Gust and downward momentum transport in the atmospheric surface layer

Hayashi, Taiichi

doi:10.1007/bf00120750

Cited by 9 publications

(6 citation statements)

References 19 publications

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“…Figure 1 should make this clear. This definition is consistent with the widely reported fact that gusts usually take the form of a sudden increase in wind speed followed by a gradual decrease (see, for example, Hayashi, 1992). It also allows computer processing of the data to identify gusts.…”

Section: Datasupporting

confidence: 86%

An investigation of possible systematic wind‐direction changes associated with sudden increases in wind speed

Brettle

1994

Meteorological Applications

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Section: Datasupporting

confidence: 86%

An investigation of possible systematic wind‐direction changes associated with sudden increases in wind speed

Brettle

1994

Meteorological Applications

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“…Small-scale structures known as microfronts (Gao et al 1989(Gao et al , 1992Mahrt and Howell 1994) or gust fronts (Hayashi 1992) have been found in field experiments investigating turbulence in the surface layer. Microfrontal structures were observed also from low-level aircraft flights (Mahrt 1991), such structures containing distinct high-speed regions, representing certain types of coherent structures in the ABL.…”

Section: Introductionmentioning

confidence: 98%

Large-Scale Turbulence Structures and Their Contributions to the Momentum Flux and Turbulence in the Near-Neutral Atmospheric Boundary Layer Observed from a 213-m Tall Meteorological Tower

Horiguchi

Hayashi

Adachi

et al. 2012

Boundary-Layer Meteorol

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Large-scale turbulence structures in the near-neutral atmospheric boundary layer (ABL) are investigated on the basis of observations made from the 213-m tall meteorological tower at Tsukuba, Japan. Vertical profiles of wind speed and turbulent fluxes in the ABL were obtained with sonic anemometer-thermometers at six levels of the tower. From the archived data, 31 near-neutral cases are selected for the analysis of turbulence structures. For the typical case, event detection by the integral wavelet transform with a large time scale (180 s) from the streamwise velocity component (u) at the highest level (200 m) reveals a descending high-speed structure with a time scale of approximately 100 s (a spatial scale of 1 km at the 200-m height). By applying the wavelet transform to the u velocity component at each level, the intermittent appearance of large-scale high-speed structures extending also in the vertical is detected. These structures usually make a large contribution to the downward momentum transfer and induce the enhancement of turbulent kinetic energy. This behaviour is like that of "active" turbulent motions. From the analysis of the two-point space-time correlation of wavelet coefficients for the u velocity component, the vertical extent and the downward influence of large-scale structures are examined. Large fluctuations in the largescale range (wavelet variance at the selected time scale) at the 200-m level tend to induce the large correlation between the higher and lower levels.

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“…Field experiments in the ABL have resolved turbulence structures called microfronts (Gao et al 1989(Gao et al , 1992 or gust fronts (Hayashi 1992), structures that are small-scale frontal structures containing distinct high-speed regions. Under near-neutral conditions at levels within and above a forest canopy, Gao et al (1989) reported a flow structure consisting of a weak ejection (the region of upward motion) from the canopy top followed by a strong sweep (the region of downward motion) into the canopy.…”

Section: Introductionmentioning

confidence: 99%

“…The sweep transports dry air into the canopy and forms a microfront in the humidity field. Hayashi (1992) observed the horizontal structure of wind speed fluctuations in the surface layer with a network of anemometers, revealing a gust front at the forward edge of the high-speed region. These structures are considered to represent certain types of coherent structures in the ABL.…”

Section: Introductionmentioning

confidence: 99%

Observations of Coherent Turbulence Structures in the Near-Neutral Atmospheric Boundary Layer

Horiguchi

Hayashi

Hashiguchi

et al. 2010

Boundary-Layer Meteorol

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Turbulence structures of high Reynolds number flow in the near-neutral atmospheric boundary layer (ABL) are investigated based on observations at Shionomisaki and Shigaraki, Japan. A Doppler sodar measured the vertical profiles of winds in the ABL. Using the integral wavelet transform for the time series of surface wind data, the pattern of a descending high-speed structure with large vertical extent (from the surface to more than 200-m level) is depicted from the Doppler sodar data. Essentially this structure is a specific type of coherent structure that has been previously shown in experiments on turbulent boundary-layer flows. Large-scale high-speed structures in the ABL are extracted using a long time scale (240 s) for the wavelet transform. The non-dimensional interval of time between structures is evaluated as 3.0-6.2 in most cases. These structures make a large contribution to downward momentum transfer in the surface layer. Quadrant analyses of the turbulent motion measured by the sonic anemometer (20-m height) suggest that the sweep motion (high-speed downward motion) plays a substantial role in the downward momentum transfer. In general, the contribution of sweep motions to the momentum flux is nearly equal to that of ejection motions (low-speed upward motions). This contribution of sweep motions is related to the large-scale high-speed structures.

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Gust and downward momentum transport in the atmospheric surface layer

Cited by 9 publications

References 19 publications

An investigation of possible systematic wind‐direction changes associated with sudden increases in wind speed

An investigation of possible systematic wind‐direction changes associated with sudden increases in wind speed

Large-Scale Turbulence Structures and Their Contributions to the Momentum Flux and Turbulence in the Near-Neutral Atmospheric Boundary Layer Observed from a 213-m Tall Meteorological Tower

Observations of Coherent Turbulence Structures in the Near-Neutral Atmospheric Boundary Layer

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