Finescale Dual-Doppler Analysis of Hurricane Boundary Layer Structures in Hurricane Frances (2004) at Landfall

2014 ◽  
Vol 142 (5) ◽  
pp. 1874-1891 ◽  
Author(s):  
Karen A. Kosiba ◽  
Joshua Wurman
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Transient Nature ◽  
Layer Structures ◽  
Characteristic Wavelength ◽  
Doppler Data ◽  
Mean Wind Speed ◽  
Average Flux ◽  
Hurricane Boundary Layer ◽  
The Right

Abstract Two Doppler on Wheels (DOW) mobile radars collected fine-spatial-scale dual-Doppler data in the right-front quadrant and eye of Hurricane Frances (2004) as it made landfall near Stuart, Florida. A 5.7-km dual-Doppler baseline established a dual-Doppler domain south and east of Fort Pierce, Florida, encompassing a 5.5 km × 5.5 km horizontal area, with a grid spacing of 20 m, allowing for the resolution of subkilometer-scale horizontal structures and associated kinematics. Three-dimensional vector wind analyses of the boundary layer revealed the presence of linear coherent structures with a characteristic wavelength of 400–500 m near the surface that increased in size and became more cellular in shape with increasing height. Average horizontal perturbation winds were proportional to average total horizontal winds. Within the eye of the hurricane, the features lost linear coherency despite a high mean wind speed, possibly due to changes in stability. A slight decrease in the characteristic wavelength of boundary layer structures was documented as the winds cross the barrier islands east of Fort Pierce. Vertical flux of horizontal momentum caused by individual vortical structures was substantially higher than values employed in turbulence parameterization schemes, but the domain-wide average flux was substantially lower than that in individual structures, likely due to the transient nature of the most intense portions of the structures. Analysis of the turbulent kinetic energy (TKE) yielded values comparable to those reported in previous observational studies over the open ocean. However, there was substantial variability in TKE within the dual-Doppler domain, emphasizing the challenge in obtaining representative samples using non-3D measurements such as dropsondes.

scholarly journals Hurricane Boundary Layer Height Relative to Storm Motion from GPS Dropsonde Composites

Atmosphere ◽  
2019 ◽  
Vol 10 (6) ◽  
pp. 339 ◽  
Author(s):  
Yifang Ren ◽  
Jun A. Zhang ◽  
Stephen R. Guimond ◽  
Xiang Wang
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Layer Depth ◽  
Layer Height ◽  
Boundary Layer Height ◽  
Tangential Wind ◽  
Hurricane Boundary Layer ◽  
The Right

This study investigates the asymmetric distribution of hurricane boundary layer height scales in a storm-motion-relative framework using global positioning system (GPS) dropsonde observations. Data from a total of 1916 dropsondes collected within four times the radius of maximum wind speed of 37 named hurricanes over the Atlantic basin from 1998 to 2015 are analyzed in the composite framework. Motion-relative quadrant mean composite analyses show that both the kinematic and thermodynamic boundary layer height scales tend to increase with increasing radius in all four motion-relative quadrants. It is also found that the thermodynamic mixed layer depth and height of maximum tangential wind speed are within the inflow layer in all motion-relative quadrants. The inflow layer depth and height of the maximum tangential wind are both found to be deeper in the two front quadrants, and they are largest in the right-front quadrant. The difference in the thermodynamic mixed layer depth between the front and back quadrants is smaller than that in the kinematic boundary layer height. The thermodynamic mixed layer is shallowest in the right-rear quadrant, which may be due to the cold wake phenomena. The boundary layer height derived using the critical Richardson number ( R i c ) method shows a similar front-back asymmetry as the kinematic boundary layer height.

scholarly journals Estimation and Mapping of Hurricane Turbulent Energy Using Airborne Doppler Measurements

2010 ◽  
Vol 138 (9) ◽  
pp. 3656-3670 ◽  
Author(s):  
Sylvie Lorsolo ◽  
Jun A. Zhang ◽  
Frank Marks ◽  
John Gamache
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Turbulent Energy ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Horizontal Shear ◽  
Retrieval Method ◽  
Hurricane Boundary Layer

Abstract Hurricane turbulent kinetic energy (TKE) was computed using airborne Doppler measurements from the NOAA WP-3D tail radars, and TKE data were retrieved for a variety of storms at different stages of their life cycle. The geometry of the radar analysis coupled with the relatively small beam resolution at ranges <8 km allowed for the estimation of subkilometer turbulent processes. Two-dimensional profiles of TKE were constructed and revealed that the strongest turbulence was generally located in convective regions, such as the eyewall, with magnitudes often exceeding 15 m2 s−2 and in the boundary layer with values of 5–10 m2 s−2 in the lowest kilometer. A correlation analysis showed that the strong turbulence was generally associated with strong horizontal shear of vertical and radial wind components in the eyewall and strong vertical shear of horizontal wind in the boundary layer. Mean vertical profiles of TKE decrease sharply above the hurricane boundary layer and level off at low magnitude for all regions outside the radius of maximum wind. The quality of the retrieval method was evaluated and showed very good agreement with TKE values directly calculated from the three-dimensional wind components of in situ measurements. The method presented here provides a unique opportunity to assess hurricane turbulence throughout the storm, especially in high-wind regions, and can be applied on extensive datasets of past and future airborne hurricane penetrations.

scholarly journals An Experimental Flow Field Study of a Bio-inspired Corrugated Wing at Low Reynolds Number

2019 ◽  
Vol 11 (3) ◽  
pp. 55-65 ◽  
Author(s):  
Y. D. DWIVEDI ◽  
Y. B. SUDHIR SASTRY
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flat Plate ◽  
Three Dimensional ◽  
Longitudinal Axis ◽  
Reynolds Numbers ◽  
Subsonic Wind Tunnel ◽  
The Right ◽  
Moderate Range ◽  
Wing Tip

The present paper examined experimentally the glide flight flow visualization and boundary layers of a bio-inspired corrugated dragonfly wing performing a comparison with the results obtained with a flat plate, at low to moderate range of chord Reynolds numbers. The experimental work is performed in an open-end low speed subsonic wind tunnel at different angles of attack ranging from 0 to 120 and Reynolds number 2.25×105. The boundary layer measurements were done at a fixed chord location (0.7 x/c) and three different semi span locations such as 30%, 60% and 90% of the wing’s semi span from the right side of the longitudinal axis of the wing. The flow patterns were visualized by using colored tufts, placed at different span locations. The flow reversal was observed at selected Reynolds numbers and angles of attack only. The boundary layer measurements demonstrated that there exists a clear distinction on the pressure and velocity parameters in all the three tested locations on both types of the wings. The corrugated wing showed significant delay in stall and flow separation compared with the flat plate. The visualization of flow in both wings showed that there subsists a spanwise flow moving from wing tip to root, indicating three dimensional natures of airflows.

Buffer layer structures associated with extreme wall stress events in a smooth wall turbulent boundary layer

2009 ◽  
Vol 633 ◽  
pp. 17-60 ◽  
Author(s):  
J. SHENG ◽  
E. MALKIEL ◽  
J. KATZ
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Buffer Layer ◽  
Inclination Angle ◽  
Three Dimensional ◽  
Wall Stress ◽  
Streamwise Vortices ◽  
Smooth Wall ◽  
Velocity Deficit ◽  
Layer Structures

Three-dimensional velocity distributions and corresponding wall stresses are measured concurrently in the inner part of a turbulent boundary layer over a smooth wall using digital holographic microscopy. The measurements are performed in a square duct channel flow atReδ= 50000 andReτ= 1470. A spatial resolution of 3–8 wall units (δυ= μm) in streamwise and spanwise directions and 1 wall unit in the wall-normal direction are sufficient for resolving buffer layer structures and for measuring the instantaneous wall shear stresses from velocity gradients in the viscous sublayer. Mean velocity and Reynolds stress profiles agree well with previous publications. Rudimentary observations classify the buffer layer three-dimensional flow into (i) a pair of counter-rotating inclined vortices, (ii) multiple streamwise vortices, some of them powerful, and (iii) no apparent buffer layer structures. Each appears in about one third of the realizations. Conditional sampling based on local wall shear stress maxima and minima reveals two types of three-dimensional buffer layer structures that generate extreme stress events. The first structure develops as spanwise vorticity lifts from the wall abruptly and within a short distance of about 10 wall units, creating initially a vertical arch. Its only precursors are a slight velocity deficit that does not involve an inflection point and low levels of vertical vorticity. This arch is subsequently stretched vertically and in the streamwise direction, culminating in formation of a pair of inclined, counter-rotating vortices with similar strength and inclination angle exceeding 45°. A wall stress minimum exists under the point of initial lifting. A pair of stress maxima develops 35δυdownstream, on the outer (downflow) sides of the vortex pair and is displaced laterally by 35–40δυfrom the minimum. This flow structure exists not only in the conditionally averaged field but in the instantaneous measurement as well and appears in 16.4% of the realizations. Most of the streamwise velocity deficit generated by this phenomenon develops during this initial lifting, but it persists between the pair of vortices. Distribution of velocity fluctuations shows that spanwise transport of streamwise momentum plays a dominant role and that vertical transport is small under the vortices. In other regions, e.g. during initial lifting, and between the vortices, vertical transport dominates. The characteristics of this structure are compared to early experimental findings, highlighting similarities and differences. Abundance of pairs of streamwise vortices with similar strength is inconsistent with conclusions of several studies based on analysis of direct numerical simulation (DNS) data. The second buffer layer structure generating high wall stresses is a single, predominantly streamwise vortex, with characteristic diameter of 20–40δυand inclination angle of 12°. It generates an elongated, strong stress maximum on one side and a weak minimum on the other and has been observed in 20.4% of the realizations. Except for a limited region of sweep above the high-stress region, this low-lying vortex mostly induces spanwise momentum transport. This structure appears to be similar to those observed in several numerical studies.

Boundary Layer Wind Characteristics over Urban Area

2014 ◽  
Vol 501-504 ◽  
pp. 2297-2300
Author(s):  
Lun Hai Zhi
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Urban Area ◽  
Atmospheric Turbulence ◽  
Wind Velocity ◽  
Three Dimensional ◽  
Tall Buildings ◽  
Gust Factor ◽  
Mean Wind Speed ◽  
Wind Characteristics

This paper presents statistical analysis results of wind speed and atmospheric turbulence data measured from a meteorological station in Beijing and is primarily intended to provide useful information on boundary layer wind characteristics for wind-resistant design of tall buildings and high-rise structures. Wind velocity data in longitudinal, lateral and vertical directions, which were recorded from an ultrasonic anemometer during windstorms, are analyzed and discussed. Atmospheric turbulence information such as turbulence intensity, gust factor, turbulence integral length scale and power spectral densities of the three-dimensional fluctuating wind velocity are presented and used to evaluate the adequacy of existing theoretical and empirical models. The objective of this study is to investigate the profiles of mean wind speed and atmospheric turbulence characteristics over a typical urban area.

scholarly journals The Boundary Layer Winds in Hurricanes Danielle (1998) and Isabel (2003)

2008 ◽  
Vol 136 (8) ◽  
pp. 3168-3192 ◽  
Author(s):  
Juliane Schwendike ◽  
Jeffrey D. Kepert
Keyword(s):  
Boundary Layer ◽  
Surface Wind ◽  
Three Dimensional ◽  
Surface Wind Speed ◽  
Layer Model ◽  
Near Surface ◽  
Gradient Wind ◽  
Hurricane Isabel ◽  
The Right ◽  
Left Front

Abstract This paper describes the boundary layer wind structure and dynamics of Hurricanes Danielle (1998) and Isabel (2003), based on the analysis of high-resolution global positioning system dropwindsonde data and simulation of the flow by a three-dimensional boundary layer model produced by Kepert and Wang. The observations show that the hurricane boundary layer has a complex three-dimensional structure with large variability over small distances. The analysis emphasizes three aspects: the degree of gradient-wind balance, the radially varying depth of the boundary layer, and the strength of the near-surface wind speed relative to that at a higher level. Each aspect is compared both with results obtained in a simulation of the individual storm by Kepert and Wang’s model and with theoretical predictions. The observations show that the boundary layer depth decreases toward the center of the storm, consistent with theoretical arguments. The strongest azimuthal winds occur near the top of, but still within, the frictional inflow layer. These strong azimuthal winds are marginally supergradient in Hurricane Danielle but strongly so in Hurricane Isabel, where the imbalance amounts to approximately 10 m s−1 near the radius of maximum winds and is statistically significantly nonzero. This layer of supergradient flow is surmounted by a layer of outflow, in which the flow returns to gradient balance. The maximum storm-relative azimuthal wind occurs in the left front of Hurricane Danielle, and the strongest inflow is located in the right front. These asymmetries rotate anticyclonically with height, but there is also a clear wavenumber-2 asymmetry superimposed, which shows less rotation with height and is possibly forced by environmental factors associated with the storm’s impending recurvature. In Hurricane Isabel, the azimuthal wind maximum is located in the left rear and the inflow maximum in the left front, with neither showing much tendency to vary in azimuth with height. The ratio of the near-surface wind speed to that farther aloft increases toward the storm center for both storms. The largest values are located near the radius of maximum wind, and in general higher values are found on the left of the storm’s track than on the right. Simulations of the two storms with the boundary layer model are able to explain several of these factors; they also show some ability to reproduce individual dropsonde wind observed profiles. Important is that the model predicts weakly supergradient flow in Danielle and strongly supergradient flow in Isabel, in excellent agreement with the observational analysis. Based on these simulations, physical arguments, and earlier studies, the authors conclude that the differences between these storms in this respect result from their differing radial profiles of gradient wind and argue that the occurrence of supergradient flow in the upper boundary layer of individual hurricanes should be readily predictable.

Prediction of Atmospheric Turbulence Characteristics for Surface Boundary Layer using Empirical Spectral Methods

2020 ◽  
Author(s):  
Yagya Dutta Dwivedi ◽  
Vasishta Bhargava Nukala ◽  
Satya Prasad Maddula ◽  
Kiran Nair
Keyword(s):  
Boundary Layer ◽  
Time Series ◽  
Surface Roughness ◽  
Wind Speed ◽  
Atmospheric Turbulence ◽  
Surface Boundary ◽  
Low Frequencies ◽  
Surface Boundary Layer ◽  
Power Spectral ◽  
Mean Wind Speed

Abstract Atmospheric turbulence is an unsteady phenomenon found in nature and plays significance role in predicting natural events and life prediction of structures. In this work, turbulence in surface boundary layer has been studied through empirical methods. Computer simulation of Von Karman, Kaimal methods were evaluated for different surface roughness and for low (1%), medium (10%) and high (50%) turbulence intensities. Instantaneous values of one minute time series for longitudinal turbulent wind at mean wind speed of 12 m/s using both spectra showed strong correlation in validation trends. Influence of integral length scales on turbulence kinetic energy production at different heights is illustrated. Time series for mean wind speed of 12 m/s with surface roughness value of 0.05 m have shown that variance for longitudinal, lateral and vertical velocity components were different and found to be anisotropic. Wind speed power spectral density from Davenport and Simiu profiles have also been calculated at surface roughness of 0.05 m and compared with k−1 and k−3 slopes for Kolmogorov k−5/3 law in inertial sub-range and k−7 in viscous dissipation range. At high frequencies, logarithmic slope of Kolmogorov −5/3rd law agreed well with Davenport, Harris, Simiu and Solari spectra than at low frequencies.

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