advektsioon

Advektion is the transport of a quantity by the bulk motion of a fluid. In meteorology and oceanography it refers to the horizontal movement of properties such as heat, moisture, pollutants or salinity by winds or currents. Advection differs from diffusion (spreading due to gradients) in that it operates through the large-scale flow of the fluid rather than through mixing at small scales.

Mathematically, if φ(x,t) denotes a scalar field (for example temperature or specific humidity) and u(x,t) is the velocity field of the fluid, the advection term is u · ∇φ. The transport of φ can be written as a partial differential equation such as ∂φ/∂t + u · ∇φ = S, where S represents sources or sinks. For incompressible flow (∇ · u = 0) the more general form ∂φ/∂t + ∇ · (φ u) = S reduces to the advection term u · ∇φ when φ is materially conserved and there are no sources or sinks.

Common examples include heat advection (transport of thermal energy by the wind), warm air advection and cold air advection in weather forecasting, and moisture advection, which affects humidity and precipitation. In the oceans, advection transports salinity and temperature along currents.

Advektion is a fundamental mechanism in atmospheric and oceanic dynamics and is often analyzed alongside diffusion and convection. It is essential for predicting the movement of fronts, air masses, and pollutant plumes.