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1.
Boundary-Layer Wind Structure in a Landfalling Tropical Cyclone 总被引：1，自引：0，他引：1
In this study, a slab boundary layer model with a constant depth is used to analyze the boundary-layer wind structure in a landfalling tropical cyclone. Asymmetry is found in both the tangential and radial components of horizontal wind in the tropical cyclone boundary layer at landfall. For a steady tropical cyclone on a straight coastline at landfall, the magnitude of the radial component is greater in the offshoreflow side and the tangential component is greater over the sea, slightly offshore, therefore the greater total wind speed occurs in the offshore-flow side over the sea. The budget analysis suggests that： （1） a greater surface friction over land produces a greater inflow and the nonlinear effect advects the maximum inflow downstream, and （2） a smaller surface friction over the sea makes the decrease of the tangential wind component less than that over land. Moreover, the boundary layer wind structures in a tropical cyclone are related to the locations of the tropical cyclone relative to the coastline due to the different surface frictions. During tropical cyclone landfall, the impact of rough terrain on the cyclone increases, so the magnitude of the radial component of wind speed increases in the offshore-flow side and the tangential component outside the radius of maximum wind speed decreases gradually. 相似文献
2.
Steven M. Babin Todd D. Sikora Nathaniel S. Winstead 《Boundary-Layer Meteorology》2003,106(3):527-546
A case study of a particularly intense cold air outbreak over the northAtlantic Ocean extending from the northeast coast of the UnitedStates to the Gulf Stream is described. A RADARSAT satellite synthetic apertureradar (SAR) image of this outbreak dramatically illustrates the spatialevolution of convection. Nearly coincident images from the National Oceanic and Atmospheric Administration's Advanced Very HighResolution Radiometer are used to compare many interesting features.In addition, National Weather Service rawinsonde data, National Data Buoy Center buoy data, and Woods Hole Oceanographic Institute Coastal Mixing and Optics mooring data arepresented. We use these data to help describe the spatial evolution of the atmospheric boundary-layer processes involved in this outbreak.Rows of cellular convective clouds begin to appear some distance offshore and then slowly increase in horizontal diameter and wavelength in the downwind direction, with a subsequent jump in cloud diameter downwind of the Gulf Stream North Wall (GSNW). The SAR image shows a similar evolution of sea-surface footprints of these boundary-layer features. This change in boundary-layer structure is attributed to corresponding changes in static stability. About 300 km south of the GSNW in the SAR image, an even larger jump in cell diameter appears and the cells becomenon-uniform with bright crescents and filled semi-circles on thedownwind sides of the cells. These are believed to be surface effectsof gust fronts induced by the mesoscale cellular convection and enhanced by the overall northwesterly flow. 相似文献
3.
J.-P. LHOMME 《Boundary-Layer Meteorology》1997,82(2):179-191
The relationship between potential evaporation and arealevaporation is assessed using a closed-box model of the convectiveboundary layer (CBL). Potential evaporation is defined as theevaporation that would occur from a hypothetical saturated surface,with radiative properties similar to those of the whole area, and smallenough that the excess moisture flux does not modify thecharacteristics of the CBL. It is shown that the equilibrium rate ofpotential evaporation is given by Ep0=E0,where E0 is the equilibrium evaporation (radiative termof the Penman formula), and is a coefficient similar to thePriestley-Taylor coefficient. Its expression is
, where
is the areal surface resistance, ra is the localaerodynamic resistance, and is the dimensionless slope of thesaturation specific humidity at the temperature of the air. Itscalculated value is around 1 for any saturated surface surrounded bywater, about 1.3 for saturated grass surrounded by well-watered grassand can be greater than 3 over saturated forest surrounded by forest.The formulation obtained provides a theoretical basis to the overallmean value of 1.26, empirically found by Priestley and Taylor for thecoefficient . Examining, at the light of this formulation, thecomplementary relationship between potential and actual evaporation(as proposed by Bouchet and Morton), it appears that the sum ofthese two magnitudes is not a constant at equilibrium, but depends onthe value of the areal surface resistance. 相似文献
4.
In this paper,a tropical atmospheric model of relevance to shorts-term climate variations(Wang and Li 1993)is util-ized for study of the development of Madden-Julian oscillation.The model contains an interactive process ofboundary-layer Ekman convergence and precipitation heating.The model is solved by expanding dependent variables interms of parabolic cylindrical functions in the meridional direction and truncating three meridional modes n=0,2,4 forequatorial symmetric solutions.The free wave solutions obtained under long-wave approximation are induced as aKelvin wave and two Rossby waves.After considering the effect of boundary-layer dynamic process,the modifiedKelvin wave becomes unstable in long-wave bands with a typical growth rate on an order of 10~(-6) s~(-1)and an eastwardphase speed of 10 m s~(-1);the most unstable mode is wavenumber one.These theoretical results are consistent with the ob-served Madden-Julian oscillation in equatorial area.For the two modified Rossby waves,one with a smaller meridionalscale(n=4)decays except for extra long-waves;the other with a larger meridional scale(n=2)grows in short-wavebands.This may be relevant to explaining the westward propagation of super cloud clusters in the Madden-Julianoscillation.The theory suggests that the boundary-layer dynamic process is an important mechanism in the develop-ment of the Madden-Julian oscillation. 相似文献
5.
Ralph C. Foster 《Boundary-Layer Meteorology》2009,131(3):321-344
We present similarity solutions for the mean boundary-layer profiles under an axisymmetric vortex that is in gradient wind
balance; the similarity model includes the nonlinear momentum advection and curvature terms. These solutions are a generalization
of the Ekman layer mean flow, which is the canonical boundary-layer basic state under a uniform, geostrophically-balanced
flow. Near-surface properties such as inflow angle, surface wind factor, diffusive transport of kinetic energy into the surface
layer and dissipational heating are calculated and shown to be sensitive to the choice of turbulence parameterization. 相似文献
6.
Two weeks of measurements of the boundary-layer height over a small island (Christiansø) in the Baltic Sea are discussed. The meteorological conditions are characterised by positive heat flux over the sea. The boundary-layer height was simulated with two models, a simple applied high-resolution (2 km × 2 km) model, and the operational numerical weather prediction model HIRLAM (grid resolution of 22.5 km × 22.5 km). For southwesterly winds it was foundthat a relatively large island (Bornholm) lying 20-km upwind of the measuring site influences the boundary-layer height. In this situation the high-resolution simple applied model reproduces the characteristics of the boundary-layer height over the measuring site. Richardson-number based methods using data from simulations with the HIRLAM model fail, most likely because the island and the water fetch to the measuring site are about the size of the grid resolution of the HIRLAM model and therefore poorly resolved. For northerly winds, the water fetch to the measuring site is about 100 km. Both models reproduce the characteristics of the height of the marine boundary layer. This suggests that the HIRLAM model adequately resolves a water fetch of 100 km with respect to predictions of the height of the marine boundary layer. 相似文献
7.
Antony?Z.?OwinohEmail author Julian?C.?R.?Hunt Andrew?Orr Peter?Clark Rupert?Klein H.?J.?S.?Fernando Frans?T.?M.?Nieuwstadt 《Boundary-Layer Meteorology》2005,116(2):331-361
We examine the unsteady response of a neutral atmospheric boundary layer (ABL) of depth h and friction velocity u * when a uniform surface heat flux is applied abruptly or decreased rapidly over a time scale t<inf>θ</inf> less than about h /(10u *). Standard Monin–Obukhov (MO) relationships are used for the perturbed eddy viscosity profile in terms of the changes to
the heat flux and mean shear. Analytical solutions for changes in temperature, mean wind and shear stress profile are obtained
for the surface layer, when there are small changes in h /|LMO| over the time scale tMO~|L MO|/(10u*) (where L MO and t MO are the length and time scales, respectively). They show that a maximum in the wind speed profile occurs at the top of the
thermal boundary layer for weak surface cooling, i.e. a wind jet, whereas there is a flattening of the profile and no marked
maximum for weak surface heating. The modelled profiles are approximately the same as those obtained from the U.K. Met Office
Unified Model when operating as a mesoscale model at 12-km horizontal resolution. The theoretical model is modified when strong
surface heating is suddenly applied, resulting in a large change in h /|L MO| (>>1), over the time scale t MO. The eddy structure is predicted to change significantly and the addition of convective turbulence increases the shear turbulence
at the ground. A low-level wind jet can form, with convective turbulence adding to the mean momentum of the flow. This was
verified by our laboratory experiment and direct numerical simulations. Additionally, it is shown that the effects of Coriolis
acceleration diminish (rather than as suggested in the literature, amplify) the formation of the wind jets in the situations
considered here. Hence, only when the surface heat flux changes over time scales greater than 1/f (where f is the Coriolis parameter) does the ABL adjust monotonically between its equilibrium states. These results are also applicable
to the ABL passing over spatially varying surface heat fluxes. 相似文献
8.
The results from a one-dimensional photochemical model of the troposphere representative of summertime conditions at Northern Hemisphere mid-latitudes are presented. A parameterization of mixing processes within the planetary boundary layer (PBL) has been incorporated into the model for both the daytime convective PBL and the formation of the nocturnal PBL. One result of the parameterized PBL is that the concentrations of some trace species in the free troposphere are 20–30% higher than when mixing processes are described by a vertical eddy diffusion coefficient which is held constant with respect to height and time.The calculations indicate that the lifetime of the oxides of nitrogen (NO
x
=NO+NO2) against photochemical conversion to nitric acid (HNO3) during summertime conditions is on the order of 6 h. This lifetime is short enough to deplete most of the NO
x
in the PBL, resulting in the finding that other reactive nitrogen species (HNO3 and peroxyacetyl nitrate) are more abundant than NO
x
throughout the free troposphere, even though NO
x
is the most abundant reactive nitrogen species at the surface. The effects of the inclusion of anthropogenic nonmethane hydrocarbon (NMHC) chemistry are also discussed. The inclusion of NMHC chemistry has a pronounced effect on the photochemistry of tropospheric oxone and increases thein situ column production by more than 30%. 相似文献
9.
归纳了地质流体力学研究中目前常用的三个基础理论,即双扩散对流理论,边界层理论和相似理论,重点总结了其在岩浆岩石学、成矿学、地球物理学及沉积岩石学等研究领域内的进展。 相似文献
10.
A three-dimensional (3-D) inertial particle – Lagrangian stochastic model for heavy particles in turbulent flows has been
constructed. In this model, particle velocities are computed by adopting a non-linear drag law, while fluid velocity in the
vicinity of a particle is calculated using a 3-D Langevin equation. Our model results have shown that the inclusion of the
horizontal fluid velocity fluctuation computations and a non-linear drag law have an impact on the statistics of both fluid
and particles when compared with our earlier one-dimensional (1-D) model with a linear drag law. Model results are compared
and contrasted with Businger’s 1965 theory in terms of effective settling velocity. 相似文献