Kinematics of the Secondary Eyewall Observed in Hurricane Rita (2005)

2011 ◽  
Vol 68 (8) ◽  
pp. 1620-1636 ◽  
Author(s):  
Anthony C. Didlake ◽  
Robert A. Houze
Keyword(s):  
Doppler Radar ◽  
Three Dimensional ◽  
Heavy Precipitation ◽  
Radar Data ◽  
Outer Edge ◽  
Vorticity Field ◽  
Wind Maximum ◽  
Comparable Rate ◽  
Hurricane Rita ◽  
Tangential Wind

Abstract Airborne Doppler radar data collected from the concentric eyewalls of Hurricane Rita (2005) provide detailed three-dimensional kinematic observations of the secondary eyewall feature. The secondary eyewall radar echo shows a ring of heavy precipitation containing embedded convective cells, which have no consistent orientation or radial location. The axisymmetric mean structure has a tangential wind maximum within the reflectivity maximum at 2-km altitude and an elevated distribution of its strongest winds on the radially outer edge. The corresponding vertical vorticity field contains a low-level maximum on the inside edge, which is part of a tube of increased vorticity that rises through the center of the reflectivity tower and into the midlevels. The secondary circulation consists of boundary layer inflow that radially overshoots the secondary eyewall. A portion of this inflowing air experiences convergence and supergradient forces that cause the air to rise and flow radially outward back into the center of the reflectivity tower. This mean updraft stretches and tilts the vorticity field to increase vorticity on the radially inner side of the tangential wind maximum. Radially outside this region, perturbation motions decrease the vorticity at a comparable rate. Thus, both mean and perturbation motions actively strengthen the wind maximum of the secondary eyewall. These features combine to give the secondary eyewall a structure different from the primary eyewall as it builds to become the new replacement eyewall.

Retrieved Thermodynamic Structure of Hurricane Rita (2005) from Airborne Multi-Doppler Radar Data

2021 ◽  
Author(s):  
Annette M. Boehm ◽  
Michael M. Bell
Keyword(s):  
Wind Shear ◽  
Doppler Radar ◽  
Three Dimensional ◽  
Vertical Wind Shear ◽  
Vertical Motion ◽  
Radar Data ◽  
Vertical Wind ◽  
Vertical Acceleration ◽  
Hurricane Rita ◽  
Doppler Radar Data

AbstractThe newly developed SAMURAI-TR is used to estimate three-dimensional temperature and pressure perturbations in Hurricane Rita on 23 September 2005 from multi-Doppler radar data during the RAINEX field campaign. These are believed to be the first fully three-dimensional gridded thermodynamic observations from a TC. Rita was a major hurricane at this time and was affected by 13 m s−1 deep-layer vertical wind shear. Analysis of the contributions of the kinematic and retrieved thermodynamic fields to different azimuthal wavenumbers suggests the interpretation of eyewall convective forcing within a three-level framework of balanced, quasi-balanced, and unbalanced motions. The axisymmetric, wavenumber-0 structure was approximately in thermal-wind balance, resulting in a large pressure drop and temperature increase toward the center. The wavenumber-1 structure was determined by the interaction of the storm with environmental vertical wind shear resulting in a quasi-balance between shear and shear-induced kinematic and thermo-dynamic perturbations. The observed wavenumber-1 thermodynamic asymmetries corroborate results of previous studies on the response of a vortex tilted by shear, and add new evidence that the vertical motion is nearly hydrostatic on the wavenumber-1 scale. Higher-order wavenumbers were associated with unbalanced motions and convective cells within the eyewall. The unbalanced vertical acceleration was positively correlated with buoyant forcing from thermal perturbations and negatively correlated with perturbation pressure gradients relative to the balanced vortex.

scholarly journals The Formation of Concentric Vorticity Structures in Typhoons

2004 ◽  
Vol 61 (22) ◽  
pp. 2722-2734 ◽  
Author(s):  
H-C. Kuo ◽  
L-Y. Lin ◽  
C-P. Chang ◽  
R. T. Williams
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Separation Distance ◽  
Outer Edge ◽  
Moist Convection ◽  
Vorticity Field ◽  
Wind Maximum ◽  
Central Vortex ◽  
The Core ◽  
Tangential Wind

Abstract An important issue in the formation of concentric eyewalls in a tropical cyclone is the development of a symmetric structure from asymmetric convection. It is proposed herein, with the aid of a nondivergent barotropic model, that concentric vorticity structures result from the interaction between a small and strong inner vortex (the tropical cyclone core) and neighboring weak vortices (the vorticity induced by the moist convection outside the central vortex of a tropical cyclone). The results highlight the pivotal role of the vorticity strength of the inner core vortex in maintaining itself, and in stretching, organizing, and stabilizing the outer vorticity field. Specifically, the core vortex induces a differential rotation across the large and weak vortex to strain out the latter into a vorticity band surrounding the former. The straining out of a large, weak vortex into a concentric vorticity band can also result in the contraction of the outer tangential wind maximum. The stability of the outer band is related to the Fjørtoft sufficient condition for stability because the strong inner vortex can cause the wind at the inner edge to be stronger than the outer edge, which allows the vorticity band and therefore the concentric structure to be sustained. Moreover, the inner vortex must possess high vorticity not only to be maintained against any deformation field induced by the outer vortices but also to maintain a smaller enstrophy cascade and to resist the merger process into a monopole. The negative vorticity anomaly in the moat serves as a “shield” or a barrier to the farther inward mixing the outer vorticity field. The binary vortex experiments described in this paper suggest that the formation of a concentric vorticity structure requires 1) a very strong core vortex with a vorticity at least 6 times stronger than the neighboring vortices, 2) a large neighboring vorticity area that is larger than the core vortex, and 3) a separation distance between the neighboring vorticity field and the core vortex that is within 3 to 4 times the core vortex radius.

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).

scholarly journals The genesis of Typhoon Nuri as observed during the Tropical Cyclone Structure 2008 (TCS-08) field experiment – Part 3: Dynamics of low-level spin-up during the genesis

2013 ◽  
Vol 13 (10) ◽  
pp. 26795-26840
Author(s):  
L. L. Lussier ◽  
M. T. Montgomery ◽  
M. M. Bell
Keyword(s):  
Tropical Cyclone ◽  
Doppler Radar ◽  
Three Dimensional ◽  
Tangential Velocity ◽  
Radar Data ◽  
Tropical Cyclogenesis ◽  
Low Level ◽  
Tangential Wind ◽  
Tropical Wave ◽  
Wind Profiles

Abstract. Aircraft reconnaissance data collected during the Tropical Cyclone Structure 2008 field campaign are used to examine further kinematical, dynamical and thermodynamical aspects of the genesis of Typhoon Nuri. Data from the first two missions into the pre-Nuri disturbance document the transition from a tropical wave to a tropical depression. Dropwindsonde-derived tangential wind profiles at several radii from the low-level circulation center indicate that the magnitude of low-level circulation increases and that the corresponding tangential velocity maximum moves inward from the first to second reconnaissance mission. To compliment these findings, a three-dimensional variational analysis incorporating both dropwindsonde and aircraft Doppler radar data is conducted. These data are used to perform circulation tendency calculations at multiple distances from the low-level circulation center. The results demonstrate a net spin-up of the system-scale circulation in the low-levels near the center and in the outer regions of the recirculating Kelvin cat's eye circulation. In these regions, the spin-up tendency due to the influx of cyclonic absolute vorticity exceeds the frictional spin-down tendency for both Nuri missions. The system-scale spin up is found to be accompanied by areas of low-level vorticity concentration through vortex-tube stretching associated with cumulus convection. The areal coverage and intensity of these high-vorticity regions increase between the first and second Nuri missions. The findings of this study are consistent in some respects to the Nuri observational analysis carried out by Raymond and Lopez (2011), but differ in their suggested key result and related scientific implication that the pre-Nuri disturbance was spinning down on the first day of observations. The findings herein strongly support a recent tropical cyclogenesis model positing that the Kelvin cat's eye circulation of the parent wave-like disturbance provides a favorable environment for convective-vorticity organization and low-level spin-up on the mesoscale.

scholarly journals The genesis of Typhoon Nuri as observed during the Tropical Cyclone Structure 2008 (TCS-08) field experiment – Part 3: Dynamics of low-level spin-up during the genesis

2014 ◽  
Vol 14 (16) ◽  
pp. 8795-8812 ◽  
Author(s):  
L. L. Lussier III ◽  
M. T. Montgomery ◽  
M. M. Bell
Keyword(s):  
Tropical Cyclone ◽  
Doppler Radar ◽  
Three Dimensional ◽  
Tangential Velocity ◽  
Radar Data ◽  
Tropical Cyclogenesis ◽  
Low Level ◽  
Tangential Wind ◽  
Tropical Wave ◽  
Wind Profiles

Abstract. Aircraft reconnaissance data collected during the Tropical Cyclone Structure 2008 field campaign are used to examine further kinematical, dynamical, and thermodynamical aspects of the genesis of Typhoon Nuri. Data from the first two missions into the pre-Nuri disturbance document the transition from a tropical wave to a tropical depression. Dropwindsonde-derived tangential wind profiles at several radii from the low-level circulation center indicate that the magnitude of low-level circulation increases and that the corresponding tangential velocity maximum moves inward from the first to second reconnaissance mission. To compliment these findings, a three-dimensional variational analysis incorporating both dropwindsonde and aircraft Doppler radar data is conducted. These data are used to perform circulation tendency calculations at multiple distances from the low-level circulation center. The results demonstrate a net spin-up of the system-scale circulation in the low levels near the center and in the outer regions of the recirculating Kelvin cat's eye circulation. In these regions, the spin-up tendency due to the influx of cyclonic absolute vorticity exceeds the frictional spin-down tendency for both Nuri missions. The system-scale spin-up is found to be accompanied by areas of low-level vorticity concentration through vortex-tube stretching associated with cumulus convection. The areal coverage and intensity of these high-vorticity regions increase between the first and second Nuri missions. The findings of this study are consistent in some respects to the Nuri observational analysis carried out by Raymond and López-Carrillo (2011), but differ in their suggested key results and related scientific implications that the pre-Nuri disturbance was spinning down in the planetary boundary layer on the first day of observations. The findings herein strongly support a recent tropical cyclogenesis model positing that the Kelvin cat's eye circulation of the parent wave-like disturbance provides a favorable environment for convective vorticity organization and low-level spin-up on the mesoscale.

Convective-Scale Downdrafts in the Principal Rainband of Hurricane Katrina (2005)

2009 ◽  
Vol 137 (10) ◽  
pp. 3269-3293 ◽  
Author(s):  
Anthony C. Didlake ◽  
Robert A. Houze
Keyword(s):  
Hurricane Katrina ◽  
Doppler Radar ◽  
Extended Period ◽  
Heavy Rain ◽  
Radar Data ◽  
Intensity Change ◽  
Wind Maximum ◽  
Tangential Wind ◽  
Convective Scale ◽  
Negative Buoyancy

Abstract Airborne Doppler radar data collected during the Hurricane Rainband and Intensity Change Experiment (RAINEX) document downdrafts in the principal rainband of Hurricane Katrina (2005). Inner-edge downdrafts (IEDs) originating at 6–8-km altitude created a sharp reflectivity gradient along the inner boundary of the rainband. Low-level downdrafts (LLDs) evidently driven by precipitation drag originated at 2–4 km within the heavy rain cells of each convective element. The IED and LLD were spatially separated by but closely associated with the updrafts within the rainband. The IED was forced aloft by pressure perturbations formed in response to the adjacent buoyant updrafts. Once descending, the air attained negative buoyancy via evaporative cooling from the rainband precipitation. A convective-scale tangential wind maximum tended to occur in the radial inflow at lower levels in association with the IED, which enhanced the inward flux of angular momentum at lower levels. Convergence at the base of the downdrafts on the upwind end of the principal rainband contributed to the principal rainband growing in length. New updraft elements triggered by this convergence led to the formation of new IED and LLD pockets, which were subsequently advected downwind around the storm by the vortex winds while additional new cells continued to form on the upwind end of the band. These processes sustained the principal rainband and helped to make it effectively stationary relative to the storm center, thus maintaining its impact on the hurricane dynamics over an extended period.

scholarly journals Wind Structure of a Subtropical Squall Line in China: Results from Dual-Doppler Radar Data

2016 ◽  
Vol 2016 ◽  
pp. 1-18
Author(s):  
Haiguang Zhou
Keyword(s):  
Doppler Radar ◽  
Three Dimensional ◽  
Leading Edge ◽  
Heavy Precipitation ◽  
Radar Data ◽  
Squall Line ◽  
Stratiform Region ◽  
Convective Region ◽  
Doppler Data ◽  
Mature Period

A subtropical squall line moved from Guangxi to Guangdong province in South China on 23-24 April 2007, which resulted in gale and heavy precipitation. The three-dimensional (3D) wind field of the squall line in its mature period was retrieved by Guangzhou-Shenzhen dual-Doppler data. The 3D conceptual model of this squall line was proposed. On the horizontal plane, the storm-relative front-to-rear inflow prevailed at the lower altitudes of the leading edge. The rear-to-front cold inflow in the stratiform region was observed below 3 km height, which enhanced the convergence in the convective region. At the middle altitudes of the squall line, the front-to-rear horizontal flow prevailed. Strong updrafts were observed at the lower and middle altitudes of the leading edge. Some convergence centers were located at the lower altitudes of the convective region. Furthermore, the storm-relative flow in the vertical cross-section perpendicular to the squall line was revealed. The front-to-rear warm flow extended from the surface to 7.5 km altitude at the leading edge. Above it, part of the front-to-rear inflow blew upward and then forward, and the other part of the inflow blew backward. The descending rear-to-front cold flow was only seen below 3 km height in the stratiform region.

scholarly journals Retrieval of three-dimensional wind fields from Doppler radar data using an efficient two-step approach

2010 ◽  
Vol 3 (5) ◽  
pp. 4459-4495 ◽  
Author(s):  
C. López Carrillo ◽  
D. J. Raymond
Keyword(s):  
Variational Approach ◽  
Continuity Equation ◽  
Doppler Radar ◽  
Three Dimensional ◽  
Relevant Information ◽  
Radar Data ◽  
Wind Fields ◽  
Wind Retrieval ◽  
Complex Sampling ◽  
Doppler Radar Data

Abstract. In this work, we describe an efficient approach for wind retrieval from dual Doppler radar data. The approach produces a gridded field that not only satisfies the observations, but also satisfies the anelastic mass continuity equation. The method is based on the so-called three-dimensional variational approach to the retrieval of wind fields from radar data. The novelty consists in separating the task into steps that reduce the amount of data processed by the global minimization algorithm, while keeping the most relevant information from the radar observations. The method is flexible enough to incorporate observations from several radars, accommodate complex sampling geometries, and readily include dropsonde or sounding observations in the analysis. We demonstrate the usefulness of our method by analyzing a real case with data collected during the TPARC/TCS-08 field campaign.

scholarly journals Vertical Vortex Development in Hurricane Michael (2018) during Rapid Intensification

2021 ◽  
Author(s):  
Alexander J. DesRosiers ◽  
Michael M. Bell ◽  
Ting-Yu Cha
Keyword(s):  
Inner Core ◽  
Doppler Radar ◽  
Three Dimensional ◽  
Vertical Gradient ◽  
Machine Learning Techniques ◽  
Rapid Intensification ◽  
Wind Retrieval ◽  
Retrieval Technique ◽  
Budget Analysis ◽  
Tangential Wind

AbstractThe landfall of Hurricane Michael (2018) at category 5 intensity occurred after rapid intensification (RI) spanning much of the storm’s lifetime. Four Hurricane Hunter aircraft missions observed the RI period with tail Doppler radar (TDR). Data from each of the 14 aircraft passes through the storm were quality controlled via a combination of interactive and machine learning techniques. TDR data from each pass were synthesized using the SAMURAI variational wind retrieval technique to yield three-dimensional kinematic fields of the storm to examine inner core processes during RI. Vorticity and angular momentum increased and concentrated in the eyewall region. A vorticity budget analysis indicates the tendencies became more axisymmetric over time. In this study we focus in particular on how the eyewall vorticity tower builds vertically into the upper levels. Horizontal vorticity associated with the vertical gradient of tangential wind was tilted into the vertical by the eyewall updraft to yield a positive vertical vorticity tendency inward atop the existing vorticity tower, that is further developed locally upward and outward along the sloped eyewall through advection and stretching. Observed maintenance of thermal wind balance from a thermodynamic retrieval shows evidence of a strengthening warm core, which aided in lowering surface pressure and further contributed to the efficient intensification in the latter stages of this RI event.

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