scholarly journals On the Vertical Decay Rate of the Maximum Tangential Winds in Tropical Cyclones

2011 ◽  
Vol 68 (9) ◽  
pp. 2073-2094 ◽  
Author(s):  
Daniel P. Stern ◽  
David S. Nolan
Keyword(s):  
Tropical Cyclones ◽  
Doppler Radar ◽  
Weather Research And Forecasting ◽  
Vortex Model ◽  
Tangential Wind ◽  
Hurricane Dennis ◽  
Dependent Model ◽  
The Individual ◽  
Individual Profiles ◽  
Time Dependent Model

Abstract In this study, it is shown that the maximum tangential winds within tropical cyclones decrease with height at a percentage rate that is nearly independent of both the maximum wind speed and the radius of maximum winds (RMW). This can be seen by normalizing the profiles of maximum tangential winds Vmax by their respective values at 2-km height. From Doppler radar analyses, profiles of maximum normalized tangential wind Vmaxnorm are found to share a common shape, despite spanning a great range of intensities. There is a systematic dependence of Vmaxnorm on intensity and size, but it is shown to be small, and the mean profile of Vmaxnorm can be used to accurately “predict” the individual profiles of Vmax. Using Emanuel’s steady-state analytical vortex model, it is shown that Vmaxnorm is essentially independent of the size of the RMW. It is shown mathematically that the near independence of Vmaxnorm from size is due to the facts that the RMW is nearly a surface of constant absolute angular momentum M and that its outward slope increases linearly with radius. As the slope of the RMW is not a function of intensity, Vmaxnorm is also nearly independent of intensity in theory, and this is confirmed using Emanuel’s simple time-dependent model. In contrast to intensity, it is shown that Vmaxnorm increases with potential intensity. A suite of idealized simulations using the Weather Research and Forecasting model (WRF) are used to further examine the manner in which the maximum winds change with height. Above 2-km height, vertical profiles of Vmaxnorm are nearly independent of both intensity and size. Occasional deviations from this near-universal profile in these simulations are due to unbalanced winds, and it is proposed that this is the cause of occasional observations of maximum winds that are nearly constant with height through the midtroposphere, as in Hurricane Gloria (1985) and Hurricane Dennis (2005).

scholarly journals The Experimental HWRF System: A Study on the Influence of Horizontal Resolution on the Structure and Intensity Changes in Tropical Cyclones Using an Idealized Framework

2011 ◽  
Vol 139 (6) ◽  
pp. 1762-1784 ◽  
Author(s):  
Sundararaman G. Gopalakrishnan ◽  
Frank Marks ◽  
Xuejin Zhang ◽  
Jian-Wen Bao ◽  
Kao-San Yeh ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclones ◽  
Horizontal Resolution ◽  
Grid Resolution ◽  
Weather Research And Forecasting ◽  
Maximum Wind ◽  
Tangential Wind ◽  
Intensity Changes ◽  
Horizontal Grid ◽  
Weather Research

Abstract Forecasting intensity changes in tropical cyclones (TCs) is a complex and challenging multiscale problem. While cloud-resolving numerical models using a horizontal grid resolution of 1–3 km are starting to show some skill in predicting the intensity changes in individual cases, it is not clear at this time what may be a reasonable horizontal resolution for forecasting TC intensity changes on a day-to-day-basis. The Experimental Hurricane Weather Research and Forecasting System (HWRFX) was used within an idealized framework to gain a fundamental understanding of the influence of horizontal grid resolution on the dynamics of TC vortex intensification in three dimensions. HWFRX is a version of the National Centers for Environmental Prediction (NCEP) Hurricane Weather Research and Forecasting (HWRF) model specifically adopted and developed jointly at NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML) and Earth System Research Laboratory (ESRL) for studying the intensity change problem at a model grid resolution of about 3 km. Based on a series of numerical experiments at the current operating resolution of about 9 km and at a finer resolution of about 3 km, it was found that improved resolution had very little impact on the initial spinup of the vortex. An initial axisymmetric vortex with a maximum wind speed of 20 m s−1 rapidly intensified to 50 m s−1 within about 24 h in either case. During the spinup process, buoyancy appears to have had a pivotal influence on the formation of the warm core and the subsequent rapid intensification of the modeled vortex. The high-resolution simulation at 3 km produced updrafts as large as 48 m s−1. However, these extreme events were rare, and this study indicated that these events may not contribute significantly to rapid deepening. Additionally, although the structure of the buoyant plumes may differ at 9- and 3-km resolution, interestingly, the axisymmetric structure of the simulated TCs exhibited major similarities. Specifically, the similarities included a deep inflow layer extending up to about 2 km in height with a tangentially averaged maximum inflow velocity of about 12–15 m s−1, vertical updrafts with an average velocity of about 2 m s−1, and a very strong outflow produced at both resolutions for a mature storm. It was also found in either case that the spinup of the primary circulation occurred not only due to the weak inflow above the boundary layer but also due to the convergence of vorticity within the boundary layer. Nevertheless, the mature phase of the storm’s evolution exhibited significantly different patterns of behavior at 9 and 3 km. While the minimum pressure at the end of 96 h was 934 hPa for the 9-km simulation, it was about 910 hPa for the 3-km run. The maximum tangential wind at that time showed a difference of about 10 m s−1. Several sensitivity experiments related to the initial vortex intensity, initial radius of the maximum wind, and physics were performed. Based on ensembles of simulations, it appears that radial advection of the tangential wind and, consequently, radial flux of vorticity become important forcing terms in the momentum budget of the mature storm. Stronger convergence in the boundary layer leads to a larger transport of moisture fluxes and, subsequently, a stronger storm at higher resolution.

scholarly journals Evaluation of the Hurricane Research Division Doppler Radar Analysis Software Using Synthetic Data

2013 ◽  
Vol 30 (6) ◽  
pp. 1055-1071 ◽  
Author(s):  
Sylvie Lorsolo ◽  
John Gamache ◽  
Altug Aksoy
Keyword(s):  
Doppler Radar ◽  
Three Dimensional ◽  
Synthetic Data ◽  
Vertical Component ◽  
Radar Data ◽  
Weather Research And Forecasting ◽  
Analysis Software ◽  
Wind Fields ◽  
Research Division ◽  
Tangential Wind

Abstract The Hurricane Research Division Doppler radar analysis software provides three-dimensional analyses of the three wind components in tropical cyclones. Although this software has been used for over a decade, there has never been a complete and in-depth evaluation of the resulting analyses. The goal here is to provide an evaluation that will permit the best use of the analyses, but also to improve the software. To evaluate the software, analyses are produced from simulated radar data acquired from an output of a Hurricane Weather Research and Forecasting (HWRF) model nature run and are compared against the model “truth” wind fields. Comparisons of the three components of the wind show that the software provides analyses of good quality. The tangential wind is best retrieved, exhibiting an overall small mean error of 0.5 m s−1 at most levels and a root-mean-square error less than 2 m s−1. The retrieval of the radial wind is also quite accurate, exhibiting comparable errors, although the accuracy of the tangential wind is generally better. Some degradation of the retrieval quality is observed at higher altitude, mainly due to sparser distribution of data in the model. The vertical component of the wind appears to be the most challenging to retrieve, but the software still provides acceptable results. The tropical cyclone mean azimuthal structure and wavenumber structure are found to be very well captured. Sources of errors inherent to airborne Doppler measurements and the effects of some of the simplifications used in the simulation methodology are also discussed.

scholarly journals A Latent Heat Retrieval and Its Effects on the Intensity and Structure Change of Hurricane Guillermo (1997). Part II: Numerical Simulations

2012 ◽  
Vol 69 (11) ◽  
pp. 3128-3146 ◽  
Author(s):  
Stephen R. Guimond ◽  
Jon M. Reisner
Keyword(s):  
Numerical Simulations ◽  
Tropical Cyclones ◽  
Latent Heat ◽  
Inner Core ◽  
Doppler Radar ◽  
Model Parameters ◽  
Saturation State ◽  
Wind Structure ◽  
Tangential Wind ◽  
Airborne Doppler Radar

Abstract In Part I of this study, a new algorithm for retrieving the latent heat field in tropical cyclones from airborne Doppler radar was presented and fields from rapidly intensifying Hurricane Guillermo (1997) were shown. In Part II, the usefulness and relative accuracy of the retrievals is assessed by inserting the heating into realistic numerical simulations at 2-km resolution and comparing the generated wind structure to the radar analyses of Guillermo. Results show that using the latent heat retrievals as forcing produces very low intensity and structure errors (in terms of tangential wind speed errors and explained wind variance) and significantly improves simulations relative to a predictive run that is highly calibrated to the latent heat retrievals by using an ensemble Kalman filter procedure to estimate values of key model parameters. Releasing all the heating/cooling in the latent heat retrieval results in a simulation with a large positive bias in Guillermo’s intensity that motivates the need to determine the saturation state in the hurricane inner-core retrieval through a procedure similar to that described in Part I of this study. The heating retrievals accomplish high-quality structure statistics by forcing asymmetries in the wind field with the generally correct amplitude, placement, and timing. In contrast, the latent heating fields generated in the predictive simulation contain a significant bias toward large values and are concentrated in bands (rather than discrete cells) stretched around the vortex. The Doppler radar–based latent heat retrievals presented in this series of papers should prove useful for convection initialization and data assimilation to reduce errors in numerical simulations of tropical cyclones.

Revisiting the Relationship between Eyewall Contraction and Intensification

2015 ◽  
Vol 72 (4) ◽  
pp. 1283-1306 ◽  
Author(s):  
Daniel P. Stern ◽  
Jonathan L. Vigh ◽  
David S. Nolan ◽  
Fuqing Zhang
Keyword(s):  
Tropical Cyclones ◽  
Wind Profile ◽  
Diabatic Heating ◽  
Initial Size ◽  
Radial Gradient ◽  
Vortex Model ◽  
Ring Model ◽  
Peak Intensity ◽  
Tangential Wind ◽  
The Relationship

Abstract In the widely accepted convective ring model of tropical cyclone intensification, the intensification of the maximum winds and the contraction of the radius of maximum winds (RMW) occur simultaneously. This study shows that in idealized numerical simulations, contraction and intensification commence at the same time, but that contraction ceases long before peak intensity is achieved. The rate of contraction decreases with increasing initial size, while the rate of intensification does not vary systematically with initial size. Utilizing a diagnostic expression for the rate of contraction, it is shown that contraction is halted in association with a rapid increase in the sharpness of the tangential wind profile near the RMW and is not due to changes in the radial gradient of the tangential wind tendency. It is shown that a number of real storms exhibit a relationship between contraction and intensification that is similar to what is seen in the idealized simulations. In particular, the statistical distribution of intensifying tropical cyclones indicates that, for major hurricanes, most contraction is completed prior to most intensification. By forcing a linearized vortex model with the diabatic heating and frictional tendencies from a simulation, it is possible to qualitatively reproduce the simulated secondary circulation and separately examine the vortex responses to heating and friction. It is shown that heating and friction both contribute substantially to boundary layer inflow. They also both contribute to the contraction of the RMW, as the positive wind tendency from heating-induced inflow is maximized inside of the RMW, while the net negative wind tendency from friction and frictionally induced inflow is maximized outside of the RMW.

scholarly journals Large Roll Vortices Exhibited by Post-Tropical Cyclone Sandy during Landfall

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 259
Author(s):  
James A. Schiavone ◽  
Kun Gao ◽  
David A. Robinson ◽  
Peter J. Johnsen ◽  
Mathieu R. Gerbush
Keyword(s):  
Tropical Cyclone ◽  
Doppler Radar ◽  
Surface Wind ◽  
Weather Research And Forecasting ◽  
Wind Fields ◽  
Horizontal Scale ◽  
Vortex Model ◽  
Roll Vortices ◽  
O 10 ◽  
Horizontal Wavelength

Roll vortices are frequent features of a hurricane’s boundary layer, with kilometer or sub-kilometer horizontal scale. In this study, we found that large roll vortices with O (10 km) horizontal wavelength occurred over land in Post-Tropical Cyclone Sandy (2012) during landfall on New Jersey. Various characteristics of roll vortices were corroborated by analyses of Doppler radar observations, a 500 m resolution Weather Research and Forecasting (WRF) simulation, and an idealized roll vortex model. The roll vortices were always linear-shaped, and their wavelengths of 5–14 km were generally larger than any previously published for a tropical cyclone over land. Based on surface wind observations and simulated WRF surface wind fields, we found that roll vortices significantly increased the probability of hazardous winds and likely caused the observed patchiness of treefall during Sandy’s landfall.

scholarly journals A predictable smoothing evolution model for computer-controlled polishing

2020 ◽  
Vol 16 (1) ◽  
Author(s):  
Jing Hou ◽  
Pengli Lei ◽  
Shiwei Liu ◽  
Xianhua Chen ◽  
Jian Wang ◽  
...  
Keyword(s):  
Evolution Model ◽  
Quantitative Prediction ◽  
Theoretical Support ◽  
Model Combining ◽  
Process Guidance ◽  
Dependent Model ◽  
Computer Controlled Optical Surfacing ◽  
Computer Controlled ◽  
Time Dependent Model ◽  
Selection Of

AbstractQuantitative prediction of the smoothing of mid-spatial frequency errors (MSFE) is urgently needed to realize process guidance for computer controlled optical surfacing (CCOS) rather than a qualitative analysis of the processing results. Consequently, a predictable time-dependent model combining process parameters and an error decreasing factor (EDF) were presented in this paper. The basic smoothing theory, solution method and modification of this model were expounded separately and verified by experiments. The experimental results show that the theoretical predicted curve agrees well with the actual smoothing effect. The smoothing evolution model provides certain theoretical support and guidance for the quantitative prediction and parameter selection of the smoothing of MSFE.

A time-dependent model for high-pressure discharges in narrow ablative capillaries

1993 ◽  
Vol 50 (1) ◽  
pp. 51-70 ◽  
Author(s):  
D. Zoler ◽  
S. Cuperman ◽  
J. Ashkenazy ◽  
M. Caner ◽  
Z. Kaplan
Keyword(s):  
High Pressure ◽  
Equation Of State ◽  
Time Dependent ◽  
Dimensional Model ◽  
Plasma Sources ◽  
One Dimensional ◽  
Space And Time ◽  
Dependent Model ◽  
Energy Equations ◽  
Time Dependent Model

A time-dependent quasi-one-dimensional model is developed for studying high- pressure discharges in ablative capillaries used, for example, as plasma sources in electrothermal launchers. The main features of the model are (i) consideration of ablation effects in each of the continuity, momentum and energy equations; (ii) use of a non-ideal equation of state; and (iii) consideration of space- and time-dependent ionization.

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