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1.
William Blumen 《地球物理与天体物理流体动力学》2013,107(1-3):89-104
Abstract Adiabatic, two-dimensional, steady-state finite-amplitude, hydrostatic gravity waves produced by flow over a ridge are considered. Nonlinear self advection steepens the wave until the streamlines attain a vertical slope at a critical height zc. The height zc , where this occurs, depends on the ridge crest height and adiabatic expansion of the atmosphere. Dissipation is introduced in order to balance nonlinear self advection, and to maintain a marginal state above zc. The approach is to assume that the wave is inviscid except in a thin layer, small compared to a vertical wavelength, where dissipation cannot be neglected. The solutions in each region are matched to obtain a continuous solution for the streamline displacement δ. Solutions are presented for different values of the nondimensional dissipation parameter β. Eddy viscosity coefficients and the thickness of the dissipative layer are expressed as functions of β, and their magnitudes are compared to other theoretical evaluations and to values inferred from radar measurements of the stratosphere. The Fourier spectrum of the solution for z ≫ zc is shown to decay exponentially at large vertical wave numbers n. In comparison, a spectral decay law n ?-8/3 characterizes the marginal state of the wave at z = zc . 相似文献
2.
High frequency wind and temperature measurements, obtained in March 1995 from a 10-m tower array situated in south-east Kansas, are used to analyze the structure of a shallow density current. This current is approximately 7 m deep and exhibits a current head that is estimated to be about twice the current depth. The event lasted approximately 900 s and its origin appears to be a shallow slope 2–:5 km to the west of the site, where cold air drainage occurs. The onset of the event is marked by a 5 °C temperature decrease at the 3-m level, increased variance of temperature and of wind velocity, and increased dissipation of kinetic energy, measured by a hot-wire anemometer at the 3-m level. The primary contributors to temperature changes following the frontal passage are both horizontal and vertical advections; contributions from flux divergences of temperature and of radiation, and from dew formation, do not appear to be significant. Postulated frontogenesis, prior to the arrival of the apparent equilibrated front of approximately 176-m width at the site, is examined by means of a theoretical model. The time required to equilibrate the front, by means of kinetic energy dissipation within the frontal zone, is determined to be less than 300 s, or less than the estimated travel time from the orographic slope to the observational site. The absence of upstream data is determined, however, to be a limitation of the analysis performed. 相似文献
3.
W. Blumen 《Meteorology and Atmospheric Physics》1992,48(1-4):37-50
Summary Frontal propagation and its evolution over complex terrain features is not well understood. Moreover, one of the major sources of forecast error occurs over the earth's orography. This presentation reviews model studies of frontal interaction with smooth and relatively simple orographic profiles. Emphasis is placed on model predictions, of propagation speed and on the properties of the flow that favor either frontogenesis or frontolysis. The physical processes involved in the front-mountain interaction are isolated, with the aim of providing a basic physical understanding of the interaction process that may be used in the interpretation of more realistic but more complex flow models. Considered are bot homogeneous and density stratified fluid, both two- and three-dimensional orographic features, and both filtered (geostrophic and semigeostrophic) and unfiltered flow models. Potentially important areas of research that may add to knowledge of front-mountain interactions are briefly explored.With 10 Figures 相似文献
4.
William Blumen 《地球物理与天体物理流体动力学》2013,107(4):265-272
Abstract The process of wave steepening in Long's model of steady, two-dimensional stably stratified flow over orography is examined. Under conditions of the long-wave approximation, and constant values of the background static stability and basic flow, Long's equation is cast into the form of a nonlinear advection equation. Spectral properties of this latter equation, which could be useful for the interpretation of data analyses under mountain wave conditions, are presented. The principal features, that apply at the onset of convective instability (density constant with height), are: i) a power spectrum for available potential energy that exhibits a minus eight-thirds decay, in terms of the vertical wavenumber k z -; ii) a rate of energy transfer across the spectrum that is inversely proportional to the wavenumber for large k z -; iii) an equipartition between the kinetic energy of the horizontal motion and the available potential energy, under the longwave approximation, although all the disturbance energy is kinetic at the point where convective instability is initiated. It is also shown that features i) and ii) apply to more general conditions that are appropriate to Long's model, not just the long-wave approximation. Application to fully turbulent flow or to conditions at the onset of shearing instability are not considered to be warranted, since the development only applies to conditions at the onset of convective instability. 相似文献
5.
Orna Blumen 《Area》1998,30(4):343-357
Summary Occupational prestige is the social value attributed to occupation, and in most instances indicates socio-economic status. It is obtained at the workplace and manifested in one's lifestyle in a specific place of residence, and its spatial distribution therefore follows the repetitive flow of commuters. The geography of such prestige has not previously been studied; this study uses the 1983 census to examine the spatial distribution of occupational prestige in metropolitan Tel Aviv, Israel. It was found that most workers use short, local commuting routes, which point to relatively closed secondary spatial labour markets. Common generalizations in research regarding commuting length and occupational status reflect the social composition of the entire workforce, with workers of higher occupational status tending towards longer commutes. Yet, this study shows that such commuting is also undertaken by workers of lower occupational status, while short commuting is also undertaken by workers of higher status. In addition, the results show that such generalizations are spatially differentiated. 相似文献
6.
This paper highlights three major aspects of gender differences in employment in Haifa, Israel (1972 and 1983): commuting distance, place of residence, and employment location. In 1972 working womenaposs residences were more central-city-oriented, whereas in 1983 they were more suburbanized. Commuting distances increased between 1972 and 1983 for both sexes, but more for men than for women. This shorter “female'’distance is related to the location of employment and its occupational segregation. The lower commuting values in Haifa compared to other places relate to the size, housing patterns, and structure of the study area, and to its levels of suburbanization and automobile ownership. 相似文献
7.
Summary Frontal propagation and development in the presence of orography and moisture are examined using the objective cross-section analysis method of Shapiro and Hastings (1973). The method is applied to a real data case on 4–5 March 1982 during the Alpine Experiment (ALPEX). Surface data are added to the analysis method to improve the lowlevel depiction of the frontal zone.The ageostrophic winds are computed from the isentropic representation of =dp/dt and the horizontal momentum equations. Diabatic contributions to the circulation, computed from the isentropic form of the continuity equation, are compared with observed moisture fields. Cross-sections of observed data and computed vertical motions are compared with similar fields computed from analyses on pressure surfaces. It is shown that the Shapiro and Hastings scheme provides a relatively clear depiction of the small-scale frontal features in the thermal and wind field but the analysis also exhibits more noise, which can have an adverse effect on the accurarcy of derived fields.With 8 Figures 相似文献
8.
William Blumen 《地球物理与天体物理流体动力学》2013,107(1):189-200
Abstract Arnold's (1965a) method is used to investigate the stability of a stationary, nonparallel, plane flow, with horizontal shear, to three-dimensional nondivergent disturbances in a Boussinesq fluid. It is shown that, if the fluid is statically stable, the Rayleigh condition is not sufficient to insure inertial stability to all disturbance modes. For channel flow it is possible to establish the sufficiency condition for stability to some of these modes. 相似文献
9.
William Blumen Robert Banta Sean P. Burns David C. Fritts Rob Newsom Gregory S. Poulos Jielun Sun 《Dynamics of Atmospheres and Oceans》2001,34(2-4)
An apparent shear flow instability occurred in the stably stratified night-time boundary layer on 6 October 1999 over the Cooperative Atmosphere–Surface Exchange Study (CASES-99) site in southeast Kansas. This instability promoted a train of billows which appeared to be in different stages of evolution. Data were collected by sonic anemometers and a high-frequency thermocouple array distributed on a 60 m tower at the site, and a high resolution Doppler lidar (HRDL), situated close to the tower. Data from these instruments were used to analyze the characteristics of the instability and the billow event. The instability occurred in a layer characterized by a minimum Richardson number Ri0.13, and where an inflection in the background wind profile was also documented. The billows, which translated over the site for approximately 30 min, were approximately L320 m in length and, after billow evolution they were contained in a layer depth H30 m. Their maximum amplitude, determined by HRDL data, occurred at a height of 56 m. Billow overturns, responsible for mixing of heat and momentum, and high-frequency intermittent turbulence produce kurtosis values above the Gaussian value of 3, particularly in the lower part of the active layer. 相似文献
10.
Abstract The steady, hydrostatic, inviscid, Boussinesq flow of a stably stratified fluid over a bell-shaped ridge is investigated within the framework of a linear model. The three layer model atmosphere introduced is such that the Brunt-Väisälä frequency is constant in each layer but the interfaces of the middle layer are allowed to vary gently in the cross-ridge direction. In essence, the model can be tuned in both vertical and horizontal directions. These cross-ridge variations can produce significant differences in both the cross-ridge surface wind and the surface drag compared to the response obtained by use of a horizontally uniform reflecting layer. These changes are sensitive to both the vertical location of the middle layer and to the slope of its lower interface at the ridge crest. Many of these features are explained by means of a conventional layered-model analysis. 相似文献