 is 35, 10, 12, 30, 35, and 25, with a mean of 24.5. The predicted Planetary K Index is 6, 3, 3, 5, 6,
and 5, with a mean of 4.7. The predicted 10.7 centimeter flux is 180, 180,
185, 185, 180, and 175, with a mean of 180.8.

NNNN
/EX

ARRL The National Association for Amateur Radio(R)
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SB PROP @ ARL $ARLP012
ARLP012 The ARRL Solar Report

ZCZC AP12
QST de W1AW
Propagation Forecast Bulletin 12 ARLP012

From ARRL Headquarters

Newington, CT, March 20, 2026
To all radio amateurs

SB PROP ARL ARLP012
ARLP012 The ARRL Solar Report

Solar activity was at moderate levels following an M2.7 flare from Region
4392 on March 18. This region has shown sporadic growth and reorganization in the peripheral spots, but has remained relatively unchanged in its magnetic configuration. New Region 4397 rotated further onto the visible disk and was numbered, yet remained mostly inactive. The remaining regions were relatively stable and quiescent.


The M2.7 flare was accompanied by a ten-flare and Type II radio burst with an estimated velocity of 740-860 km/s. An EUV wave is visible in GOES SUVI,
along with faint field line movement in the NW quadrant.


The associated coronal mass ejection (CME) became visible in SOHO LASCO C2 imagery early on March 18. Analysis indicated a possible arrival at Earth
early on March 21. Confidence is fairly low with the fit of this event, due
to limited C2/C coronagraph imagery.


Solar activity is expected to be low on March 21, with a chance for M-class (R1-R2; minor-moderate) level events, due primarily to the minor instability and variability of Region 4392.


Solar wind parameters reflected near background conditions. Solar wind speed gradually decreased from 450 km/s to end the period at around 380 km/s. The
phi angle was predominantly positive. The disturbed solar environment is
likely to continue as CME passage persists into March 20. By March 21, the
CME from March 18 is expected to arrive in conjunction with the onset of a negative polarity coronal hole high-speed stream (CH HSS).


Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere, March 19, 2026, by F. K. Janda, OK1HH:


"Solar activity has been declining over the past two weeks and, despite forecasts that generally predicted an increase, it remains low.

Furthermore, there is no reason to expect a significant rise.
While increases in geomagnetic activity usually recur every 27 days (which happened, for example, on March 14), on March 19, for instance, a recurrence
of the disturbance from February 22-23 was expected in vain.

This was despite the presence of extensive coronal holes No.
31 and 33 in the center of the solar disk.

"However, it appears that the geomagnetic disturbance will arrive later. The same applies to the increase in solar activity, which will also arrive later, but still within the third decade of March. Although it will be smaller than
it was during the previous solar rotation. Given the proximity of the
equinox, however, both surges will still significantly affect shortwave ionospheric propagation."


Unsettled to G1 (Minor) levels are expected on March 22 as the Coronal Mass Ejection and Coronal Hole High Speed Stream effects persist.


The Predicted Planetary A Index for March 21 to 27 is 35, 25, 15, 15, 18, 10, and 8, with a mean of 16.9. Predicted Planetary K Index is 5, 5, 4, 4, 5, 3, and 3, with a mean of 4.1. 10.7 centimeter flux is 100, 102, 105, 110, 100, 110, and 120, with a mean of 106.7.


For more information concerning shortwave radio propagation, see www.arrl.org/propagation [ http://www.arrl.org/propagation?utm_source=Informz&utm_medium=Email&utm_campaign=ARRL
] and the ARRL Technical Information Service web page at www.arrl.org/propagation-of-rf-signals [ http://arrl.org/propagation-of-rf-signals ] . For an explanation of numbers used in this bulletin, see www.arrl.org/the-sun-the-earth-the-ionosphere [ http://arrl.org/the-sun-the-earth-the-ionosphere ] . Information and
tutorials on propagation can be found at http://k9la.us [ http://k9la.us/ ] .


Also, check this: "Understanding Solar Indices" from September 2002 QST. https://bit.ly/3Rc8Njt [ https://bit.ly/3Rc8Njt ]

NNNN
/EX

ARRL The National Association for Amateur Radio(R)


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