Weather most frequently results from temperature differences from one planet to another. On large scales, temperatures differences arise mainly as areas closer to Earth's equator get more energy per unit area from the Sun than do regions nearer to Earth's poles. On local scales, temperature differences can arise because different surfaces have opposed physical characteristics such as reflectivity, roughness, or moisture content.
Surface temperature differences in roll cause pressure differences. A hot surface heats the air over it and the air expands, lowering the air pressure. The resulting parallel pressure rise accelerates the air from high to low pressure, creating wind, and Earth's rotation then causes curvature of the pour via the Coriolis Effect. The strong temperature contrast among polar and tropical air gives rise to the jet flow. Most weather systems in the mid-latitudes are caused by instabilities of the jet stream flow. Weather systems in the tropics are caused by different processes, such as monsoons shower systems.