On Jan 18, 8:36*am, dave wrote:
On 01/18/2011 04:30 AM, Keith wrote:

* The sun spots are very low right now which effects the ionosphere.
Here is a short article on the concept:

http://hamchatforum.lefora.com/2009/11/13/hf-radio-propagation-and-su....

Here's a shorter one:

In order for signals to refract (be bent back toward the Earth) the
ionosphere needs ions. These are produced when UV radiation interacts
with the atmosphere. UV radiation comes from Sunspots.

And nobody can figure out what causes the sunspots. Unknown.