DF2PY Said:
As the last days,despite low WWV numbers, yielded almost no DX to North
America i tried to check with magnetograms along the suspected route of
signals......
Thomas KN4LF Says:
The poor 160 meter band conditions as of late, even with low A/Ap and K/Kp
values, is due to polar cap absorption and polar radio blackouts. Polar cap
absorption and polar radio blackouts are caused by high energy protons
arriving via a solar flare. These high energy protons emitted in a solar
flare create the auroras we see and the overionization of the D layer and
therefore absorption of high latitude path broadcast band and 160 meter
radio signals. End result, what we call auroral conditions, when high
latitude paths are basically dead but low latitude paths from the Caribbean
and Central and South America are predominate. As the A/Ap and K/Kp values
are tied to geomagnetic disturbances and ionospheric storms, these events
basically tear up the F layer only and affect the higher shortwave
frequencies only, not the E layer which is the predominate propagation layer
for 160 meter propagation. Low A and K values can fool you into thinking
high latitude conditions on the broadcast band and 160 should be good.
Forget the A and K indices for 160, you have to look at the proton flux
values at http://sec.noaa.gov/rt_plots/pro_3d.html . If the levels are at
and above 10 Mev then there is going to be high absorption of 160 meter
signals by the D layer on high latitude paths and skewed propagation paths,
as the transmitted 160 meter signal seeks a path of least resistance or a
more southerly path. This has been the case repeatedly so far this fall,
with many X class solar flares and we have been above the 10 Mev proton
level for many days at a time.
POLAR CAP ABSORPTION (PCA). An anomalous condition of the polar IONOSPHERE
whereby HF and VHF (300- 3000 khz) radiowaves are absorbed, and
LF and VLF (3 - 300 khz) radiowaves are reflected at lower altitudes
than normal. In practice, the absorption is inferred from the
proton flux at energies greater than 10 MeV, so that PCAs and
PROTON EVENTs are simultaneous. Transpolar radio paths may still
be disturbed for days, up to weeks, following the end of a proton
event.
PROTON. Solar activity levels with at least on high energy event (Class X
Flares)
PROTON EVENT. By definition, the measurement of at least 10
protons/sq.cm/sec/steradian at energies greater than 10 MeV.
PROTON FLARE. Any FLARE producing significant FLUXes of greater-than-10 MeV
protons in the vicinity of the earth.
http://www.windows.ucar.edu/spaceweather/polar_com.html
73,
Thomas Giella, KN4LF
Plant City, FL
Grid Square- EL88wx
CQ Zone 5
ITU Zone 8
Email: kn4lf@tampabay.rr.com
KN4LF 160 Meter Amateur Radio Resources And More:
http://www.kn4lf.com
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