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THICK.  MICROWAVE SIGNALS MAY BE REFRACTED BY A LAYER ONLY 100 FEET THICK.
WEATHER SYSTEMS AND TROPO THE MOST COMMON WEATHER SYSTEMS FORMING LONG
DISTANCE TROPO ARE STABLE ANTICYCLONIC HIGH PRESSURE SYSTEMS AND WAVE
CYCLONES.  STABLE HIGH PRESSURE SYSTEMS OCCUR IN LATE SUMMER AND EARLY
FALL.  THESE BRING THE MAJORITY OF LONG DISTANCE AND LONG DURATION TROPO
OPENINGS.  THESE HIGH PRESSURE SYSTEMS MAY STALL OUT OVER EASTERN NORTH
AMERICA, AND SOMETIMES A HURRICANE MAY BLOCK THEM FOR DAYS.  THE AIR IN A
HIGH PRESSURE SYSTEM SINKS TOWARDS GROUND IN A PROCESS CALLED SUBSIDENCE.
AS THE AIR IS FORCED DOWN, IT IS COMPRESSED, HEATED, AND DRIED.  THIS
CREATES LAYERS OF WARM, DRY AIR OVER COOL MOIST AIR AN INVERSION.
SUBSIDENCE THUS CREATES STRONG, STABLE INVERSIONS.  ACCORDING TO EMIL
POCOCK, W3EP, WHO WROTE THE ARTICLE, THE WEATHER THAT BRINGS VHF DX IN THE
MAY 1983 ISSUE OF QST, WAVE CYCLONES CAN ALSO CREATE TROPO.  THESE SYSTEMS
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