Gravity waves are not something outside your daily experience. Have you ever watched the wake that forms behind a boat? The waves you see gravity waves. Every noticed the clouds which form in regular bands of cloud and clear sky? These clouds are the result of gravity waves. Gravity waves carry momentum and energy from the troposphere to the middle and upper atmosphere. The gravity waves cause a "drag" on the polar front jet stream, which affects the development of cyclones and anticyclones and thus, the weather on the surface. Gravity waves can also modify the behaviour of the tides in the middle atmosphere and are responsible for the large departure of the middle atmosphere from radiative equilibrium.