DEFINITION:

The process of transport of an atmospheric property by the velocity field of the atmosphere. In other words, the process by which a property of the atmosphere is transported by the wind.

In three-dimensional Cartesian coordinates, it is

-(u(dA/dx) + v(dA/dy) + w(dA/dz))

where u,v and w are the wind components in the eastward, northward and vertically upward directions and A is the atmospheric property under investigation.

Traditionally advection refers only to the horizontal components of motion whereas convection usally refeers to the vertical, locally induced motions.