View source for Mean underStorm Level

Mean underStorm Level, or MSL, is the altitude where the [[Understorm]] and the habitable zone of [[Azimuth|Azimuth's]] atmosphere meet. It is typically very narrow, sometimes no more than 30 ft, with terrific windshear often exceeding 50 knots. The level is taken as a datum from which all altitude is derived: heights above the boundary are expressed as '''Above Mean underStorm Level''' (eg. 1000 ft AMSL); while below they are termed as '''Neg'''ative altitudes (eg. Neg 500 ft). Where notation is not given, positive altitude is assumed.