The "Swirlies"

Does anyone else ever see this phenomenon? -see attached WSPR screen captures

I have been seeing it during the late afternoon and early evening time frame here in the southwestern US.

http://axis1.bizland.com/ac7sm/wspr_002.JPG
http://axis1.bizland.com/ac7sm/wspr_005.JPG

Also if anyone has any links to homebrew attenuator projects please post.

Cheers from chilly Las Vegas! (currently 47 degrees F)

-Larry AC7SM