气象模式术语与介绍

内容来自AMS-Glossary of Meteorology

• hydrostatic equation
  The form assumed by the vertical component of the vector equation of motion when all Coriolis, earth curvature, frictional, and vertical acceleration terms are considered negligible compared with those involving the vertical pressure force and the force of gravity.
  For cyclonic-scale motions the error committed in applying the hydrostatic equation to the atmosphere is less than 0.01%. Strong vertical accelerations in thunderstorms and mountain waves may be 1% of gravity or more in extreme situations.
• hydrostatic equilibrium
  The state of a fluid with surfaces of constant pressure and constant mass ( or density) coincident and horizontal throughout.
  Complete balance exists between the force of gravity and the pressure force. The relation between the pressure and the geometric height is given by the hydrostatic equation. The analysis of atmospheric stability has been developed most completely for an atmosphere in hydrostatic equilibrium.
• hydrostatic approximation
  The assumption that the atmosphere is in hydrostatic equilibrium.
  Same as quasi-hydrostatic approximation.
  An approximation in geophysical fluid dynamics that is based on the assumption that the horizontal scale is large compared to the vertical scale, such that the vertical pressure gradient may be given as the product of density times the gravitational acceleration.
• nonhydrostatic model
  An atmospheric model in which the hydrostatic approximation is not made, so that the vertical momentum equation is solved.
  This allows nonhydrostatic models to be used successfully for horizontal scales of the order of 100 m, resolving small-scale mesoscale circulations such as cumulus convection and sea-breeze circulations. In recent years, computer power has made mesoscale weather prediction with nonhydrostatic models feasible, and several such models are in routine use by major meteorological modeling groups and operational centers.
• anelastic approximation
  An approximate system of equations for deep and shallow atmospheric convection.
  The equations are derived under the assumptions that the percentage range in potential temperature is small and that the timescale is set by the Brunt–Väisälä frequency. Acoustic waves are thereby filtered—hence the term anelastic, meaning elastic energy is not allowed. If the vertical scale of motion is small compared to the depth of an adiabatic atmosphere, the anelastic equations reduce to the Boussinesq equations for shallow convection.
• potential temperature
  The temperature that an unsaturated parcel of dry air would have if brought adiabatically and reversibly from its initial state to a standard pressure, p_0, typically 100 kPa.
• adiabatic atmosphere
  (Or dry-adiabatic atmosphere; also called convective atmosphere, homogeneous atmosphere.) A model atmosphere characterized by a dry-adiabatic lapse rate throughout its vertical extent.
  Such a condition is never observed and is also rather poorly designated, since “adiabatic” represents a process, not a condition.
• homogeneous atmosphere
  A hypothetical atmosphere in which the density is constant with height.
  The lapse rate of temperature in such an atmosphere is known as the autoconvective lapse rate and is equal to g/R (or approximately 3.4°C/100 m), where g is the acceleration of gravity and R is the gas constant for air. A homogeneous atmosphere has a finite total thickness that is given by RdTv/g, where Rd is the gas constant for dry air and Tv is the virtual temperature (K) at the surface. For a surface temperature of 273 K, the vertical extent of the homogeneous atmosphere is approximately 8000 m. At the top of such an atmosphere both the pressure and absolute temperature vanish.
• source
  In hydrodynamics, a point, line, or area at which mass or energy is added to a system, either instantaneously or continuously. Conversely, a sink is a point where mass or energy is removed from the system.
  An incompressible fluid will possess sources or sinks of mass only at points where the divergence of its velocity vector is nonzero; a source is associated with positive divergence and a sink with negative divergence (convergence). The fluid is usually assumed to pass outward from a source or inward to a sink equally in all directions along radial lines.
• sink
  A route or reservoir by which a measurable quantity may exit a system, such as by accumulation (in a reservoir) or chemical conversion.
• incompressible fluid
  A fluid in which the density remains constant for isothermal pressure changes, that is, for which the coefficient of compressibility is zero.
  Expansion and contraction of an incompressible fluid under diabatic heating or cooling is thus allowed for. In the more usual problem of isothermal processes, the fluid may or may not be stratified (have density differences within it), but motion of a parcel from higher to lower pressure or vice versa will not change the density of that parcel. Stated mathematically, the density gradient ∇ρ and the local derivative ∂ρ/∂t may not be zero, but the individual derivative Dρ/Dt vanishes. By the equation of continuity, it follows that the total divergence vanishes:
• heterogeneous fluid
  A fluid in which the density varies from point to point.
  For most purposes, the atmosphere must be treated as heterogeneous, particularly with regard to the decrease of density with height.

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