Thermal plumes and turbulence spectra in the atmospheric boundary layer

Ting, C. L.; Hay, D. R.

doi:10.1007/bf02166807

Cited by 6 publications

(3 citation statements)

References 43 publications

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“…The echoes in Figure 2a show no appreciable tilt which indicates, given the perpendicular orientation of the wind direction to the sounder beam, that the plumes observed are simply advected by the wind (Hall et al, 1975). With an average wind of 3.1 m s ' at 100 m height, the width of the horizontal returns on the facsimile record shown in Figure 2a corresponds to a plume dimension in the direction along the wind of the order of 150 m, in agreement with the results of Ting and Hay (1977). The cross-wind dimension is difficult to ascertain since the horizontal sounder sees only along one direction and its reliable maximum range is about 120 m. Assuming that plumes do not follow preferential paths in their horizontal advective motion, they will be dissected by the tower in different proportions, sometimes near the centerline, other times close to -2 '0 r the near and far edges.…”

Section: Resultssupporting

confidence: 78%

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

Moulsley

Asimakopoulos

Helmis

et al. 1985

Boundary-Layer Meteorol

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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$, 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.

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Section: Resultssupporting

confidence: 78%

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

Moulsley

Asimakopoulos

Helmis

et al. 1985

Boundary-Layer Meteorol

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“…It seems plausible that d should decrease with increasing [L[, since the effect of increased momentum transport is likely to be a c,orresponding increase of smaller-scale eddies generated by shear production near the surface as compared to the larger-scale eddies generated by buoyancy through most of the boundary layer. Using dimensional arguments, Ting and Hay (1977) have suggested that d -(-L)4'3z-1'3. This, however, disregards any dependence of the size of thermals on the depth of the mixed layer, which is unlikely except, perhaps, very near the surface.…”

Section: Mean Quantitiesmentioning

confidence: 99%

The role of thermals in the convective boundary layer

Lenschow

Stephens

1980

Boundary-Layer Meteorol

211

119

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Detailed measurements of the structure of thermals throughout the convective boundary layer were obtained from the NCAR Electra aircraft over the ocean during the Air Mass Transformation Experiment (AMTEX). Humidity was used as an indicator of thermals. The variables were first high-pass filtered with a 5 km cutoff digital filter to eliminate mesoscale variations. Segments of the 5 min (30 km length) horizontal flight legs with humidity greater than half the standard deviation of humidity fluctuations for that leg were defined as thermals. This was found to be a better indicator of thermals than temperature in the upper part of the boundary layer since the temperature in a thermal is cooler than its environment in the upper part of the boundary layer. Using mixed-layer scaling, the normalized length and number of thermals were found to scale with the 4 and -; powers, respectively, of normalized height, while vertical velocity and temperature scaled according to similarity predictions in the free convection region of the surface layer. The observational results presented here extend throughout the entire mixed layer. Using these results in the equation for mean updraft velocity of a field of thermals, the sum of the vertical pressure gradient and edge-effect terms can be estimated. This residual term is found to be important throughout most of the boundary layer. The magnitude of the divergence of vertical velocity variance within a thermal is found to be larger than the magnitude of the mean updraft velocity term throughout most of the mixed layer.

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“…During outbreaks of cold, continental air over the Kuroshio Current, thermal plumes transport 50% of the heat flux from the ocean surface [Lenschow and Stephens, 1980]. Plumes have diameters of 40-1000 m and occupy 40-45% of the ocean surface area [Grant, 1965;Manton, 1977;Ting and Hay, 1977;Khalsa, 1980;Grossman, 1982;Yamamoto et al, 1982]. At high wind speeds, mechani-cal mixing by wind shear-produced turbulence is increasingly dominant in the heat and momentum transfer process of the lowest layer of the atmosphere.…”

Section: Introductionmentioning

confidence: 99%

Mesoscale variability in marine winds at mid‐latitude

Wilson¹

1984

J. Geophys. Res.

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Wind data were collected by the National Oceanic and Atmospheric Administration WP‐3D aircraft on low‐level (50 and 90 m) crosswind and along‐mean‐wind tracks of approximately 350 km during the Storm Transfer and Response Experiment in November and December 1980. Observed mesoscale variations in the marine wind fields are characterized by the velocity correlation tensor for three atmospheric regimes: cloud streets, open and closed cellular convection, and prefrontal warm air advection. The dominant scale of mesoscale variation in the offshore wind field normal to the mean wind direction in the case of old continental air flowing over a warmer ocean, producing cloud streets, was 27 km. For this case, the standard deviation in momentum transfer, which was calculated from 2‐km subsets of the flight track by the bulk aerodynamic method assuming a constant drag coefficient, was 13% of the synoptic scale (330km) mean. The dominant scale of mesoscale variation for open cellular convection was 62km, and the dominant scale for closed cellular convection was 90 km. The standard deviation of mesoscale momentum transfer (scales greater than 2 km; constant drag coefficient) for a 345‐km flight track containing both cell types was 26% of the synoptic scale mean. The warm air advection case had no measurable mesoscale variability. For each regime a model of the horizontal velocity correlation tensor, which can be used to estimate a mesoscale variability, is fitted to the observed velocity correlation tensor with velocity component and weather regime dependent coefficients. This general model is consistent with an interpretation of the mesoscale wind field as an ensemble of coherent structures, associated with cloud type, in which the spatial variability of the wind field in each weather regime is associated with physically determined dominant length scales (i.e., cells or rolls), as contrasted with a continuum interpretation of two‐dimensional turbulence. To accurately describe regional winds and fluxes at the sea surface, wind speed and temperature data should be averaged over the dominant mesoscale length scale with either a suitable time average or a spatial average, such as can be obtained by scatterometry, or an estimate of the mesoscale variability should be explicitly stated. It is also suggested that enhanced vertical flux in the oceanic mixed layer occurs at length scales of atmospheric boundary layer structures.

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Thermal plumes and turbulence spectra in the atmospheric boundary layer

Cited by 6 publications

References 43 publications

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

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

The role of thermals in the convective boundary layer

Mesoscale variability in marine winds at mid‐latitude

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