Effect of planetary boundary layer schemes on the development of intense tropical cyclones using a cloud‐resolving model

Abstract

We studied the role of the planetary boundary layer (PBL) in intensity and inner core structure of extremely intense tropical cyclones (TC) using a 2 km mesh nonhydrostatic atmospheric model (NHM2) developed for operational use by the Japan Meteorological Agency. To investigate the effects of the PBL on simulated TCs, we used four PBL schemes: level 2.5 and level 3 Mellor‐Yamada‐Nakanishi‐Niino closure schemes, a nonlocal scheme, and the Deardorff‐Blackadar scheme. The numerical results indicated that the subgrid‐scale mixing length determined by the PBL scheme plays a critical role in the determination of maximum TC intensity and inner core structure, even when the same expressions are provided for surface roughness lengths and the air‐sea momentum and heat transfer coefficients. Different vertical eddy‐diffusivity coefficient values derived from the PBL schemes cause differences in the TC intensity, inner core structure, and the relationship between maximum wind speed (MWS) and central pressure (CP). In particular, large vertical eddy diffusivities in lower layers (height <300 m) lead to large heat and water vapor transfers, resulting in extremely intense TCs accompanied by an upright, contracted eyewall structure. We also conducted numerical experiments using a 5 km mesh nonhydrostatic atmospheric model (NHM5) and the same PBL schemes to investigate the effect of horizontal resolution on simulated TCs. The NHM5 was insufficient to accurately represent the MWS or CP of an extremely intense TC, suggesting that NHM2 is required to simulate an extremely intense TC characterized by an upright, contracted eyewall structure.