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The American Meteorological Society promotes the development and dissemination of information and education on the atmospheric and related oceanic and hydrologic sciences and the advancement of their professional applications. Founded in 1919, AMS has a membership of more than 14,000 professionals, ...
A line of constant potential temperature on a thermodynamic diagram.
In terms of pressure ''p'', and specific volume α, the equation for a dry adiabat may be written
<center>[[File:ams2001glos-De49.gif
Industry:Weather
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.
This lapse rate is ''g/c<sub>pd</sub>'', where ''g'' is gravitational acceleration and ''c<sub>pd</sub>'' is the specific heat of dry air at constant pressure, approximately 9.8°C km<sup>−1</sup>. Potential temperature is constant with height in an atmospheric layer with this lapse rate. 2. The adiabatic lapse rate of unsaturated air containing water vapor.
This differs from definition 1 by the factor
<center>[[File:ams2001glos-De50.gif
Industry:Weather
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.
This lapse rate is ''g/c<sub>pd</sub>'', where ''g'' is gravitational acceleration and ''c<sub>pd</sub>'' is the specific heat of dry air at constant pressure, approximately 9.8°C km<sup>−1</sup>. Potential temperature is constant with height in an atmospheric layer with this lapse rate. 2. The adiabatic lapse rate of unsaturated air containing water vapor.
This differs from definition 1 by the factor
<center>[[File:ams2001glos-De50.gif
Industry:Weather
A line of constant potential temperature on a thermodynamic diagram.
In terms of pressure ''p'', and specific volume α, the equation for a dry adiabat may be written
<center>[[File:ams2001glos-De49.gif
Industry:Weather
The frictional impedance offered by air to the motion of bodies passing through it. More precisely, the component of aerodynamic force parallel to the direction of mean flow.
At very low speeds, most of the drag exerted by the air on a body moving through it is due to viscous drag (or skin friction) acting through a fairly thin boundary layer. In the case of spheres, the low-speed air resistance is given by Stokes's law. For higher speeds, so-called form drag or pressure drag arises as a result of separation of the laminar boundary layer creating a wake region of chaotic flow in which the pressure is reduced. In general, for large Reynolds numbers, form drag is far more significant than viscous drag. The velocity dependence of air resistance changes more or less continuously from linear dependence in the viscous range to velocity-squared dependence at high speeds. The latter dependence is given by Rayleigh's formula,
<center>[[File:ams2001glos-De45.gif
Industry:Weather
A thermodynamic variable similar to potential temperature, except that the concept of static energy assumes that any kinetic energy is locally dissipated into heat.
The amount of this dissipative heating is often negligible. When dry static energy, s, is expressed in units of kJ kg<sup>−1</sup>, the resulting values are of order 300 kJ kg<sup>−1</sup>, which reinforces the analogy with potential temperatures in units of Kelvin. Dry static energy is conserved during unsaturated vertical and horizontal motion, and is defined as
<center>[[File:ams2001glos-De51.gif
Industry:Weather
A dimensionless ratio of the component of force parallel to the direction of flow (drag) exerted on a body by a fluid to the kinetic energy of the fluid multiplied by a characteristic surface area of the body.
In symbols, the drag coefficient ''C<sub>D</sub>'' is
<center>[[File:ams2001glos-De46.gif
Industry:Weather
In radar and radio propagation studies, a value for the radius of the earth that may be used in place of the actual radius to correct for refraction by the atmosphere.
The effective earth radius is a convenient fiction that makes straight the actual curved path of a radio ray in the atmosphere by presenting it relative to an imaginary earth with a radius larger than the radius of the real earth, thus maintaining the relative curvature between earth and radio ray. The effective earth radius ''R''<sub>e</sub> is approximately
<center>[[File:ams2001glos-Ee10.gif
Industry:Weather
These are the four mathematical/physical conditions used when integrating the fourth-order differential equations governing the Ekman layer.
These conditions are
<center>[[File:ams2001glos-Ee12.gif
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A dimensionless number relating the ratio of eddy viscous forces to Coriolis forces.
Explicitly, the vertical Ekman number is
<center>[[File:ams2001glos-Ee14.gif
Industry:Weather
