Question

air masses move based on what

Answer 1

Primarily by winds, which themselves form because of pressure and temperature differences. Key factors:

- Pressure gradient force: air moves from high pressure toward low pressure (this is the basic driver).
- Coriolis effect (Earth’s rotation): moving air is deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, so winds are steered rather than flowing straight from high to low.
- Friction at the surface: slows winds and causes them to cross isobars into lows and out of highs; above the surface friction is negligible and winds more closely follow pressure contours (geostrophic flow).
- Upper-level steering (jet streams and upper winds): strong winds aloft steer large air masses and weather systems.
- Temperature contrasts and fronts: differences in temperature/density drive movement and formation of fronts; warm air tends to rise and be advected over colder air, etc.
- Geography/topography: mountains, coastlines and land/sea temperature differences redirect and modify air-mass movement.

Example: mid-latitude weather systems generally move eastward with the westerlies because of the combined action of pressure gradients and the jet stream. If you want, I can show a simple diagram or explain how this works differently in the tropics vs. mid/high latitudes.