What causes differences in air pressure

Air flowing from zones of high pressure to zones of low pressure causes winds, just like the way air gushes from a punctured tire or balloon. Uneven heating and convection generate the pressure differences; the same tendencies create currents in a saucepan of water heating on a stove.

Due to the difference of temperature

Air pressure is the force exerted onto a surface by the weight of the air. Some variations in air pressure are due to temperature differences caused by variations in solar energy received at the surface of the earth.Wind results from a horizontal difference in air pressure and since the sun heats different parts of the Earth differently, causing pressure differences, the Sun is the driving force for most winds.  

it will increase due to the time span

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