A quantitative comparison between acoustic sounder returns and the direct measurement of atmospheric temperature fluctuations

Results are presented which show that reasonably accurate estimates of the atmospheric temperature structure paparmeter C _T ² can be derived from the returns of a monostatic acoustic sounder in both stable and convective atmospheric conditions.     

A general radar equation for the bistatic acoustic sounder

A radar equation which can be applied to any bistatic acoustic sounder is derived. The equation reduces to the expression normally used for the special case of the monostatic sounder. Numerical results using this equation are given for specific acoustic sounders, including the relative contributions to the scattering from the temperature and velocity parameters (C _T ² and C _V ²), the effect of wind speed on the scattered intensity and the measurement of horizontal wind velocity.Now with the Department of Electrical and Electronic Engineering, Portsmouth Polytechnic, Anglesea Road, Portsmouth PO1 3DJ.     

A phase-sensitive acoustic sounder for the detection of atmospheric temperature

An acoustic interferometer was built and operated during nocturnal temperature inversions to detect atmospheric temperature differences between the surface air and that at 50 m above the ground. The system departs from earlier succesful designs by using a time-multiplexed two-sided approach to attempt to correct for phase fluctuations caused by wind. Preliminary results from the apparatus indicate that the signals lack the necessary phase stability to permit calculation of temperature, even when subjected to averaging over 20-min intervals. It is concluded that simultaneous insonification of the scattering volume is a requisite for stable phase measurements in such a system.     

Simultaneous acoustic sounder measurements at two locations

The application of air quality models requires a knowledge of the meteorological structure of the lower atmosphere. This information can be obtained by the use of acoustic sounders, or airborne sondes. Such studies were carried out at the Athabasca Oil Sands area, Alberta, Canada, during summer and winter seasons. Two acoustic sounders were operated simultaneously at two topographically different locations 4 km apart. The sounding data were supplemented by meteorological observations from minisondes and a tethersonde at one location. The majority of the sounder data from both locations showed turbulent, thin layers often associated with the presence of inversion layers, particularly in the winter season. The data exhibited a number of features common to this type of topography. Both sounder echoes were characterized by a wavy structure indicating a vertical oscillation in the height of the echoes. Although agreeing in general, the data had a few differences especially close to the ground. To determine whether the return of the sounder signal was related to the actual atmospheric structure, the sounder records were compared with local temperature measurements. The result shows good agreement between the different systems.     

The effect of sea breezes on atmospheric stability as observed with acoustic sounder

Acoustic sounder data obtained for a period of three years have been analysed to estimate the monthly mean percentage time of occurrences of sea breezes, thermal plumes, and nocturnal radiative inversion layers. The intrusion of marine air has been found to suppress daytime convection and also to inhibit the development of nocturnal inversions.     

The remote sensing of wind velocity in the lower troposphere using an acoustic sounder

Acoustic sounding is a remote sensing technique which may be employed not only for the study of the structure of the lower troposphere, but also for the measurement of wind velocity using turbulent scattering regions as tracers or natural targets. Principles involved in the use of both angle of arrival and Doppler techniques for such wind measurements are summarized. Experimental results, which are presented for thermal plumes, structure associated with airflow over hills and a turbulent region of the radiation inversion, illustrate the potential of the acoustic sounding technique for research into boundary-layer meteorology.     

Planetary boundary-layer turbulence studies from acoustic echo sounder and in-situ measurements

Clear-air plume and wave-like structures are revealed in the atmospheric boundary layer by combined acoustic remote sensing and meteorological tower measurements. The magnitude of turbulent production and dissipation plus properties of velocity and temperature spectra determined from the tower measurements are well correlated with phenomena indicated by the acoustic sounder. Interpretation of either set of records is greatly enhanced by the other. For example, the onset of a sudden burst of turbulent production from the tower measurements may correspond to plume passage or breaking of stable waves recorded by the acoustic echo sounder.     

Atmospheric waves observed in the planetary boundary layer using an acoustic sounder and a microbarograph array

Acoustic sounder and microbarograph records of atmospheric waves propagating in the planetary boundary layer over Table Mountain, Colorado, are presented and compared. The two observing techniques are complementary in that the array provides wave amplitude, horizontal phase speed, direction, and wavelength, while the sounder provides a detailed picture of temporal changes in the structure of the lowermost kilometer or so of the Earth's atmosphere.     

Atmospheric thermic structure studied by acoustic echo sounder, boundary layer model, and direct measurements

In this work, the thermic structure of the atmospheric boundary layer is analyzed by means of direct measurements with radiosonde equipment, remote exploration with a three-monostatic Doppler sodar, and a boundary layer model of order one-and-a-half. Intercomparisons of radiosonde data, sodar data, and model results are made through the study of radiative nocturnal inversion, subsidence inversion, development and height of the mixing layer, and calculus of the temperature structure parameter. The ability of sodar to find the mixing layer height and to detect stable layers is enhanced when these layers are low enough.     

A note on the effects of virtual temperature: Research note

Abstract

The effects of virtual temperature on parcel buoyancy are investigated and the following results obtained. For descent or unsaturated ascent, the buoyancy acceleration is enhanced if the mixing ratio increases with pressure. However, for saturated ascent, the buoyancy acceleration is inhibited unless the lapse rate of mixing ratio exceeds a value slightly greater than that along a moist adiabat. This criterion is evaluated for several mean soundings. For the case of Oklahoma supercells, the mixing ratio lapse rate is clearly large enough. However, for other cases it often is not. Horizontal gradients in water vapour and condensed water can have a significant influence on the thermal wind.     

Observations of complex terrain flows using acoustic sounders: Echo interpretation

We examine methods for the interpretation of sodar facsimile records obtained in the study of complex terrain flows. Acoustic scattering theory is presented first and then interpreted using a simpolified second-order turbulence closure scheme. The use of this theory suggests the strong sensitivity of acoustic scatter to changes in the wind shear. With this introduction, detailed sodar facsimile records, temperature and wind profiles, and model calculations follow. Characteristic scattering patterns are described for simple drainage jets, complex basin flows, convection with a capping inversion, stratus, and dynamical instabilities. Examples are also shown of bistatic facsimile records detailing the strong temporal and spatial variability in small-scale turbulence.     

A note on free convection

The limiting condition of µ_*, 0 in the unstable atmospheric boundary layer is usually referred to as free convection. Some of the similarity laws that are proposed for this condition do not agree with experiment. A mechanism is proposed in this paper to show why the asymptotic free convection condition is never completely reached near the surface. It is shown that local turbulent shear production plays an important role in shaping the temperature profile even when the average velocity is zero.Contribution No. 267, Dept. of Atmospheric Sciences, University of Washington.     

A note on the dynamics of the quasi-stationary Kunming front

Summary The quasi-stationary Kunming front is oriented parallel to the north-south running major mountain chains of south-western China and normal to the upper-level westerlies. The front curves towards the east off the mountain. We hypothesize that the shape of the Kunming front is due to ageostrophic flow along the mountains which is induced by westerly flow in the cold air and at upper levels. Eventually the front must become stagnant. This conjecture is supported by numerical experiments with simple models.With 7 Figures     

有关Gorenstein投射猜想的一个注记

证明了对一个Artinian代数A,如果它的左有限维数或右有限维数有限,则A满足Gorenstein投射猜想.由此可知,Gorenstein代数和表示维数小于等于3的代数上的Gorenstein投射猜想是成立的.