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1

Digitale Medien

The role of gravity waves in tropospheric processes (1978)

Einaudi, F. ; Lalas, D. P. ; Perona, G. E.

Springer

Pure and applied geophysics 117 (1978), S. 627-663

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ISSN: 1420-9136

Schlagwort(e): Gravity waves ; Tropospheric dynamics

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie , Physik

Notizen: Summary The nature and the role of gravity waves in the troposphere is briefly discussed and reviewed. After describing some basic properties of gravity waves and their generation mechanisms, we analyze their ability to influence phase changes, trigger and organize convective cells, to produce and interact with turbulence, and to affect diffusive processes in the atmosphere. Throughout, the emphasis is placed on the physical processes involved in the interaction of gravity waves with mesoscale and planetary boundary layer phenomena. Also discussed and reviewed are those remote sensing devices which are particularly useful in revealing and measuring such waves. Finally, an attempt is made to outline possible lines of future work for the purpose of fully understanding the role of gravity waves in mesoscale and microscale dynamics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00879972

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2

Digitale Medien

The effect of moist layer location on the stability of trapped gravity waves in an almost saturated atmosphere (1991)

Jacovides, C. P. ; Lalas, D. P.

Springer

Meteorology and atmospheric physics 45 (1991), S. 65-74

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ISSN: 1436-5065

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geographie , Physik

Notizen: Summary The stability characteristics of trapped gravity waves, generated by an isothermal bounded tanh (z) velocity profile in the presence of a saturated finite layer, are studied. The saturated layer is introduced at different levels above the inlection point and the variations of moisture content, layer thickness and distance from the origin are examined. The growthyrates and phase speeds of the unstable modes are obtained by solving numerically the equations of motion in the linear, inviscid, Boussinesq limit, via the technique of Lalas and Einaudi (1976). It is shown that the presence of the saturated layer can significantly affect the stability characteristics of the waves. inereases in moisture, layer thickness and distance of the layer from the inflection point are found to amplify the wave response because the saturated layer behaves as a top boundtry to the shear flow. The presence of such effective boundaries is found to stabilize short wavelengths and destabilize longer wavelengths. Finally, an application of the results to a rainband case produces values of the wave parameters in good agreement with the observed ones.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01027475

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3

Digitale Medien

Observations of sea-breeze fronts near the shoreline (1987)

Helmis, C. G. ; Asimakopoulos, D. N. ; Deligiorgi, D. G. ; [weitere]

Springer

Boundary layer meteorology 38 (1987), S. 395-410

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ISSN: 1573-1472

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie , Physik

Notizen: Abstract Results from an observational study of sea-breeze fronts as they cross a shoreline are presented. Two kinds of fronts are analyzed, one with an offshore regional wind and one without. Their structure is found to be substantially different, the former being steeper and having stronger gradients. Measurements of the profiles of the vertical component of the wind speed, its standard deviation and the structure parameter for temperature are presented along with time series of the structure parameters for water vapor pressure and wind speed. The vertical wind component, w, is found to be of the order of 1.0–1.5 ms−1 in the front zone of the sharp front but only 5 as large in the weaker front. The usual height variation laws under convective conditions are found to apply for both the vertical velocity variance and the temperature structure parameter, which in conjunction with the appropriate spectra indicate that local equilibrium is re-established fairly quickly after the passage of the front. Substantial differences have also been noted in the values of the structure parameters before and after the front, especially in the water vapor pressure and wind speed, differences which are of dissimilar magnitude and sign for the two kinds of fronts.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00120854

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4

Digitale Medien

A quantitative comparison of horizontal and vertical acoustic sounding with in-situ measurements (1985)

Moulsley, T. J. ; Asimakopoulos, D. N. ; Helmis, C. G. ; [weitere]

Springer

Boundary layer meteorology 33 (1985), S. 85-100

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ISSN: 1573-1472

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie , Physik

Notizen: Abstract In this paper, we present some results on an experiment to test the accuracy and utility of a horizontally-aimed acoustic sounder. A high-frequency, high-resolution mini-sounder was mounted on the mast of the Boulder Atmospheric Observatory aimed in the cross-wind direction. Measurements of C T 2, wind velocity and temperature and velocity variances were obtained under both stable and unstable conditions. These measurements were found to be in agreement with the equivalent values obtained, where appropriate, by the tower-fixed instrumentation and a vertically-pointed sounder, confirming the accuracy of the horizontal sounder. In addition, some information into the horizontal structure of plumes and gravity waves was obtained along with evidence of lack of excess attenuation at least for lengths within the unambiguous range of mini-sounders.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00137039

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Digitale Medien

The stability analysis of an inflexion-free velocity profile and its application to the night-time boundary layer in the atmosphere (1976)

Fua, D. ; Einaudi, F. ; Lalas, D. P.

Springer

Boundary layer meteorology 10 (1976), S. 35-54

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ISSN: 1573-1472

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie , Physik

Notizen: Abstract The characteristics of waves excited in a stratified shear flow with a velocity profile monotonically increasing above the ground are calculated numerically. It is shown that unstable modes exist when the Brunt-Väisälä frequency of the ambient atmosphere decreases sufficiently fast with height. Their growth rates as a function of the horizontal wavelength and the local Richardson number are given, and a comparison between them and experimental data obtained for the night-time-boundary layer of the Earth's atmosphere is carried out. Finally, the characteristics of the singular neutral modes that the system can support are presented.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00218723

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6

Digitale Medien

Quantitative low-level acoustic sounding and comparison with direct measurements (1983)

Asimakopoulos, D. N. ; Moulsley, T. J. ; Helmis, C. G. ; [weitere]

Springer

Boundary layer meteorology 27 (1983), S. 1-26

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ISSN: 1573-1472

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie , Physik

Notizen: Abstract In this paper, measurements of the first 150 m of the atmospheric boundary layer obtained by a high-frequency acoustic mini-sounder are compared with measurements obtained by a full complement of instruments including sonic anemometers mounted on the Boulder Atmospheric Observatory tower. The acoustic mini-sounder, starting as low as 6 m from the ground, measures in the monostatic mode the profiles of the vertical wind speed, w, and of the temperature structure parameter, C T 2 with enhanced height resolution of the order of 1 m and time resolution of the order of 30 s. The results of the comparison show that the high-frequency mini-sounder is an effective atmospheric boundary-layer profiler that is also portable and relatively inexpensive. Measurements of the spectrum of C T 2 are presented that provide information on the local isotropy of the temperature field. Statistics of the variability of C T 2 in both stable and unstable conditions are also given. The sounder's capabilities are further demonstrated by some detailed observations of the structure and time evolution of a thermal plume root at noon and of a nocturnal, stably stratified layer in which a dynamic instability develops. The plume starts at a height of less than 5 m, possesses substantial internal structure, and includes vertical velocities in excess of 2 m s-1.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00119969

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7

Digitale Medien

SOME MEASUREMENTS OF TURBULENCE CHARACTERISTICS OVER COMPLEX TERRAIN (1997)

FOUNDA, D. ; TOMBROU, M. ; LALAS, D. P. ; [weitere]

Springer

Boundary layer meteorology 83 (1997), S. 221-245

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ISSN: 1573-1472

Schlagwort(e): Wind flow ; Complex terrain ; Turbulence spectra ; Turbulence measurements

Quelle: Springer Online Journal Archives 1860-2000

Thema: Geologie und Paläontologie , Physik

Notizen: Abstract Results are presented from a windturbulence measurements campaign at the summit of ahill in complex terrain in Andros island (Greece)where a wind turbine park has been constructed. Meanturbulence parameters and power spectra from three 30 mmasts located at the summit, upwind and downwind ofthe hill are analysed to ascertain the differencesfrom respective parameters in flat terrain and toassess the influence of the irregular topography. Thevariances of the horizontal (vertical) wind components are found tobe smaller (larger) than the onesfrom flat terrain. Of the available correlations forthe power spectra, the Von Karman one was found togive better results, although the low frequency partsshow pronounced lags. The asymmetry of the upwindterrain for different wind directions and especiallyits slope is clearly felt both by variances and byspectra. This influence, as expected, is found toincrease with increasing stability. These results havean important significance for wind turbine design andwind energy utilisation.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1023/A:1000288002105

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