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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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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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T. Connor Nelson, Lee Harrison, and Kristen L. Corbosiero

in the TCI dataset, as well as to examine the updrafts and downdrafts observed by the XDDs. Hock and Franklin (1999) used RD-93 dropsondes to derive vertical velocity from GPS fall speeds and a single drag force estimate presumed to be representative for all individual sondes. This method is now routine, but more recent studies use a hydrostatic pressure-derived fall speed rather than the GPS fall speed (e.g., Wang et al. 2015 ). Sonde-derived vertical velocities have been used to examine the

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

-level forcing mechanism), and this study identifies and quantifies a set of key common features for this class of TCs. The analyses in this study primarily rely on satellite observations, since these data typically provide the most complete spatial and temporal coverage over the storms, given that aircraft observations of TCs are rare in the eastern North Pacific (EPAC) and western Pacific (WPAC; Knabb et al. 2008 ). Without in situ reconnaissance data, intensity estimations and analyses are primarily

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Shixuan Zhang, Zhaoxia Pu, and Christopher Velden

,c,e,f , 9b–f ). In addition, the “DA without VI” can cause large initial errors for MSW ( Figs. 8f , 9f ), indicating that the enhanced AMVs data only are not enough to force the storm intensity to match the observed intensity for this case. However, it is worth noting that the assimilation of enhanced AMVs in the inner-core region produces smaller average MSLP and MSW errors over the whole 72-h forecasts in most of the cases (e.g., the blue numbers at the top of each panel in Figs. 8b,c , 8e,f , and

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Patrick Duran and John Molinari

). This stable stratification is a necessary ingredient for adiabatic subsidence to warm the eye. Regardless of the forcing mechanisms, the strong upper-tropospheric warming between 22 and 23 October was enough to completely eliminate the TIL within the eye, allowing the tropopause height and temperature to increase dramatically. Fig . 10. Vertical cross sections of (a),(b) storm-relative radial and (c),(d) tangential velocity (m s −1 ) and the cold-point tropopause height (green lines) in Hurricane

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Jie Feng and Xuguang Wang

1. Introduction In recent decades, research has shown that the tropical cyclone (TC) outflow layer is critically related to the TC structure evolution and intensity change rather than just a mechanism to export TC energy at the upper troposphere. The outflow layer relative to the low- and midtroposphere has weaker inertial stability and thus is more susceptible to the environmental forcing ( Holland and Merrill 1984 ; Rappin et al. 2011 ). For example, the outflow can interact with a

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