We’ve had yet another week with unsettled geomagnetic conditions. This time
the Kp index hit five on Wednesday, and even six on Thursday, caused by a plasma
emission from the Sun with a prolonged southward-facing Bz field. This was a
shame as the field had been very settled on Monday, with a Kp index of zero,
which usually bodes well for good HF conditions.
On
Monday the critical F2 layer frequency, as measured by the Chilton ionosonde,
hit 6.8MHz at noon, giving a predicted maximum usable frequency of about
21MHz.
By Wednesday it was 7.6MHz, giving a MUF of
about 25MHz over 3,000km. This shows that, perversely, a higher K index can
sometimes result in better conditions as the initial onset of solar plasma can
cause a positive phase with better maximum useable frequencies, before the
subsequent negative phase with depressed MUFs, noisy bands and auroral
conditions.
The moral of the story is that the best thing
to do is monitor the HF bands as often as you can, as you never really know what
you might hear.
The forecast for the next week is more of the
same, with a further high risk of unsettled geomagnetic conditions at times,
especially on the 28th and 29th.
VHF and up propagation news:
The
edge of a high pressure system sits well to the East over the continent, so
stations in the South and East of the country could get some enhanced conditions
this week.
The second half of the week looks the best,
with the F5LEN tropo maps showing a long narrow finger of enhancement over
Southern England, into the Low Countries and the Southern Baltic. This could
link up with the Azores high, providing slightly-enhanced conditions into
Western France, Spain and Portugal. Otherwise, the bulk of the country offers
windier weather with low pressure and frontal rain bands, with not much tropo on
offer for VHF and UHF. However, some active weather fronts could introduce the
prospect of some rain scatter on the GHz bands.
We are
now in the year’s quiet period for meteor activity, extending from early January
until the Lyrids shower at the end of April, so it’s back to early mornings
waiting patiently for the random meteors to provide fleeting low VHF DX
opportunities.
Moon declination is falling and goes negative
on Thursday and, with apogee next Saturday, path losses will continue to
increase throughout the week.
