The Phenomenon of Solar Flares and Shortwave Propagation
Solar flares, intense bursts of radiation from the Sun can significantly impact shortwave radio broadcasts on Earth. These flares occur when magnetic energy built up in the solar atmosphere is suddenly released. The energy from a solar flare can disrupt the Earth’s ionosphere, a layer of the atmosphere crucial for shortwave propagation. When solar flares happen, they can cause sudden ionospheric disturbances (SID), leading to degraded or completely blocked shortwave radio signals, a phenomenon often referred to as “solar flare and radio disturbances.”
The relationship between solar flares and radio disturbances is complex. Shortwave radio waves travel long distances by reflecting off the ionosphere. During a solar flare, the ionosphere’s density and composition change rapidly, causing shortwave signals to be absorbed rather than reflected. This can lead to shortwave radio blackouts, significantly weakening or losing transmission. Such occurrences are often termed “solar flares and radio blackouts.”
Solar activity, particularly solar flares, can significantly impact shortwave radio propagation, likely contributing to the issues you’re experiencing with broadcast reception. The National Oceanic and Atmospheric Administration’s (NOAA) Space Weather Prediction Center provides detailed and current information on space weather conditions that affect radio communications. The NOAA website provides various resources, including forecasts, reports, and models that track and predict solar activity and its impact on different aspects of space weather, including HF radio communications.
Solar flares emit X-rays that can penetrate the Earth’s ionosphere, particularly the D-layer, causing it to become more ionized. This increased ionization can reflect or absorb radio waves at different frequencies, leading to HF (High Frequency) radio communications disruptions. This is particularly problematic for frequencies in the 1 to 30 MHz range, commonly used for shortwave broadcasting. The impact of these solar flares is most intense on the Earth’s dayside, where the sun is directly overhead, and can cause radio blackouts.
Moreover, other space weather phenomena like Radiation Storms caused by solar protons can also disrupt HF radio communication. These protons, guided by Earth’s magnetic field, collide with the upper atmosphere near the poles, enhancing the D-Layer and blocking HF radio communication at high latitudes.
The sunspot cycle, approximately 11 years, significantly influences shortwave radio propagation. Sunspots, dark spots on the Sun’s surface, are indicators of solar magnetic activity, which can lead to solar flares. During periods of high sunspot numbers (SSN), the Sun is more active, increasing the likelihood of solar flares. High SSN usually means better shortwave propagation conditions due to a more reflective ionosphere, except during solar flares. Understanding the “sunspot cycle” is essential for predicting shortwave radio propagation conditions.
SSN, or Sun Spot Number, is a simple count of the number of sunspots and groups of sunspots visible on the Sun’s surface. A higher SSN indicates a more active Sun, which can enhance or disrupt shortwave propagation. Increased solar radiation can boost the ionosphere’s reflectivity during a high SSN period, improving shortwave signal reach. However, the increased solar activity also raises the risk of solar flares, which can cause shortwave radio blackouts. Therefore, the relationship between SSN and shortwave propagation is a delicate balance.
Source: https://www.nexus.org/solar-flares-impact-on-shortwave-radio-broadcasts/
On Wednesday, March 26, around 2130 UTC a Major Storm occurred. At
one point, the Planetary A Index was 49, and the Planetary K Index
was at 6.
Solar wind parameters are expected to remain enhanced due to
continued coronal hole high-speed stream influences with waning
effects likely by March 29.
The Solar Radiation Storm Forecast for March 29 and 30 has a 1
percent chance of a S1 or greater storm.
No S1 (Minor) or greater solar radiation storms are expected. No
significant active region activity favorable for radiation storm
production is forecast.
The Radio Blackout forecast calls for a chance for isolated R1-R2
(Minor-Moderate) radio blackouts due to M-class flare activity will
persist through March 30 primarily due to the potential exhibited by
AR4043.
From Space Weather Prediction Center: "Since February 25, 2025, the
Space Weather Prediction Center (SWPC) has presented new coronagraph images and data from the GOES-19 Compact Coronagraph-1 (CCOR-1). The images and data are updated every 15 minutes.
"Imagery from the Compact Coronagraph (CCOR) instruments is used by
the SWPC Forecast Office to characterize activity in the outermost
part of the Sun's atmosphere known as the corona. This includes
monitoring data for transient events like coronal mass ejections
(CMEs), as well as monitoring the impacts the corona has on the
steady stream of plasma, referred to as the solar wind, emanating
from the Sun. Ultimately, information derived from CCOR images will
be used as inputs to the WSA-Enlil model to forecast the impacts of
CMEs and the solar wind on Earth.
"Note: Until such time as GOES-19 becomes operational, currently
planned for April 4th, the animations and data are to be considered
'preliminary and non-operational.' In particular, CCOR-1 data will
not update between 3/21 and 4/1 due to the spacecraft drifting to
its operational location."
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere - March 27, 2025, by F. K. Janda, OK1HH:
"Most forecasts, including those from NOAA, have been consistent
over the past week that a strong G3-class geomagnetic storm would
develop on Sunday, March 23. In fact, a CME was expected to directly
impact the Earth. Although the source of the CME was only the
M1-class solar flare from AR4028, even weaker CMEs can produce
strong geomagnetic disturbances, especially on days around the
equinoxes. In the end, however, paradoxically, 23 March was the
relatively quietest day.
"However, a large coronal hole caught our attention this week, while
we expected that once it reached the central meridian region, the
solar wind stream would head directly towards Earth. This is what
happened and in the following days, especially on March 26, a G2
class geomagnetic storm developed. The solar wind speed increased
from 400 km/s to 700 km/s. On March 27, the increase continued to
over 800 km/s (1.8 million mph).
"Shortwave propagation conditions were particularly degraded along
paths through the higher latitudes of the Northern Hemisphere.
Outside of these, there was also a more pronounced decrease in MUF
on routes that crossed South America and the South Atlantic where
geomagnetic anomalies are located.
"While late March and early April are periods with traditionally
better-than-average shortwave propagation conditions, this time our
expectations will only be partially met. Solar activity is lower
than would be consistent with the current phase of the solar cycle -
and disturbances are relatively common."
A partial Solar Eclipse occurs on March 29, 2025. Details can be
found at,
https://science.nasa.gov/eclipses/future-eclipses/mar-29-2025-eclipse/
.
For more information concerning shortwave radio propagation, see
http://www.arrl.org/propagation and the ARRL Technical Information
Service web page at, http://arrl.org/propagation-of-rf-signals. For
an explanation of numbers used in this bulletin, see
http://arrl.org/the-sun-the-earth-the-ionosphere . Information and
tutorials on propagation can be found at, http://k9la.us/ .
Solar activity reached moderate levels due to an isolated M1.5/1n
flare on March 19 at 2040 UTC from Region AR4031. Regions AR4028,
AR4034, and AR4035 exhibited slight growth.
Region AR4026 re-emerged in the Southwest quadrant. Regions in the
Northwest quadrant, including AR4020, AR4022, AR4025, and AR4031 all
appeared to be in a decay phase.
No Earth-directed CMEs were detected in available coronagraph
imagery.
No S1 (Minor) or greater solar radiation storms are expected through
March 23.
No significant active region activity favorable for radiation storm
production is forecast.
C-class flares are expected to continue to March 22, with a chance
for isolated M-class (R1-Minor) flares.
A chance for R1-R2 (Minor to Moderate) radio blackouts due to
M-class flares will persist through March 23.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere - March 20, 2025, by F. K. Janda, OK1HH:
"While the current solar activity is a bit lower than we would like
and then would be consistent with the current phase of the solar
cycle, it may be a prelude to another peak within the current
11-year cycle maximum.
"This hypothesis is supported by the starting shift of the sunspot
activity from the southern hemisphere of the Sun to the northern
hemisphere (see also the M-class flares in AR4031 and the following
filament flare, i.e., in the northwest quadrant of the solar disc).
"At the same time, the presently forecasted period is likely to
begin with a transient decrease in geomagnetic activity. But this
may be interrupted as early as March 23 if an enhanced solar wind
blowing from Solar Coronal Hole 24 hits Earth.
"If this happens in the daytime, a so-called positive phase of the
disturbance could follow with an increase in MUF and a general
improvement in ionospheric shortwave propagation conditions."
Spaceweather.com has a link to an article that discusses new
evidence that cosmic rays spark lightning.
Weak disturbances in the solar wind are anticipated through March 20
in response to persistent transient/High-Speed Stream (HSS) effects
as well as possible flanking influences of a nearby CME passage that
departed the Sun on March 17. Solar wind parameters are expected to
slowly diminish on March 21. Another enhancement is expected late
on March 22 due to the arrival of a CIR preceding a negative
polarity Coronal Hole HSS.
A CIR - or Corotating Interaction Region - is a recurring plasma
structure in the heliosphere formed when fast solar wind streams
interact with slower solar wind ahead of them.
Quiet to unsettled levels are expected on March 21. By late on March
22, unsettled to active levels are likely due to the aforementioned
CIR arrival.
For more information concerning shortwave radio propagation, see
http://www.arrl.org/propagation and the ARRL Technical Information
Service web page at, http://arrl.org/propagation-of-rf-signals. For
an explanation of numbers used in this bulletin, see
http://arrl.org/the-sun-the-earth-the-ionosphere . Information and
tutorials on propagation can be found at, http://k9la.us/ .
Geomagnetic field activity is expected to be at minor storm levels
for March 18, and then from March 27 and 27 all due to recurrent
Coronal Hole influences.
Solar activity was at low levels. Multiple C-Class flares were
observed from newly numbered Region 4028. More spots are rotating
around the Southeast limb that maybe connected to the spot group.
The largest flare of the period was a C6.8 on March 13 at 0752 UTC
from old Region 4012 that recently rotated around the Southwest
limb.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere - March 13, 2025, by F. K. Janda, OK1HH:
"The two geomagnetic disturbances (8-9 March and 12-13 March) were
both triggered by an enhanced solar wind blowing from the border
between the coronal holes and the adjacent active sunspot group. OM
Kevin VE3EN has largely restored the content of his website at
https://www.solarham.com/, so that we could conveniently observe the
entire solar evolution in the five images at the top of the main
page (HMI Intensity, HMI Magnetogram, Coronal Holes, AIA 131, and
SUVI 304).
"Again, it is not surprising that both disturbances were correctly
predicted, including the expected worsening on the second day of
each disturbance (March 9 and March 13).
"Even with thanks to relative simplicity of the situation and the
clear images, it was not surprising that both disturbances were
predicted (including the likely deterioration on the second day of
each disturbance, i.e., 9 and 13 March). Both disturbances were
followed by only gradual improvement, i.e., a return to normal.
"If solar activity had been higher, the improvement after the
disturbances would have been faster. However, there was no large
area of spots on the Sun this time, and certainly not any with a
more complex configuration of magnetic fields.
"In the second half of March, solar activity will increase slightly,
and the Spring Equinox will occur. While until recently it appeared
that the increase in solar activity would be more rapid, even the
current expectation of solar flux values only slightly above 200
s.f.u. should result in a noticeable overall improvement, including
an increase in MUF at mid-latitudes during the day up to the VHF
region."
Spaceweatherlive.com contains informative charts and graphs on
Real-time auroral and solar activity.
Slight growth was observed in Regions 4025, 4026, and in the leader
spots of 4019. The rest of the spotted regions were either stable or
in decay. No Earth-directed CMEs were observed.
Solar activity is expected to be low with a chance for M-class (R1
to R2, Minor to Moderate) flares on March 13 to 15.
A persistent connection to a negative polarity Coronal Hole is
expected to cause unsettled to active levels, with periods of G1
(Minor) storm conditions possible through March 15.
The Space Weather Prediction Center also reports there is an
increased chance for M-class flaring (R1-R2, Minor to Moderate) on
March 14 to 16. The SWPC predicts that Geomagnetic Activity
Probabilities for March 14 to 16 are calling for 40, 20, and 10%
chances of a Minor storm during this reporting period.
For more information concerning shortwave radio propagation, see
http://www.arrl.org/propagation and the ARRL Technical Information
Service web page at, http://arrl.org/propagation-of-rf-signals. For
an explanation of numbers used in this bulletin, see
http://arrl.org/the-sun-the-earth-the-ionosphere . Information and
tutorials on propagation can be found at, http://k9la.us/ .
Spaceweather.com is reporting "A Hole In The Sun's Atmosphere" that
should reach Earth on March 9 and 10.
Solar activity has been at moderate levels for the past 24 hours.
The largest solar event of the period was a M1 event observed on
March 5 at 1150z from Region 4016. There are currently 10 numbered
sunspot regions on the disk.
Solar activity is expected to be low with a chance for M-class
flares and a slight chance for an X-class flare on March 7 and 8.
There is a chance for isolated minor solar radiation storm levels
throughout the period if any of the returning/developing
magnetically complex regions are active and produce an event.
Geomagnetic field activity is expected to be at quiet to unsettled
levels on March 7 to 9, 19 to 24, and on March 29. Active levels
are expected on March 10 to 18, and then on March 25 to 28, with
possible G1 (Minor geomagnetic storm) conditions on March 12 to 15
associated with recurrent negative polarity Coronal Hole influences.
Quiet to unsettled conditions are expected on as weak, glancing CME
effects continue to wane with quiet conditions prevailing on March
7. Unsettled to active levels are expected on March 8 as CIR - a
CIR is a Corotating Interaction Region, its primary effect creates
disturbances in the solar wind by interacting between fast and slow
streams of solar plasma - effects ahead of a recurrent, negative
polarity Coronal Hole become geoeffective.
The NOAA Space Weather Prediction Center with its Geomagnetic
Activity forecast for March 7 to 9 has a 40% chance of Active
activity on March 8, a 40% chance of a Minor storm on March 9, a 15%
chance of a Moderate storm on March 9, and a 1% chance of a
Strong/Extreme storm during this same reporting period.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere - March 6, 2025, by F. K. Janda, OK1HH:
"The combination of relatively low total solar activity and a larger
number of geomagnetic disturbances caused a worsening of shortwave
propagation conditions in February. However, the outlook for March
is better, not least because of the approaching equinox (which
occurs on 20 March).
"Solar activity will begin to increase more rapidly after the larger
sunspot groups return to the Sun's disk (which is the half of the
Sun's surface visible from Earth). At its eastern limb we should see
their activity as early as mid-March. They will approach the centre
of the disk just around the Vernal Equinox on March 20.
"But even before that, the scenario may be somewhat different. In
the north-west of the solar disk, we see a large coronal hole, which
is likely to be the source of a strong solar wind that will probably
affect the Earth's ionosphere sooner than we expect. But this too
could be a harbinger of a further upsurge in solar activity. So -
within reason - all good news."
For more information concerning shortwave radio propagation, see
http://www.arrl.org/propagation and the ARRL Technical Information
Service web page at, http://arrl.org/propagation-of-rf-signals. For
an explanation of numbers used in this bulletin, see
http://arrl.org/the-sun-the-earth-the-ionosphere . Information and
tutorials on propagation can be found at, http://k9la.us/ .
Also, check this:
"Understanding Solar Indices" from September 2002 QST.
The forecast 10.7 centimeter flux for March 7 to 13 is 150, 150,
150, 155, 160, 170, and 180, with a mean of 59.3. The forecasted
Planetary A Index for March 7 to 13 is 5, 5, 8, 15, 15, 25, and 30,
with a mean of 14.7. The forecast Planetary K Index for March 7 to
13 is 2, 2, 3, 4, 4, 5, and 5, with a mean of 3.6.
A Coronal Mass Ejection (CME) associated with a filament eruption
became visible on February 26 at 1448 UTC. Model analysis
determined this CME to be a miss ahead of the Sun/Earth line.
Unsettled to active levels are likely on February 28 to March 1 as a
Coronal Hole influence continues, and a glancing blow is possible
from a Coronal Mass Ejection that occurred on February 25.
Solar activity is forecast to range from low to moderate levels
through March 22.
Minor to Moderate activity (R1 to R2) is possible at different
points throughout the period as active regions grow, evolve, and
return from the far-side of the Sun. There is a slight chance for R3
(Major) or greater events if any of the active regions develop
additional complex magnetic structures.
Geomagnetic field activity is expected to be at quiet to unsettled
levels until March 6 with periodic, weak Coronal Hole influences.
Unsettled to active levels, with isolated G1 (Minor) storming
conditions are likely from March 7 to 18 as recurrent negative
polarity Coronal Holes are expected to be in a geoeffective
position.
NOAA Space Weather forecasts a 55% chance of a Class-M flare, and a
10% chance of a Class-X flare, both within the next 48 hours
(February 28 to March 1).
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere - February 27, 2025, by F. K. Janda, OK1HH:
"Solar activity is now increasing, but the increase is irregular,
which causes, among other things, a decrease in the reliability of
forecasts. Geomagnetically quiet periods, especially when associated
with an increase in total solar activity (such as 20-23 February),
are accompanied by improved conditions for ionospheric radio wave
propagation. A subsequent disturbance can cause even further
improvement (which happened on 24 February).
"Following the increase in solar flare activity (from 23 February),
two proton flares were observed on 24 February. In the following
days, the Earth's ionosphere was under the influence of a
solar-derived proton rain, after which the density of free electrons
in it decreased due to recombination.
"However, the worsening of conditions was only noticeable on 25
February. The very next day, 26 February, there was an improvement,
in particular an increase in the MUF on a global scale. The jump in
the solar wind speed also contributed. However, the changes were so
rapid, even within a single day, that our assessment of the level of
conditions could have been reversed, depending on the time of day
and the frequency bands used.
"The developments described can be considered as a harbinger of a
March increase in solar activity. Since the Spring Equinox is
approaching, it will contribute to an improvement in ionospheric
shortwave propagation, more accurately called decameter waves. The
possible shorter worse spells on March 1-2 and March 5-6 will make
no difference, with the seasonal improvement not fully manifesting
itself until the second half of the month."
This weekend is the ARRL International DX SSB contest. Information
can be found at, https://www.arrl.org/arrl-dx .
For more information concerning shortwave radio propagation, see
http://www.arrl.org/propagation and the ARRL Technical Information
Service web page at, http://arrl.org/propagation-of-rf-signals. For
an explanation of numbers used in this bulletin, see
http://arrl.org/the-sun-the-earth-the-ionosphere . Information and
tutorials on propagation can be found at, http://k9la.us/ .
Also, check this:
"Understanding Solar Indices" from September 2002 QST.
The predicted 10.7 cm flux for February 28 to March 6 is 195, 195,
190, 190, 190, 190, and 185, with a mean of 190.7. The predicted
Planetary A Index for February 28 to March 6 is 12, 10, 8, 5, 5, 5,
and 5, with a mean of 7.1. The predicted K Index for February 28 to
March 6 is 4, 3, 3, 2, 2, 2, and 2, with a mean of 2.6.
Solar activity is expected to range from low to moderate levels
through March 15. There is a varying chance for R1 or R2 (Minor or
Moderate) events, and a slight chance for R3 or greater events.
Geomagnetic field activity is likely to reach G1 (Minor) levels on
February 28, March 9, and March 12 to 14. Active levels are
predicted for March 1. Quiet, and quiet to unsettled conditions are
expected to prevail throughout the remainder of the period.
The NOAA Ap Index Forecast is 5 for February 21 and 22.
The NOAA Space Weather Prediction Center reports no space weather
storms predicted for the next 24 hours.
For the last 24 hours, solar flare activity has been at low levels
with only a C-Class observed. The largest flare was a C8.1 on
February 19.
This flare was accompanied by a Type II radio emission and
associated CME off the Southwest edge of the solar disk. Modelling
efforts determined the bulk of the CME to miss ahead of Earth's
orbit. However, a weak glancing influence cannot be ruled out late
on February 24.
Region AR3996 is the largest and most complex region on the disk but
was responsible for only one C-Class flare. Flux emergence and an
increase in interior spots can be seen in Region AR3998 but overall
the region has been fairly quiet.
Spaceweather.com has an article link from the "Advancing Earth And
Space Sciences" website concerning an extreme compression of Earth's
magnetic field that was caused by the May 2024 solar superstorm.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere - February 20, 2025, by F. K. Janda, OK1HH:
"The increase in geomagnetic activity following the decrease in
solar activity is a simple phenomenon to explain: systems of
magnetic field lines over active regions in the Sun open up and
charged particles (both free electrons and the nuclei of hydrogen
atoms, or protons themselves) slip through them more easily into
space.
"In Earth's orbit, we see an increase in the solar wind and,
consequently, an increase in geomagnetic activity. At the same time,
the ionization rate of the ionosphere is increasing, while the
shortwave propagation conditions may not only worsen (due to
scattering on inhomogeneities) but also improve as the MUF may grow.
This was well known, for example, on Saturday 15 February on the
Europe-North America route.
"The only geomagnetically quiet days in the first half of the month
were 3-7 February. Then the solar wind, blowing from the long
canyon-shaped coronal hole, intensified and geomagnetic activity was
elevated for most of the second third of February. A calm trend can
be expected on most days of the last third of the month. Although
there does not appear to be a significant increase in solar
activity, it is sufficiently high. In addition, spring is
approaching, which is good news for the state of the ionosphere."
The predicted Planetary A Index is 5 for February 21 to 26, and 10
on February 27. The predicted Planetary K Index is 2 on February 22
to 26, and 3 on February 27. Predicted 10.7 cm solar flux is 170
for February 22 to 23, 190 on February 24, 195 on February 25, 200
on February 26, and 195 on February 27.
Sunspot numbers for February 16 to 20, 2025 were 271, 218, 187, 119,
and 123, with a mean of 183.6.
NOAA reports a G1 (Minor) geomagnetic Storm Watch has been issued
for 14 Feb, 2025. A coronal hole high speed stream is expected to
move into a position favorable for enhanced interaction between the
high speed stream and Earth's magnetosphere. These enhancements are
likely to cause elevated geomagnetic responses, with G1 (Minor)
storm levels likely.
From Spaceweather.com: Another solar wind stream is heading for
Earth. It is flowing from a canyon-like hole in the Sun's
atmosphere. First contact with the stream on February 14th could
cause a minor G1-class geomagnetic storm with Arctic auroras for
Valentine's Day.
The greatest observed 3 hr Kp over the past 24 hours was 4. The
greatest expected 3 hr Kp for February 13 to 15 is 4.67.
No Minor S1 or greater solar radiation storms are expected. No
significant active region activity favorable for radiation storm
production is forecast.
Radio blackouts reaching the R1 levels were observed over the past
24 hours. The largest was at February 13 at 1109 UTC.
Solar activity is expected to be low with a chance for R1 to R2, and
Minor to Moderate activity on February 13 to 15.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere - February 13, 2025, by F. K. Janda, OK1HH:
"Total solar activity was highest last October in the current
11-year cycle. Since then, it has been declining, but slowly. This
is also true for flare activity. Medium strong solar flares were
produced mainly by the active region of AR3981. Some of these were
accompanied by CMEs, none of which hit the Earth directly, but
passed close enough to affect its atmosphere.
"NOAA predicted on February 8 that there was a possibility of G1
class geomagnetic storms on February 10 and 11. The prediction
turned out to be fairly accurate - although geomagnetic field
activity increased as early as February 9, it was highest on
February 10 and was elevated on February 11. Therefore, ionospheric
shortwave propagation conditions were at their worst on 10 February
and subsequently improved only very slowly in the following days.
"We now observe a large coronal hole, resembling a canyon, on the
Sun, which could be another source of enhanced solar wind. Earth
should be hit by it on Valentine's Day, or February 14. The days
ahead will also be rather unsettled, but the active regions now
rising near the southeastern limb of the solar disk will cause an
uptick in solar activity, nevertheless, causing improved propagation
conditions.
"The good news at the end: at https://www.solarham.com on the bottom
left, after an eleven-week hiatus, we can see a map of the entire
Sun, especially the Sun's far side, under the 'Farside Watch'
banner. So the JSOC glitch has been fixed, and after another click
on http://jsoc.stanford.edu/data/timed we can read more under the
heading 'Time-Distance Helioseismic Far-Side Imaging.'"
The latest report from Dr. Tamitha Skov, WX6SWW, can be found online
at, https://youtu.be/v5H2QsbiCqo .
Spaceweather.com reports that sunspot 3981 has produced more than 20
M-class solar flares, including two that almost reached category X.
The activity is likely to continue today. The sunspot retains a
delta-class magnetic field that harbors energy for frequent
explosions.
The current solar forecast calls for there to be no G1 (Minor) or
greater geomagnetic storms. A potential glancing blow is possible
on February 7 and 8.
Solar radiation - as observed by NOAA GOES-18 over the past 24 hours
- was below the S-scale storm level thresholds. (The S-scale is
used to indicate the severity of energetic particles emitted from
the Sun.) The scale ranges from S1 (minor) to S5 (extreme).
There is a chance for S1 (Minor) or greater solar radiation storms
due to the complex cluster of sunspot groups in the Northwest
Quadrant of the Sun.
Radio Blackouts are expected through February 8, with a chance for
R3 (Strong) events due to several magnetically complex sunspot
groups.
There is a chance for S1 (Minor) or greater solar radiation storms
through February 9 as the complex cluster of sunspot regions in the
north continues to rotate closer to the western limb.
The geomagnetic field activity is expected to be unsettled to active
levels on February 10 to 19.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere, February 6, 2025, from F. K. Janda, OK1HH:
"The current 11-year solar cycle beautifully shows how little we
still know about the universe we live in. Including the Sun, which
is a relatively very stable star (otherwise we wouldn't be here).
Each 'eleven year' cycle is different from all the previous ones,
and all previous attempts to predict the next one have always
failed. Better said - some of them have proven to be valid. But only
some.
"The current developments do not appear to be complex. Coronal holes
11 and 12 were followed by the somewhat surprisingly active regions
of AR3976 - 3971, where eruptive activity rose and fell irregularly.
Occasionally including CMEs, which although they mostly did not hit
the Earth, sometimes partially did.
"The ionospheric shortwave propagation conditions were therefore
mostly above average, but at the same time very variable. There was
no way to accurately predict their course, even if only for the next
24 hours. On the other hand, there was no major disturbance that
would have made them significantly worse. There is only one thing to
say about the future development: it will be relatively easy to
predict at first sight. But only at first sight, the reality will
probably be more different than usual."
For more information concerning shortwave radio propagation, see
http://www.arrl.org/propagation and the ARRL Technical Information
Service web page at, http://arrl.org/propagation-of-rf-signals .
For an explanation of numbers used in this bulletin, see
http://arrl.org/the-sun-the-earth-the-ionosphere .
An archive of past propagation bulletins is located at,
http://arrl.org/w1aw-bulletins-archive-propagation .
Check out this QST article about Solar Indices:
The predicted Planetary A index for the period February 9 to 14 is
5, 10, 15, 15, 20, and 10. The predicted largest Kp index is 2, 3,
3, 4, 5, and 3. Predicted 10.7 cm flux is 200, 200, 195, 195, 195,
and 190.
The sun has been moderately active this past week. The greater than 2 MeV (solar particle event) electron flux at geostationary orbit is expected to remain mostly at normal to moderate levels January 30 - 31. A coronal hole high-speed stream is expected to arrive February 1. Particle injection during this time will likely elevate the 2 MeV electron flux to high levels.
Solar wind speeds have been at nominal levels and are expected to continue into January 30. There remains a slight chance for enhancement due to a weak coronal mass ejection (CME) associated with a Type II radio sweep off the west limb around January 28. Confidence in the arrival of this CME is low as modeling suggests arrival late January 31.
The geomagnetic field has been quiet to unsettled with a slight chance for active conditions on January 31, due to possible influence from the CME. The most notable effects will be from the high-speed stream from the positive polarity coronal hole that is expected to become fully geoeffective on February 1.
The 10.7 -centimeter radio flux and geomagnetic indices: January 30 – 31, 150; February 1, 145, and 150 on February 2.
EarthSky.org reports a large coronal hole which has been under observation since this past Tuesday is now facing Earth. The fast solar wind it produces is expected to arrive late January 31 to early February 1. This could cause disturbances in Earth’s geomagnetic field from unsettled (Kp=3) to active levels (Kp=4) with a chance for G1 (minor) geomagnetic storm (Kp=5) levels. Solar activity is at low levels with only C-class flares but a cluster of regions AR3977, AR3976, and AR3978, are emerging onto the visible solar disk and showing signs of magnetic complexity.
Here’s a shocker for you: we live at the bottom of the sky. Above us there are multiple layers of the atmosphere, pressing down on us at 14.7 pounds per square inch.
Of particular relevance to us as shortwave listeners and hams, there is a special layer of the atmosphere, not shown on the chart above called the ionosphere. The ionosphere starts around 30 miles above us and extends up to about 600 miles and includes parts of the layers above.
The Sun’s upper atmosphere, the corona, is very hot and produces a constant stream of Ultra-Violet and X-rays, some of which reach our atmosphere. When the high energy UV and X-rays strike the atmosphere, electrons are knocked loose from their parent atoms and molecules, creating a layer of electrons.
Now, here’s the cool part: this layer – the ionosphere – is important because radio waves bounce off of it.
The sun, however, is not constant in its action on the ionosphere. The amount of UV and x-ray energy (photon flux) produced by the sun varies at by nearly a factor of ten as the sun goes through an 11 year cycle. The density of the ionosphere changes accordingly, and so does the ability of the ionosphere to bounce radio waves. When the sun is at peak activity, and the ionosphere is “hot,” SWLs and hams are likely to experience excellent long-range propagation. When the sun is quieter, long-range propagation diminishes.
Every 11-year solar cycle is unique, but early indications are that we may on the verge a cycle that favors long-range propagation: https://swling.com/blog/2022/03/termination-event-may-indicate-solar-cycle-strength/
The results can be spectacular. Decades ago, during a particularly hot solar cycle, I once spoke from my station near Albany, NY, to a station in the state of Georgia on a mere 4 watts. On another occasion, I conversed with a ham in Christchurch, New Zealand – a distance of over 9,000 miles – with 100 watts single sideband transmit power. During that same period, I would routinely listen to shortwave stations halfway around the world.
Ain't this solar maximum great?
Solar Cycle 25 is now much, much stronger than anyone anticipated,
and it's slowly growing stronger through at least this weekend.
Today's estimated international sunspot number is 281.
It's increasingly likely that we'll have widespread coast-to-coast and
worldwide 6 meter F2 propagation during about half of the days
between late October and at least early February. Widespread F2
openings are likely to bring 6 meter CW and SSB to life like we haven't
experienced in more than 20 years.
The first sign of enhanced 6 meter F2 will be increasingly frequent TEP
from Europe and North America to South America and the South Atlantic islands. TEP may begin very sporadically by late August and become increasingly frequent later in September and especially during October.
Coast-to-coast F2 propagation and propagation crossing the Atlantic
to Europe and Africa may begin sporadically during September and
October and become frequent and long lasting by early November.
Effective 6 meter antennas can be very small. 3 element Yagis are small, lightweight and very effective. 20 foot antenna height is adequate but sloping terrain or higher antennas perform much better. Heights higher than 50 feet are unnecessary and in many cases perform poorly.
Are you ready for this once in a lifetime experience?
73
Frank
W3LPL
Thanks to ionospheric propagation of radio waves, ham radio operators can rely on HF ionospheric radio signal propagation to communicate with fellow hams located way beyond the horizon.
The ionized layers of the ionosphere make HF radio wave propagation possible much beyond line of sight distances. These layers can be viewed as our "Seven League Boots" which, by leaps and rebounds, give our ham ra
I'll explain, in a moment, how the 'F' layer is the most useful ionized layer for DX.
Best of all, solar sunspot cycles improve HF propagation because they revitalize our ionosphere. The good news is, solar cycle 25 has begun! Ham radio operators, all over the world, are looking forward to its increasing activity.
The simplified drawing above illustrates how radio wave 'C' is refracted, by the ionized layer 'F', back toward the earth's surface, rebounds off the earth's surface a great distance away from its origin, goes upwards again as 'C1' to be refracted again by the 'F' layer and bounce off the earth further on as 'C2' and so on.
The radio signals 'A' and 'B', arriving at the ionized 'F' layer at too
The HF signals will gradually lose energy after each refraction by the 'F' layer and after each rebound off the earth's surface... until it is no longer discernible. But, by that time, it will have traveled thousands of miles and been heard by countless radio amateurs and shortwave listeners!
That's the magic of HF ionospheric radio signal propagation.
Ionization of the upper reaches of earth's atmosphere occurs when ultraviolet radiation from the sun collides with hydrogen and helium molecules that are few and far between up there. These collisions detach electrons from the gaseous molecules.
As a result, positive hydrogen and helium ions are generated and negatively charged free electrons are liberated from their nucleus. These regroup into ionized layers above the earth.
However, ionized layers only form when the sun is "active", which it is for about 9-10 years, every eleven years or so. It's commonly called the 11-year sunspot cycle.
We can see the progression of the last few sunspot cycles in the graph shown earlier. You can obtain more information on the 11-year cycle of sunspots here.
During the day, the ionized layer 'D' mostly hinders ionospheric propagation of radio waves.
It is the ionized layer closest to the earth's surface. It is located between 60 km and 100 km (37-62 miles) above the earth.
In the daytime, it forms under the sun's intense UV radiation and constitutes a barrier preventing amateur radio signals in the 40-meter, 80-meter and 160-meter bands from getting far and from being heard in the intense atmospheric noise.
Meanwhile, signals 10 MHz and above can get through to reach the ionized layers above and make their way beyond the horizon.
The 'D' layer dissipates at sunset.
Signals in the 160-meter to 40-meter bands then become free to reach the 'F' layer and reach DX amateur radio stations like the other higher-frequency signals.
The 'E' layer lies between 90 km and 150 km (56-93 miles) above the earth but its most useful portion is located between 95 km and 120 km (59-75 miles) of altitude.
During daytime hours, in theory, layer 'E' could refract 5-20 MHz signals and help them along their way.
However, in reality, the 'D' layer (below) absorbs much of the energy of signals at these frequencies. Only signals in the 7-14 MHz range - transmitted near vertically - will be able to punch through the 'D' layer with enough remaining energy to reach the 'E' layer and be refracted along to reach as far as 1200 km (750 miles) at times.
That's where NVIS antennas come in handy.
The periods just before dawn and right after dusk are best to make use of the 'E' layer. At night, the 'E' layer disappears almost completely, while still remaining somewhat useful to the propagation of signals in the 160-meter band.
Sometimes, dense ionized clouds will form suddenly in the 'E' layer and disappear just as suddenly, minutes, rarely hours later.
Sporadic 'E' propagation (Es) is useful at frequencies above 28 MHz, in the VHF range, rarely below. We cover their usefulness in extending the reach of VHF signals beyond the horizon on another page of this website.
Both 'E' and 'Es' propagation contribute to 50 MHz activity.
During daytime hours, in summer, this layer will often be useful to the propagation of HF radio signals of the 30-meter and 20-meter bands. Its role in the propagation of HF signals is rather negligible.
The 'F2' layer forms during daytime hours between 200 km and 400 km (125-250 miles) above the earth. It is higher in altitude in the summer than it is in the winter.
It is usually around all year round.
At night, layers 'F1' and 'F2' merge into one 'F' layer, a little lower than the daytime 'F2' was located.
The 'F2' ionized layer is present during the major part of a solar cycle.
However, it will sometimes disappear completely for days on end during a deep solar cycle minimum!
The 'F2' layer will reach its highest density at the peak of a solar sunspot cycle.
It will then refract toward earth radio signals ranging from 7 MHz to 30 MHz and enable them to reach distances as far as 4000 km from their origin, rebound off the earth to rise again to the 'F2' layer... and repeatedly do so… sometimes to travel right around the earth and come back from behind their point of origin!
During the better nine years or so of a solar cycle, QRP operators (5 watts of radiated power or less), using simple dipoles, can make DX contacts as far and as often as the QRO operators (using up to 200 to 300 times more power) using a multi-element directional antenna!
During such wonderful periods, every ham radio operator has an equal chance under the sun to make DX contacts.
The information I have presented to you in this article is a very brief summary of what could be said about HF ionospheric radio signal propagation. I have really only scratched the surface!
Countless scientific publications have covered many aspects of the subject since the discovery of the ionosphere's existence and, later, its role in the propagation of HF radio signals.
Research is ongoing, involving and scientists and ham radio operators alike.
For more on our sun's behaviour, visit the Solar and Heliospheric Observatory
by VE2DPE
https://www.hamradiosecrets.com/ionospheric-propagation-of-radio-waves.html
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