[Ref Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25B Page 12-7, ISBN978-1-56027-901-3]
Before we learn the definition of wind, please help ourselves to remember than wind has at least two component:
- wind SPEED
- wind DIRECTION
Okay, so what cause wind?
Uneven heating causes change in (air) density, which results in pressure gradients.
Due to uneven heating as well as the pressure gradients, the differences in pressure try to equalize through the flow of air molecules. This movement cause wind.
Notes: air always seeks out lower pressure – air tends to flow from area of high pressure into areas of low pressure.
Pressure gradient force (PGF) is proportion to the pressure gradient
Therefore, the greater the pressure gradient, the higher the PGF, and the stronger the wind
Uneven heating → pressure gradients PGF Wind (horizontal motion)
Wind (horizontal motion) is only one of the two atmospheric motion.