Topband: 27 days rotation Moon & Sun

[by way of Bill Tippett <btippett@alum.mit.edu>]

Subject: Re: Topband: 27 days rotation Moon & Sun
From: "Thomas Damboldt" <Thomas.Damboldt at T-Online.de>
Date: 05 Mar 2007 15:51 GMT

Hello Cristie,

as I said in my earlier mail, we are talking about physical
effects causing the ionosphere and its variations. There is
no doubt that solar radiation (electromagnetic waves and
particles) is the main source. Sometimes individual "active
regions" on the sun remain more or less stable in the same
position and that is the reason for the 27-day recurrences,
because this is the rotation period of the sun in middle
latitudes.

Other sources affecting HF and particularly MF propagation
like tidal effects of the moon and planets, gravity waves
(TID's = Travelling Ionospheric Disturbances) and effects
of the neutral atmosphere ("weather") are only secondary,
but may perhaps at times be the decisive factor for good
or bad conditions: speculation, we just don't know.

The discussion of "rotation periods" and "astronomical data"
is totally misleading in the context of HF and topband
propagation. The solar radiation causes the ionosphere and
most of its variations and therefore the questions to be
discussed here are: When does an "active region" on the sun
point at the earth?  What is an "active region" in this
context? Can we "observe" it? How long does it live?

It is most unlikely that non-solar effects (moon etc), if at
all influencing propagation, also show a recurrence tendency
after 27 days.

Best regards
Thomas, DJ5DT