Evaluation of Tropical Cyclone Center Identification Methods in Numerical Models

2014 ◽  
Vol 142 (11) ◽  
pp. 4326-4339 ◽  
Author(s):  
Leon T. Nguyen ◽  
John Molinari ◽  
Diana Thomas
Keyword(s):  
High Resolution ◽  
Tropical Cyclone ◽  
Model Simulation ◽  
Numerical Models ◽  
Vortex Center ◽  
Identification Methods ◽  
Cyclone Center ◽  
Tangential Wind ◽  
Wind Profiles ◽  
Tropical Cyclone Center

Abstract Identifying the center of a tropical cyclone in a high-resolution model simulation has a number of operational and research applications, including constructing a track, calculating azimuthal means and perturbations, and diagnosing vortex tilt. This study evaluated several tropical cyclone center identification methods in a high-resolution Weather Research and Forecasting (WRF) Model simulation of a sheared, intensifying, asymmetric tropical cyclone. The simulated tropical cyclone (TC) contained downshear convective cells and a mesovortex embedded in a broader TC vortex, complicating the identification of the TC vortex center. It is shown that unlike other methods, the pressure centroid method consistently 1) placed the TC center within the region of weak storm-relative wind, 2) produced a smooth track, 3) yielded a vortex tilt that varied smoothly in magnitude and direction, and 4) was insensitive to changes in horizontal grid resolution. Based on these results, the authors recommend using the pressure centroid to define the TC center in high-resolution numerical models. The pressure centroid was calculated within a circular region representing the size of the TC inner core. To determine this area, the authors propose normalizing by the innermost radius at which the azimuthally averaged storm-relative tangential wind at 2-km height equals 80% of the maximum (R80) at 2-km height. Although compositing studies have often normalized by the radius of maximum wind (RMW), R80 proved less sensitive to slight changes in flat tangential wind profiles. This enables R80 to be used as a normalization technique not only with intense TCs having peaked tangential wind profiles, but also with weaker TCs having flatter tangential wind profiles.

Tropical Cyclone Center and Symmetric Structure Estimating from SMAP Data

2021 ◽  
pp. 1-1
Author(s):  
Guosheng Zhang ◽  
Chao Xu ◽  
Xiaofeng Li ◽  
Ziqiang Zhu ◽  
William Perrie
Keyword(s):  
Tropical Cyclone ◽  
Cyclone Center ◽  
Symmetric Structure ◽  
Tropical Cyclone Center

scholarly journals Combining a Cloud-Resolving Model with Satellite for Cloud Process Model Simulation Validation

2014 ◽  
Vol 53 (2) ◽  
pp. 521-533 ◽  
Author(s):  
Renato G. Negri ◽  
Luiz A. T. Machado ◽  
Stephen English ◽  
Mary Forsythe
Keyword(s):  
High Resolution ◽  
Spatial Resolution ◽  
Process Model ◽  
Model Simulation ◽  
Numerical Models ◽  
Tropical Convection ◽  
Infrared Observation ◽  
Cloud Resolving Model ◽  
The Uk ◽  
High Level

AbstractAdvances in computer power have made it possible to increase the spatial resolution of regional numerical models to a scale encompassing larger convective elements of less than 5 km in size. One goal of high resolution is to begin to resolve convective processes, and therefore it is necessary to evaluate the realism of convective clouds resolved explicitly at this resolution. This paper presents a method that is based on satellite comparisons to examine the simulation of continental tropical convection over Africa, in a high-resolution integration of the Met Office Unified Model (UK UM), developed under the Cascade project. The spatial resolution of these simulations is 1.5 km, the temporal resolution is 15 min, and the convection is resolved explicitly. The Spinning Enhanced Visible and Infrared Imager (SEVIRI) radiometer measurements were simulated by the Radiative Transfer for the Television and Infrared Observation Satellite (TIROS) Operational Vertical Sounder (RTTOV) model, and then a comparison between the simulations and real SEVIRI measurements was performed. The analysis using the presented method shows that the UK UM can represent tropical convection dynamics realistically. However, an error has been found in the high-level humidity distribution, which is characterized by strong humidity gradients. A key point of this paper is to present a method for establishing the credibility of a convection-permitting model by direct comparison with satellite data.

scholarly journals A New Parametric Tropical Cyclone Tangential Wind Profile Model

2013 ◽  
Vol 141 (6) ◽  
pp. 1884-1909 ◽  
Author(s):  
Vincent T. Wood ◽  
Luther W. White ◽  
Hugh E. Willoughby ◽  
David P. Jorgensen
Keyword(s):  
Tropical Cyclone ◽  
Wind Profile ◽  
Tangential Velocity ◽  
Pressure Rise ◽  
Central Pressure ◽  
Velocity Parameter ◽  
Profile Model ◽  
Tangential Wind ◽  
Multiple Maxima ◽  
Wind Profiles

Abstract A new parametric tropical cyclone (TC) wind profile model is presented for depicting representative surface pressure profiles corresponding to multiple-maxima wind profiles that exhibit single-, dual-, and triple-maximum concentric-eyewall wind peaks associated with the primary (inner), secondary (first outer), and tertiary (second outer) complete rings of enhanced radar reflectivity. One profile employs five key parameters: tangential velocity maximum, radius of the maximum, and three different shape velocity parameters related to the shape of the profile. After tailoring the model for TC applications, a gradient wind is computed from a cyclostrophic wind formulated in terms of the cyclostrophic Rossby number. A pressure, via cyclostrophic balance, was partitioned into separate pressure components that corresponded to multiple-maxima cyclostrophic wind profiles in order to quantitatively evaluate the significant fluctuations in central pressure deficits. The model TC intensity in terms of varying growth, size, and decay velocity profiles was analyzed in relation to changing each of five key parameters. Analytical results show that the first shape velocity parameter, changing a sharply to broadly peaked wind profile, increases the TC intensity and size by producing the corresponding central pressure fall. An increase (decrease) in the second (third) shape velocity parameter yields the pressure rise (fall) by decreasing (increasing) the inner (outer) wind profile inside (outside) the radius of the maximum. When a single-maximum tangential wind profile evolves to multiple-maxima tangential wind profiles during an eye replacement cycle, the pressure falls and rises are sensitively fluctuated.

scholarly journals Characteristics of Convective Processes and Vertical Vorticity from the Tropical Wave to Tropical Cyclone Stage in a High-Resolution Numerical Model Simulation of Tropical Cyclone Fay (2008)

2014 ◽  
Vol 71 (3) ◽  
pp. 896-915 ◽  
Author(s):  
Zhuo Wang
Keyword(s):  
High Resolution ◽  
Tropical Cyclone ◽  
Model Simulation ◽  
Upward Motion ◽  
Model Resolution ◽  
Cyclonic Vorticity ◽  
Convective Processes ◽  
Areal Fraction ◽  
The Mean ◽  
Tropical Wave

Abstract The statistics of convective processes and vertical vorticity from the tropical wave to tropical cyclone stage are examined in a high-resolution simulation of Tropical Cyclone Fay (2008). The intensity of vertical velocity follows approximately the truncated lognormal distribution in the model simulation, which is consistent with previous observational studies. The upward motion at the pregenesis stage is weaker compared to mature hurricanes or midlatitude thunderstorms. The relatively strong upward velocities occupying a small areal fraction make a substantial contribution to the upward mass and moisture fluxes and condensation. It is also found that upward motion and downward motion both intensify with time, but the former is stronger than the latter, and the mean vertical motion and the mean vertical mass flux thus increase with time. By contrast, the maximum anticyclonic vorticity is comparable to the maximum cyclonic vorticity in magnitude. Both cyclonic vorticity and anticyclonic vorticity intensify with time, but the former covers a larger areal fraction in the lower and middle troposphere and becomes dominant throughout the troposphere after genesis. Sensitivity tests with different model resolutions were carried out to test the robustness of the results. When the horizontal grid spacing is reduced, the size of updrafts decreases and the number of updrafts increases, but the areal fraction of updrafts, the mean vertical velocity, and the mean vertical mass flux are rather insensitive to the model resolution, especially in the lower troposphere and when the model resolution is 1 km or higher. This may explain why models with relatively coarse resolution can simulate tropical cyclogenesis reasonably well.

Stochastic Variability of Tropical Cyclone Intensity at the Maximum Potential Intensity Equilibrium

2020 ◽  
Vol 77 (9) ◽  
pp. 3105-3118
Author(s):  
Phuong Nguyen ◽  
Chanh Kieu ◽  
Wai-Tong (Louis) Fan
Keyword(s):  
Tropical Cyclone ◽  
Intensity Distribution ◽  
Numerical Models ◽  
Absolute Intensity ◽  
Intrinsic Variability ◽  
Stochastic Representation ◽  
Thermodynamic Structure ◽  
Warm Core ◽  
Tangential Wind ◽  
Random Fluctuations

Abstract This study examines the variability of tropical cyclone (TC) intensity associated with stochastic forcings at the maximum potential intensity (PI) equilibrium. By representing TC intensity as an Itô diffusion process in the framework of TC-scale dynamics, we show from both theoretical and numerical analyses that there exists an invariant intensity distribution whose variance is proportional to the variances of stochastic forcings. This result provides further evidence that TC dynamics possess an intrinsic variability that prevents the TC absolute intensity errors in numerical models from being reduced below an arbitrarily small threshold. Analysis of the invariant intensity distribution at the PI limit reveals also that the stochastic forcing component associated with tangential wind and the warm-core anomaly in the TC central region have the largest contribution to TC intensity variability. These results suggest that future development of stochastic representation in TC models should focus on the tangential wind and thermodynamic structure to capture proper TC intensity random fluctuations.

scholarly journals Evaluation of the contribution of tropical cyclone seeds to changes in tropical cyclone frequency due to global warming in high-resolution multi-model ensemble simulations

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Yohei Yamada ◽  
Chihiro Kodama ◽  
Masaki Satoh ◽  
Masato Sugi ◽  
Malcolm J. Roberts ◽  
...  
Keyword(s):  
Global Warming ◽  
Survival Rate ◽  
High Resolution ◽  
Tropical Cyclone ◽  
Model Simulation ◽  
Tropical Cyclone Genesis ◽  
Model Intercomparison ◽  
Model Ensemble ◽  
Intercomparison Project ◽  
Cyclone Genesis

AbstractPrevious projections of the frequency of tropical cyclone genesis due to global warming, even in terms of sign of the change, depends on the chosen model simulation. Here, we systematically examine projected changes in tropical cyclones using six global atmospheric models with medium-to-high horizontal resolutions included in the sixth phase of the Coupled Model Intercomparison Project/High-Resolution Model Intercomparison Project. Changes in the frequency of tropical cyclone genesis could be broken down into the contributions from (i) the tropical cyclone seed, a depression having a closed contour of sea level pressure with a warm core and (ii) the survival rate, the ratio of the frequency of tropical cyclone genesis to that of tropical cyclone seeds. The multi-model ensemble mean indicates that tropical cyclone genesis frequencies are significantly decreased during the period 1990–2049, which is attributable to changes in tropical cyclone seeds. Analysis of the individual models shows that although most models project a more or less decreasing trend in tropical cyclone genesis frequencies and seeds, the survival rate also contributes to the result in some models. The present study indicates the usefulness of decomposition into the frequency of the tropical cyclone seeds and the survival rate to understand the cause of uncertainty in projected frequencies of tropical cyclone genesis.

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