|
SB PROP @ ARL
$ARLP037
ARLP037 The
ARRL Solar
Report
ZCZC AP37
QST de W1AW
Propagation
Forecast
Bulletin 37
ARLP037
From ARRL
Headquarters
Newington CT,
October 3,
2025
To all radio
amateurs
SB PROP ARL
ARLP037
ARLP037 The
ARRL Solar
Report
Solar
activity,
which has been
at low levels,
has returned
to moderate
levels. Region
AR4232
produced the
largest event
of the period,
an impulsive
M3.6 flare
(R1-minor) on
October 1,
2025.
An associated
Coronal Mass
Ejection (CME)
was observed
in subsequent
SOHO LASCO/C2
coronagraph
imagery that
began on
September 29.
Analysis and
modelling of
the ejecta is
ongoing.
Newly numbered
Region AR4237
remained
relatively
quiet as it
developed.
Region AR4263
also produced
an R1 event
with an
M1.0/Sf flare
near the end
of the
reporting
period.
It is
important to
note that,
after careful
assessment of
recent
magnetograph
imagery, a
spot
previously
associated to
region AR4239
is now
considered
part of the
AR4230,
explaining its
reported size
increase. A
new region
appeared but
remained
unnumbered
until further
observation.
With multiple
regions
continuing to
exhibit
growth, flare
activity is
likely to
remain at
moderate
levels
(R1-R2/minor-moderate)
with a slight
chance for an
X-class flare
(R3-strong)
through
October 30.
Weak
enhancements
in the solar
wind
environment,
that began
September 29,
are likely to
continue as
influence from
a negative
polarity
Coronal Hole
High Speed
Stream (CH
HSS) persists.
The CH HSS
influences on
the solar wind
conditions
near Earth are
expected to
persist
through
October 5, as
the planet
continues to
be embedded at
the CH
associated
co-rotating
interactive
region (CIR).
A recurrent
negative CH
was observed
rotating into
the East limb
of the visible
solar disk
during the
period, but no
impact is
expected from
it in the
upcoming days.
Weekly
Commentary on
the Sun, the
Magnetosphere,
and the
Earth's
Ionosphere,
October 2,
2025, by F. K.
Janda, OK1HH:
"During
September, a
relatively
large number
of sunspot
groups were
observed on
the solar
disk, but
there were
almost no
energetically
significant
eruptions. It
seemed to be
the calm
before the
storm. The
question was
what would
cause the
storm and how
the
disturbance
would develop.
Important
factors were:
the proximity
of the Autumn
Equinox and
the
configuration
of areas on
the solar
disk.
"The following
phenomena were
key to further
developments:
- The
Russell-McPherron
effect, in
which the
magnetic field
lines of the
Sun and Earth
can connect
around the
equinox.
- The source
of the
intensified
solar wind
heading
towards Earth.
"The second
condition was
also met - we
observed
coronal holes
No. 83 and 84
on the solar
disk near
active regions
No. 4230 and
4238, with the
space between
them being
close enough
to the central
meridian.
"The
disturbance
began with a
so-called
positive phase
on the
afternoon of
September 29
UTC, while the
critical
frequencies in
the F2
ionospheric
layer
initially rose
for several
hours. In the
following
days, the
solar wind
speed
gradually
increased to
an impressive
800 km/s. The
intensity of
the
geomagnetic
disturbance
reached grade
G3 (three-hour
K indices rose
to 6 to 7).
"The return of
the ionosphere
to normal
conditions
will be slow,
as solar
activity is
expected to
gradually
decline in the
first half of
October. In
addition,
after a slight
lull, another
disturbance
can be
expected
around October
7, and even
after that,
the situation
will not be
very calm."
The latest
report from
Dr. Tamitha
Skov, WX6SWW,
can be found
on YouTube at
https://www.youtube.com/watch?v=a7mWOPWe0NA.
The NOAA Space
Weather
Prediction
Center has a
webpage that
discusses the
current solar
cycle
progression: www.swpc.noaa.gov/products/solar-cycle-progression
The Predicted
Planetary A
Index for
October 4 to
10 is 8, 8, 8,
5, 5, 5, and
5, with a mean
of 6.3. The
Predicted
Planetary K
Index is 3, 3,
3, 2, 2, 2,
and 2, with a
mean of 2.4.
10.7
centimeter
flux is 170,
165, 165, 165,
155, 155, and
155, with a
mean of 161.4.
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
|
