Advection is the horizontal transport of an atmospheric property (heat, moisture, vorticity, pollutants) by wind movement. It is distinguished from convection, which is vertical transport. It is one of the most important processes in meteorology because it determines how atmospheric conditions at a location change when air masses with different properties arrive.
Types of advection
- Warm advection: wind transporting warmer air into a region. Detected when isotherms cross wind vectors such that warmer air advances. It favours air ascent (warm air rises over cold) and the formation of clouds and precipitation.
- Cold advection: wind transporting colder air. It generates instability (cold air undercuts warm air) and is the main cause of post-frontal showers and cumulus skies.
- Moisture advection: transport of water vapour, fundamental for feeding precipitation systems like Mediterranean DANAs.
On weather maps, advection is estimated by analysing the angle between the wind and the isotherms (or lines of equal humidity). Numerical models calculate advection at every grid point to predict how temperature, humidity, and wind fields evolve.
For Spain, warm Saharan advection is responsible for the most severe heat waves, while cold polar advection causes winter frost and snow episodes. Moisture advection from the Mediterranean feeds torrential rains on the coast. See also: vorticity, cold front, air mass.