Observational study of waves in Hong Kong- Kelvin-Helmholtz waves and stationary mountain waves

Two observed cases of Kelvin-Helmholtz (K-H) waves in Hong Kong have been presented in this paper, based on radial velocity data of a Doppler light detection and ranging (LIDAR) system and from cloud observation. Analysis of atmospheric conditions under which the waves occurred was carried out using ground-based remote-sensing meteorological instrumentation data and simulations on a high-resolution numerical weather prediction (NWP) model. The calculated Richardson number profiles are supportive of the occurrence of K-H waves, while the model simulations for one of the cases reproduced the wave features quite well. The case studies suggest that the advancement of remote-sensing instruments and NWP models reveals the possibility to observe and analyze K-H waves in greater detail. On the other hand, many mountain wave cases near the Hong Kong International Airport (HKIA) are also studied in this paper, namely, the wave-like structure of Eddy dissipation rate, a mountain wave downstream of the terrain on the western side of Lantau Island, and a mountain wave extending to heights near the sea surface. Using the vertical profile of the Scorer parameter based on nearby radiosonde observations, these cases are likely to be stationary mountain waves. The success of NWP simulations in reproducing the mountain wave feature in these cases, however, was mixed. This points to the difficulty of real-time forecasting of mountain waves that may have operational implications for airport operations due to the disrupted airflow.