Impact of Changbai Mountain Topography on the Spring Fog over the Bohai Sea

Fog is a highly complex weather phenomenon influenced by numerous factors. This study aims to investigate the impact of Changbai Mountain topography on the formation and development of the spring fog in the Bohai Sea. From May 12 to 14, 2021, the Bohai region experienced a sea fog event. Utilizing the Himawari-8 satellite retrieval data, the European Centre for Medium-Range Weather Forecasts (ECMWF) 5th Generation ERA5 reanalysis dataset, land and sea station observations, the WRF model, the topography sensitivity experiment, and the backward trajectory tracking, a study was conducted to assess the influence of Changbai Mountain topography on the evolution of the Bohai sea fog. The results indicated that the Changbai Mountain topography significantly impacted the propagation and concentration of the Bohai sea fog through the dual effects of Venturi Effect and Foehn Clearance Effect. Comparative simulations incorporating and excluding the Changbai Mountain revealed that its topography favored weak convergence (Venturi Effect) of low-level airflow in the Bohai Sea induced by a high-pressure system, promoting westward fog expansion. Additionally, the backward trajectory further indicated that the Foehn Clearance Effect of Changbai Mountain extended its influence far beyond the immediate lee side, contributing to significant changes in atmospheric conditions such as reductions in relative humidity and increases in potential temperature. The dry, warm foehn contributed to a reduction in the liquid water content, ultimately leading to the weakening or even dissipation of the sea fog in the region close to Changbai Mountain. This study emphasizes the crucial role of Changbai Mountain topography in the development and evolution of fog, providing valuable insights for forecasting fog in complex terrain.