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Benjamin C. Trabing, Michael M. Bell, and Bonnie R. Brown

complexities of the real atmosphere make diagnosing the impact of individual PI parameters very difficult. In this study, we employ a high-resolution, three-dimensional, full-physics model on a “weather” time scale of 8 days to diagnose the physical mechanisms behind why changing upper-tropospheric temperatures modify TC intensification, and to investigate the use of PI theory in understanding TC maximum intensity on weather time scales. One potential mechanism by which a colder upper

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Jonathan Martinez, Michael M. Bell, Robert F. Rogers, and James D. Doyle

1. Introduction Accurate forecasts of tropical cyclone (TC) intensity changes remain one of the most difficult weather predictions, even for short lead times. This is in part due to multiscale interactions, which require operational forecast models to precisely capture the evolution of the atmosphere over a vast range of scales in the vicinity of a TC. DeMaria et al. (2014) demonstrated that although intensity forecast errors have not improved as much as track forecast errors over the past

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Nannan Qin and Da-Lin Zhang

evident in the planetary boundary layer (PBL), where radial inflows are peaked. In addition, Xu and Wang (2015) found that TC intensification rate is negatively and positively correlated with the RMW and storm intensity (i.e., V MAX ), respectively. The highest RI tends to occur when the RMW is less than 40 km with V MAX of about 40 m s −1 . Although little progress has been made in operationally predicting the RI of TCs, cloud-permitting simulations of some rapidly intensifying TCs, such as

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Russell L. Elsberry, Eric A. Hendricks, Christopher S. Velden, Michael M. Bell, Melinda Peng, Eleanor Casas, and Qingyun Zhao

) field. Model dynamics will then adjust the mean and asymmetric wind fields, which in the lower model levels will take into account the planetary boundary layer frictional effects and enthalpy fluxes. Whereas these internal adjustments will determine the intensity change, the TC vortex dynamics and physics prediction are expected to also improve the interaction between the vortex and its environment in conjunction with the better depiction of the outflow jets from the high temporal and spatial

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Xu Lu and Xuguang Wang

simulated maximum intensity in both the idealized and the operational HWRF. On the other hand, Bryan and Rotunno (2009b) found in the axisymmetric model that the maximum intensity of storms is insensitive to vertical diffusivity. Zhu et al. (2018) found that there was an unrealistic discontinuity of vertical diffusion near the boundary layer top in the HWRF planetary boundary layer (PBL) scheme applied in the HWRF Model (e.g., Fig. 1 ). This parameterization of vertical diffusivity K m was

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William A. Komaromi and James D. Doyle

to systematically explore the effect of modifying the environmental inertial stability and the resulting effect on the strength, structure, and direction of the storm outflow. Last, predictability issues associated with TC intensity change and the relative positions of the TC and the trough will be investigated. 2. Methodology a. Numerical model configuration The numerical simulations in this study are performed using the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) for Tropical

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Patrick Duran and John Molinari

of the background environment. More recent literature (e.g., Wirth 2003 ) has noted that strong, shallow temperature inversions immediately above the cold-point tropopause are a common feature in the tropics, now known as the tropopause inversion layer (TIL). On the planetary scale, TIL formation and maintenance has been tied to planetary wave dynamics ( Grise et al. 2010 ) and vertical gradients of radiative heating across the tropopause ( Randel et al. 2007 ), but the relative contributions of

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Jie Feng and Xuguang Wang

and Pan 2006 ), and the Ferrier–Aligo microphysics scheme ( Ferrier 1994 , 2005 ), 2) the modified surface layer ( Kwon et al. 2010 ) and nonlocal planetary boundary layer ( Hong and Pan 1996 ) parameterization schemes, and 3) the Eta Geophysical Fluid Dynamics Laboratory (GFDL) longwave and shortwave radiation schemes ( Schwarzkopf and Fels 1991 ; Lacis and Hansen 1974 ). Note that the SAS cumulus scheme is only implemented for the outer two domains (i.e., 18- and 6-km grids), but not for the

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Yi Dai, Sharanya J. Majumdar, and David S. Nolan

boundaries are periodic while free-slip boundary conditions are used on the northern and southern boundaries. Both radiation and cumulus parameterizations are not used in the model. The Yonsei University (YSU) scheme ( Hong et al. 2006 ) is used for the planetary boundary layer; the WRF 5-class scheme (WSM5; Hong et al. 2004 ) is adopted for the microphysics parameterization. The initial TC is a modified Rankine vortex with a peak tangential wind speed of 20 m s −1 at the radius of maximum winds (RMW

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