| Section S | S index | 1161-1169 of 1376 terms |
|---|
|
substandard propagation—The propagation of radio energy under conditions of substandard refraction in the atmosphere; that is, refraction by an atmosphere or section of the atmosphere in which the refractive index decreases with height at a rate of less than 40 N-units per kilometer. Substandard propagation produces less than the normal downward bending, or even upward bending, of radio waves as they travel through the atmosphere, giving closer radio horizons and decreased radar and radio coverage. It occurs primarily when propagation takes place through a layer in which the specific humidity is constant or increases with height. See standard propagation, superstandard propagation.
|
|
subsun—A halo in the form of a bright white spot as far below the horizon as the sun is above it. The subsun is explained by reflection by the horizontal faces of oriented ice crystals (e.g., large hexagonal plates). Such crystals are never perfectly horizontal with the result that the shape of the subsun changes slightly with solar elevation, being circular for high suns and increasingly teardrop-shaped for low suns.
|
|
subsurface float—A centrally buoyant device, designed to drift at a specific depth below the water's surface, used to measure water velocity at that depth.
|
|
subsurface flow—All water flowing below the land surface, which may eventually (after a long time) contribute to base flow or become deep percolation.
|
|
subsurface storm flow—Part of the storm rainfall that flows below the land surface for a certain distance before eventually reaching the surface channel after a fairly short time.
|
|
subsurface water—Water in the lithosphere, that is, below the ground surface.
|
|
