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SB PROP @ ARL
$ARLP040
ARLP040 The
ARRL Solar
Report
ZCZC AP40
QST de W1AW
Propagation
Forecast
Bulletin 40
ARLP040
From ARRL
Headquarters
Newington CT
October 24,
2025
To all radio
amateurs
SB PROP ARL
ARLP040
ARLP040 The
ARRL Solar
Report
Solar activity
reached
moderate
levels this
past week, but
has now
returned to,
and remains
at, lower
levels.
Region 4248
produced an
M1.1 flare on
October 20,
which was the
largest event
of the period.
Region 4261
was numbered
this period as
it rotated
into better
viewing
conditions.
Region 4262
was numbered
this period as
well,
splitting it
from Region
4257.
Additionally,
new spots were
noted near
N08W00 and
N09E67 but
went
unnumbered due
to a lack of
flaring and
time of
emergence.
No
Earth-directed
CMEs were
observed in
available
coronagraph
imagery.
Solar activity
is expected to
remain low,
with a chance
for isolated
M-class flares
(R1-R2/minor-moderate).
Additional
notable
activity
included a
type II radio
sweep with an
estimated
speed of 2,474
km/s and a
type IV radio
sweep that
began on
October 21.
Significant
field line
movement,
appearing to
originate from
beyond the
northwestern
limb, was
observed in
GOES SUVI
imagery
beginning on
October 21.
The subsequent
coronal mass
ejection (CME)
was then first
seen on LASCO
C2 coronagraph
imagery on
October 21.
This event has
been analyzed
as a far-sided
asymmetric
halo.
Solar wind
parameters
were mildly
enhanced this
period due to
negative
polarity
coronal hole
high speed
stream (CH
HSS)
influences.
Solar wind
speeds
exhibited a
decreasing
trend from
approximately
600 km/s to
under 500 km/s
by the
period's end.
Phi was
predominantly
positive while
undertaking
brief
excursions
into the
positive solar
sector.
Mildly
enhanced solar
wind
conditions and
waning
negative
polarity CH
HSS influences
were expected
to continue.
Solar activity
is expected to
be at moderate
levels from
October 31 to
November 15
due to the
return of
Region 4246.
Low levels are
expected to
prevail to
October 30,
and then on
November 14
and 15.
Geomagnetic
field activity
is expected to
reach G1-G2
(Minor-Moderate)
storm levels
on October 28
to 30.
Weekly
Commentary on
the Sun, the
Magnetosphere,
and the
Earth's
Ionosphere,
October 23,
2025, by F. K.
Janda, OK1HH:
"Although it
may not seem
so at first
glance, solar
activity is
still at the
peak of its
25th cycle.
Although the
number of
sunspot groups
fell to six in
mid-October, a
week later it
had risen to
ten.
Few eruptions
were observed
on the solar
disk, or the
side of the
Sun facing
Earth,
including only
a few that
could be
classified as
moderately
strong based
on the
intensity of
X-ray
emissions.
"However,
something is
brewing on the
far side of
the Sun.
This is
evidenced by
the occurrence
of three CMEs,
the first on
October 21 and
the other two
on October 22.
The increased
concentration
of protons
with an energy
of 10 MeV (and
a lower
concentration
of 100 MeV) in
the solar wind
confirms that
this is
significant
activity.
To analyze the
development of
the relevant
activity, we
will have to
wait until it
appears on the
eastern limb
of the solar
disk.
"The
geomagnetic
field has
calmed down in
recent days.
The next
disturbance is
expected
around October
28. At first
glance, this
is very good
news for
shortwave
propagation
conditions
during the
weekend of
October 25-26,
but if
geomagnetic
activity
increases
during these
days, it will
come as no
surprise.
"In fact, with
the right
timing of the
disturbance,
it could be
followed by an
increase in
MUF and an
overall
improvement.
Although a
significant
deterioration
in propagation
conditions is
expected with
a relatively
high
probability
only after the
aforementioned
disturbance
(i.e., around
October 29),
it may occur
earlier."
The Predicted
Planetary A
Index for
October 25 to
31 is 10, 5,
5, 25, 35, 25,
and 15, with a
mean of 17.1.
Predicted
Planetary K
Index is 3, 2,
2, 5, 6, 5,
and 4, with a
mean of 3.9.
10.7-centimeter
flux is 150,
150, 150, 145,
145, 145, and
140, with a
mean of 146.4.
For more
information
concerning
shortwave
radio
propagation,
see www.arrl.org/propagation
and the ARRL
Technical
Information
Service web
page at www.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.
Information
and tutorials
on propagation
can be found
at http://k9la.us.
NNNN
/EX
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