A high-fidelity parametric model for tropical cyclone boundary layer wind field by considering effects of land cover and terrain

2021 ◽  
pp. 105701
Author(s):  
Jian Yang ◽  
Yu Chen ◽  
Yanan Tang ◽  
Guirong Yan ◽  
Zhongdong Duan
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Land Cover ◽  
Wind Field ◽  
Parametric Model ◽  
High Fidelity ◽  
Tropical Cyclone Boundary Layer

The Evolution of Asymmetries in the Tropical Cyclone Boundary Layer Wind Field during Landfall

2021 ◽  
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Wind Field ◽  
Surface Wind ◽  
Frictional Stress ◽  
Homogeneous Surface ◽  
Sudden Decrease ◽  
The Right ◽  
Tropical Cyclone Boundary Layer

Abstract The evolution of the tropical cyclone boundary layer (TCBL) wind field before landfall is examined in this study. As noted in previous studies, a typical TCBL wind structure over the ocean features a supergradient boundary layer jet to the left of motion and Earth-relative maximum winds to the right. However, the detailed response of the wind field to frictional convergence at the coastline is less well known. Here, idealized numerical simulations reveal an increase in the offshore radial and vertical velocities beginning once the TC is roughly 200 km offshore. This increase in the radial velocity is attributed to the sudden decrease in frictional stress once the highly agradient flow crosses the offshore coastline. Enhanced advection of angular momentum by the secondary circulation forces a strengthening of the supergradient jet near the top of the TCBL. Sensitivity experiments reveal that the coastal roughness discontinuity dominates the friction asymmetry due to motion. Additionally, increasing the inland roughness through increasing the aerodynamic roughness length enhances the observed asymmetries. Lastly, a brief analysis of in-situ surface wind data collected during the landfall of three Gulf of Mexico hurricanes is provided and compared to the idealized simulations. Despite the limited in-situ data, the observations generally support the simulations. The results here imply that assumptions about the TCBL wind field based on observations from over horizontally-homogeneous surface types - which have been well-documented by previous studies - are inappropriate for use near strong frictional heterogeneity.

Dynamic impact of the vertical shear of gradient wind on the tropical cyclone boundary layer wind field

2014 ◽  
Vol 28 (1) ◽  
pp. 127-138 ◽  
Author(s):  
Ninghao Cai ◽  
Xin Xu ◽  
Lili Song ◽  
Lina Bai ◽  
Jie Ming ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Wind Field ◽  
Vertical Shear ◽  
Dynamic Impact ◽  
Gradient Wind ◽  
Tropical Cyclone Boundary Layer

scholarly journals Observed Boundary Layer Wind Structure and Balance in the Hurricane Core. Part I: Hurricane Georges

2006 ◽  
Vol 63 (9) ◽  
pp. 2169-2193 ◽  
Author(s):  
Jeffrey D. Kepert
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Tropical Cyclone ◽  
Radial Profile ◽  
Lower Altitude ◽  
Near Surface ◽  
Wind Structure ◽  
The Right ◽  
Tropical Cyclone Boundary Layer ◽  
Upper Boundary

Abstract The GPS dropsonde allows observations at unprecedentedly high horizontal and vertical resolution, and of very high accuracy, within the tropical cyclone boundary layer. These data are used to document the boundary layer wind field of the core of Hurricane Georges (1998) when it was close to its maximum intensity. The spatial variability of the boundary layer wind structure is found to agree very well with the theoretical predictions in the works of Kepert and Wang. In particular, the ratio of the near-surface wind speed to that above the boundary layer is found to increase inward toward the radius of maximum winds and to be larger to the left of the track than to the right, while the low-level wind maximum is both more marked and at lower altitude on the left of the storm track than on the right. However, the expected supergradient flow in the upper boundary layer is not found, with the winds being diagnosed as close to gradient balance. The tropical cyclone boundary layer model of Kepert and Wang is used to simulate the boundary layer flow in Hurricane Georges. The simulated wind profiles are in good agreement with the observations, and the asymmetries are well captured. In addition, it is found that the modeled flow in the upper boundary layer at the eyewall is barely supergradient, in contrast to previously studied cases. It is argued that this lack of supergradient flow is a consequence of the particular radial structure in Georges, which had a comparatively slow decrease of wind speed with radius outside the eyewall. This radial profile leads to a relatively weak gradient of inertial stability near the eyewall and a strong gradient at larger radii, and hence the tropical cyclone boundary layer dynamics described by Kepert and Wang can produce only marginally supergradient flow near the radius of maximum winds. The lack of supergradient flow, diagnosed from the observational analysis, is thus attributed to the large-scale structure of this particular storm. A companion paper presents a similar analysis for Hurricane Mitch (1998), with contrasting results.

Contribution of vertical advection to supergradient wind in tropical cyclone boundary layer: A numerical study

2021 ◽  
Author(s):  
Rong Fei ◽  
Yuqing Wang ◽  
Yuanlong Li
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Wind Speed ◽  
Tropical Cyclone ◽  
Vertical Structure ◽  
Numerical Study ◽  
Substantial Reduction ◽  
Vertical Advection ◽  
Physics Model ◽  
Tropical Cyclone Boundary Layer

AbstractThe existence of supergradient wind in the interior of the boundary layer is a distinct feature of a tropical cyclone (TC). Although the vertical advection is shown to enhance supergradient wind in TC boundary layer (TCBL), how and to what extent the strength and structure of supergradient wind are modulated by vertical advection are not well understood. In this study, both a TCBL model and an axisymmetric full-physics model are used to quantify the contribution of vertical advection process to the strength and vertical structure of supergradient wind in TCBL. Results from the TCBL model show that the removal of vertical advection of radial wind reduces both the strength and height of supergradient wind by slightly more than 50%. The removal of vertical advection of agradient wind reduces the height of the supergradient wind core by ~30% but increases the strength of supergradient wind by ~10%. Results from the full-physics model show that the removal of vertical advection of radial wind or agradient wind reduces both the strength and height of supergradient wind but the removal of that of radial wind produces a more substantial reduction (52%) than the removal of that of agradient wind (35%). However, both the intensification rate and final intensity of the simulated TCs in terms of maximum 10-m wind speed show little differences in experiments with and without the vertical advection of radial or agradient wind, suggesting that supergradient wind contributes little to either the intensification rate or the steady-state intensity of the simulated TC.

scholarly journals Shock-like structures in the tropical cyclone boundary layer

2013 ◽  
Vol 5 (2) ◽  
pp. 338-353 ◽  
Author(s):  
Gabriel J. Williams ◽  
Richard K. Taft ◽  
Brian D. McNoldy ◽  
Wayne H. Schubert
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Tropical Cyclone Boundary Layer

scholarly journals Time and Space Scales in the Tropical Cyclone Boundary Layer, and the Location of the Eyewall Updraft

2017 ◽  
Vol 74 (10) ◽  
pp. 3305-3323 ◽  
Author(s):  
Jeffrey D. Kepert
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Nonlinear Models ◽  
Vertical Motion ◽  
Oscillation Period ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Radial Profiles ◽  
Sinusoidal Oscillations ◽  
Tropical Cyclone Boundary Layer

Abstract The transient response of the tropical cyclone boundary layer is studied using linearized and nonlinear models, with particular focus on the frictionally forced vertical motion. The impulsively started, linearized tropical cyclone boundary layer is shown to adjust to its equilibrium solution via a series of decaying oscillations with the inertial period . In the nonlinear case, the oscillation period is slightly lengthened by inward advection of the slower-evolving flow from larger radii, but the oscillations decay more quickly. In an idealized cyclone with small sinusoidal oscillations superimposed on the gradient wind, the equilibrium nonlinear boundary layer acts as a low-pass filter with pass length scaling as , where is the 10-m frictional inflow. This filter is absent from the linearized boundary layer. The eyewall frictional updraft is similarly displaced inward of the radius of maximum winds (RMW) by a distance that scales with , owing to nonlinear overshoot of the inflowing air as it crosses the relatively sharp increase in I near the eyewall. This displacement is smaller (other things being equal) when the RMW is small, and greater when it is large, including in secondary eyewalls. The dependence of this distance on may explain, at least partially, why observed RMW are seldom less than 20 km, why storms with relatively peaked radial profiles of wind speed can intensify more rapidly, and why some secondary eyewalls initially contract rapidly with little intensification, then contract more slowly while intensifying.

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