Evaluation of a Wind-Wave System for Ensemble Tropical Cyclone Wave Forecasting. Part I: Winds

2013 ◽  
Vol 28 (2) ◽  
pp. 297-315 ◽  
Author(s):  
Steven M. Lazarus ◽  
Samuel T. Wilson ◽  
Michael E. Splitt ◽  
Gary A. Zarillo
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Synthetic Data ◽  
Radial Distance ◽  
Wave System ◽  
Computationally Efficient ◽  
Wind Fields ◽  
Translation Speed ◽  
Maximum Wind ◽  
Regional Reanalysis

Abstract A computationally efficient method of producing tropical cyclone (TC) wind analyses is developed and tested, using a hindcast methodology, for 12 Gulf of Mexico storms. The analyses are created by blending synthetic data, generated from a simple parametric model constructed using extended best-track data and climatology, with a first-guess field obtained from the NCEP–NCAR North American Regional Reanalysis (NARR). Tests are performed whereby parameters in the wind analysis and vortex model are varied in an attempt to best represent the TC wind fields. A comparison between nonlinear and climatological estimates of the TC size parameter indicates that the former yields a much improved correlation with the best-track radius of maximum wind rm. The analysis, augmented by a pseudoerror term that controls the degree of blending between the NARR and parametric winds, is tuned using buoy observations to calculate wind speed root-mean-square deviation (RMSD), scatter index (SI), and bias. The bias is minimized when the parametric winds are confined to the inner-core region. Analysis wind statistics are stratified within a storm-relative reference frame and by radial distance from storm center, storm intensity, radius of maximum wind, and storm translation speed. The analysis decreases the bias and RMSD in all quadrants for both moderate and strong storms and is most improved for storms with an rm of less than 20 n mi. The largest SI reductions occur for strong storms and storms with an rm of less than 20 n mi. The NARR impacts the analysis bias: when the bias in the former is relatively large, it remains so in the latter.

Tracking a Long-Lasting Outer Tropical Cyclone Rainband: Origin and Convective Transformation

2019 ◽  
Vol 76 (10) ◽  
pp. 3267-3283 ◽  
Author(s):  
Cheng-Ku Yu ◽  
Che-Yu Lin ◽  
Jhang-Shuo Luo
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Radial Distance ◽  
Vertical Shear ◽  
Convective Precipitation ◽  
Squall Line ◽  
Mature Stage ◽  
Clear Trend ◽  
Dynamical Interaction ◽  
Cold Pools

Abstract This study used radar and surface observations to track a long-lasting outer tropical cyclone rainband (TCR) of Typhoon Jangmi (2008) over a considerable period of time (~10 h) from its formative to mature stage. Detailed analyses of these unique observations indicate that the TCR was initiated on the eastern side of the typhoon at a radial distance of ~190 km as it detached from the upwind segment of a stratiform rainband located close to the inner-core boundary. The outer rainband, as it propagated cyclonically outward, underwent a prominent convective transformation from generally stratiform precipitation during the earlier period to highly organized, convective precipitation during its mature stage. The transformation was accompanied by a clear trend of surface kinematics and thermodynamics toward squall-line-like features. The observed intensification of the rainband was not simply related to the spatial variation of the ambient CAPE or potential instability; instead, the dynamical interaction between the prerainband vertical shear and cold pools, with progression toward increasingly optimal conditions over time, provides a reasonable explanation for the temporal alternation of the precipitation intensity. The increasing intensity of cold pools was suggested to play an essential role in the convective transformation for the rainband. The propagation characteristics of the studied TCR were distinctly different from those of wave disturbances frequently documented within the cores of tropical cyclones; however, they were consistent with the theoretically predicted propagation of convectively generated cold pools. The convective transformation, as documented in the present case, is anticipated to be one of the fundamental processes determining the evolving and structural nature of outer TCRs.

Global Scatterometer Observations of the Structure of Tropical Cyclone Wind Fields

2020 ◽  
Vol 148 (11) ◽  
pp. 4673-4692
Author(s):  
Ali Tamizi ◽  
Ian R. Young ◽  
Agustinus Ribal ◽  
Jose-Henrique Alves
Keyword(s):  
Tropical Cyclone ◽  
Surface Wind ◽  
Radial Distance ◽  
Wind Fields ◽  
Forward Movement ◽  
Left Right Asymmetry ◽  
The Right ◽  
Very Large Database ◽  
Left Front ◽  
Tropical Cyclone Center

AbstractA very large database containing 24 years of scatterometer passes is analyzed to investigate the surface wind fields within tropical cyclones. The analysis confirms the left–right asymmetry of the wind field with the strongest winds directly to the right of the tropical cyclone center (Northern Hemisphere). At values greater than 2 times the radius to maximum winds, the asymmetry is approximately equal to the storm velocity of forward movement. Observed wind inflow angle (i.e., storm motion not subtracted) is shown to vary both radially and azimuthally within the tropical cyclone. The smallest observed wind inflow angles are found in the left-front quadrant with the largest values in the right-rear quadrant. As the velocity of forward movement increases and the central pressure decreases, observed inflow angles ahead of the storm decrease and those behind the storm increase. In the right-rear quadrant, the observed inflow angle increases with radius from the storm center. In all other quadrants, the observed inflow angle is approximately constant as a function of radial distance.

Tropical Cyclone Inner-Core Kinetic Energy Evolution

2008 ◽  
Vol 136 (12) ◽  
pp. 4882-4898 ◽  
Author(s):  
Katherine S. Maclay ◽  
Mark DeMaria ◽  
Thomas H. Vonder Haar
Keyword(s):  
Tropical Cyclone ◽  
Kinetic Energy ◽  
Inner Core ◽  
Surface Wind ◽  
Statistical Testing ◽  
Vertical Shear ◽  
Structure Evolution ◽  
Wind Fields ◽  
Secondary Eyewall Formation ◽  
Wind Structure

Abstract Tropical cyclone (TC) destructive potential is highly dependent on the distribution of the surface wind field. To gain a better understanding of wind structure evolution, TC 0–200-km wind fields from aircraft reconnaissance flight-level data are used to calculate the low-level area-integrated kinetic energy (KE). The integrated KE depends on both the maximum winds and wind structure. To isolate the structure evolution, the average relationship between KE and intensity is first determined. Then the deviations of the KE from the mean intensity relationship are calculated. These KE deviations reveal cases of significant structural change and, for convenience, are referred to as measurements of storm size [storms with greater (less) KE for their given intensity are considered large (small)]. It is established that TCs generally either intensify and do not grow or they weaken/maintain intensity and grow. Statistical testing is used to identify conditions that are significantly different for growing versus nongrowing storms in each intensification regime. Results suggest two primary types of growth processes: (i) secondary eyewall formation and eyewall replacement cycles, an internally dominated process, and (ii) external forcing from the synoptic environment. One of the most significant environmental forcings is the vertical shear. Under light shear, TCs intensify but do not grow; under moderate shear, they intensify less but grow more; under very high shear, they do not intensify or grow. As a supplement to this study, a new TC classification system based on KE and intensity is presented as a complement to the Saffir–Simpson hurricane scale.

Impact of Tropical Cyclone Initialization on Its Convection Development and Intensity: A Case Study of Typhoon Megi (2010)

2020 ◽  
Vol 77 (2) ◽  
pp. 443-464 ◽  
Author(s):  
Yi-Pin Chang ◽  
Shu-Chih Yang ◽  
Kuan-Jen Lin ◽  
Guo-Yuan Lien ◽  
Chien-Ming Wu
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Surface Wind ◽  
Synthetic Data ◽  
Asymmetric Structure ◽  
Wind Structure ◽  
Axisymmetric Surface ◽  
Moisture Supply ◽  
High Level ◽  
The Impact

Abstract This study investigates the impact of tropical cyclone (TC) initialization methods on TC intensity prediction under a framework coupling the Weather Research and Forecasting Model with the TC Centered-Local Ensemble Transform Kalman Filter (WRF TCC-LETKF). While the TC environments are constrained by assimilating the same environmental observations, two different initialization strategies, assimilating real dropsonde observations (the DP experiment) and synthetic axisymmetric surface wind structure (the VT experiment), are employed to construct the TC inner-core structure. These two experiments have distinct results on predicting the rapid intensification (RI) of Typhoon Megi (2010), which can be attributed to their different convective burst (CB) development. In DP, the assimilation of the dropsondes helps establish a realistic TC structure with asymmetry information, leading to scattered CB distribution and persistent RI with abundant moisture supply. In VT, assimilating the axisymmetric surface wind structure spins up the TC efficiently. However, the initially excessive CB coverage causes a too-early high-level warm core, and the reduced moisture supply hinders RI. The forecast results imply that if the TC structure is initialized using a scheme considering only the axisymmetric vortex structure, the RI potential can possibly be underestimated due to the inability to represent the realistic asymmetric structure. Finally, assimilation of both the real and synthetic data can be complementary, giving a strong TC initially that undergoes a longer RI period.

scholarly journals The Influence of Oceanic Barrier Layers on Tropical Cyclone Intensity as Determined through Idealized, Coupled Numerical Simulations

2019 ◽  
Vol 49 (7) ◽  
pp. 1723-1745 ◽  
Author(s):  
James Hlywiak ◽  
David S. Nolan
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Wrf Model ◽  
Vertical Wind Shear ◽  
Ocean Model ◽  
Upper Ocean ◽  
Translation Speed ◽  
Barrier Layers ◽  
Plume Region ◽  
Ocean Salinity

AbstractThe connection relating upper-ocean salinity stratification in the form of oceanic barrier layers to tropical cyclone (TC) intensification is investigated in this study. Previous works disagree on whether ocean salinity is a negligible factor on TC intensification. Relationships derived in many of these studies are based on observations, which can be sparse or incomplete, or uncoupled models, which neglect air–sea feedbacks. Here, idealized ensemble simulations of TCs performed using the Weather Research and Forecasting (WRF) Model coupled to the 3D Price–Weller–Pinkel (PWP) ocean model facilitate examination of the TC–upper-ocean system in a controlled, high-resolution, mesoscale environment. Idealized vertical ocean profiles are modeled after barrier layer profiles of the Amazon–Orinoco river plume region, where barrier layers are defined as vertical salinity gradients between the mixed and isothermal layer depths. Our results reveal that for TCs of category 1 hurricane strength or greater, thick (24–30 m) barrier layers may favor further intensification by 6%–15% when averaging across ensemble members. Conversely, weaker cyclones are hindered by thick barrier layers. Reduced sea surface temperature cooling below the TC inner core is the primary reason for additional intensification. Sensitivity tests of the results to storm translation speed, initial oceanic mixed layer temperature, and atmospheric vertical wind shear provide a more comprehensive analysis. Last, it is shown that the ensemble mean intensity results are similar when using a 3D or 1D version of PWP.

scholarly journals A Model for the Complete Radial Structure of the Tropical Cyclone Wind Field. Part II: Wind Field Variability

2016 ◽  
Vol 73 (8) ◽  
pp. 3093-3113 ◽  
Author(s):  
Daniel R. Chavas ◽  
Ning Lin
Keyword(s):  
Tropical Cyclone ◽  
Physical Model ◽  
Wind Field ◽  
Inner Core ◽  
Outer Radius ◽  
Maximum Wind ◽  
Modes Of Variability ◽  
Simple Physical Model ◽  
Radial Structure ◽  
Field Variability

Abstract Part I of this work developed a simple physical model for the complete radial structure of the low-level azimuthal wind field in a tropical cyclone that compared well with observations. However, wind field variability in the model is tied principally to its external parameters given by the maximum wind speed and the radius of maximum wind, the latter of which lacks a credible independent physical model for its variability. Here the authors explore the modes of variability that arise from the alternative specification of the model, which takes the outer radius in lieu of the radius of maximum wind. Nondimensionalization of the model reveals two theoretical modes of structural variability in absolute angular momentum that are shown to closely match observations. These two modes correspond to three modes of wind field variability associated with variations in intensity, outer storm size, and latitude. These wind field modes are demonstrated to mirror the dominant modes of variability found in nature, in particular the intrastorm variation of inner-core structure and the interstorm variation of overall storm size. In combination, the model offers a credible physical solution for the complete time-dependent tropical cyclone wind field in conjunction with the external specification of intensity, outer size, and latitude. More broadly, the model offers theoretical and conceptual insight into the nature of the tropical cyclone wind field, including the oft-conflated terms “size” and “structure” and their distinct variabilities.

scholarly journals An Ensemble Approach to Investigate Tropical Cyclone Intensification in Sheared Environments. Part II: Ophelia (2011)

2016 ◽  
Vol 73 (4) ◽  
pp. 1555-1575 ◽  
Author(s):  
Rosimar Rios-Berrios ◽  
Ryan D. Torn ◽  
Christopher A. Davis
Keyword(s):  
Tropical Cyclone ◽  
Large Scale ◽  
Inner Core ◽  
Deep Convection ◽  
Three Dimensional ◽  
Vertical Wind Shear ◽  
Wind Fields ◽  
Convective Scale ◽  
Intensity Changes ◽  
Large Scale Flow

Abstract The mechanisms leading to tropical cyclone (TC) intensification amid moderate vertical wind shear can vary from case to case, depending on the vortex structure and the large-scale conditions. To search for similarities between cases, this second part investigates the rapid intensification of Hurricane Ophelia (2011) in an environment characterized by 200–850-hPa westerly shear exceeding 8 m s−1. Similar to Part I, a 96-member ensemble was employed to compare a subset of members that predicted Ophelia would intensify with another subset that predicted Ophelia would weaken. This comparison revealed that the intensification of Ophelia was aided by enhanced convection and midtropospheric moisture in the downshear and left-of-shear quadrants. Enhanced left-of-shear convection was key to the establishment of an anticyclonic divergent outflow that forced a nearby upper-tropospheric trough to wrap around Ophelia. A vorticity budget showed that deep convection also contributed to the enhancement of vorticity within the inner core of Ophelia via vortex stretching and tilting of horizontal vorticity enhanced by the upper-tropospheric trough. These results suggest that TC intensity changes in sheared environments and in the presence of upper-tropospheric troughs highly depend on the interaction between convective-scale processes and the large-scale flow. Given the similarities between Part I and this part, the results suggest that observations from the three-dimensional moisture and wind fields could improve both forecasting and understanding of TC intensification in moderately sheared environments.

High-Resolution Wind Fields within the Inner Core and Eye of a Mature Tropical Cyclone from GOES 1-min Images

1998 ◽  
Vol 79 (11) ◽  
pp. 2483-2496 ◽  
Author(s):  
A. F. Hasler ◽  
K. Palaniappan ◽  
C. Kambhammetu ◽  
P. Black ◽  
E. Uhlhorn ◽  
...  
Keyword(s):  
High Resolution ◽  
Tropical Cyclone ◽  
Inner Core ◽  
Wind Fields

EFFECTS OF MAXIMUM WIND SPEED RADIUS AND TRANSLATION SPEED OF SCENARIO TYPHOON ON STORM SURGE AND WAVE

2018 ◽  
Vol 74 (2) ◽  
pp. I_583-I_588
Author(s):  
Masafumi KIMIZUKA ◽  
Tomotsuka TAKAYAMA ◽  
Hiroyasu KAWAI ◽  
Masafumi MIYATA ◽  
Katsuya HIRAYAMA ◽  
...  
Keyword(s):  
Wind Speed ◽  
Storm Surge ◽  
Maximum Wind Speed ◽  
Translation Speed ◽  
Maximum Wind

scholarly journals Recent Advances in Our Understanding of Tropical Cyclone Intensity Change Processes from Airborne Observations

Atmosphere ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 650
Author(s):  
Robert F. Rogers
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Vertical Shear ◽  
Intensity Change ◽  
Change Processes ◽  
Cyclone Intensity ◽  
Secondary Eyewall Formation ◽  
Warm Core ◽  
Major Hurricane ◽  
Upper Level

Recent (past ~15 years) advances in our understanding of tropical cyclone (TC) intensity change processes using aircraft data are summarized here. The focus covers a variety of spatiotemporal scales, regions of the TC inner core, and stages of the TC lifecycle, from preformation to major hurricane status. Topics covered include (1) characterizing TC structure and its relationship to intensity change; (2) TC intensification in vertical shear; (3) planetary boundary layer (PBL) processes and air–sea interaction; (4) upper-level warm core structure and evolution; (5) genesis and development of weak TCs; and (6) secondary eyewall formation/eyewall replacement cycles (SEF/ERC). Gaps in our airborne observational capabilities are discussed, as are new observing technologies to address these gaps and future directions for airborne TC intensity change research.

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