scholarly journals A Model for the Complete Radial Structure of the Tropical Cyclone Wind Field. Part II: Wind Field Variability

2016 ◽  
Vol 73 (8) ◽  
pp. 3093-3113 ◽  
Author(s):  
Daniel R. Chavas ◽  
Ning Lin
Keyword(s):  
Tropical Cyclone ◽  
Physical Model ◽  
Wind Field ◽  
Inner Core ◽  
Outer Radius ◽  
Maximum Wind ◽  
Modes Of Variability ◽  
Simple Physical Model ◽  
Radial Structure ◽  
Field Variability

Abstract Part I of this work developed a simple physical model for the complete radial structure of the low-level azimuthal wind field in a tropical cyclone that compared well with observations. However, wind field variability in the model is tied principally to its external parameters given by the maximum wind speed and the radius of maximum wind, the latter of which lacks a credible independent physical model for its variability. Here the authors explore the modes of variability that arise from the alternative specification of the model, which takes the outer radius in lieu of the radius of maximum wind. Nondimensionalization of the model reveals two theoretical modes of structural variability in absolute angular momentum that are shown to closely match observations. These two modes correspond to three modes of wind field variability associated with variations in intensity, outer storm size, and latitude. These wind field modes are demonstrated to mirror the dominant modes of variability found in nature, in particular the intrastorm variation of inner-core structure and the interstorm variation of overall storm size. In combination, the model offers a credible physical solution for the complete time-dependent tropical cyclone wind field in conjunction with the external specification of intensity, outer size, and latitude. More broadly, the model offers theoretical and conceptual insight into the nature of the tropical cyclone wind field, including the oft-conflated terms “size” and “structure” and their distinct variabilities.

scholarly journals A Model for the Complete Radial Structure of the Tropical Cyclone Wind Field. Part I: Comparison with Observed Structure*

2015 ◽  
Vol 72 (9) ◽  
pp. 3647-3662 ◽  
Author(s):  
Daniel R. Chavas ◽  
Ning Lin ◽  
Kerry Emanuel
Keyword(s):  
Tropical Cyclone ◽  
Wind Field ◽  
Inner Core ◽  
Outer Region ◽  
Global Database ◽  
Wind Speeds ◽  
Wind Structure ◽  
Radial Structure ◽  
Region Model ◽  
Spiral Rainbands

Abstract Part I of this work develops a simple model for the complete radial structure of the low-level tropical cyclone wind field. The model is constructed by mathematically merging existing theoretical solutions for the radial wind structure at the top of the boundary layer in the inner ascending and outer descending regions. The model is then compared with two observational datasets. First, the outer solution is compared with a global database from the QuikSCAT satellite (1999–2009) and found to reproduce the characteristic wind structure of the broad outer region of tropical cyclones at large radii, indicating that the solution successfully captures the physics of this region. Second, the inner solution is compared with the HWind database (2004–12) for the Atlantic and eastern Pacific basins and is shown to be capable of reproducing the inner-core structure while substantially underestimating wind speeds at larger radii. The complete model is then shown to largely, though not entirely, rectify this underestimation. Limitations of the model are discussed, including the need for a formal evaluation of the physics of the inner core as well as a transition-region model at intermediate radii characterized by intermittent convection, such as spiral rainbands. Part II will characterize the model’s modes of wind field variability and their relationship to the variability observed in nature.

Evaluation of a Wind-Wave System for Ensemble Tropical Cyclone Wave Forecasting. Part I: Winds

2013 ◽  
Vol 28 (2) ◽  
pp. 297-315 ◽  
Author(s):  
Steven M. Lazarus ◽  
Samuel T. Wilson ◽  
Michael E. Splitt ◽  
Gary A. Zarillo
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Synthetic Data ◽  
Radial Distance ◽  
Wave System ◽  
Computationally Efficient ◽  
Wind Fields ◽  
Translation Speed ◽  
Maximum Wind ◽  
Regional Reanalysis

Abstract A computationally efficient method of producing tropical cyclone (TC) wind analyses is developed and tested, using a hindcast methodology, for 12 Gulf of Mexico storms. The analyses are created by blending synthetic data, generated from a simple parametric model constructed using extended best-track data and climatology, with a first-guess field obtained from the NCEP–NCAR North American Regional Reanalysis (NARR). Tests are performed whereby parameters in the wind analysis and vortex model are varied in an attempt to best represent the TC wind fields. A comparison between nonlinear and climatological estimates of the TC size parameter indicates that the former yields a much improved correlation with the best-track radius of maximum wind rm. The analysis, augmented by a pseudoerror term that controls the degree of blending between the NARR and parametric winds, is tuned using buoy observations to calculate wind speed root-mean-square deviation (RMSD), scatter index (SI), and bias. The bias is minimized when the parametric winds are confined to the inner-core region. Analysis wind statistics are stratified within a storm-relative reference frame and by radial distance from storm center, storm intensity, radius of maximum wind, and storm translation speed. The analysis decreases the bias and RMSD in all quadrants for both moderate and strong storms and is most improved for storms with an rm of less than 20 n mi. The largest SI reductions occur for strong storms and storms with an rm of less than 20 n mi. The NARR impacts the analysis bias: when the bias in the former is relatively large, it remains so in the latter.

scholarly journals The Role of Inner-Core Moisture in Tropical Cyclone Predictability and Practical Forecast Skill

2017 ◽  
Vol 74 (7) ◽  
pp. 2315-2324 ◽  
Author(s):  
Kerry Emanuel ◽  
Fuqing Zhang
Keyword(s):  
Tropical Cyclone ◽  
Wind Field ◽  
Inner Core ◽  
Forecast Skill ◽  
Initial Condition ◽  
Tropical Cyclone Intensity ◽  
Cyclone Intensity ◽  
Storm Intensity ◽  
Tropical Cyclone Intensity Forecasts

Abstract Errors in tropical cyclone intensity forecasts are dominated by initial-condition errors out to at least a few days. Initialization errors are usually thought of in terms of position and intensity, but here it is shown that growth of intensity error is at least as sensitive to the specification of inner-core moisture as to that of the wind field. Implications of this finding for tropical cyclone observational strategies and for overall predictability of storm intensity are discussed.

scholarly journals Comparative assessment of validity of gradient wind models for a translating tropical cyclone

2021 ◽  
Vol 3 (4) ◽  
Author(s):  
Yuzuru Eguchi ◽  
Yasuo Hattori ◽  
Mitsuharu Nomura
Keyword(s):  
Wind Speed ◽  
Tropical Cyclone ◽  
Wind Field ◽  
Comparative Assessment ◽  
Maximum Wind Speed ◽  
Observation Data ◽  
High Wind ◽  
Maximum Wind ◽  
Gradient Wind ◽  
The Difference

AbstractAccurate and conservative evaluations of the gradient wind in the free atmosphere are needed to account for high-wind hazards when designing wind resistance for critical infrastructure. This paper compared the validity of three existing gradient wind models to select an appropriate evaluation model, which enables us to accurately compute the asymmetric gradient wind field of a translating tropical cyclone under the condition of a symmetric pressure distribution and a constant translation velocity. The validity of the three models was assessed by evaluating the residuals in momentum conservation equations for the gradient wind under a specific tropical cyclone condition. The magnitude of the residuals was considered to be the measure of error in the gradient wind derived from each model. The results showed that the most frequently used model yielded the largest magnitude of residuals with the lowest maximum wind speed among the three models. The wind characteristics of the three models were validated using archived observation data of hurricanes. The physical reason for the difference in maximum wind speed among the three models was explained by the difference in the streamline feature of the gradient wind field. It was also revealed that the differences in maximum wind speed and magnitude of residuals became more pronounced as the translation speed and the intensity of a tropical cyclone increased. The comparative assessment of the three gradient wind models allowed us to identify the best model for use in conservative wind-resistant design and high-wind risk estimates.

scholarly journals Lilly’s Model for Steady-State Tropical Cyclone Intensity and Structure

2020 ◽  
Vol 77 (11) ◽  
pp. 3701-3720
Author(s):  
Dandan Tao ◽  
Richard Rotunno ◽  
Michael Bell
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Tropical Cyclone ◽  
Inner Core ◽  
Cloud Model ◽  
Surface Boundary ◽  
Unpublished Manuscript ◽  
Tangential Wind ◽  
Radial Structure ◽  
Simplifying Assumptions

AbstractThis study revisits the axisymmetric tropical cyclone (TC) theory from D. K. Lilly’s unpublished manuscript (Lilly model) and compares it to axisymmetric TC simulations from a nonhydrostatic cloud model. Analytic solutions of the Lilly model are presented through simplifying assumptions. Sensitivity experiments varying the sea surface, boundary layer and tropopause temperatures, and the absolute angular momentum (M) at some outer radius in the Lilly model show that these variations influence the radial structure of the tangential wind profile V(r) at the boundary layer top. However, these parameter variations have little effect on the inner-core normalized tangential wind, V(r/rm)/Vm, where Vm is the maximum tangential wind at radius rm. The outflow temperature T∞ as a function of M (or saturation entropy s*) is found to be the only input that changes the normalized tangential wind radial structure in the Lilly model. In contrast with the original assumption of the Lilly model that T∞(s*) is determined by the environment, it is argued here that T∞(s*) is determined by the TC interior flow under the environmental constraint of the tropopause height. The present study shows that the inner-core tangential wind radial structure from the Lilly model generally agrees well with nonhydrostatic cloud model simulations except in the eyewall region where the Lilly model tends to underestimate the tangential winds due to its balanced-dynamics assumptions. The wind structure in temperature–radius coordinates from the Lilly model can largely reproduce the numerical simulation results. Though the Lilly model is based on a number of simplifying assumptions, this paper shows its utility in understanding steady-state TC intensity and structure.

scholarly journals Influence of Cloud Microphysics and Radiation on Tropical Cyclone Structure and Motion

2016 ◽  
Vol 56 ◽  
pp. 11.1-11.27 ◽  
Author(s):  
Robert G. Fovell ◽  
Yizhe Peggy Bu ◽  
Kristen L. Corbosiero ◽  
Wen-wen Tung ◽  
Yang Cao ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Wind Field ◽  
Radiative Forcing ◽  
Inner Core ◽  
Longwave Radiation ◽  
Outer Core ◽  
Cloud Microphysics ◽  
Convective Activity ◽  
Radiative Processes ◽  
Structure And Motion

Abstract The authors survey a series of modeling studies that have examined the influences that cloud microphysical processes can have on tropical cyclone (TC) motion, the strength and breadth of the wind field, inner-core diabatic heating asymmetries, outer-core convective activity, and the characteristics of the TC anvil cloud. These characteristics are sensitive to the microphysical parameterization (MP) in large part owing to the cloud-radiative forcing (CRF), the interaction of hydrometeors with radiation. The most influential component of CRF is that due to absorption and emission of longwave radiation in the anvil, which via gentle lifting directly encourages the more extensive convective activity that then leads to a radial expansion of the TC wind field. On a curved Earth, the magnitude of the outer winds helps determine the speed and direction of TC motion via the beta drift. CRF also influences TC motion by determining how convective asymmetries develop in the TC inner core. Further improvements in TC forecasting may require improved understanding and representation of cloud-radiative processes in operational models, and more comprehensive comparisons with observations are clearly needed.

scholarly journals The Transient Responses of an Axisymmetric Tropical Cyclone to Instantaneous Surface Roughening and Drying

2020 ◽  
Vol 77 (8) ◽  
pp. 2807-2834 ◽  
Author(s):  
Jie Chen ◽  
Daniel R. Chavas
Keyword(s):  
Tropical Cyclone ◽  
Wind Field ◽  
Inner Core ◽  
Surface Roughening ◽  
Surface Drag ◽  
Transient Responses ◽  
Overturning Circulation ◽  
Thermodynamic Stabilization ◽  
Surface Drying ◽  
High Winds

Abstract Inland tropical cyclone (TC) impacts due to high winds and rainfall-induced flooding depend strongly on the evolution of the wind field and precipitation distribution after landfall. However, research has yet to test the detailed response of a mature TC and its hazards to changes in surface forcing in idealized settings. This work tests the transient responses of an idealized hurricane to instantaneous transitions in two key surface properties associated with landfall: roughening and drying. Simplified axisymmetric numerical modeling experiments are performed in which the surface drag coefficient and evaporative fraction are each systematically modified beneath a mature hurricane. Surface drying stabilizes the eyewall and consequently weakens the overturning circulation, thereby reducing inward angular momentum transport that slowly decays the wind field only within the inner core. In contrast, surface roughening initially (~12 h) rapidly weakens the entire low-level wind field and enhances the overturning circulation dynamically despite the concurrent thermodynamic stabilization of the eyewall; thereafter the storm gradually decays, similar to drying. As a result, total precipitation temporarily increases with roughening but uniformly decreases with drying. Storm size decreases monotonically and rapidly with surface roughening, whereas the radius of maximum wind can increase with moderate surface drying. Overall, this work provides a mechanistic foundation for understanding the inland evolution of real storms in nature.

scholarly journals Recent Advances in Our Understanding of Tropical Cyclone Intensity Change Processes from Airborne Observations

Atmosphere ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 650
Author(s):  
Robert F. Rogers
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Vertical Shear ◽  
Intensity Change ◽  
Change Processes ◽  
Cyclone Intensity ◽  
Secondary Eyewall Formation ◽  
Warm Core ◽  
Major Hurricane ◽  
Upper Level

Recent (past ~15 years) advances in our understanding of tropical cyclone (TC) intensity change processes using aircraft data are summarized here. The focus covers a variety of spatiotemporal scales, regions of the TC inner core, and stages of the TC lifecycle, from preformation to major hurricane status. Topics covered include (1) characterizing TC structure and its relationship to intensity change; (2) TC intensification in vertical shear; (3) planetary boundary layer (PBL) processes and air–sea interaction; (4) upper-level warm core structure and evolution; (5) genesis and development of weak TCs; and (6) secondary eyewall formation/eyewall replacement cycles (SEF/ERC). Gaps in our airborne observational capabilities are discussed, as are new observing technologies to address these gaps and future directions for airborne TC intensity change research.

Tracking a Long-Lasting Outer Tropical Cyclone Rainband: Origin and Convective Transformation

2019 ◽  
Vol 76 (10) ◽  
pp. 3267-3283 ◽  
Author(s):  
Cheng-Ku Yu ◽  
Che-Yu Lin ◽  
Jhang-Shuo Luo
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Radial Distance ◽  
Vertical Shear ◽  
Convective Precipitation ◽  
Squall Line ◽  
Mature Stage ◽  
Clear Trend ◽  
Dynamical Interaction ◽  
Cold Pools

Abstract This study used radar and surface observations to track a long-lasting outer tropical cyclone rainband (TCR) of Typhoon Jangmi (2008) over a considerable period of time (~10 h) from its formative to mature stage. Detailed analyses of these unique observations indicate that the TCR was initiated on the eastern side of the typhoon at a radial distance of ~190 km as it detached from the upwind segment of a stratiform rainband located close to the inner-core boundary. The outer rainband, as it propagated cyclonically outward, underwent a prominent convective transformation from generally stratiform precipitation during the earlier period to highly organized, convective precipitation during its mature stage. The transformation was accompanied by a clear trend of surface kinematics and thermodynamics toward squall-line-like features. The observed intensification of the rainband was not simply related to the spatial variation of the ambient CAPE or potential instability; instead, the dynamical interaction between the prerainband vertical shear and cold pools, with progression toward increasingly optimal conditions over time, provides a reasonable explanation for the temporal alternation of the precipitation intensity. The increasing intensity of cold pools was suggested to play an essential role in the convective transformation for the rainband. The propagation characteristics of the studied TCR were distinctly different from those of wave disturbances frequently documented within the cores of tropical cyclones; however, they were consistent with the theoretically predicted propagation of convectively generated cold pools. The convective transformation, as documented in the present case, is anticipated to be one of the fundamental processes determining the evolving and structural nature of outer TCRs.

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