Observational Characteristics of the Boundary Layer during Tropical Cyclone Landfalls from the Boseong Tall Tower

The Boseong Tall Tower in South Korea is the second highest multi-level meteorological tower in Asia so that it can provide vertical profiles of lower planetary boundary layer (PBL). This makes it possible to investigate the characteristics of the lower PBL over land. Especially, it is useful when a tropical cyclone (TC) makes landfall because of difficulty in observations with sonde over land. Previous studies suggested that the track, intensity and structure of TC are influenced by turbulent process in the PBL and the parameterization of TC boundary layer used in the ocean might match with land poorly. Thus, it is important to understand the characteristics of PBL over land especially when TCs landfall for better TC prediction. In this study, the characteristics of PBL were examined with some landfalling TC cases by using data from the Boseong Tall Tower. According to our result, the depth of surface layer is not clearly represented by the log layer under the assumption of the near-neutral surface layer, implying that other assumptions could be required. Unlike some previous studies, fitted surface frictional speed (u_*s) increases a bit with the wind speed, while fitted roughness length (z₀) decreases with the mean wind speed. This suggests that the stronger surface wind speeds lead to a broader range of wind speeds, which may be affected by ocean surface features due to the proximity of the Boseong Tall Tower to the coastline. We also compare the vertical eddy diffusivity (K_m) measured by observation and parameterization of the Hurricane Weather and Research Forecast (HWRF) model, which shows that the parameterization in HWRF underestimates at higher levels and overestimates at lower levels.