Magnetic Field / Geomagnetic field

Description of the strength of the magnetic force exerted by an object. Field of force created as a result of the movement of electric charges. The intensity of a magnetic field is measured in Gauss (G) or Tesla (T). The flux decreases with distance from the source that causes the field. The Earth has a substantial magnetic field.

Magnetic Field Lines

Lines of force that trace the flow of charged particles within the magnetic field. Field lines converge where magnetic force is intense and spread out where it is weak. The behavior of field lines in the Earth’s magnetic field is similar to the one in a compact bar magnet, where field lines spread out from one pole and converge towards the other, being magnetic force strongest near the poles where they come together. In the space, magnetic field lines are basic to the way free electrons and ions move. These electrically charged particles tend to attach to the field lines, spiraling around them while sliding along them; so the behavior of plasma is determined by the structure of field lines.

Magnetic storm

Worldwide disturbance of the Earth’s magnetic field. With a sudden beginning, the magnetic field suffers marked changes in a short lapse, and then gradually conditions return back to normalcy. When sever enough, magnetic storms may interfere the operations of power lines and satellites. The exact linkage between solar and terrestrial disturbances remains uncertain, but they are known to be caused by solar disturbances.


Region of rarefied ionized gas in which dynamical motions of electrons and ions are conditioned or even determined by the Earth’s magnetic field. It extends from an altitude of about 60 miles (100 km) to the magnetopause or outer boundary that marks the beginning of the interplanetary space.


Outer layer of the Earth’s structure, between crust and core. It has a depth of 1800 miles (2900 km) and it is composed of solid rocky material, largely substances rich in iron and magnesium.

Maunder Minimum

Period from early 17th Century to early 18th Century, when apparently, sunspot activity would have ceased. This period correspond to what is known as the Little Ice Age, the coldest years of recent history.

Mean temperature

Average temperature of the air as indicated by a thermometer during a given period, a day, a month or a year. For climatological purposes, it is calculated for each month and for the year.


Looping changes of direction of a stream.

Medieval Climatic Optimum

Unusually warm period in history, much warmer than present, lasting from the 10th to about the 14th Century, whose maximum took place around A.D. 1200.

Medium-range forecast

Forecast for a period extending from 3 to 10 days in advance; limits to the period embraces are not absolute.


Top of the mesosphere, limiting with the thermosphere, located at heights of 53-60 miles (85-95 km).


Region of the atmosphere lying above the stratosphere, between the stratopause (30 miles / 50 km of height) and the mesopause (53-60 miles / 85-95 km of height). In this atmospheric layer, temperature decreases with altitude.


Any phenomenon observed in the air or on the earth’s surface, consisting of a suspension, or precipitation or a deposit of aqueous (hydrometeors) or non-aqueous or solid particles (lithometeors), optical phenomena (optical meteors) or electrical manifestations (electrometeors).

Meteorological drought

Kind of drought that is defined by comparing the rainfall in a particular place and at a particular time with the average rainfall for that place. It is the amount of dryness and the duration of the dry period.


Study of the Atmosphere and its phenomena.

Middle cloud / Middle level cloud, medium level cloud

Type of cloud of the medium cloud étage. Typically, altocumulus.

Mid-Holocene Thermal Maximum

Warm climate period, about 5000 years ago.


Image formed in the atmosphere of distant objects by optical refraction. Objects appear to be displaced from their true position. Normally, they are seen close to the horizon, including also image distortions. They can be steady or wavering, single or multiple, upright or inverted, vertically reduced or enlarged.

Mirror point

Point in the magnetosphere where the spiral which a particle is describing around a field line is flattened and then unwinded again in the opposite direction.


Result of irregular fluctuation in fluid motions on all scales, from the molecular to large eddies.

Mixing Height

Thickness of the mixed layer (layer mixed by convection or frictionally-induced turbulence or both) defined as the location of a capping temperature inversion or statistically stable layer of air. It is the mean distance of travel, characteristic of a particular motion and over which an eddy maintains its identity.

Mixing ratio

Ratio of the mass of water vapor molecules within an air parcel, to the mass of all other gases in that sample.

Model Output Statistics (MOS)

Forecasting method used in numerical weather prediction model, consisting of statistical relations between parameters of a numerical model-forecast and locally observed weather variables, taking account of local climate and biases in the model. It is used for correction of model-forecast variables or for prediction of variables not explicitly contemplated by the model.

Moist adiabatic lapse rate

Rate of temperature decrease in a saturated air parcel, which is rising. Typical values oscillate from 4° C to 7° C per kilometer.


Water vapor content of the atmosphere. Same as Humidity. Total water substance present in a given volume of air. Specifically, in climatology, it may refer to quantities of precipitation or precipitation effectiveness.

Monostatic radar

Radar configuration by which the receiver is at the same location as the radar transmitter; it is the most common one.


Wind characterized by a seasonal persistent wind direction and by a ostensible change in direction from one season to the other. The primary cause of this kind of wind is the differential heating of land and sea that is continent and the adjacent waters, which causes a pressure deficit over continents in summer and an excess of pressure in winter, determining therefore the direction in which the wind will be blowing. Other factors besides temperature difference may have a considerable effect. Monsoons are typical of south and eastern Asia but they can occur on other coasts where the planetary circulation is not intense enough to inhibit their formation.

Mountain-valley wind system

System of diurnal winds (mesoscale circulation) which develops in mountainous terrains, blowing along the axis of a valley, upvalley and uphill during the day and downvalley and downhill during the night, resulted from the combination of diurnal heating and cooling with topography. Usually, this kind of wind prevails in clear and calm conditions.

MST (Maritime Surface Temperature)

Temperature of the water film at sea surface. Generally, MST or sea surface temperature (SST) refers to the temperature of the water at one meter below the sea surface.

Mudslide / Mud sliding

Slide of a large mass of mud, eventually with dirt and rocks, down a mountain or cliff.

Multicell thunderstorm

Thunderstorm that consists of two or more cell, often visible at a given time as different domes or towers in various stages of development.