The Experts below are selected from a list of 2094 Experts worldwide ranked by ideXlab platform
Inanc Senocak - One of the best experts on this subject based on the ideXlab platform.
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linear stability of katabatic prandtl slope flows with ambient Wind forcing
Journal of Fluid Mechanics, 2020Co-Authors: Cheng-nian Xiao, Inanc SenocakAbstract:We investigate the stability of katabatic slope flows over an infinitely wide and uniformly cooled planar surface subject to a downslope uniform ambient Wind Aloft. We adopt an extension of Prandtl’s original model for slope flows (Lykosov & Gutman, Izv. Acad. Sci. USSR Atmos. Ocean. Phys. , vol. 8 (8), 1972, pp. 799–809) to derive the base flow, which constitutes an interesting basic state in stability analysis because it cannot be reduced to a single universal form independent of external parameters. We apply a linear modal analysis to this basic state to demonstrate that for a fixed Prandtl number and slope angle, two independent dimensionless parameters are sufficient to describe the flow stability. One of these parameters is the stratification perturbation number that we have introduced in Xiao & Senocak ( J. Fluid Mech. , vol. 865, 2019, R2). The second parameter, which we will henceforth designate the Wind forcing number, is hitherto uncharted and can be interpreted as the ratio of the kinetic energy of the ambient Wind Aloft to the damping due to viscosity and the stabilising effect of the background stratification. For a fixed Prandtl number, stationary transverse and travelling longitudinal modes of instabilities can emerge, depending on the value of the slope angle and the aforementioned dimensionless numbers. The influence of ambient Wind forcing on the base flow’s stability is complicated, as the ambient Wind can be both stabilising as well as destabilising for a certain range of the parameters. Our results constitute a strong counterevidence against the current practice of relying solely on the gradient Richardson number to describe the dynamic stability of stratified atmospheric slope flows.
Cheng-nian Xiao - One of the best experts on this subject based on the ideXlab platform.
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linear stability of katabatic prandtl slope flows with ambient Wind forcing
Journal of Fluid Mechanics, 2020Co-Authors: Cheng-nian Xiao, Inanc SenocakAbstract:We investigate the stability of katabatic slope flows over an infinitely wide and uniformly cooled planar surface subject to a downslope uniform ambient Wind Aloft. We adopt an extension of Prandtl’s original model for slope flows (Lykosov & Gutman, Izv. Acad. Sci. USSR Atmos. Ocean. Phys. , vol. 8 (8), 1972, pp. 799–809) to derive the base flow, which constitutes an interesting basic state in stability analysis because it cannot be reduced to a single universal form independent of external parameters. We apply a linear modal analysis to this basic state to demonstrate that for a fixed Prandtl number and slope angle, two independent dimensionless parameters are sufficient to describe the flow stability. One of these parameters is the stratification perturbation number that we have introduced in Xiao & Senocak ( J. Fluid Mech. , vol. 865, 2019, R2). The second parameter, which we will henceforth designate the Wind forcing number, is hitherto uncharted and can be interpreted as the ratio of the kinetic energy of the ambient Wind Aloft to the damping due to viscosity and the stabilising effect of the background stratification. For a fixed Prandtl number, stationary transverse and travelling longitudinal modes of instabilities can emerge, depending on the value of the slope angle and the aforementioned dimensionless numbers. The influence of ambient Wind forcing on the base flow’s stability is complicated, as the ambient Wind can be both stabilising as well as destabilising for a certain range of the parameters. Our results constitute a strong counterevidence against the current practice of relying solely on the gradient Richardson number to describe the dynamic stability of stratified atmospheric slope flows.
R G Harrison - One of the best experts on this subject based on the ideXlab platform.
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coupling between air flow in streets and the well developed boundary layer Aloft
Atmospheric Environment, 2000Co-Authors: P Louka, S E Belcher, R G HarrisonAbstract:A "eld experiment was conducted to study the mean and turbulent characteristics of air#ow within, and above, a street under neutral strati"cation. Pro"les of the mean Wind and turbulent statistics were obtained and compared with #ow over smoother terrain. Our results modify the conventional picture of a persistent re-circulation within the street with small-scale turbulent #uctuations about this mean (Oke, 1987). Instead, the mean re-circulation within the street was found to be much weaker than the unsteady turbulent #uctuations. Hence, the mean #ow is merely a residual of an unsteady turbulent re-circulation. The re-circulation in the street is coupled to the Wind Aloft through a shear layer that develops at the roof-level. The shear layer is unstable, through Kelvin}Helmholtz instability, which leads to intermittency in the re-circulation in the street, and thence to ventilation of the air in the street. This "nding is likely to be important for dispersion in urban areas. ( 2000 Elsevier Science Ltd. All rights reserved.
Eric S. Michel - One of the best experts on this subject based on the ideXlab platform.
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The effect of weather on the decision to migrate from stopover sites by autumn-migrating ducks
BMC, 2018Co-Authors: Benjamin J. O’neal, Joshua D. Stafford, Ronald P. Larkin, Eric S. MichelAbstract:Abstract Background Previous investigations of autumn-migrating ducks have reported weak connections between weather conditions and the decision to migrate from stopover sites. We leveraged relatively new weather surveillance radar technology to remotely detect departures of discrete groups of various species of migratory dabbling ducks (Anatidae) in autumn to more directly assess the effect of specific weather conditions on departure from discrete stopover sites. Methods Using radar data collected over fifteen years (1995–2009), we documented a consistent phenomenon where a single, identifiable group departed from our study area on 30% of days during the autumn study period, and no ducks departed on the other days. We gathered weather variables from nearby stations and used them to develop competing models to explain temporal patterns of departure versus non-departure to better understand the potential mechanisms associated with binomial patterns of departures. Results The best approximating model of departure probability was our integrated model, which included variables accounting for Wind Aloft direction favorable for departure (i.e., tailWind), absence of precipitation, and a partially or completely clear sky. The integrated model accounted for all model weight in the candidate set and explained 55% of the variation in departure probability. Estimated probability of departure was 0.76 after parameterizing the best model with favorable conditions for all covariates. Conclusions Our results contrasted those of previous studies of autumn duck migration as a small set of simplistic, extrinsic conditions substantially influenced departure decision
Senocak Inanc - One of the best experts on this subject based on the ideXlab platform.
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Linear Stability of Katabatic Slope Flows with Ambient Wind Forcing
'Cambridge University Press (CUP)', 2019Co-Authors: Xiao Cheng-nian, Senocak InancAbstract:We investigate the stability of katabatic slope flows over an infinitely wide and uniformly cooled planar surface subject to an additional forcing due to a uniform downslope Wind field Aloft. We adopt an extension of Prandtl's original model for slope flows (Lykosov & Gutman 1972) to derive the base flow, which constitutes an interesting basic state in stability analysis because it cannot be reduced to a single universal form independent of external parameters. We apply a linear modal analysis to this basic state to demonstrate that for a fixed Prandtl number and slope angle, two independent dimensionless parameters are sufficient to describe the flow stability. One of these parameters is the stratification perturbation number that we have introduced in Xiao & Senocak (2019). The second parameter, which we will henceforth designate the Wind forcing number, is hitherto uncharted and can be interpreted as the ratio of the kinetic energy of the ambient Wind Aloft to the damping due to viscosity and stabilizing effect of the background stratification. For a fixed Prandtl number, stationary transverse and travelling longitudinal modes of instabilities can emerge, depending on the value of the slope angle and the aforementioned dimensionless numbers. The influence of ambient Wind forcing on the base flow's stability is complicated as the ambient Wind can be both stabilizing as well as destabilizing for a certain range of the parameters. Our results constitute a strong counter-evidence against the current practice of relying solely on the gradient Richardson number to describe the dynamic stability of stratified atmospheric slope flows.Comment: 10 pages, 5 figure
