| Section A | A index | 211-219 of 917 terms |
|---|
|
advection—The process of transport of an atmospheric property solely by the mass motion (velocity field) of the atmosphere; also, the rate of change of the value of the advected property at a given point. Advection may be expressed in vector notation by  where u is the wind vector, φ the atmospheric property, and ∇φ the gradient of the property. In three-dimensional Cartesian coordinates, it is  where u, v, and w are the wind components in the eastward, northward, and vertically upward directions, respectively. The first two terms compose the horizontal advection and the last term is the vertical advection. Also, it should be noted that the property φ may itself be a vector field. Often, particularly in synoptic meteorology, advection refers only to the horizontal or isobaric components of motion, that is, the wind field as shown on a synoptic chart. Regarding the general distinction (in meteorology) between advection and convection, the former describes the predominantly horizontal, large-scale motions of the atmosphere, while convection describes the predominantly vertical, locally induced motions. In oceanography, advection refers to the horizontal or vertical flow of seawater as a current.
|
|
advective change of temperature—The contribution to local temperature change that is caused by the horizontal or vertical advection of air. The horizontal component of change, usually the most important in the troposphere, is proportional to the horizontal temperature gradient and the magnitude of the component of the wind in the direction of the gradient. The vertical component is proportional to the vertical velocity and the static stability and depends also on whether the air is saturated.
|
|
advective-gravity flows—A type of cold-air downslope flow at the bottom of the boundary layer where the two dominant processes are advection and buoyancy. Once fully developed, this idealized flow is constant in time as long as cold air is supplied or produced. Wind speed increases with the square root of downslope distance, and flow depth increases linearly with distance. Typical depths are 2–10 m. See katabatic wind, slope flow, gravity flow, drainage wind.
|
|
advective model—A numerical forecast model based on discrete advection terms only, with less or no emphasis on forcing, dissipation, and physics. Advective models are most appropriately applied to nearly conserved quantities in the atmosphere or ocean, such as potential vorticity. Advective models are usually for one level only, or for a vertically integrated fluid. Historically, the barotropic model has been remarkably successful given its simplicity. A more recent example of an advective model is the divergent anomaly vorticity advection model.
Qin, J., and H. M. van den Dool, 1996: Simple extensions of an NWP model. Mon. Wea. Rev., 124, 277–287.
|
|
advective region—(Obsolete; also called advection region, advection layer, advective layer.) The region of the atmosphere just above the tropopause, that is, the stratosphere. This term arose from the fact that this part of the atmosphere is relatively more stable than the troposphere, so that temperature changes at a point in it occur primarily by means of advection rather than by convection.
|
|
advective thunderstorm—A thunderstorm resulting from instability produced by advection of relatively colder air at high levels, or relatively warmer air at low levels, or by a combination of both conditions.
|
|
