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

Abstract

The 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.

Sensitivity of the Tropical Cyclone Boundary Layer to Vertical Diffusion in a Turbulent Kinetic Energy‐Based Boundary Layer Parameterization Scheme at Gray‐Zone Resolution

“…In addition, the results indicate a nonlinear role of vertical diffusivities in influencing TC intensity, which agrees with idealized TC simulations with K ‐profile‐based PBL parameterizations (Gopalakrishnan et al., 2013; Ma et al., 2018; Zhang et al., 2020). When the eddy diffusivities increased (200% and 400%), the intensification was sensitive to the eddy diffusivities.…”

“…However, because of the sparseness and limited availability of TCBL observational data, PBL parameterization is rarely developed for TCs. Thus, TC simulations are not only sensitive to the PBL parameterization scheme (Kanada et al., 2012; Nolan, Stern, et al., 2009; Nolan, Zhang, et al., 2009; Tang et al., 2018) but also to variations in the parameters of the scheme (Gopalakrishnan et al., 2013; Ma et al., 2018; Zhang et al., 2015, 2020). PBL parameterization relies heavily on key parameters, such as eddy diffusivity (scalar and momentum) to calculate the subgrid‐scale turbulent flux from the means of variables.…”

“…The impact of eddy diffusivity in PBL schemes on TCs has been actively studied in recent years (Gopalakrishnan et al., 2013; Ma et al., 2018; Xu & Zhao, 2021). For example, Gopalakrishnan et al.…”

An Investigation of the Impact of Different Turbulence Schemes on the Tropical Cyclone Boundary Layer at Turbulent Gray‐Zone Resolution

“…A combination of the value and height of maximum tangential wind in PBL schemes suggests that lower height of maximum tangential wind is accompanied with a more intense TC. This result is consistent with previous PBL schemes sensitivity studies (Braun & Tao, 2000) and PBL diffusivity studies (Gopalakrishnan et al, 2013;Ma et al, 2018;Zhang et al, 2015) made in tropical cyclone. It is possible that this difference in turbulence schemes is due to the different magnitude of PBL diffusivity. )…”

“…It is well‐known that the tropical‐cyclone boundary layer (TCBL) is crucial for the evolution of tropical cyclone (TC) intensity because of its important role in moisture and energy transfer between air and sea (Emanuel, 1995; Ma et al., 2018; Montgomery & Smith, 2014; Rotunno et al., 2009). However, the planetary boundary layer (PBL) is still one of the poorly understood parts of a TC (Green & Zhang, 2015a).…”