Damming-
The piling up, or complete blocking, of cold air approaching the slopes of a mountain barrier.
Deepening-
A decrease in the central pressure of a pressure system as depicted on a constant- height chart, or an analogous decrease in height on a constant-pressure chart; the opposite of filling.
Deformation-
The change in shape of a fluid mass by spatial variations in the velocity field, specifically by stretching or shearing.
Deliquescence-
The process of liquefaction of a solid by dissolution in solution resulting from absorbed water vapor.
Dendritic crystal-
A crystal, particularly a planar ice crystal, with its macroscopic form (crystal habit) characterized by intricate branching structures of a treelike nature.
Density-
1. The ratio of the mass of any substance to the volume occupied by it (usually expressed in kilograms per cubic meter, but any other unit system may be used); the reciprocal of specific volume.
Dependent variable-
Any variable considered as a function of other variables, the latter being called independent.
Deposition-
Processes by which traces gases or particles are transferred from the atmosphere to the surface of the earth.
Depression-
In meteorology, an area of low pressure; a low or trough.
Derecho-
A widespread convectively induced straight-line windstorm.
Desert wind-
A wind blowing from the desert.
Dew-
Water condensed onto grass and other objects near the ground, the temperatures of which have fallen below the dewpoint of the surface air due to radiational cooling during the night, but are still above freezing;
hoarfrost may form if the dewpoint is below freezing (see frost point).
Dewpoint-
The temperature to which a given air parcel must be cooled at constant pressure and constant water vapor content in order for saturation to occur.
Diffluence-
The rate at which adjacent flow diverges along an axis oriented normal to the flow at the point in question; the opposite of confluence.
Divergence-
The expansion or spreading out of a vector field; also, a precise measure thereof.
Doldrums-
A nautical term for the equatorial trough, with special reference to the light and variable nature of the winds.
Downburst-
An area of strong, often damaging winds produced by a convective downdraft over an area from less than 1 to 10 km in horizontal dimensions.
Downdraft-
Small scale downward moving air current in a cumulonimbus cloud.
Downslope wind-
A wind directed down a slope, often used to describe winds produced by processes larger in scale than the slope.
Drizzle-
Very small, numerous, and uniformly distributed water drops that may appear to float while following air currents.
Droplet-
A small spherical particle of any liquid; in meteorology, particularly a water droplet.
Dropsonde-
A radiosonde with a parachute dropped from an airplane carrying receiving equipment for the purpose of obtaining an upper-air sounding during descent.
Dry adiabat-
A line of constant potential temperature on a thermodynamic diagram.
Dry adiabatic lapse rate-
A process lapse rate of temperature, the rate of decrease of temperature with height of a parcel of dry air lifted by a reversible adiabatic process through an atmosphere in hydrostatic equilibrium.
Dryline-
A low-level mesoscale boundary or transition zone hundreds of kilometers in length and up to tens of kilometers in width separating dry air from moist air.
