Differences in air pressure (vertical or horizontal) produce a pressure gradient. Pressure gradient force in the absence of other forces, air moves from high pressure to low pressure: steep pg (closely spaced isobars) indicate strong pgf. Because the earth rotates, the rotation directly results in a fictitious force called coriolis. Gustave de coriolis (1835: northern hemisphere deflects wind to the right, southern hemisphere deflects wind to the left. Below 1 km, wind is influenced by friction (three way balance: wind flows towards centre of a low and away from the high pressure centre. Sensible heat heat that you can feel. Latent heat stored as water vapour; heat absorbed as water evaporates, released as water condenses. One cell theory one large hadley cell, george hadley 1970s: air rises at the equator, moves poleward (towards the pole) and sinks at the pole, energy is transported as sensible heat and latent heat.