Glenn Hauser
09-29-2008, 11:22 PM
Scott Bidstrup, WA7UZO who lives in Costa Rica, sent an interesting
article about noctilucent clouds as a possible medium for UHF
propagation. According to the article in Science Daily --- see
http://www.sciencedaily.com/releases/2008/09/080925144806.htm
--- the clouds contain ice coated with sodium and iron from micro-meteors, and sit at about 53 miles (85 km) altitude, mostly between 50-70 degrees latitude, and sometimes as far south (or north, in the
southern hemisphere) as 40 degrees latitude or less.
The clouds are highly reflective of radar signals, and instead of
diffraction as we see in ionospheric propagation, ripples in the
clouds seem to reflect in unison, reinforcing each other.
Noctilucent clouds are sometimes visible at night, because their
altitude is so high that they reflect sunlight into areas of
darkness. They are also known as polar mesospheric clouds, and
appear most often at twilight during the summer.
Go to http://www.spaceweather.com/nlcs/gallery2008_page13.htm
to see images of noctilucent clouds (ARRL Propagation Forecast Bulletin 40 ARLP040, From Tad Cook, K7RA, Seattle, WA September 26, 2008, To all radio amateurs, via Mike Terry, dxldyg via DXLD)
So could that explain some unexplained TVDX on UHF? Just because radar may be in the UHF range, doesn`t necessarily mean VHF would not work, unless there is something else about their characteristics to favor those frequencies. 85 km up is a bit lower than sporadic E, so skip distances should be shorter but still notable (Glenn Hauser, DX LISTENING DIGEST) ###
article about noctilucent clouds as a possible medium for UHF
propagation. According to the article in Science Daily --- see
http://www.sciencedaily.com/releases/2008/09/080925144806.htm
--- the clouds contain ice coated with sodium and iron from micro-meteors, and sit at about 53 miles (85 km) altitude, mostly between 50-70 degrees latitude, and sometimes as far south (or north, in the
southern hemisphere) as 40 degrees latitude or less.
The clouds are highly reflective of radar signals, and instead of
diffraction as we see in ionospheric propagation, ripples in the
clouds seem to reflect in unison, reinforcing each other.
Noctilucent clouds are sometimes visible at night, because their
altitude is so high that they reflect sunlight into areas of
darkness. They are also known as polar mesospheric clouds, and
appear most often at twilight during the summer.
Go to http://www.spaceweather.com/nlcs/gallery2008_page13.htm
to see images of noctilucent clouds (ARRL Propagation Forecast Bulletin 40 ARLP040, From Tad Cook, K7RA, Seattle, WA September 26, 2008, To all radio amateurs, via Mike Terry, dxldyg via DXLD)
So could that explain some unexplained TVDX on UHF? Just because radar may be in the UHF range, doesn`t necessarily mean VHF would not work, unless there is something else about their characteristics to favor those frequencies. 85 km up is a bit lower than sporadic E, so skip distances should be shorter but still notable (Glenn Hauser, DX LISTENING DIGEST) ###