scholarly journals Generalized VTD Retrieval of Atmospheric Vortex Kinematic Structure. Part I: Formulation and Error Analysis

2008 ◽  
Vol 136 (3) ◽  
pp. 995-1012 ◽  
Author(s):  
Ben Jong-Dao Jou ◽  
Wen-Chau Lee ◽  
Su-Ping Liu ◽  
Yu-Cheng Kao
Keyword(s):  
Doppler Radar ◽  
Geometric Distortion ◽  
Doppler Velocity ◽  
New Paradigm ◽  
Wind Fields ◽  
Radar Signature ◽  
Tangential Wind ◽  
The Mean ◽  
Domain 3 ◽  
Atmospheric Vortices

Abstract The primary circulation of atmospheric vortices, such as tropical cyclones and tornadoes, can be estimated from single-Doppler radar observations using the ground-based velocity track display (GBVTD) algorithm. The GBVTD algorithm has limitations in the following four areas: 1) distortion in the retrieved asymmetric wind fields, 2) a limited analysis domain, 3) the inability to resolve the cross-beam component of the mean wind, and 4) the inability to separate the asymmetric tangential and radial winds. This paper presents the generalized velocity track display (GVTD) algorithm, which eliminates the first two limitations inherent in the GBVTD technique and demonstrates the possibility of subjectively estimating the mean wind vector when its signature is visible beyond the influence of the vortex circulation. In this new paradigm, the GVTD algorithm fits the atmospheric vortex circulation to a new variable VdD/RT in a linear azimuth angle (θ′), rather than the Doppler velocity Vd in a nonlinear angle (ψ), which is used in GBVTD. Key vortex kinematic structures (e.g., mean wind, axisymmetric tangential wind, etc.) in the VdD/RT space simplify the interpretation of the radar signature and eliminate the geometric distortion inherent in the Vd display. This is a significant improvement in diagnosing vortex structures in both operations and research. The advantages of using VdD/RT are illustrated using analytical atmospheric vortices, and the properties are compared with GBVTD. The characteristics of the VdD/RT display of Typhoon Gladys (1994) can be approximated by a constant mean wind plus an axisymmetric vortex.

Reducing Errors in Velocity–Azimuth Display (VAD) Wind and Deformation Retrievals from Airborne Doppler Radars in Convective Environments

2020 ◽  
Vol 37 (12) ◽  
pp. 2251-2266
Author(s):  
Charles N. Helms ◽  
Matthew L. Walker McLinden ◽  
Gerald M. Heymsfield ◽  
Stephen R. Guimond
Keyword(s):  
Wind Field ◽  
Doppler Radar ◽  
Weighting Function ◽  
Deep Convection ◽  
Absolute Error ◽  
Doppler Velocity ◽  
Wind Fields ◽  
Time Data ◽  
Single Antenna ◽  
Median Absolute Error

AbstractThe present study describes methods to reduce the uncertainty of velocity–azimuth display (VAD) wind and deformation retrievals from downward-pointing, conically scanning, airborne Doppler radars. These retrievals have important applications in data assimilation and real-time data processing. Several error sources for VAD retrievals are considered here, including violations to the underlying wind field assumptions, Doppler velocity noise, data gaps, temporal variability, and the spatial weighting function of the VAD retrieval. Specific to airborne VAD retrievals, we also consider errors produced due to the radar scans occurring while the instrument platform is in motion. While VAD retrievals are typically performed using data from a single antenna revolution, other strategies for selecting data can be used to reduce retrieval errors. Four such data selection strategies for airborne VAD retrievals are evaluated here with respect to their effects on the errors. These methods are evaluated using the second hurricane nature run numerical simulation, analytic wind fields, and observed Doppler radar radial velocities. The proposed methods are shown to reduce the median absolute error of the VAD wind retrievals, especially in the vicinity of deep convection embedded in stratiform precipitation. The median absolute error due to wind field assumption violations for the along-track and for the across-track wind is reduced from 0.36 to 0.08 m s−1 and from 0.35 to 0.24 m s−1, respectively. Although the study focuses on Doppler radars, the results are equally applicable to conically scanning Doppler lidars as well.

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.

The Improvement to the Environmental Wind and Tropical Cyclone Circulation Retrievals with the Modified GBVTD (MGBVTD) Technique

2013 ◽  
Vol 52 (11) ◽  
pp. 2493-2508 ◽  
Author(s):  
Xiaomin Chen ◽  
Kun Zhao ◽  
Wen-Chau Lee ◽  
Ben Jong-Dao Jou ◽  
Ming Xue ◽  
...  
Keyword(s):  
Inner Core ◽  
Doppler Radar ◽  
Three Dimensional ◽  
Radar Data ◽  
Accurate Estimation ◽  
Doppler Radar Data ◽  
Tangential Wind ◽  
The Mean ◽  
Landfalling Tropical Cyclones ◽  
Beam Component

AbstractThe ground-based velocity track display (GBVTD) was developed to deduce a three-dimensional primary circulation of landfalling tropical cyclones from single-Doppler radar data. However, the cross-beam component of the mean wind cannot be resolved and is consequently aliased into the retrieved axisymmetric tangential wind . Recently, the development of the hurricane volume velocity processing method (HVVP) enabled the independent estimation of ; however, HVVP is potentially limited by the unknown accuracy of empirical assumptions used to deduce the modified Rankine-combined vortex exponent . By combing the GBVTD with HVVP techniques, this study proposes a modified GBVTD method (MGBVTD) to objectively deduce from the GBVTD technique and provide a more accurate estimation of and via an iterative procedure to reach converged and cross-beam component of solutions. MGBVTD retains the strength of both algorithms but avoids their weaknesses. The results from idealized experiments demonstrate that the MGBVTD-retrieved cross-beam component of is within 2 m s−1 of reality. MGBVTD was applied to Hurricane Bret (1999) whose inner core was captured simultaneously by two Weather Surveillance Radar-1988 Doppler (WSR-88D) instruments. The MGBVTD-retrieved cross-beam component of from single-Doppler radar data is very close to that from dual-Doppler radar synthesis using extended GBVTD (EGBVTD); their difference is less than 2 m s−1. The mean difference in the MGBVTD-retrieved from the two radars is ~2 m s−1, which is significantly smaller than that resolved in GBVTD retrievals (~5 m s−1).

Velocity–Azimuth Display Analysis of Doppler Velocity for HIWRAP

2015 ◽  
Vol 54 (8) ◽  
pp. 1792-1808 ◽  
Author(s):  
Lin Tian ◽  
Gerald M. Heymsfield ◽  
Anthony C. Didlake ◽  
Stephen Guimond ◽  
Lihua Li
Keyword(s):  
Deep Convection ◽  
Doppler Velocity ◽  
Rapid Intensification ◽  
Wind Fields ◽  
Operational Forecasts ◽  
Analysis Technique ◽  
The Mean ◽  
Conical Scan ◽  
Along Track ◽  
Doppler Analysis

AbstractThe velocity–azimuth display (VAD) analysis technique established for ground-based scanning radar is applied to the NASA High-Altitude Imaging Wind and Rain Airborne Profiler (HIWRAP). The VAD technique provides a mean vertical profile of the horizontal winds for each complete conical scan of the HIWRAP radar. One advantage of this technique is that it has shown great value for data assimilation and for operational forecasts. Another advantage is that it is computationally inexpensive, which makes it suitable for real-time retrievals. The VAD analysis has been applied to the HIWRAP data collected during NASA’s Genesis and Rapid Intensification Processes (GRIP) mission. The traditional dual-Doppler analysis for deriving wind fields in the nadir plane is also presented and is compared with the VAD analysis. The results show that the along-track winds from the VAD technique and dual-Doppler analysis agree in general. The VAD horizontal winds capture the mean vortex structure of two tropical cyclones, and they are in general agreement with winds from nearby dropsondes. Several assumptions are made for the VAD technique. These assumptions include a stationary platform for each HIWRAP scan and constant vertical velocity of the hydrometeors along each complete scan. As a result, the VAD technique can produce appreciable errors in regions of deep convection such as the eyewall, whereas in stratiform regions the retrieval errors are minimal. Despite these errors, the VAD technique can still adequately capture the larger-scale structure of the hurricane vortex given a sufficient number of flight passes over the storm.

scholarly journals Doppler Radar Analysis of the Rapid Intensification of Typhoon Goni (2015) after Eyewall Replacement

2018 ◽  
Vol 75 (1) ◽  
pp. 143-162 ◽  
Author(s):  
Udai Shimada ◽  
Masahiro Sawada ◽  
Hiroyuki Yamada
Keyword(s):  
Angular Momentum ◽  
Wind Field ◽  
Doppler Radar ◽  
Rapid Intensification ◽  
Wind Fields ◽  
Maximum Wind ◽  
Low Level ◽  
Contraction Speed ◽  
Budget Analysis ◽  
Tangential Wind

A ground-based Doppler radar observed the rapid intensification (RI) of Typhoon Goni (2015) for 24 h immediately after it completed an eyewall replacement cycle. Goni’s RI processes were examined by using radar reflectivity and wind fields retrieved by the ground-based velocity track display (GBVTD) technique. The maximum wind at 2-km altitude increased by 30 m s−1 during the first 6 h of RI, and it further increased by 20 m s−1 during the subsequent 12 h. Around the onset of RI, relatively strong outflow (>2 m s−1) was present both inside and outside the radius of maximum wind (RMW) above the boundary layer (BL), suggesting the existence of supergradient flow in and just above the BL. Despite this outflow, angular momentum increased inside the RMW. The low-level RMW contracted rapidly from 50 to 33 km, causing the RMW to slope greatly outward with height. The radius of maximum reflectivity was a few kilometers inside the RMW. A budget analysis of absolute angular momentum showed that the outflow contributed to the contraction of the tangential wind field. During RI, eyewall convection was enhanced, and a well-defined eye appeared. The low-level outflow changed into inflow immediately outside the RMW. Then the tangential wind field and high inertial stability region expanded radially outward, followed by the formation of an outer reflectivity maximum at twice the RMW. The contraction speed of the low-level RMW slowed down.

scholarly journals The Accuracy of Radar Estimates of Ice Terminal Fall Speed from Vertically Pointing Doppler Radar Measurements

2011 ◽  
Vol 50 (10) ◽  
pp. 2120-2138 ◽  
Author(s):  
Alain Protat ◽  
Christopher R. Williams
Keyword(s):  
Statistical Methods ◽  
Doppler Radar ◽  
Doppler Velocity ◽  
Air Velocity ◽  
Ice Clouds ◽  
Microphysical Properties ◽  
Radar Measurements ◽  
The Mean ◽  
Fall Speed ◽  
Two Parameters

AbstractDoppler radar measurements at different frequencies (50 and 2835 MHz) are used to characterize the terminal fall speed of hydrometeors and the vertical air motion in tropical ice clouds and to evaluate statistical methods for retrieving these two parameters using a single vertically pointing cloud radar. For the observed vertical air motions, it is found that the mean vertical air velocity in ice clouds is small on average, as is assumed in terminal fall speed retrieval methods. The mean vertical air motions are slightly negative (downdraft) between the melting layer (5-km height) and 6.3-km height, and positive (updraft) above this altitude, with two peaks of 6 and 7 cm s−1 at 7.7- and 9.7-km height. For the retrieved hydrometeor terminal fall speeds, it is found that the variability of terminal fall speeds within narrow reflectivity ranges is typically within the acceptable uncertainties for using terminal fall speeds in ice cloud microphysical retrievals. This study also evaluates the performance of previously published statistical methods of separating terminal fall speed and vertical air velocity from vertically pointing Doppler radar measurements using the 50-/2835-MHz radar retrievals as a reference. It is found that the variability of the terminal fall speed–radar reflectivity relationship (Vt–Ze) is large in ice clouds and cannot be parameterized accurately with a single relationship. A well-defined linear relationship is found between the two coefficients of a power-law Vt–Ze relationship, but a more accurate microphysical retrieval is obtained using Doppler velocity measurements to better constrain the Vt–Ze relationship for each cloud. When comparing the different statistical methods to the reference, the distribution of terminal fall speed residual is wide, with most residuals being in the ±30–40 cm s−1 range about the mean. The typical mean residual ranged from 15 to 20 cm s−1, with different methods having mean residuals of <10 cm s−1 at some heights, but not at the same heights for all methods. The so-called Vt–Ze technique was the most accurate above 9-km height, and the running-mean technique outperformed the other techniques below 9-km height. Sensitivity tests of the running-mean technique indicate that the 20-min average is the best trade-off for the type of ice clouds considered in this analysis. A new technique is proposed that incorporates simple averages of Doppler velocity for each (Ze, H) couple in a given cloud. This technique, referred to as DOP–Ze–H, was found to outperform the three other methods at most heights, with a mean terminal fall residual of <10 cm s−1 at all heights. This error magnitude is compatible with the use of such retrieved terminal fall speeds for the retrieval of microphysical properties.

scholarly journals Principal Component Analysis of Doppler Radar Data. Part I: Geometric Connections between Eigenvectors and the Core Region of Atmospheric Vortices

2005 ◽  
Vol 62 (11) ◽  
pp. 4027-4042 ◽  
Author(s):  
Paul R. Harasti ◽  
Roland List
Keyword(s):  
Principal Component Analysis ◽  
Doppler Radar ◽  
Principal Component ◽  
Component Analysis ◽  
Radar Data ◽  
Core Region ◽  
Doppler Velocity ◽  
Maximum Wind ◽  
The Core ◽  
Atmospheric Vortices

Abstract This is the first in a three-part series of papers that present the first applications of principal component analysis (PCA) to Doppler radar data. Although this novel approach has potential applications to many types of atmospheric phenomena, the specific goal of this series is to describe and verify a methodology that establishes the position and radial extent of the core region of atmospheric vortices. The underlying assumption in the current application is that the streamlines of the nondivergent component of the horizontal wind are predominantly circular, which is a characteristic often observed in intense vortices such as tropical cyclones. The method employs an S2-mode PCA on the Doppler velocity data taken from a single surveillance scan and arranged sequentially in a matrix according to the range and azimuth coordinates. Part I begins the series by examining the eigenvectors obtained from such a PCA applied to a Doppler velocity model for a modified, Rankine-combined vortex, where the ratio of the radius of maximum wind to the range from the radar to the circulation center is varied over a wide range of values typically encountered in the field. Results show that the first two eigenvectors within the eigenspace of range coordinates represent over 99% of the total variance in the data. It is also demonstrated that the coordinates of particular cusps in the curves of the eigenvector coefficients plotted against their indices are geometrically related to both the position of circulation center and the radius of maximum wind.

Intercomparison of Ground-Based Velocity Track Display (GBVTD)-Retrieved Circulation Centers and Structures of Hurricane Danny (1997) from Two Coastal WSR-88Ds

2011 ◽  
Vol 139 (1) ◽  
pp. 153-174 ◽  
Author(s):  
Shirley T. Murillo ◽  
Wen-Chau Lee ◽  
Michael M. Bell ◽  
Gary M. Barnes ◽  
Frank D. Marks ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Doppler Radar ◽  
Simplex Algorithm ◽  
Wind Maximum ◽  
Wind Retrieval ◽  
Highly Sensitive ◽  
Tangential Wind ◽  
Center Position ◽  
The Mean

Abstract A plausible primary circulation and circulation center of a tropical cyclone (TC) can be deduced from a coastal Doppler radar using the ground-based velocity track display (GBVTD) technique and the GBVTD-simplex algorithm. The quality of the retrieved primary circulation is highly sensitive to the accuracy of the circulation center that can only be estimated from the degree of scattering of all possible centers obtained in GBVTD-simplex analyses from a single radar in real TCs. This study extends previous work to examine the uncertainties in the GBVTD-simplex-derived circulation centers and the GBVTD-derived primary circulations in Hurricane Danny (1997) sampled simultaneously from two Doppler radars [Weather Surveillance Radar-1988 Dopplers (WSR-88Ds) in Mobile, Alabama, and Slidell, Louisiana] for 5 h. It is found that the mean difference between the individually computed GBVTD-simplex-derived centers is 2.13 km, similar to the estimates in previous studies. This value can be improved to 1.59 km by imposing time continuity in the radius of maximum wind, maximum mean tangential wind, and the center position in successive volumes. These additional physical criteria, not considered in previous work, stabilized the GBVTD-simplex algorithm and paved the way for automating the center finding and wind retrieval procedures in the future. Using the improved set of centers, Danny’s axisymmetric tangential wind structures retrieved from each radar showed general agreement with systematic differences (up to 6 m s−1) in certain periods. The consistency in the wavenumber-1 tangential winds was not as good as their axisymmetric counterparts. It is suspected that the systematic differences in the axisymmetric tangential winds were caused by the unresolved wavenumber-2 sine components rather than from the relatively small cross-beam mean wind components in Danny.

scholarly journals A Variational Method for Detecting and Characterizing Convective Vortices in Cartesian Wind Fields

2013 ◽  
Vol 141 (9) ◽  
pp. 3102-3115 ◽  
Author(s):  
Corey K. Potvin
Keyword(s):  
Doppler Radar ◽  
Horizontal Wind ◽  
Wind Fields ◽  
Complex Flow ◽  
Ensemble Forecasts ◽  
Tangential Wind ◽  
Data Volume ◽  
Vortex Size ◽  
Objective Detection ◽  
Convective Vortices

Abstract Vortex detection algorithms are required for both research and operational applications in which data volume precludes timely subjective examination of model or analysis fields. Unfortunately, objective detection of convective vortices is often hindered by the strength and complexity of the flow in which they are embedded. To address this problem, a variational vortex-fitting algorithm previously developed to detect and characterize vortices observed by Doppler radar has been modified to operate on gridded horizontal wind data. The latter are fit to a simple analytical model of a vortex and its proximate environment, allowing the retrieval of important vortex characteristics. This permits the development of detection criteria tied directly to vortex properties (e.g., maximum tangential wind), rather than to more general kinematical properties that may poorly represent the vortex itself (e.g., vertical vorticity) when the background flow is strongly sheared. Thus, the vortex characteristic estimates provided by the technique may permit more effective detection criteria while providing useful information about vortex size, intensity, and trends therein. In tests with two simulated supercells, the technique proficiently detects and characterizes vortices, even in the presence of complex flow. Sensitivity tests suggest the algorithm would work well for a variety of vortex sizes without additional tuning. Possible applications of the technique include investigating relationships between mesocyclone and tornado characteristics, and detecting tornadoes, mesocyclones, and mesovortices in real-time ensemble forecasts.

Intensity and Inner-Core Structure of Typhoon Haiyan (2013) near Landfall: Doppler Radar Analysis

2018 ◽  
Vol 146 (2) ◽  
pp. 583-597 ◽  
Author(s):  
Udai Shimada ◽  
Hisayuki Kubota ◽  
Hiroyuki Yamada ◽  
Esperanza O. Cayanan ◽  
Flaviana D. Hilario
Keyword(s):  
Wind Speed ◽  
Inner Core ◽  
Doppler Radar ◽  
Core Structure ◽  
Maximum Wind Speed ◽  
Vertical Shear ◽  
Doppler Velocity ◽  
Maximum Wind ◽  
Tangential Wind ◽  
The Right

Abstract The intensity and inner-core structure of an extremely intense tropical cyclone, Typhoon Haiyan (2013), were examined using real-time ground-based Doppler radar products from the Guiuan radar over the period of about 2.5 h immediately before the storm approached Guiuan in Eastern Samar, Philippines. Haiyan’s wind fields from 2- to 6-km altitude were retrieved by the ground-based velocity track display (GBVTD) technique from the Doppler velocity data. The GBVTD-retrieved maximum wind speed reached 101 m s−1 at 4-km altitude on the right side of the track. The relatively fast forward speed of Haiyan, about 11 m s−1, increased maximum wind speed on the right-hand side of the storm. Azimuthal mean tangential wind increased with height from 2 to 5 km, and a local maximum of 86 m s−1 occurred at 5-km altitude. The central pressure was estimated as 906 hPa with an uncertainty of ±4 hPa by using the GBVTD-retrieved tangential wind and by assuming gradient wind balance. The radius of maximum radar reflectivity was about 23 km from the center, a few kilometers inside the radius of maximum wind. The reflectivity structure was highly asymmetric at and above 3-km altitude, and was more symmetric below 3-km altitude in the presence of relatively weak vertical shear (~4 m s−1). The center of the eyewall ring was tilted slightly downshear with height.

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