How does advection differ from convection?

Atmospheric and oceanographic sciences generally differentiate between vertical convection and horizontal advection. These disciplines study the atmosphere and the oceans which are both much wider in the horizontal than they are thick in the vertical. Making the distinction between horizontal (i.e. isopycnal, along surfaces of constant density) and vertical (i.e. diapycnal, through density surfaces) therefore makes sense for meteorologists and oceanographers.

In fluid mechanics on the other hand the terminology is often used interchangeably. Their study environment is frequently a tank in a laboratory and therefore is more of a cube compared to the thin oceanic layer on the Earth. In fluid mechanics, advection and convection is the same.