A Vortical Hot Tower Route to Tropical Cyclogenesis

Montgomery, Michael T.; Nicholls, Melville E.; Cram, Thomas; Saunders, Ashley B.

doi:10.1175/jas3604.1

Cited by 513 publications

(509 citation statements)

References 81 publications

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“…8c) indicate the wavy characteristics as well as the PV couplet features associated with upward motions. The association of the positive W and the positive PV for the tropical cyclone growth and axisymmetrization process has been reported recently (Hendricks et al, 2004;Montgomery et al, 2006). However, the co-existence of the positive and negative PV's in the couplet form within positive W's in the lower half of the troposphere may shed further insight into the growth of convective cells.…”

Section: Model Simulation and Discussionmentioning

confidence: 69%

Mesoscale processes for super heavy rainfall of Typhoon Morakot (2009) over Southern Taiwan

et al. 2011

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Abstract.Within 100 h, a record-breaking rainfall, 2855 mm, was brought to Taiwan by typhoon Morakot in August 2009 resulting in devastating landslides and casualties. Analyses and simulations show that under favorable largescale situations, this unprecedented precipitation was caused first by the convergence of the southerly component of the pre-existing strong southwesterly monsoonal flow and the northerly component of the typhoon circulation. Then the westerly component of southwesterly flow pushed the highly moist air (mean specific humidity >16 g/kg between 950 and 700 hPa from NCEP GFS data set) eastward against the Central Mountain Range, and forced it to lift in the preferred area. From the fine-scale numerical simulation, not only did the convergence itself provide the source of the heavy rainfall when it interacted with the topography, but also convective cells existed within the typhoon's main rainband. The convective cells were in the form of small rainbands perpendicular to the main one, and propagated as wave trains downwind. As the main rainband moved northward and reached the southern CMR, convective cells inside the narrow convergence zone to the south and those to the north as wave trains, both rained heavily as they were lifted by the west-facing mountain slopes. Those mesoscale processes were responsible for the unprecedented heavy rainfall total that accompanied this typhoon.

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Section: Model Simulation and Discussionmentioning

confidence: 69%

Mesoscale processes for super heavy rainfall of Typhoon Morakot (2009) over Southern Taiwan

et al. 2011

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“…The observational studies of Frank and Clark (1980), McBride and Zehr (1981), and others confirm the importance of low-level cyclonic circulation and vorticity in determining formation potential. This increase enhances the heat and moisture fluxes from the ocean surface and, in the presence of deep convective bursts, leads to the development of the low-level, warmcore TC vortex (Hendricks et al 2004;Montgomery et al 2006;Hendricks and Montgomery 2006). The 850-hPa circulation (CIRC) is calculated as the line integral of the 850-hPa GFS wind field over the perimeter of an 88 3 88 subgrid of the GFS data field that is centered on the algorithm subregion, so CIRC 5…”

Section: E Vertical Shearmentioning

confidence: 99%

“…Furthermore, the explicit role of tropical convection in TC formation has received considerable attention. Research in this area has spanned various spatial scales, including large-scale factors such as convective instability (Gray 1975;Ooyama 1990;DeMaria et al 2001) and the intertropical convergence zone (ITCZ), the development of TCs from mesoscale disturbances such as easterly waves and midlevel convective vortices in the presence of deep convective bursts (McBride and Zehr 1981;Zehr 1992), and convectivescale features such as individual ''hot towers'' (Simpson et al 1998) and their associated thermodynamic and dynamic anomalies [e.g., ''vortical hot towers''; Hendricks et al (2004); Montgomery et al (2006); Hendricks and Montgomery (2006)] .…”

Section: Introductionmentioning

confidence: 99%

Objective Estimation of the 24-h Probability of Tropical Cyclone Formation

Schumacher

DeMaria

Knaff

2009

Weather and Forecasting

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A new product for estimating the 24-h probability of TC formation in individual 58 3 58 subregions of the North Atlantic, eastern North Pacific, and western North Pacific tropical basins is developed. This product uses environmental and convective parameters computed from best-track tropical cyclone (TC) positions, National Centers for Environmental Prediction (NCEP) Global Forecasting System (GFS) analysis fields, and water vapor (;6.7 mm wavelength) imagery from multiple geostationary satellite platforms. The parameters are used in a two-step algorithm applied to the developmental dataset. First, a screening step removes all data points with environmental conditions highly unfavorable to TC formation. Then, a linear discriminant analysis (LDA) is applied to the screened dataset. A probabilistic prediction scheme for TC formation is developed from the results of the LDA.Coefficients computed by the LDA show that the largest contributors to TC formation probability are climatology, 850-hPa circulation, and distance to an existing TC. The product was evaluated by its Brier and relative operating characteristic skill scores and reliability diagrams. These measures show that the algorithmgenerated probabilistic forecasts are skillful with respect to climatology, and that there is relatively good agreement between forecast probabilities and observed frequencies. As such, this prediction scheme has been implemented as an operational product called the National Environmental Satellite, Data, and Information Services (NESDIS) Tropical Cyclone Formation Probability (TCFP) product. The TCFP product updates every 6 h and displays plots of TC formation probability and input parameter values on its Web site. At present, the TCFP provides real-time, objective TC formation guidance used by tropical cyclone forecast offices in the Atlantic, eastern Pacific, and western Pacific basins.

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“…Frank and Ritchie, 1999;Reasor et al, 2000;Frank and Ritchie, 2001;Black et al, 2002;Schecter and Montgomery, 2003;Rogers et al, 2003;Reasor et al, 2004); others have examined the structure of vortex-wave 564 N. VAN SANG ET AL. Montgomery and Enagonio, 1998;Möller and Montgomery, 2000;Enagonio and Montgomery, 2001;Heymsfield et al, 2001;Braun, 2002;Hendricks et al, 2004;Montgomery et al, 2006a). Collectively, the emerging concept is one of intensity and structural change (including warming in the eye) occurring through bursts, fundamentally stochastic in nature, associated with life cycles of asymmetries, rather than though a continuous 'slow' evolution connected with the axisymmetric secondary circulation.…”

Section: Introductionmentioning

confidence: 99%

Tropical‐cyclone intensification and predictability in three dimensions

Sáng¹,

Smith²,

Montgomery

2008

Quart J Royal Meteoro Soc

240

105

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ABSTRACT:We present numerical-model experiments to investigate the dynamics of tropical-cyclone amplification and its predictability in three dimensions. For the prototype amplification problem beginning with a weak-tropical-storm-strength vortex, the emergent flow becomes highly asymmetric and dominated by deep convective vortex structures, even though the problem as posed is essentially axisymmetric. The asymmetries that develop are highly sensitive to the boundarylayer moisture distribution. When a small random moisture perturbation is added in the boundary layer at the initial time, the pattern of evolution of the flow asymmetries is changed dramatically, and a non-negligible spread in the local and azimuthally-averaged intensity results. We conclude, first, that the flow on the convective scales exhibits a degree of randomness, and only those asymmetric features that survive in an ensemble average of many realizations can be regarded as robust; and secondly, that there is an intrinsic uncertainty in the prediction of maximum intensity using either maximumwind or minimum-surface-pressure metrics. There are clear implications for the possibility of deterministic forecasts of the mesoscale structure of tropical cyclones, which may have a major impact on the intensity and on rapid intensity changes.Some other aspects of vortex structure are addressed also, including vortex-size parameters, and sensitivity to the inclusion of different physical processes or higher spatial resolution. We investigate also the analogous problem on a β-plane, a prototype problem for tropical-cyclone motion. A new perspective on the putative role of the wind-evaporation feedback process for tropical-cyclone intensification is offered also.The results provide new insight into the fluid dynamics of the intensification process in three dimensions, and at the same time suggest limitations of deterministic prediction for the mesoscale structure. Larger-scale characteristics, such as the radius of gale-force winds and β-gyres, are found to be less variable than their mesoscale counterparts.

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A Vortical Hot Tower Route to Tropical Cyclogenesis

Cited by 513 publications

References 81 publications

Mesoscale processes for super heavy rainfall of Typhoon Morakot (2009) over Southern Taiwan

Mesoscale processes for super heavy rainfall of Typhoon Morakot (2009) over Southern Taiwan

Objective Estimation of the 24-h Probability of Tropical Cyclone Formation

Tropical‐cyclone intensification and predictability in three dimensions

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