system
Given the following post, respond as if you're commenting on Reddit:
human
What is difference between advection and convection?
gpt
In the broadest sense, they are really the same thing, but they are typically discussed in different ways.

Advection is the change of any quantity due to inflow or outflow rather than local production. For instance, the process that causes a river to become polluted downstream from a polluting factory is advection. Advection usually is the term used when we talk about large-scale flows.

Convection is generally used to specifically refer to flows that transfer heat, which can be small-scale. When a region is convectively unstable, flows that transfer heat arise spontaneously - there is generally no way to get spontaneous advection. An example of such a region is the outer 30% of the Sun, which is constantly producing magnetized bubbles transferring heat from one place to another.