The Effects of Environmental Wind Shear Direction on Tropical Cyclone Boundary Layer Thermodynamics and Intensity Change from Multiple Observational Datasets

2021 ◽  
Author(s):  
Joshua B. Wadler ◽  
Joseph J. Cione ◽  
Jun A. Zhang ◽  
Evan A. Kalina ◽  
John Kaplan
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Wind Shear ◽  
Large Scale ◽  
Deep Layer ◽  
Potential Temperature ◽  
Intensity Change ◽  
Asymmetric Distribution ◽  
Shear Direction ◽  
The Impact

AbstractThe relationship between deep-layer environmental wind shear direction and tropical cyclone (TC) boundary layer thermodynamic structures is explored in multiple independent databases. Analyses derived from the tropical cyclone buoy database (TCBD) show that when TCs experience northerly-component shear, the 10-m equivalent potential temperature (θe) tends to be more symmetric than when shear has a southerly component. The primary asymmetry in θe in TCs experiencing southerly-component shear is radially outwards from twice the radius of maximum wind speed, with the left-of-shear quadrants having lower θe by 4–6 K than the right-of-shear quadrants. As with the TCBD, an asymmetric (symmetric) distribution of 10-m θe for TCs experiencing southerly-component (northerly-component) shear was found using composite observations from dropsondes. These analyses show that differences in the degree of symmetry near the sea surface extend through the depth of the boundary layer. Additionally, mean dropsonde profiles illustrate that TCs experiencing northerly-component shear are more potentially unstable between 500 m and 1000 m altitude, signaling a more favorable environment for the development of surface-based convection in rainband regions.Analyses from the Statistical Hurricane Intensity Prediction Scheme (SHIPS) Database show that subsequent strengthening (weakening) for TCs in the Atlantic Basin preferentially occurs in northerly-component (southerly-component) deep-layer environmental wind shear environments which further illustrates that the asymmetric distribution of boundary layer thermodynamics is unfavorable for TC intensification. These differences emphasize the impact of deep-layer wind shear direction on TC intensity changes which likely result from the superposition of large-scale advection with the shear-relative asymmetries in TC structure.

scholarly journals Idealized Tropical Cyclone Responses to the Height and Depth of Environmental Vertical Wind Shear

2016 ◽  
Vol 144 (6) ◽  
pp. 2155-2175 ◽  
Author(s):  
Peter M. Finocchio ◽  
Sharanya J. Majumdar ◽  
David S. Nolan ◽  
Mohamed Iskandarani
Keyword(s):  
Tropical Cyclone ◽  
Wind Shear ◽  
Large Scale ◽  
Deep Layer ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Polynomial Expansions ◽  
The Impact ◽  
Tilt Response ◽  
Left Quadrant

Abstract Three sets of idealized, cloud-resolving simulations are performed to investigate the sensitivity of tropical cyclone (TC) structure and intensity to the height and depth of environmental vertical wind shear. In the first two sets of simulations, shear height and depth are varied independently; in the third set, orthogonal polynomial expansions are used to facilitate a joint sensitivity analysis. Despite all simulations having the same westerly deep-layer (200–850 hPa) shear of 10 m s−1, different intensity and structural evolutions are observed, suggesting the deep-layer shear alone may not be sufficient for understanding or predicting the impact of vertical wind shear on TCs. In general, vertical wind shear that is shallower and lower in the troposphere is more destructive to model TCs because it tilts the TC vortex farther into the downshear-left quadrant. The vortices that tilt the most are unable to precess upshear and realign, resulting in their failure to intensify. Shear height appears to modulate this tilt response by modifying the thermodynamic environment above the developing vortex early in the simulations, while shear depth modulates the tilt response by controlling the vertical extent of the convective vortex. It is also found that TC intensity predictability is reduced in a narrow range of shear heights and depths. This result underscores the importance of accurately observing the large-scale environmental flow for improving TC intensity forecasts, and for anticipating when such forecasts are likely to have large errors.

scholarly journals On the Rapid Weakening of Very Intense Tropical Cyclone Hellen (2014)

2019 ◽  
Vol 147 (8) ◽  
pp. 2717-2737 ◽  
Author(s):  
Adrien Colomb ◽  
Tarik Kriat ◽  
Marie-Dominique Leroux
Keyword(s):  
Tropical Cyclone ◽  
Wind Shear ◽  
Large Scale ◽  
Inner Core ◽  
Potential Temperature ◽  
Vertical Wind Shear ◽  
Warm Core ◽  
Operational Forecasting ◽  
Intensity Changes ◽  
The Impact

Abstract In late March 2014, very intense Tropical Cyclone Hellen threatened the Comoros Archipelago and the Madagascan northwest coastline as it became one of the strongest tropical cyclones (TCs) ever observed over the Mozambique Channel. Its steep intensity changes were not well anticipated by operational forecasting models or by La Reunion regional specialized meteorological center forecasters. In particular, the record-setting rapid weakening over the open ocean was not supported by usual large-scale predictors. AROME, a new nonhydrostatic finescale model, is able to closely reproduce these wide intensity changes. When benchmarked against available observations, the model is also consistent in terms of inner-core structure, environmental features, track, and intensity. In the simulation, a northwesterly 400-hPa environmental wind is associated with unsaturated air, while the classic 200–850-hPa wind shear remains weak, and does not suggest a specifically unfavorable environment. The 400-hPa constraint affects the simulated storm through two pathways. Air with low equivalent potential temperature (θe) is flushed downward into the inflow layer in the upshear semicircle, triggering the decay of the storm. Then, direct erosion of the upper half of the warm core efficiently increases the surface pressure and also plays an instrumental role in the rapid weakening. When the storm gets closer to the Madagascan coastline, low-θe air can be directly advected within the inflow layer. Results illustrate on a real TC case the recently proposed paradigm for TC intensity modification under vertical wind shear and highlight the need for innovative tools to assess the impact of wind shear at all vertical levels.

scholarly journals Characterization of a boreal convective boundary layer and its impact on atmospheric chemistry during HUMPPA-COPEC-2010

2012 ◽  
Vol 12 (19) ◽  
pp. 9335-9353 ◽  
Author(s):  
H. G. Ouwersloot ◽  
J. Vilà-Guerau de Arellano ◽  
A. C. Nölscher ◽  
M. C. Krol ◽  
L. N. Ganzeveld ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Chemistry ◽  
Convective Boundary Layer ◽  
Large Scale ◽  
Spatial Scales ◽  
Potential Temperature ◽  
Chemical Species ◽  
Convective Boundary ◽  
The Impact

Abstract. We studied the atmospheric boundary layer (ABL) dynamics and the impact on atmospheric chemistry during the HUMPPA-COPEC-2010 campaign. We used vertical profiles of potential temperature and specific moisture, obtained from 132 radio soundings, to determine the main boundary layer characteristics during the campaign. We propose a classification according to several main ABL prototypes. Further, we performed a case study of a single day, focusing on the convective boundary layer, to analyse the influence of the dynamics on the chemical evolution of the ABL. We used a mixed layer model, initialized and constrained by observations. In particular, we investigated the role of large scale atmospheric dynamics (subsidence and advection) on the ABL development and the evolution of chemical species concentrations. We find that, if the large scale forcings are taken into account, the ABL dynamics are represented satisfactorily. Subsequently, we studied the impact of mixing with a residual layer aloft during the morning transition on atmospheric chemistry. The time evolution of NOx and O3 concentrations, including morning peaks, can be explained and accurately simulated by incorporating the transition of the ABL dynamics from night to day. We demonstrate the importance of the ABL height evolution for the representation of atmospheric chemistry. Our findings underscore the need to couple the dynamics and chemistry at different spatial scales (from turbulence to mesoscale) in chemistry-transport models and in the interpretation of observational data.

Effect of TC–Trough Interaction on the Intensity Change of Two Typhoons

2005 ◽  
Vol 20 (2) ◽  
pp. 199-211 ◽  
Author(s):  
Hui Yu ◽  
H. Joe Kwon
Keyword(s):  
Tropical Cyclone ◽  
Wind Shear ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Intensity Change ◽  
Eddy Flux ◽  
Upper Troposphere ◽  
Shallow Layer ◽  
Upper Level

Abstract Using large-scale analyses, the effect of tropical cyclone–trough interaction on tropical cyclone (TC) intensity change is readdressed by studying the evolution of upper-level eddy flux convergence (EFC) of angular momentum and vertical wind shear for two TCs in the western North Pacific [Typhoons Prapiroon (2000) and Olga (1999)]. Major findings include the following: 1) In spite of decreasing SST, the cyclonic inflow associated with a midlatitude trough should have played an important role in Prapiroon’s intensification to its maximum intensity and the maintenance after recurvature through an increase in EFC. The accompanied large vertical wind shear is concentrated in a shallow layer in the upper troposphere. 2) Although Olga also recurved downstream of a midlatitude trough, its development and maintenance were not strongly influenced by the trough. A TC could maintain itself in an environment with or without upper-level eddy momentum forcing. 3) Both TCs started to decay over cold SST in a large EFC and vertical wind shear environment imposed by the trough. 4) Uncertainty of input adds difficulties in quantitative TC intensity forecasting.

A Balanced Tropical Cyclone Test Case for AGCMs with Background Vertical Wind Shear

2015 ◽  
Vol 143 (5) ◽  
pp. 1762-1781 ◽  
Author(s):  
Fei He ◽  
Derek J. Posselt ◽  
Colin M. Zarzycki ◽  
Christiane Jablonowski
Keyword(s):  
Tropical Cyclone ◽  
Wind Shear ◽  
General Circulation ◽  
Vertical Wind Shear ◽  
Circulation Model ◽  
Background Field ◽  
Vertical Wind ◽  
Intensity Change ◽  
Test Case ◽  
The Impact

Abstract This paper presents a balanced tropical cyclone (TC) test case designed to improve current understanding of how atmospheric general circulation model (AGCM) configurations affect simulated TC development and behavior. It consists of an analytic initial condition comprising two independently balanced components. The first provides a vortical TC seed, while the second adds a planetary-scale zonal flow with height-dependent velocity and imposes background vertical wind shear (VWS) on the TC seed. The environmental flow satisfies the steady-state hydrostatic primitive equations in spherical coordinates and is in balance with other background field variables (e.g., temperature, surface geopotential). The evolution of idealized TCs in the test case framework is illustrated in 10-day simulations performed with the Community Atmosphere Model, version 5.1.1 (CAM 5.1.1). Environmental wind profiles with different magnitudes, directions, and vertical inflection points are applied to ensure that the technique is robust to changes in the VWS characteristics. The well-known shear-induced intensity change and structural asymmetry in tropical cyclones are well captured. Sensitivity of TC evolution to small perturbations in the initial vortex is also quantitatively addressed to validate the numerical robustness of the technique. It is concluded that the enhanced TC test case can be used to evaluate the impact of model choice (e.g., resolution, physical parameterizations) on the simulation and representation of TC-like vortices in AGCMs.

Impact of Parameterized Boundary Layer Structure on Tropical Cyclone Rapid Intensification Forecasts in HWRF

2017 ◽  
Vol 145 (4) ◽  
pp. 1413-1426 ◽  
Author(s):  
Jun A. Zhang ◽  
Robert F. Rogers ◽  
Vijay Tallapragada
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Inner Core ◽  
Layer Structure ◽  
Intensity Change ◽  
Rapid Intensification ◽  
Near Surface ◽  
Boundary Layer Structure ◽  
Tangential Wind ◽  
The Impact

Abstract This study evaluates the impact of the modification of the vertical eddy diffusivity (Km) in the boundary layer parameterization of the Hurricane Weather Research and Forecasting (HWRF) Model on forecasts of tropical cyclone (TC) rapid intensification (RI). Composites of HWRF forecasts of Hurricanes Earl (2010) and Karl (2010) were compared for two versions of the planetary boundary layer (PBL) scheme in HWRF. The results show that using a smaller value of Km, in better agreement with observations, improves RI forecasts. The composite-mean, inner-core structures for the two sets of runs at the time of RI onset are compared with observational, theoretical, and modeling studies of RI to determine why the runs with reduced Km are more likely to undergo RI. It is found that the forecasts with reduced Km at the RI onset have a shallower boundary layer with stronger inflow, more unstable near-surface air outside the eyewall, stronger and deeper updrafts in regions farther inward from the radius of maximum wind (RMW), and stronger boundary layer convergence closer to the storm center, although the mean storm intensity (as measured by the 10-m winds) is similar for the two groups. Finally, it is found that the departure of the maximum tangential wind from the gradient wind at the eyewall, and the inward advection of angular momentum outside the eyewall, is much larger in the forecasts with reduced Km. This study emphasizes the important role of the boundary layer structure and dynamics in TC intensity change, supporting recent studies emphasizing boundary layer spinup mechanism, and recommends further improvement to the HWRF PBL physics.

scholarly journals Challenges in Mesoscale Prediction of a Nocturnal Stratocumulus-Topped Marine Boundary Layer and Implications for Operational Forecasting

2007 ◽  
Vol 22 (5) ◽  
pp. 1101-1122 ◽  
Author(s):  
Ramesh Vellore ◽  
Darko Koračin ◽  
Melanie Wetzel ◽  
Steven Chai ◽  
Qing Wang
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Marine Boundary Layer ◽  
Mesoscale Model ◽  
Numerical Study ◽  
Potential Temperature ◽  
Turbulence Structure ◽  
Layer Depth ◽  
The Impact ◽  
Marine Layer

Abstract A numerical study using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) was performed to assess the impact of initial and boundary conditions, the parameterization of turbulence transfer and its coupling with cloud-driven radiation, and cloud microphysical processes on the accuracy of mesoscale predictions and forecasts of the cloud-capped marine boundary layer. Aircraft, buoy, and satellite data and the large eddy simulation (LES) results during the Dynamics and Chemistry of Marine Stratocumulus field experiment (DYCOMS II) in July 2001 were used in the assessment. Three of the tested input fields (Eta, NCEP, and ECMWF) show deficiencies, mainly in the thermodynamic structure of the lowest 1500 m of the marine atmosphere. On a positive note, the simulated marine-layer depth showed good agreement with aircraft observations using the Eta fields, while using the NCEP and ECMWF datasets underestimated the marine-layer depth by about 20%–30%. The predicted turbulence kinetic energy (inversion strength) was about 50% of that obtained from the LES results (aircraft observed). As a consequence of moisture overprediction, the predicted liquid water path was twice the observed by 1–2 g kg−1. The sensitivity tests have shown that the selections of turbulence and cloud microphysical schemes significantly influence the turbulence estimates and cloud parameters. Two of the tested turbulence schemes (Eta PBL and Burk–Thompson) did not exhibit the coupling with radiation. The significant differences in the simulated turbulence estimates appear to be a consequence of the use of water-conserving potential temperature variables. The microphysical parameterization, which uses the number concentration of cloud drops in the autoconversion process, simulates a realistic evolution of precipitable hydrometeors in the cloudy marine layer on the positive side, but on the other hand enhances the decoupling in the turbulence structure. This study can provide guidance to operational forecasters concerning accuracy issues of the commonly used large-scale analyses for model initialization, and optimal selection of model parameterizations in order to simulate and forecast the cloudy atmospheric boundary layer over the ocean.

scholarly journals Ensemble Sensitivity Analysis of Tropical Cyclone Intensification Rate during the Development Stage

2020 ◽  
Vol 77 (10) ◽  
pp. 3387-3405
Author(s):  
Chih-Chi Hu ◽  
Chun-Chieh Wu
Keyword(s):  
Boundary Layer ◽  
Sensitivity Analysis ◽  
Tropical Cyclone ◽  
Potential Temperature ◽  
Vertical Motion ◽  
Development Stage ◽  
Intensity Change ◽  
Sensitive Region ◽  
Ensemble Simulations ◽  
Partial Correlations

AbstractEnsemble sensitivity analysis based on convective-permitting ensemble simulations is used to understand the processes associated with tropical cyclone (TC) intensification under idealized conditions. Partial correlations between different variables and the future TC intensification rate, with the effect of intensity removed, are used to identify the sensitive factors. It is found that the equivalent potential temperature (θe) in the region from the radius of maximum wind (RMW) to 3 times the RMW below 2 km (hereafter, the sensitive region) has the largest correlation (over 0.7) with 2.5-h intensity change. It is found that higher θe in the sensitive region is associated with not only a stronger updraft but also an inward shift of vertical motion in the mid- to upper eyewall. This suggests that higher θe just outside the RMW is favorable to TC intensification not only because of the larger amount of the heating, but also due to the heating location that is closer to the center. Trajectory analysis shows that the parcels in the sensitive region are mainly from the boundary layer inflow and the midlevel inflow. It is found that when the outer rainband is active, the midlevel inflow becomes stronger and is able to bring more low-θe air into the boundary layer, and the θe radially inward to the rainband decreases. Verification experiments justify that higher θe around the RMW to 3 times the RMW is favorable to TC intensification, while higher θe away from 5 times the RMW is shown to be unfavorable for TC intensification.

A Statistical Perspective on Wind Profiles and Vertical Wind Shear in Tropical Cyclone Environments of the Northern Hemisphere

2017 ◽  
Vol 145 (1) ◽  
pp. 361-378 ◽  
Author(s):  
Peter M. Finocchio ◽  
Sharanya J. Majumdar
Keyword(s):  
Tropical Cyclone ◽  
Northern Hemisphere ◽  
Wind Shear ◽  
Deep Layer ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Vertical Shear ◽  
Intensity Change ◽  
Upper Level ◽  
Wind Profiles

Abstract A statistical analysis of tropical cyclone (TC) environmental wind profiles is conducted in order to better understand how vertical wind shear influences TC intensity change. The wind profiles are computed from global atmospheric reanalyses around the best track locations of 7554 TC cases in the Northern Hemisphere tropics. Mean wind profiles within each basin exhibit significant differences in the magnitude and direction of vertical wind shear. Comparisons between TC environments and randomly selected “non-TC” environments highlight the synoptic regimes that support TCs in each basin, which are often characterized by weaker deep-layer shear. Because weaker deep-layer shear may not be the only aspect of the environmental flow that makes a TC environment more favorable for TCs, two new parameters are developed to describe the height and depth of vertical shear. Distributions of these parameters indicate that, in both TC and non-TC environments, vertical shear most frequently occurs in shallow layers and in the upper troposphere. Linear correlations between each shear parameter and TC intensity change show that shallow, upper-level shear is slightly more favorable for TC intensification. But these relationships vary by basin and neither parameter independently explains more than 5% of the variance in TC intensity change between 12 and 120 h. As such, the shear height and depth parameters in this study do not appear to be viable predictors for statistical intensity prediction, though similar measures of midtropospheric vertical wind shear may be more important in particularly challenging intensity forecasts.

scholarly journals Rapidly Intensifying Hurricane Guillermo (1997). Part II: Resilience in Shear

2012 ◽  
Vol 140 (2) ◽  
pp. 425-444 ◽  
Author(s):  
Paul D. Reasor ◽  
Matthew D. Eastin
Keyword(s):  
Tropical Cyclone ◽  
Large Scale ◽  
Doppler Radar ◽  
Deep Layer ◽  
Vertical Wind Shear ◽  
Vertical Motion ◽  
Intensity Change ◽  
Cyclone Intensity ◽  
Statistical Confidence ◽  
Balanced Dynamics

This paper examines the structure and evolution of a mature tropical cyclone in vertical wind shear (VWS) using airborne Doppler radar observations of Hurricane Guillermo (1997). In Part I, the modulation of eyewall convection via the rotation of vorticity asymmetries through the downshear-left quadrant was documented during rapid intensification. Here, the focus is on the relationship between VWS, vortex tilt, and associated asymmetry within the tropical cyclone core region during two separate observation periods. A method for estimating local VWS and vortex tilt from radar datasets is further developed, and the resulting vertical structure and its evolution are subjected to statistical confidence tests. Guillermo was a highly resilient vortex, evidenced by its small tilt magnitude relative to the horizontal scale of the vortex core. The deep-layer tilt was statistically significant, oriented on average ~60° left of shear. Large-scale vorticity and thermal asymmetries oriented along the tilt direction support a response of Guillermo to shear forcing that is consistent with balanced dynamics. The time-averaged vertical motion asymmetry within the eyewall exhibited maximum ascent values ~40° left of the deep-layer shear, or in this case, right of the deep-layer tilt. The observation-based analysis of Guillermo’s interaction with VWS confirms findings of recent theoretical and numerical studies, and serves as the basis for a more comprehensive investigation of VWS and tropical cyclone intensity change using a recently constructed multistorm database of Doppler radar analyses.

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