Appleton layer CAT F layer Heaviside-Kennelly layer Olympian heights Van Allen belt acme aerial heights aerospace aerosphere air hole air pocket airspace apex belt bump ceiling chemosphere crosswind dizzy heights elevation eminence empty space ether favorable wind fog front head wind heaven heavens height heights high-pressure area hole ionosphere isothermal region jetstream layer lift low-pressure area lower atmosphere outer atmosphere overcast photosphere pocket raise rise rising ground roughness sky soup space steep stratum substratosphere tail wind tropopause troposphere trough turbulence upper atmosphere uprise vantage ground vantage point visibility visibility zero zenith