Transport Processes in the Tropical Warm Pool Boundary Layer. Part I: Spectral Composition of Fluxes

Williams, Alastair G.; Kraus, Helmut; Hacker, Josh

doi:10.1175/1520-0469(1996)053<1187:tpittw>2.0.co;2

Cited by 29 publications

(28 citation statements)

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“…1, this conceptual model is consistent with observational evidence (for more information see: Hacker 1992, 1993;Williams et al 1996). It is also strongly supported by our LES (see subsection 2(d)).…”

Section: Large-eddy Boundary-layer Modelsupporting

confidence: 90%

The influence of large convective eddies on the surface-layer turbulence

Zilitinkevich

Hunt

Esau

et al. 2006

Q. J. R. Meteorol. Soc.

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SUMMARYClose to the surface large coherent eddies consisting of plumes and downdraughts cause convergent winds blowing towards the plume axes, which in turn cause wind shears and generation of turbulence. This mechanism strongly enhances the convective heat/mass transfer at the surface and, in contrast to the classical formulation, implies an important role of the surface roughness. In this context we introduce the stability-dependence of the roughness length. The latter is important over very rough surfaces, when the height of the roughness elements becomes comparable with the large-eddy Monin-Obukhov length. A consistent theoretical model covering convective regimes over all types of natural surfaces, from the smooth still sea to the very rough city of Athens, is developed; it is also comprehensively validated against data from measurements at different sites and also through the convective boundary layer. Good correspondence between model results, field observations and large-eddy simulation is achieved over a wide range of surface roughness lengths and convective boundary-layer heights.

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Section: Large-eddy Boundary-layer Modelsupporting

confidence: 90%

The influence of large convective eddies on the surface-layer turbulence

Zilitinkevich

Hunt

Esau

et al. 2006

Q. J. R. Meteorol. Soc.

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“…A spectral decomposition of aircraft data (not presented) showed that T and q were anticorrelated on scales greater than about 1-5 km, consistent with previous ndings (e.g. Williams et al 1996). It is possible, therefore, that largerscale processes are creating the observed skewness anticorrelation for the aircraft data.…”

Section: Results (A) Comparison Of Momentssupporting

confidence: 86%

Comparison of probability density functions for total specific humidity and saturation deficit humidity, and consequences for cloud parametrization

Price¹,

Wood²

2002

Quart J Royal Meteoro Soc

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SUMMARYVarious models which predict cloud variables use probability density functions of either speci c humidity or saturation de cit humidity to represent subgrid-scale variations. Using the former is considered to be an approximation since it does not allow variation of dew-point across the grid. In this paper the validity of that approximation is investigated and typical errors incurred are stated. Aircraft data from subtropical regions and tethered-balloon data from midlatitudes are examined to compare differences between the two types of distribution. The average relative error in cloud fraction introduced by assuming a constant value of saturation across a grid is found to be approximately half an okta. However, results suggest that there is a xed relation between the widths of both distributions allowing easy conversion between the two.

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“…Attack angle is measured by means of flow angle sensors mounted on or near the nose of the aircraft. Most commonly, the flow angle is obtained from pressure difference measurements δ P between a set of ports either located directly on the nose of the aircraft (radome technique; see, e.g., Brown et al 1983), or on a probe mounted near the front of an aircraft (e.g., Williams et al, 1996)-usually on a boom projecting forward of the aircraft nose (e.g., Khelif et al 1999). It is difficult to quantify the drift that may occur in this measurement, but we proceed as follows: we use a typical differential pressure sensitivity factor of κ = 3.7 (rad) −1 (Brown et al 1983), where κ is defined by the relation…”

Section: Measurement Accuracymentioning

confidence: 99%

The spectral composition of fluxes and variances over land and sea out to the mesoscale

Lenschow

Sun

2007

Boundary-Layer Meteorol

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We discuss the accuracy requirements for measuring mesoscale (roughly horizontal scales >10 km or 5 to 10 times the planetary boundary-layer (PBL) depth) fluxes in the convective PBL, and the ability of current research aircraft to achieve this accuracy. We conclude that aircraft equipped with inertial nagivation systems capable of < 3 km hr −1 navigational accuracy are able to resolve mesoscale fluctuations in velocity, and thus variances and fluxes on the mesoscale. We then discuss measurements of velocity and scalar spectra, and cospectra of vertical velocity with horizontal velocity components and scalars, obtained from long flight legs with the National Center for Atmospheric Research Electra aircraft over the boreal forest of Canada in summer during the BOreal Ecosystem-Atmosphere Study (BOREAS), over the tropical Pacific Ocean from the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE), and over the East China Sea during wintertime cold-air outbreaks from the Air Mass Transformation Experiment (AMTEX). Each of these studies has somewhat different forcings and boundary conditions, so we can compare their consequences on the spectra and cospectra. On average, we found no significant scalar or momentum fluxes for horizontal scales >10 km. We also develop a simple model based on observed thermal structure to explain the phase angle between vertical velocity and the along-wind horizontal velocity as a function of height, which shows good agreement with the observed phase angle in AMTEX.

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Transport Processes in the Tropical Warm Pool Boundary Layer. Part I: Spectral Composition of Fluxes

Cited by 29 publications

References 0 publications

The influence of large convective eddies on the surface-layer turbulence

The influence of large convective eddies on the surface-layer turbulence

Comparison of probability density functions for total specific humidity and saturation deficit humidity, and consequences for cloud parametrization

The spectral composition of fluxes and variances over land and sea out to the mesoscale

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