Re: Unusual conditions on the AM band locally last night

["Kaimbridge M. GoldChild" <kaimbridge@my-deja.com>]

Martin Waters wrote,

> --- "Kaimbridge M. GoldChild" <kaimbridge@my-deja.com>
> wrote:
>> Yup, it's El Sol alright, though it is not the
>> sunspot or even flare itself--it's the "coronal
>> mass ejection" (CME) that the flare emits
> <snip>
>
>  I've observed these conditions a few other times in
> the past few years, although last night was a very
> strong case of it. However, why are the Cubans
> thundering in when nearly all the other skywaves seem
> to be suppressed? Is it compass heading? Castro exempt
> from laws of physics?
          <snip>
> How does this work?

It's nothing really complicated--just "absorption of the bounce"! P=)

Think of a night where the AM/MW band is fully active, with 50Kw
"clear" stations boomming in from +1000mi and local, "graveyard"
frequencies a 5-6+ station pulsating, noise floor blob:  The
"electrical sky" is crystal clear and you can "see" the signals
bouncing off of the ionosphere.
As geomagnetic activity increases, a "haze" develops, meaning you
can't see the signals bouncing off the ionosphere as well, meaning
that the AM/MW band absorption starts to dampen reception--almost
like an RF "haze".  This "haze" continues to thicken as the
geomagnetic storming gets stronger, until there is blanket
absorption, meaning that the AM/MW band has daytime conditions, with
no signs of any skip whatsoever and the graveyard locals in like
high noon.
The catch is that geomagnetic/auroral activity usually radiates from
the poles:
               http://sec.noaa.gov/pmap/gif/pmapN.gif

The yellow (weak) to dark brownish-red (strong) activity radiates
from the poles, meaning if storm levels extend down to the Carolinas,
anything that **BOUNCES OFF OF THE IONOSPHERE** from the Carolinas,
northward, will be absorbed, while signals south of it will bounce
through:  In this example, the WSB-GA and WSM-TN signals (which
bounce to us above the Carolinas) would be absorbed up here in New
England--with most of the band sounding like daytime--while Cuba and
the Caribbean may bounce right in like usual (depending on the actual
angle of the bounce, etc.).
A couple of things to remember, though.
Besides acute geomagnetic storming, there is regular day to day flux
variation (that storming remnants may or may not reconcile with),
that will likely affect signal conditions.
Also, depending on the particulars involved (especially if there is
a "proton" and/or "polar cap absorption" event(s) present), even
after the storm subsides, the lower part of the AM/MW band may be
under blanket absorption, while the mid and upper part may sound
"normal".
As I mentioned in a post long ago, at the onset of a storm, the band
may seem just as strong as usual (or maybe even a little better),
but there will frequently be a period of phasing/"wow-ing" flutter
(it sounds like you're hearing it under water)--the regular AM type
(like the effect of WLLH's old co-transmitter days), but widespread
and sometimes intense--right before the band goes down for the count.

     ~Kaimbridge~