A recent study (http://onlinelibrary.wiley.com/doi/10.1002/2016GL068179/abstract) found a possible explanation for mysterious VHF radar echoes observed each day at an elevation of 100-200 km. Echoes have a peak intensity at 150 km, at the top of the E region. This could be of particular interest to all who experiment with VHF propagation VHF, the data used in the study comes from a 50 MHz radar. Here's a link to the news report by AGU: http://blogs.agu.org/geospace/2016/04/28/new-study-explains-source-mysterious-radar-echoes-2/ Best, Stefano N5STT
Unfortunately , though dependable, the prop is at high elevation for the most part. More of an NVIS mode. Here's an amusing excerpt on (lower) ionospheric waves which I analyzed in 1972 from OMEGA data on the 1961 H bomb... research assistant at Harvard....in manuscript at moment ... H- bomb prop. NOT a preferred mode... ======================================= The early pre-OMEGA data had the results of the H-bomb on the lower ionosphere, where its havoc would be most pronounced. The date was Halloween, 1961. The Russians dropped the bomb over Siberia. But the whole planet went into turmoil. The data showed the effect almost instantaneously. The usually slowly changing data went crazy. At the time it reminded me of someone taking a nail to an LP record and going up and down the entire surface. After 2 hours it calmed down somewhat, only to start gyrating again 10 hours later. It gyrated with wiggles beating against each other. It repeated this for several days, weakening in magnitude each time. Overall, the lower ionosphere was not normal for a few weeks, almost into 1962. The behavior reminded me of the sloshing you see in a swimming pool, when a very big person does a very big belly flop. The most striking thing about the data was the timing of the waves. There was a long cycle, a medium one, and a short one. Over time the short and medium periods of these waves increased and then they became so weak as to be undetected. Having just studied waves in a Berkeley Physics book, I interpreted this as boundary conditions causing the waves to bounce off clouds of neutral or ionized and form shorter periods of reflection. It appeared that waves made littler waves of shorter periods, and these made more waves of even shorter period. Waves making littler waves, making littler waves. They were what we now call ‘self-similar’, the heart of fractal geometry. This meant the lower ionosphere broke into chunks of ionization that moved apart and dispersed. It could alternatively have to do with magnetic fields that trapped these temporary ionization clouds. Since the ionosphere tended to be fairly uniform and slowly changing, these weird phenomena were new and perplexing. They meant…something. After working with the data for almost a month, noting times and effects, Jack Pierce had me draw up a summary. “I think we should tell our Navy friends what you found”, he said. A week later, three Navy brass and a scientist came, took us to lunch at Harvard Square’s Wursthaus and politely asked me questions. This I could not fathom --a 17 year-old telling the Navy something new. I thus thought I had come up with something scientifically important. A heady feeling! But it did not last. After conferring with Jack Pierce behind closed doors, he announced that the data was being taken, to Washington, along with my notes and summaries, for further analysis. I was told that I could not pursue it and was not to discuss it further (45 years later, with the effects of the H bomb now public on the internet, I no longer feel so bound). I was dumb struck. ------------------------------------------------------------ 73 Chip W1YW
Ionosondes and Digisondes are nothing new. They are vertical measurement radars and there is nothing mysterious about them. I didn't see any information in the abstract (I am not willing to pay to read someone's paper) which makes me say "Gee!" 150km that's the boundary between the E and F layers, which will support 50 MHz signals. The boundary between the two layers is different between day and night (discovered around 1931) etc etc. Either way, nothing to even raise an eyebrow about here.
Old news to any radar men who ever stepped into a Super Connie out of Otis ... This little propagation trick was put to very good use. The 551st Wing at Otis is the only Air Force organization flying the E C-121H "Warning Star" Super Constellation known as Airborne long Range Input (ALRI) aircraft. This new integrated radar station on wings provides instantaneous automated relay of air defense surveillance and early warning information by data-link direct to ground based communication facilities. The 551st Wing flew their continuous missions over the Atlantic Ocean 24 hours a day. The Wing has flown thousands of missions totaling more than 300.000 flying hours since January 1955 without a single accident involving personal injury or a fatality. k5biz - www.bandconditions.com
The authors clearly acknowledge that the phenomenon is nothing new. What is novel is understanding the physics behind it. Perhaps we can predict such phenomenon now that we have a plausible explanation, which is something we probably couldn't do before.
