Sensitivity of the Simulated Tropical Cyclone Intensification to the Boundary‐Layer Height Based on a K‐Profile Boundary‐Layer Parameterization Scheme

Abstract

AbstractThe sensitivity of simulated tropical cyclone intensification to the boundary‐layer height is investigated in this study, using the Yonsei University (YSU) scheme to parameterize boundary‐layer processes. Results reveal nonlinear effects of the boundary‐layer height on the intensification of simulated tropical cyclones. For shallow boundary layer (e.g., below 1,000 m), the storm intensification is sensitive to the depth of the boundary layer; decreasing the boundary‐layer height would lead to a progressive increase in the intensification. For deep boundary layer, the storm intensification is weakly affected by the boundary‐layer height. The roles of unbalanced processes are primarily responsible for these discrepancies. The frictional dissipation is confined in a relatively thin layer for shallow boundary layer, and decreasing the boundary‐layer height causes a larger extent of gradient wind imbalance and stronger radial inflow in the boundary layer. As a consequence, the unbalanced flow effects are more pronounced and contribute to a more rapidly intensifying tropical cyclone. The vertical mixing is intense in a deep boundary layer, resulting in weak unbalanced processes; therefore, further enhancing the boundary‐layer height has less appreciable influence on the tropical cyclone intensification than that in a shallow boundary layer. Increasing the boundary‐layer height has also consequences of drying and warming the lower part of the boundary layer while moistening and cooling the atmosphere aloft, which may be favorable for encouraging outer‐core convection activities. These results underscore the importance of accurately estimating the boundary‐layer height in a K‐profile boundary‐layer scheme for tropical cyclone simulations.