Atmospheric waves associated with a valley of Lantau Island: observation, theory and numerical simulation

The LIDAR at the Hong Kong International Airport performs regular scanning across Tung Chung Gap, a valley with a height of about 370 m AMSL in the middle of Lantau Island. It reveals many interesting features of the airflow disrupted by this valley. This paper discusses two different kinds of waves in the cross-valley airflow, namely, stationary mountain wave in southeasterly flow and upstream propagating wave in northwesterly flow. These wave motions are found to compare well with numerical simulations and theoretical considerations, viz. three-layer linear wave model for the stationary wave, and soliton in a two-layer system for the upstream propagating wave.