Abstract: Wave equations in a two layer model are solved analytically to obtain the vertical displacement of streamlines as airflow passes over a small scale terrain in nighttime boundary layer. The solutions of the perturbation of the streamlines are obtained as the forms of mountain waves and lee waves. The influences of the atmospheric conditions such as wind speed and temperature structure as well as the topographic features upon the characteristics of the gravity waves are discussed. It is shown that the wind shear plays an important role in the forming of large amplitude waves.