بررسي تحليلي شارش هواي روي كوهستان

An analytical study of airflow over the mountains.

In this paper, atmospheric circulations caused by airflow over mountains and hills with different experimental setups are investigated. It is known that in a stable atmosphere the airflow over wide mountains makes the air parcels move in a wave like pattern in the vertical plane. First, the steady state of the momentum equation in the zonal and vertical directions, the thermodynamic and continuity equations are linearized, neglecting friction and rotation. Then combining the linearized equations into a Helmholtz type equation for the vertical velocity, W (or stream function, Cp) is solved using the Fourier transform method. The experiments are performed for one and two isolated mountain peaks with different heights and varying horizontal velocity and Scorer parameter using a one and two layer models. Results show that, if the Scorer parameter is larger in the lower layer then the airflow follows the shape of the mountain and associated troughs and ridges are deeper with increased mountain height and horizontal wind speed. Moreover, ascending and descending vertical motions are formed in the mountain side and leeward side with their cores located at around 3 km altitude. Their amplitudes are extended to higher levels up to 10 km.