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Mesaverde Group
Mesaverde Formation (Mesaverde Group), Upper Cretaceous sandstone, shale, and coal unit along the Western Interior Seaway margin, first named 1875-1877 at Mesa Verde, Colorado; raised to group rank in several basins and a major tight-gas target in Wyoming, Utah, and Colorado.
Mesoarchean
The Mesoarchean is the third of four Archean Eon eras, spanning 3200 to 2800 million years ago, an interval that records the stabilization of the first large cratons.
Mesocyclone
A mesocyclone is a storm-scale region of cyclonic rotation, typically 2 to 6 miles in diameter, found in the right rear flank of a supercell thunderstorm and defined by a Doppler radar rotation signature.
Mesoscale convective system
A mesoscale convective system (MCS) is an organized grouping of thunderstorms acting as a single system, spanning thousands of square kilometers and persisting for several hours or more.
Mesoscale eddy
A mesoscale eddy is a rotating body of ocean water, typically 10 to 100 km across, that drifts for weeks to over a year carrying heat and salt.
Mesosphere
The mesosphere is the third layer of Earth's atmosphere, between the stratosphere and thermosphere at about 50 to 80 kilometers, where most meteors burn up.
Mesovortex
A mesovortex is a strong, long-lived, low-level vortex a few kilometers wide that forms in quasi-linear convective systems such as squall lines and bow echoes, and spawns most of their tornadoes.
Mesozoic
The Mesozoic Era, informally the Age of Reptiles, spans 251.9 to 66.0 million years ago and comprises the Triassic, Jurassic, and Cretaceous periods, when dinosaurs dominated the land.
Messinian
The Messinian is the last age and stage of the Miocene, from 7.251 to 5.333 million years ago, named after Messina, Sicily, and known for the Messinian salinity crisis.
Met Office
The Met Office, formally the Meteorological Office, is the United Kingdom's national weather service, founded in 1854 by Robert FitzRoy of HMS Beagle to improve safety at sea.
Met Office Hadley Centre
The Met Office Hadley Centre is the United Kingdom's primary source of climate change information and one of the world's principal climate research institutes, founded in 1990 as part of the Met Office.
Metal factor (geophysics)
The metal factor (MF) is an induced polarization parameter in geophysics, defined as percent frequency effect or chargeability divided by resistivity, with units of conductivity.
Metamorphic core complex
A metamorphic core complex is a domal geological structure where deep metamorphic and granitic rocks are brought to the surface by extension on a low-angle detachment fault.
Metamorphic facies
A metamorphic facies is a set of mineral assemblages that characterizes a range of pressure and temperature conditions during metamorphism, a concept introduced by Finnish geologist Pentti Eskola in 1915.
Metamorphic grade
Metamorphic grade is the relative intensity of metamorphism recorded in a rock, used as a qualitative proxy for metamorphic temperature; index minerals such as garnet and staurolite mark increasing grades.
Metamorphic rock
Metamorphic rock, or metamorphosed rock, forms when heat, pressure, or hot fluids transform pre-existing rock in the solid state deep in the crust, producing rocks such as marble, slate, schist, and gneiss.
Metamorphism
Metamorphism is the geological process that changes pre-existing rocks in mineralogy and texture through heat, pressure, and fluids, without melting them, deep in the Earth's crust.
METAR
METAR, short for Meteorological Aerodrome Report, is a coded hourly report of surface weather at an airport, covering wind, visibility, clouds, temperature, and altimeter setting.
Metasomatism
Metasomatism is the transformation of a rock's chemical composition through reactions with infiltrating fluids, distinguishing it from metamorphism and forming skarns and many ore deposits.
Météo-France
Météo-France is the French national meteorological service, a public establishment created in 1993 and headquartered in Toulouse, which issues forecasts and warnings for France and its overseas territories.
Meteorological reanalysis
Meteorological reanalysis is a method that reprocesses historical weather observations through a fixed, unchanging numerical weather prediction system, yielding consistent gridded estimates of past atmospheric states.
Meteorological Service of Canada
The Meteorological Service of Canada, founded in 1871, is Canada's federal agency for weather forecasts, warnings, and climate information, operating within Environment and Climate Change Canada.
Meteorologist
A meteorologist, also known as a weather forecaster, is a physical scientist who observes, studies, or forecasts the weather, typically holding a degree in meteorology or a related physical science.
Meteorology
Meteorology is the science of the Earth's atmosphere and its physical processes; modern weather forecasting rests on numerical weather prediction, a global observing system, and machine-learning models.
Meteosat Third Generation
Meteosat Third Generation (MTG) is a European system of geostationary weather satellites developed by ESA and operated by EUMETSAT to image weather over Europe and Africa.
Meteotsunami
A meteotsunami is a tsunami-like series of ocean waves generated by fast-moving atmospheric pressure disturbances rather than earthquakes or landslides, known regionally as the rissaga in the Balearic Islands.
Methane capture
Methane capture is the interception of methane before it reaches the atmosphere, from landfills, anaerobic digesters, coal mines, or leaking fossil fuel infrastructure, followed by flaring or use as fuel.
MetOp-C
MetOp-C is a European weather satellite launched on a Soyuz rocket from Kourou in 2018, the third and final satellite of the first-generation EUMETSAT Polar System.
MetOp-SG
MetOp-SG (Metop Second Generation) is a series of six European polar-orbiting weather satellites serving weather forecasting and climate monitoring into the 2040s, with the first launched in August 2025.
Mica
Mica is a group of 37 layered silicate minerals whose perfect cleavage lets crystals split into thin, flexible sheets used for electrical insulation and cosmetics.