Cryosphere glossary
melt ponds
pools of melted snow and ice on the sea ice surface created during the summer melt.
Image
Scientist taking measurements in a melt pond.
Don Perovich, U.S. Army Cold Regions Research and Engineering Laboratory
meltwater conduit
a channel within, underneath, on top of, or near the side of a glacier that drains meltwater out of the glacier; usually kept open by the frictional heating of flowing water that melts the ice walls of the conduit.
mercury barometer
a mercury-filled glass tube in which the height of the mercury column is a measure of air pressure.
meridional circulation
an atmospheric circulation in a vertical plane oriented along a meridian; it consists of the vertical and the meridional (north or south) components of motion only.
mesopause
top of the mesosphere, situated at about 80-85 kilometers (50-53 miles).
mesosphere
the region of the atmosphere between about 50 kilometers (31 miles) and 80-85 kilometers (50-53 miles), extending from the top of the stratosphere to the upper temperature minimum; it is characterized by a broad temperature maximum (near 0 degrees Celsius) at its base, from which the temperature decreases to a minimum (about -90 degrees Celsius) at the mesopause level.
metamorphism
changes in the structure and texture of snow grains which result from variations in temperature, migration of liquid water and water vapor, and pressure within the snow cover.
meteorological element
any one of the properties or conditions of the atmosphere which together specify the weather at a given place for any particular time (for example, air temperature, pressure, wind, humidity, thunderstorm and fog).
meteorology
study of the atmosphere and its phenomena, including its structure, properties, and physical processes.
micro-scale polygon
closed, multi-sided, roughly equidimensional, patterned ground features, less than 2 meters (6.6 feet) in diameter; usually caused by desiccation cracking of fine-grained soil materials.
microwave sensors
in terms of wavelength, microwaves range from 1 millimeter to 1 meter, and are much longer than the shorter visible (0.38-0.78 micrometer) wavelengths; these longer wavelengths allow microwave energy to penetrate through clouds; because these sensors measure microwave energy, they do not rely on sunlight for illumination so they can acquire images regardless of time of day; can be either passive or active; passive sensors detect and record naturally upwelling microwave energy emitted from objects; active sensors generate their own beam of energy, generally with an antenna, which then detects the returned energy patterns (backscatter) that indicate the presence of features and their position relative to the sensor; radar (radio detection and ranging) was an original active microwave sensor that became widely operational with the onset of World War II.
middle-level clouds
clouds composed of ice crystals and water droplets in the middle region of the atmosphere, from 2,000 - 6,000 meters (6,500 to 23,000 feet); includes altocumulus, altostratus, nimbostratus, and portions of cumulus and cumulonimbus clouds.
minerogenic palsa
a palsa in which the frozen core extends below the peat into underlying mineral material.
mires
Also known as tundra mires, generally described as an area of wet, soggy, muddy ground., and often feature a layer of peat over permafrost.
mixed precipitation
precipitation consisting of a mixture of rain and wet snow; it usually occurs when the temperature of the air layer near the ground is slightly above freezing; the British term for this mixture is sleet (which has a different meaning in the United States).
moraine
a mound, ridge, or other distinct accumulation of glacial till.
Image
Lateral and terminal moraines of a valley glacier, Bylot Island, Canada. The glacier formed a massive sharp-crested lateral moraine at the maximum of its expansion during the Little Ice Age. The more rounded terminal moraine at the front consists of medial moraines that were created by the junction of tributary glaciers upstream.
Natural Resources Canada, copyright Terrain Sciences Division, Geological Survey of Canada
moraine shoal
glacial moraine that has formed a shallow place in water.
moulin
a nearly vertical channel in ice that is formed by flowing water; usually found after a relatively flat section of glacier in a region of transverse crevasses; also called a pothole.
mountain glacier
a glacier that is confined by surrounding mountain terrain; also called an alpine glacier.
Image
Taku Glacier winds through the mountains of southeastern Alaska, calving small icebergs into Taku Inlet. This photograph dates from 1929.
U. S. Navy, archived at the World Data Center for Glaciology, Boulder, CO
mountain permafrost
permafrost existing at high altitudes in high, middle, and low latitudes.