The Evolution of Vortex Tilt and Vertical Motion of Tropical Cyclones in Directional Shear Flows

Gu, Jian‐Feng; Tan, Zhimin; Qiu, Xin

doi:10.1175/jas-d-18-0024.1

Cited by 22 publications

(15 citation statements)

References 35 publications

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“…Last, the ambient and TC winds in the two remaining quadrants are sufficiently out of phase such that there is not a nonlinear enhancement of the helicity associated with the total wind field beyond the sum of TC and ambient wind components. Together, these results suggest that the downshearright quadrant in strongly sheared TCs is most frequently kinematically favorable for tornadoes potentially in association with four factors: d Constructive superposition of the TC and ambient winds, which nonlinearly contributes to enhanced helicity Vollaro 2008, 2010;Gu et al 2018);…”

mentioning

confidence: 85%

“…Moreover, winds are strongest throughout the troposphere in the downshear-right quadrant likely due to constructive superposition between the TC and ambient winds and VWS-induced enhancement of the TC secondary circulation (Jones 1995;Frank and Ritchie 1999;Molinari and Vollaro 2010). In contrast, the downshear-left quadrant hodograph has comparatively weaker near-surface speed shear in strongly sheared TCs (Molinari and Vollaro 2010;Gu et al 2018), while the two upshear quadrants are characterized by more marginal speed and directional shear. Compared to TCs in strong VWS, weakly and moderately sheared TCs (Figs.…”

Section: Kinematic Environmentsmentioning

confidence: 97%

“…12). The downshear-right quadrant hodograph in strongly sheared TCs is dominated by strong speed shear in the lowest 1 km, with directional shear immediately above that level Vollaro 2008, 2010;Gu et al 2018), typical of tornadic supercell environments (Brown et al 1973;Markowski et al 2003;Thompson et al 2003). Moreover, winds are strongest throughout the troposphere in the downshear-right quadrant likely due to constructive superposition between the TC and ambient winds and VWS-induced enhancement of the TC secondary circulation (Jones 1995;Frank and Ritchie 1999;Molinari and Vollaro 2010).…”

Section: Kinematic Environmentsmentioning

confidence: 99%

“…d Vector superposition: Constructive superposition between veering of the ambient and TC winds that most strongly occurs in the downshear-right quadrant enhances the lower-tropospheric veering of the total wind field (i.e., environment plus TC) and nonlinearly increases its convective cell-relative helicity as VWS increases, all else being equal (Fig. 2f; Vollaro 2008, 2010;Gu et al 2018);…”

Section: Introductionmentioning

confidence: 99%

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A Climatological Analysis of Ambient Deep-Tropospheric Vertical Wind Shear Impacts upon Tornadoes in Tropical Cyclones

Schenkel

Edwards²,

Coniglio

2020

Weather and Forecasting

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The cyclone-relative location and variability in the number of tornadoes among tropical cyclones (TCs) are not completely understood. A key understudied factor that may improve our understanding is ambient (i.e., synoptic-scale) deep-tropospheric (i.e., 850–200-hPa) vertical wind shear (VWS), which impacts both the symmetry and strength of deep convection in TCs. This study conducts a climatological analysis of VWS impacts upon tornadoes in TCs from 1995–2018, using observed TC and tornado data together with radiosondes. TC tornadoes were classified by objectively defined VWS categories, derived from reanalyses, to quantify the sensitivity of tornado frequency, location, and their environments to VWS. The analysis shows that stronger VWS is associated with enhanced rates of tornado production—especially more damaging ones. Tornadoes also become localized to the downshear half of the TC as VWS strengthens, with tornado location in strongly sheared TCs transitioning from the downshear left quadrant in the TC inner core to the downshear right quadrant in the TC outer region. Analysis of radiosondes shows that the downshear right quadrant in strongly sheared TCs is most frequently associated with sufficiently strong near-surface speed shear and veering aloft, and lower-tropospheric thermodynamic instability for tornadoes. These supportive kinematic environments may be due to the constructive superposition of the ambient and TC winds, and the VWS-induced downshear enhancement of the TC circulation among other factors. Together, this work provides a basis for improving forecasts of TC tornado frequency and location.

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mentioning

confidence: 85%

Section: Kinematic Environmentsmentioning

confidence: 97%

Section: Kinematic Environmentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

A Climatological Analysis of Ambient Deep-Tropospheric Vertical Wind Shear Impacts upon Tornadoes in Tropical Cyclones

Schenkel

Edwards²,

Coniglio

2020

Weather and Forecasting

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show abstract

“…This downshear strengthening of the TC overturning circulation is associated with enhanced ascent, moisture, and vertical wind shear (Molinari & Vollaro, 2008; Schenkel et al., 2020). Second, a constructive superposition between the TC and ambient winds, yields a nonlinear enhancement of helicity in the downshear sector, particularly downshear right (Gu et al., 2018; Schenkel et al., 2020).…”

Section: Introductionmentioning

confidence: 99%

Tropical Cyclone Outer Size Impacts the Number and Location of Tornadoes

Paredes

Schenkel

Edwards

et al. 2021

Geophysical Research Letters

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Landfalling tropical cyclones (TCs) often produce tornadoes in addition to other hazards. Most tornadoes occur during the afternoon within 100-500 km of the TC center during the 48-h period before and after landfall (Novlan & Gray, 1974;Schultz & Cecil, 2009). Compared to their non-TC counterparts, TC tornadoes typically: 1) are less damaging (Edwards, 2010;Edwards, 2012), 2) are produced by "miniature" supercells (Spratt et al., 1997;Edwards et al., 2012), and 3) occur in strong vertical wind shear and sufficient thermodynamic instability concentrated over a shallow lower-tropospheric layer (McCaul, 1991;McCaul & Weisman, 1996). These favorable kinematic conditions are due to the TC warm-core structure and surface friction (Novlan & Gray, 1974;Gentry, 1983), while favorable thermodynamic environments are associated with weak convective inhibition and CAPE typical of the tropics (McCaul, 1991;Molinari et al., 2012). Moreover, recent work has shown that ambient deep-tropospheric vertical wind shear (VWS; i.e., the difference between the 850-and 200-hPa ambient winds) is a key factor controlling the number and TC-relative azimuthal location of tornadoes (Schenkel et al., 2020;Schenkel et al., 2021). However, we lack a complete understanding of the factors controlling the number and TC-relative radial location of tornadoes. One understudied factor that may impact the number and TC-relative radius of tornadoes is the outer size of the TC (McCaul, 1991). Indeed, TC outer size is crucial in describing the scale and magnitude of hazards (Lin et al., 2014;Chavas et al., 2017), and is the focus of this study.

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Modulation of tropical cyclone rapid intensification by mesoscale asymmetries

Nolan,

Nebylitsa,

McNoldy

et al. 2023

Quart J Royal Meteoro Soc

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Computer model simulations are one of the most important tools in current use for understanding tropical cyclone (TC) formation and rapid intensification (RI). These include “idealized” simulations in which a TC‐like vortex is placed in a hypothetical environment with pre‐defined sea surface temperature and vertical profiles of temperature, humidity, and wind that are either constant or slowly varying across a large domain. The vast majority of such simulations begin with a perfectly circular vortex as the precursor to a TC. However, most real TCs form or intensify while interacting with asymmetric wind fields either within or external to the vortex circulation. This study introduces a method to initialize idealized TC simulations with asymmetries, and investigates the extent to which such asymmetries might delay RI in favorable environments. It is shown that mesoscale asymmetries can delay RI and reduce the fastest rates of intensification, and that these effects are statistically significantly increased when relatively low values of vertical shear of the horizontal wind are present. In some cases the asymmetries tilt the vortex directly through advection. In other cases, the wind asymmetries increase the disorganization of the convection, increase the size of the inner core wind field, and thus make the weaker TC more susceptible to environmental wind shear. The results suggest that mesoscale asymmetries of the wind field could be useful predictors for delay of RI in otherwise favorable environments.This article is protected by copyright. All rights reserved.

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The Evolution of Vortex Tilt and Vertical Motion of Tropical Cyclones in Directional Shear Flows

Cited by 22 publications

References 35 publications

A Climatological Analysis of Ambient Deep-Tropospheric Vertical Wind Shear Impacts upon Tornadoes in Tropical Cyclones

A Climatological Analysis of Ambient Deep-Tropospheric Vertical Wind Shear Impacts upon Tornadoes in Tropical Cyclones

Tropical Cyclone Outer Size Impacts the Number and Location of Tornadoes

Modulation of tropical cyclone rapid intensification by mesoscale asymmetries

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