Aeronautical Terms beginning with M
Mammato cumulus
Obsolete. Now referred to as cumulonimbus mamma.
Mare’s tail
Irregularly curved wisps of cirriform clouds.
Maritime polar air (abbreviated mP)
Also called polar air. An air mass with characteristics developed over high latitudes, especially within the subpolar highs. Maritime polar (mP) initially possesses similar properties to those of continental polar air, but in passing over warmer water it becomes unstable with a higher moisture content.
Maritime tropical air (abbreviated mT)
Also called tropical air. An air mass with characteristics developed over low latitudes. Maritime tropical air (mT), the principal type, is produced over the tropical and subtropical seas; very warm and humid.
Maximum wind axis
On a constant pressure chart, a line denoting the axis of maximum wind speeds at that constant pressure surface.
Mean sea level
The average height of the surface of the sea for all stages of tide; used as reference for elevations throughout the U.S.
Measured ceiling
A ceiling classification applied when the ceiling value has been determined by instruments or the known heights of unobscured portions of objects, other than natural landmarks.
Median Volume Diameter (MVD)
The diameter such that half the liquid water in a region of cloud is contained in drops of a smaller diameter, and half in drops of a larger diameter.
Melting
The change of ice to liquid water.
Mercurial barometer
A barometer in which pressure is determined by balancing air pressure against the weight of a column of mercury in an evacuated glass tube.
Mesophere
A layer of the atmosphere directly above the stratosphere.
METAR
Aviation Routine Weather Report
Meteorological visibility
In U.S. observing practice, a main category of visibility which includes the subcategories of prevailing visibility and runway visibility. Meteorological visibility is a measure of horizontal visibility near the earth’s surface, based on sighting of objects in the daytime or unfocused lights of moderate intensity at night. Compare slant visibility, runway visual range, vertical visibility. Examples are surface visibility, tower visibility, and sector visibility.
Meteorology
The science of the atmosphere.
Microbarograph
An aneroid barograph designed to record atmospheric pressure changes of very small magnitudes.
Microburst
A strong downdraft which normally occurs over horizontal distances of 1 NM or less and vertical distances of less than 1,000 feet. In spite of its small horizontal scale, an intense microburst could induce windspeeds greater than 100 knots and downdrafts as strong as 6,000 feet per minute.
Millibar (abbreviated mb.)
An internationally used unit of pressure equal to 1,000 dynes per square centimeter. It is convenient for reporting atmospheric pressure.
Mist
A popular expression for drizzle or heavy fog.
Mixed Ice.
Simultaneous appearance of rime and clear ice or an ice formation that has the characteristics of both rime and clear ice.
Mixing ratio
The ratio by weight of the amount of water vapor in a volume of air to the amount of dry air; usually expressed as grams per kilogram (g/kg).
Moderate Icing
The rate of ice accumulation requires frequent cycling of manual deicing systems1 to minimize ice accretions on the airframe. The rate of accumulation is such that anything more than a short encounter is potentially hazardous. A representative accretion rate for reference purposes is 1 to 3 inches (2.5 to 7.5 cm) per hour4 on the outer wing.5
Moist-adiabatic lapse rate
Saturated-adiabatic lapse rate—The rate of decrease of temperature with height as saturated air is lifted with no gain or loss of heat from outside sources; varies with temperature, being greatest at low temperatures.
Moisture
An all-inclusive term denoting water in any or all of its three states.
Monsoon
A wind that in summer blows from sea to a continental interior, bringing copious rain, and in winter blows from the interior to the sea, resulting in sustained dry weather.
Mountain wave
A standing wave or lee wave to the lee of a mountain barrier.
MTOS
Mountain Obscuration
MWA
Mountain Wave Activity
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