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David R. Ryglicki, Daniel Hodyss, and Gregory Rainwater

the flow upwind of the convective cell and causing sinking. They noted ( Klemp and Wilhelmson 1978 , p. 1105), “The weak downdraft to the west of the updraft z = 2.25 km ([their] Fig.12) is possibly due to blocking westerly flow by the storm forcing the approaching air to descend rather than flow around the storm.” Fritsch and Maddox (1981) , in their analyses of upper-level observations of mesoscale convective complexes (MCC), noted the presence of mesohighs above the MCCs. While their

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Jie Feng and Xuguang Wang

–pressure relationship of TC vortices approximately satisfies the gradient wind balance. In this subsection, we evaluate the impact of increasing resolution during DA on wind–pressure relationship in the analyzed vortices for an initial-hurricane case. The metric used is the net radial force field F as defined by Smith et al. (2009) , Pu et al. (2016) , and Lu and Wang (2019) . A closer-to-zero value of F indicates a better approximation to the gradient wind balance. Figure 10 shows the net radial force

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

-mean tangential winds (RMW) of 90 km. It also has a Gaussian-like decay in the vertical with the maximum wind speed at z = 1500 m. The environmental shear profile and how it is introduced in the model are described below. b. Time-varying point-downscaling method The large-scale environmental shear is incorporated into the model using the point-downscaling method (PDS; Nolan 2011 ). Using PDS, the initial environmental flow is balanced by an artificial force that is added to the momentum equation so that

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Patrick Duran and John Molinari

therein. Since ocean coupling and asymmetric forcing are present in nature, the intent of this paper is not to formally simulate Hurricane Patricia. Rather, the intent is to simulate a storm with a similar intensification rate and to examine the processes that produced the stability variations in the simulated storm. After an initial spinup period of about 20 h, the modeled storm ( Fig. 1 , blue lines) began an RI period that lasted approximately 18 h. After this RI, the storm continued to intensify

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David R. Ryglicki, James D. Doyle, Yi Jin, Daniel Hodyss, and Joshua H. Cossuth

internally to CM1r18 was not used, in part for simplicity to remove any diurnal forcing and since the current domain, roughly 6000 km × 4000 km, is very large. In lieu of a diurnally varying radiation forcing, the simulations were carried out with Newtonian cooling capped at 2 K day −1 . To calculate the respective simulated brightness temperatures—both IR and WV—the CM1 output was passed to the Community Radiative Transfer Model (CRTM; Van Delst 2013 ; Grasso et al. 2008 ; Bikos et al. 2012 ; Jin et

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Xu Lu and Xuguang Wang

analysis of Patricia are presented in Part II. To further diagnose the differences among NoDA, VM, and DA, the gradient wind balance (GWB) relationship within each experiment is investigated. Following Smith et al. (2009) , a net radial force (NRF) field defined as the difference between the local radial pressure gradient force and the sum of centrifugal force and Coriolis force is used to describe the GWB relationship. This NRF is calculated on the pressure coordinates following Pu et al. (2009

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Robert G. Nystrom and Fuqing Zhang

between large-scale forcing (e.g., rising branch of the Madden–Julian oscillation and deep convection coupled with a Central American gyre) and mesoscale processes including a localized gap wind event ( Kimberlain et al. 2016 ; Bosart et al. 2017 ). Patricia reached tropical storm intensity 18 h after becoming a tropical depression, eventually becoming a hurricane 24 h later, near 0000 UTC 22 October. At this time, Patricia was located in a very favorable environment with anomalously warm ocean

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David R. Ryglicki, James D. Doyle, Daniel Hodyss, Joshua H. Cossuth, Yi Jin, Kevin C. Viner, and Jerome M. Schmidt

ventilating TCs, inducing a potential vorticity–related spinup, and outright shearing of the TC, depending on the proximity of the upper-level synoptic forcing. Vertical wind shear (VWS) is generally a negative influence on TC intensification ( Merrill 1988b ; Wang and Wu 2004 ). Recent studies on wind shear’s negative effects have focused on the thermodynamic effects of VWS, such as the midlevel ventilation ( Tang and Emanuel 2010 ; Tang and Emanuel 2012 ; Ge et al. 2013 ) or the flushing of the

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William A. Komaromi and James D. Doyle

hypothesis, referred to as active outflow , is that a source of upper-level forcing that acts to accelerate or otherwise enhance the TC outflow can ultimately drive changes in the strength or structure of the vortex below (e.g., Sadler 1976 ; Holland and Merrill 1984 ; Nong and Emanuel 2003 ). Here, we do not seek to determine whether outflow is more likely to be passive or active. Instead, we explore the hypothesis that active outflow may contribute to TC intensification under the right set of

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

not contribute to stronger tangential winds at the surface, which may be due to the periodicity of the forcing and its concentrated location outside of the RMW. Heating anomalies in the current study extend a large horizontal distance in the upper troposphere, nearly 300 km long at later times in the extensive anvil of the Nightonly simulations (not shown). The expansive area of heating anomalies could contribute to a larger enhancement more similar to that reported by Navarro and Hakim (2016

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