scholarly journals Role of eyewall and rainband eddy forcing in tropical cyclone intensification

2019 ◽  
Vol 19 (22) ◽  
pp. 14289-14310 ◽  
Author(s):  
Ping Zhu ◽  
Bryce Tyner ◽  
Jun A. Zhang ◽  
Eric Aligo ◽  
Sundararaman Gopalakrishnan ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Turbulent Mixing ◽  
Inner Core ◽  
Weather Research And Forecasting ◽  
Rapid Changes ◽  
Flow Feature ◽  
Secondary Circulations ◽  
Vertical Turbulent Mixing ◽  
Operational Models

Abstract. While turbulence is commonly regarded as a flow feature pertaining to the planetary boundary layer (PBL), intense turbulent mixing generated by cloud processes also exists above the PBL in the eyewall and rainbands of a tropical cyclone (TC). The in-cloud turbulence above the PBL is intimately involved in the development of convective elements in the eyewall and rainbands and consists of a part of asymmetric eddy forcing for the evolution of the primary and secondary circulations of a TC. In this study, we show that the Hurricane Weather Research and Forecasting (HWRF) model, one of the operational models used for TC prediction, is unable to generate appropriate sub-grid-scale (SGS) eddy forcing above the PBL due to a lack of consideration of intense turbulent mixing generated by the eyewall and rainband clouds. Incorporating an in-cloud turbulent-mixing parameterization in the vertical turbulent-mixing scheme notably improves the HWRF model's skills in predicting rapid changes in intensity for several past major hurricanes. While the analyses show that the SGS eddy forcing above the PBL is only about one-fifth of the model-resolved eddy forcing, the simulated TC vortex inner-core structure, secondary overturning circulation, and the model-resolved eddy forcing exhibit a substantial dependence on the parameterized SGS eddy processes. The results highlight the importance of eyewall and rainband SGS eddy forcing to numerical prediction of TC intensification, including rapid intensification at the current resolution of operational models.

scholarly journals Role of eyewall and rainband eddy forcing in tropical cyclone intensification

2018 ◽  
Author(s):  
Ping Zhu ◽  
Bryce Tyner ◽  
Jun A. Zhang ◽  
Eric Aligo ◽  
Sundararaman Gopalakrishnan ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Turbulent Mixing ◽  
Inner Core ◽  
Rapid Intensification ◽  
Rapid Changes ◽  
Flow Feature ◽  
Pbl Scheme ◽  
Operational Models ◽  
Fundamental Mechanism

Abstract. The fundamental mechanism underlying tropical cyclone (TC) intensification may be understood from the conservation of absolute angular momentum, where the primary circulation of a TC is driven by the torque acting on air parcels resulting from asymmetric eddy processes, including turbulence. While turbulence is commonly regarded as a flow feature pertaining to the planetary boundary layer (PBL), intense turbulent mixing generated by cloud processes also exists above the PBL in the eyewall and rainbands. Unlike the eddy forcing within the PBL that is negative definite, the sign of eyewall/rainband eddy forcing above the PBL is indefinite and thus provides a possible mechanism to spin up a TC vortex. In this study, we show that the Hurricane Weather Research & forecasting (HWRF) model, one of the operational models used for TC prediction, is unable to generate appropriate sub-grid-scale (SGS) eddy forcing above the PBL due to lack of consideration of intense turbulent mixing generated by the eyewall and rainband clouds. Incorporating an in-cloud turbulent mixing parameterization in the PBL scheme notably improves HWRF's skills on predicting rapid changes in intensity for several past major hurricanes. While the analyses show that the SGS eddy forcing above the PBL is only about one-fifth of the model-resolved eddy forcing, the simulated TC vortex inner-core structure and the associated model-resolved eddy forcing exhibit a substantial dependence on the parameterized SGS eddy processes. The results highlight the importance of eyewall/rainband SGS eddy forcing to numerical prediction of TC intensification, including rapid intensification at the current resolution of operational models.

scholarly journals Impact of environmental moisture on tropical cyclone intensification

2015 ◽  
Vol 15 (11) ◽  
pp. 16111-16139 ◽  
Author(s):  
L. Wu ◽  
H. Su ◽  
R. G. Fovell ◽  
T. J. Dunkerton ◽  
Z. Wang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Inner Core ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Convective Activity ◽  
Dry Air ◽  
Moving Storm ◽  
Lagrangian Boundary ◽  
Moisture Increase

Abstract. The impacts of environmental moisture on the intensification of a tropical cyclone (TC) are investigated in the Weather Research and Forecasting (WRF) model, with a focus on the azimuthal asymmetry of the moisture impacts. A series of sensitivity experiments with varying moisture perturbations in the environment are conducted and the Marsupial Paradigm framework is employed to understand the different moisture impacts. We find that modification of environmental moisture has insignificant impacts on the storm in this case unless it leads to convective activity in the environment, which deforms the quasi-Lagrangian boundary of the storm. By facilitating convection and precipitation outside the storm, enhanced environmental moisture ahead of the northwestward-moving storm induces a dry air intrusion to the inner core and limits TC intensification. However, increased moisture in the rear quadrants favors intensification by providing more moisture to the inner core and promoting storm symmetry, with primary contributions coming from moisture increase in the boundary layer. The different impacts of environmental moisture on TC intensification are governed by the relative locations of moisture perturbations and their interactions with the storm Lagrangian structure.

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 Impact of environmental moisture on tropical cyclone intensification

2015 ◽  
Vol 15 (24) ◽  
pp. 14041-14053 ◽  
Author(s):  
L. Wu ◽  
H. Su ◽  
R. G. Fovell ◽  
T. J. Dunkerton ◽  
Z. Wang ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Moisture Transport ◽  
Inner Core ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Convective Activity ◽  
Dry Air ◽  
Moving Storm ◽  
Lagrangian Boundary ◽  
Moisture Increase

Abstract. The impacts of environmental moisture on the intensification of a tropical cyclone (TC) are investigated in the Weather Research and Forecasting (WRF) model, with a focus on the azimuthal asymmetry of the moisture impacts relative to the storm path. A series of sensitivity experiments with varying moisture perturbations in the environment are conducted and the Marsupial Paradigm framework is employed to understand the different moisture impacts. We find that modification of environmental moisture has insignificant impacts on the storm in this case unless it leads to convective activity that deforms the quasi-Lagrangian boundary of the storm and changes the moisture transport into the storm. By facilitating convection and precipitation outside the storm, enhanced environmental moisture ahead of the northwestward-moving storm induces a dry air intrusion to the inner core and limits TC intensification. In contrast, increased moisture in the rear quadrants favors intensification by providing more moisture to the inner core and promoting storm symmetry, with primary contributions coming from moisture increase in the boundary layer. The different impacts of environmental moisture on TC intensification are governed by the relative locations of moisture perturbations and their interactions with the storm Lagrangian structure.

scholarly journals Probabilistic Prediction of Tropical Cyclone Intensity with an Analog Ensemble

2018 ◽  
Vol 146 (6) ◽  
pp. 1723-1744 ◽  
Author(s):  
Stefano Alessandrini ◽  
Luca Delle Monache ◽  
Christopher M. Rozoff ◽  
William E. Lewis
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Absolute Error ◽  
Eastern Pacific ◽  
Training Dataset ◽  
Ensemble Prediction ◽  
Weather Research And Forecasting ◽  
Lead Times ◽  
Probabilistic Prediction ◽  
Cyclone Intensity

An analog ensemble (AnEn) technique is applied to the prediction of tropical cyclone (TC) intensity (i.e., maximum 1-min averaged 10-m wind speed). The AnEn is an inexpensive, naturally calibrated ensemble prediction of TC intensity derived from a training dataset of deterministic Hurricane Weather Research and Forecasting (HWRF; 2015 version) Model forecasts. In this implementation of the AnEn, a set of analog forecasts is generated by searching an HWRF archive for forecasts sharing key features with the current HWRF forecast. The forecast training period spans 2011–15. The similarity of a current forecast with past forecasts is estimated using predictors derived from the HWRF reforecasts that capture thermodynamic and kinematic properties of a TC’s environment and its inner core. Additionally, the value of adding a multimodel intensity consensus forecast as an AnEn predictor is examined. Once analogs are identified, the verifying intensity observations corresponding to each analog HWRF forecast are used to produce the AnEn intensity prediction. In this work, the AnEn is developed for both the eastern Pacific and Atlantic Ocean basins. The AnEn’s performance with respect to mean absolute error (MAE) is compared with the raw HWRF output, the official National Hurricane Center (NHC) forecast, and other top-performing NHC models. Also, probabilistic intensity forecasts are compared with a quantile mapping model based on the HWRF’s intensity forecast. In terms of MAE, the AnEn outperforms HWRF in the eastern Pacific at all lead times examined and up to 24-h lead time in the Atlantic. Also, unlike traditional dynamical ensembles, the AnEn produces an excellent spread–skill relationship.

Sensitivity on tendency perturbations of tropical cyclone short-range intensity forecasts generated by WRF

2020 ◽  
Author(s):  
Xiaohao Qin ◽  
Wansuo Duan ◽  
Hui Xu
Keyword(s):  
Tropical Cyclone ◽  
Lead Time ◽  
Short Range ◽  
Singular Vector ◽  
Inner Core ◽  
Potential Temperature ◽  
Wrf Model ◽  
Subsequent Development ◽  
Weather Research And Forecasting ◽  
Intensity Forecast

<p>The present study uses the nonlinear singular vector (NFSV) approach to identify the optimally-growing tendency perturbations of the Weather Research and Forecasting (WRF) model for tropical cyclone (TC) intensity forecasts. For nine selected TC cases, the NFSV-tendency perturbations of the WRF model, including components of potential temperature and/or moisture, are calculated when TC intensities are forecasted with a 24-hour lead time, and their respective potential temperature components are demonstrated to have more impact on the TC intensity forecasts. The perturbations coherently show barotropic structure around the central location of the TCs at the 24-hour lead time, and their dominant energies concentrate in the middle layers of the atmosphere. Moreover, such structures do not depend on TC intensities and subsequent development of the TC. The NFSV-tendency perturbations may indicate that the model uncertainty that is represented by tendency perturbations but associated with the inner-core of TCs, makes larger contributions to the TC intensity forecast uncertainty. Further analysis shows that the TC intensity forecast skill could be greatly improved as preferentially superimposing an appropriate tendency perturbation associated with the sensitivity of NFSVs to correct the model, even if using a WRF with coarse resolution.</p><div> <div> </div> </div>

scholarly journals Analyzing Simulated Convective Bursts in Two Atlantic Hurricanes. Part I: Burst Formation and Development

2017 ◽  
Vol 145 (8) ◽  
pp. 3073-3094 ◽  
Author(s):  
Andrew T. Hazelton ◽  
Robert F. Rogers ◽  
Robert E. Hart
Keyword(s):  
Radial Flow ◽  
Inner Core ◽  
Wrf Model ◽  
Tropical Meteorology ◽  
Core Region ◽  
Weather Research And Forecasting ◽  
Convective Bursts ◽  
Atlantic Hurricanes ◽  
Radial Outflow

Understanding the structure and evolution of the tropical cyclone (TC) inner core remains an elusive challenge in tropical meteorology, especially the role of transient asymmetric features such as localized strong updrafts known as convective bursts (CBs). This study investigates the formation of CBs and their role in TC structure and evolution using high-resolution simulations of two Atlantic hurricanes (Dean in 2007 and Bill in 2009) with the Weather Research and Forecasting (WRF) Model. Several different aspects of the dynamics and thermodynamics of the TC inner-core region are investigated with respect to their influence on TC convective burst development. Composites with CBs show stronger radial inflow in the lowest 2 km, and stronger radial outflow from the eye to the eyewall around z = 2–4 km, than composites without CBs. Asymmetric vorticity associated with eyewall mesovortices appears to be a major factor in some of the radial flow anomalies that lead to CB development. The anomalous outflow from these mesovortices, along with outflow from supergradient parcels above the boundary layer, favors low-level convergence and also appears to mix high- θ e air from the eye into the eyewall. Analyses of individual CBs and parcel trajectories show that parcels are pulled into the eye and briefly mix with the eye air. The parcels then rapidly move outward into the eyewall, and quickly ascend in CBs, in some cases with vertical velocities of over 20 m s−1. These results support the importance of horizontal asymmetries in forcing extreme asymmetric vertical velocity in tropical cyclones.

Understanding the response of tropical cyclone structure to the assimilation of synthetic wind profiles

2021 ◽  
Author(s):  
Lisa R. Bucci ◽  
Sharanya J. Majumdar ◽  
Robert Atlas ◽  
G. David Emmitt ◽  
Steve Greco
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Error Statistics ◽  
Once Daily ◽  
Structural Differences ◽  
Wind Profiles ◽  
Parent Domain ◽  
Mean Square Errors

AbstractThis study examines how varying wind profile coverages in the tropical cyclone (TC) core, near-environment and broader synoptic environment affect the structure and evolution of a simulated Atlantic hurricane through data assimilation. Three sets of observing system simulation experiments (OSSEs) are examined in this paper. The first experiment establishes a benchmark for the case study specific to the forecast system used by assimilating idealized profiles throughout the parent domain. The second presents how TC analyses and forecasts respond to varying the coverage of swaths produced by polar-orbiting satellites of idealized wind profiles. The final experiment assesses the role of TC inner-core observations by systematically removing them radially from the center. All observations are simulated from a high-resolution regional “Nature Run” of a hurricane and the tropical atmosphere, assimilated an Ensemble Square-Root Kalman Filter and the Hurricane Weather and Research Forecast (HWRF) regional model. Results compare observation impact to the analyses, domain-wide and TC centric error statistics, and TC structural differences among the experiments. The study concludes that the most accurate TC representation is a result of the assimilation of collocated and uniform thermodynamic and kinematics observations. Intensity forecasts are improved with increased inner core wind observations, even if the observations are only available once daily. Domain-wide root-mean-square errors are significantly reduced when the TC is observed during a period of structural change, like rapid intensification. The experiments suggest the importance of wind observations and the role of inner-core surveillance when analyzing and forecasting realistic TC structure.

scholarly journals The Impact of Idealized Terrain on Upstream Tropical Cyclone Track

2018 ◽  
Vol 75 (11) ◽  
pp. 3887-3910 ◽  
Author(s):  
Kuan-Chieh Huang ◽  
Chun-Chieh Wu
Keyword(s):  
Large Scale ◽  
Inner Core ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Core Dynamics ◽  
Underlying Mechanisms ◽  
Channeling Effect ◽  
The Impact ◽  
Steering Current

Abstract Tropical cyclones (TCs) encountering the terrain of Taiwan usually experience prominent track deflection, resulting in uncertainty in TC track forecasts. The underlying mechanisms of TC deflection are examined to better understand the pattern of TC tracks under various flow regimes. In this study, idealized experiments are carried out utilizing the Advanced Research version of the Weather Research and Forecasting (WRF) Model. This study investigates the motion of a TC that is deflected southward while moving westward toward an idealized terrain similar to Taiwan. An analysis of both the flow asymmetries and the potential vorticity tendency (PVT) demonstrates that horizontal advection contributes to the southward movement of the TC. The track deflection is examined in two separate time periods, with different mechanisms leading to the southward movement. Changes in the background flow induced by the terrain first cause the large-scale steering current to push the TC southward while the TC is still far from the terrain. As the TC approaches the idealized topography, the role of the inner-core dynamics becomes important, and the TC terrain-induced channeling effect results in further southward deflection. Asymmetries in the midlevel flow also develop during this period, in part associated with the effect of vertical momentum transport. The combination of the large-scale environmental flow, the low-level channeling effect, and asymmetries in the midlevel flow all contribute to the southward deflection of the TC track.

Application of a new scale-aware three-dimensional subgrid mixing parameterization on the simulations of tropical cyclone

2020 ◽  
Author(s):  
mengjuan liu ◽  
Xu Zhang
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Turbulent Mixing ◽  
Doppler Radar ◽  
Three Dimensional ◽  
Weather Research And Forecasting ◽  
Forecasting Model ◽  
Gray Zone ◽  
Synoptic Observations ◽  
Mobile Boundary

<p>A new scale-adaptive three-dimensional (3D) turbulent kinetic energy (TKE) subgrid mixing scheme is developed using the Advanced Research version of the Weather Research and Forecasting Model (WRF-ARW) to address the gray-zone problem in the parameterization of subgrid turbulent mixing. This scheme is based on the full 3D TKE prognostic equation and combines the horizontal and vertical subgrid turbulent mixing into a single energetically consistent framework.</p><p>A series of real tropical cyclone(TC) simulations with varying horizontal resolutions from 9km to 1km are carried out to compare the performance of the 3D mixing scheme and the conventional 1D planetary boundary layer (PBL) schemes to the observations, including conventional ones such as radiosonde and surface synoptic observations, as well as intensive ones obtained during the landfall of TC, such as mobile boundary layer wind profiler and Dual-pol Doppler Radar. This study aims to determine if the new scheme performs appropriate on TC simulation, and to evaluate the sensitivity of TC simulation to boundary layer schemes.</p>

Sign in / Sign up

Export Citation Format

Share Document