From: "ARRL" <memberlist@arrl.org>

SB PROP @ ARL $ARLP013
ARLP013 The ARRL Solar Report

ZCZC AP13
QST de W1AW
Propagation Forecast Bulletin 13 ARLP013

From ARRL Headquarters

Newington CT April 11, 2025
To all radio amateurs

SB PROP ARL ARLP013
ARLP013 The ARRL Solar Report

Due to most of the regions on the solar disk being fairly simple in their magnetic complexity, solar activity is expected to remain at low levels with
a chance for M-class flares (R1 to R2, or Minor to Moderate).


Solar wind parameters are expected to trend further towards nominal levels as the Coronal Hole High-Speed Stream effects continue to wane.


Additional enhancements from another negative polarity Coronal Hole is likely on April 12, combined with potential effects from the glancing blow of a Coronal Mass Ejection that left the Sun on April 8. Elevated conditions are likely to continue through April 13 as the influences persist of the Coronal Hole.


Solar activity has been at moderate levels for the past 24 hours. There are currently 8 numbered sunspot regions on the disk. Solar activity is expected
to be low with a chance for M-class flares on April 12.


The long range forecast of Solar and Geomagnetic Activity for April 12 to May 3.


The declining trend in solar flux and activity is expected to bottom out
around April 15, after which a slowly increasing period is expected. The anticipated return on April 22 of the active longitudes that gave rise to Region AR4046 (responsible for X-flare activity) should bring solar activity
to moderate and occasionally high levels through the end of the forecast period.


No proton events are expected at geosynchronous orbit until the expected increase in flare activity beginning on April 22. Then there will be an increasing chance for an isolated proton event as the more potent regions approach the west limb by the end of the forecast period.


Flux will subside to moderate levels after April 12 as the effects from the fast stream wane. April 19 is expected to bring a return to high levels,
again in response to another recurrent fast stream. The elevated conditions
are expected to remain through April 28 before returning to moderate levels.


Geomagnetic field activity is expected to be primarily quiet to unsettled,
with an isolated active period, until the return of a recurrent geoeffective coronal hole between April 19 to 21. Active conditions are expected to
prevail through April 24 before the fast solar wind stream wanes.


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 out this article: "Understanding Solar Indices" from September
2002 QST.

https://bit.ly/3Rc8Njt [ https://bit.ly/3Rc8Njt ]

The predicted Planetary A Index for April 12 to 18 is 12, 12, 12, 8, 5, 5,
and 5, with a mean of 8.4. The predicted Planetary K Index is 3, 3, 3, 3, 2,
2, and 2, with a mean of 2.6. Predicted 10.7 centimeter flux is 140, 140,
140, 135, 140, 140, and 145, with a mean of 140.

NNNN
/EX

ARRL The National Association for Amateur Radio(R)
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