Small-Scale Horizontal Variability of Mean and Turbulent Quantities in the Nocturnal Boundary Layer

Guerra, Viviane da Silva; Acevedo, Otávio C.; Medeiros, Luiz Eduardo; Oliveira, Pablo E. S.; Santos, Daniel Michelon dos

doi:10.1007/s10546-018-0381-3

Cited by 12 publications

(15 citation statements)

References 33 publications

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“…Therefore, other conditions are also important, and Van de Wiel et al (2012) suggested that those are related to the radiative loss at the surface. Mahrt et al (2013) found that transition wind speed increases with decreasing surface roughness and this result has been later confirmed both by Sun and French (2016) and Guerra et al (2018). In this case, rougher surfaces tend to be more turbulent for the same mean wind speed, allowing the coupling between surface and atmosphere to occur at lower mean wind speeds.…”

Section: Introductionmentioning

confidence: 66%

“…() found that transition wind speed increases with decreasing surface roughness and this result has been later confirmed both by Sun and French () and Guerra et al . (). In this case, rougher surfaces tend to be more turbulent for the same mean wind speed, allowing the coupling between surface and atmosphere to occur at lower mean wind speeds.…”

Section: Introductionmentioning

confidence: 75%

See 1 more Smart Citation

The nocturnal boundary layer transition from weakly to very stable. Part II: Numerical simulation with a second‐order model

Maroneze

Acevedo

Costa

et al. 2019

Quart J Royal Meteoro Soc

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Observations of the vertical and temporal structure of the nocturnal boundary layer before and after a transition from the weakly to the very stable regime have been presented in Part I. Here, similar transitions are investigated using a one‐dimensional second‐order closure numerical model, with an energy budget solved at the surface. The transition is driven by a decreasing mean wind at the top of the domain, and simulations with different cloud covers and surface thermal properties are considered. The time of the transition depends on the wind speed at the top of the domain and on the “coupling strength” between the surface and the atmosphere, which is affected by the cloud cover and surface thermal properties. The vertical profiles and temporal evolutions of the terms of the budgets of turbulent kinetic energy (TKE), heat flux and temperature variance are presented. Of these, only TKE budget presents the same dominant terms in both regimes. Absolute heat flux in the model is proportional to the cube of the wind speed in the very stable regime.

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Section: Introductionmentioning

confidence: 66%

Section: Introductionmentioning

confidence: 75%

The nocturnal boundary layer transition from weakly to very stable. Part II: Numerical simulation with a second‐order model

Maroneze

Acevedo

Costa

et al. 2019

Quart J Royal Meteoro Soc

Self Cite

View full text Add to dashboard Cite

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“…6). The enhanced mixing nearly eliminates horizontal variability in agreement with Guerra et al (2018) and reduces both the stratification and wind directional shear (Fig. 11).…”

Section: Warm Microfrontmentioning

confidence: 80%

“…Intermittent turbulence and associated warm and cold events in the stable nocturnal boundary layer can be induced by even modest microtopography (Pfister et al 2017;Mahrt 2017c). Guerra et al (2018) found that the microtopography induces horizontal variation of temperature that systematically increases with decreasing wind speed. Based on fine-scale measurements of the horizontal structure, Pfister et al (2019) found that spatial and temporal variations of temperature on horizontal scales of a few 100 m or less in gentle topography tended to organize into several prototype regimes: windy with limited formation of cold air; windy but with cold air drainage and pooling modulated by large shear-induced mixing and lee turbulence; and low wind speeds with more robust cold-air drainage and cold pool formation.…”

Section: Introductionmentioning

confidence: 99%

Small-Scale Variability in the Nocturnal Boundary Layer

Mahrt

Pfister

Thomas

2019

Boundary-Layer Meteorol

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Nocturnal variations of temperature and wind are examined at three contrasting sites. After the early evening period of rapid cooling, the magnitude of the variations of temperature on a time scale of 10 min to an hour often become larger than the corresponding temperature change due to the nocturnal trend. These shorter-term temperature variations are forced by wave-like motions and more complex modes. Observations from a network of stations across a shallow valley at one of the sites are analyzed in more detail. Typically, decreasing wind speed corresponds to less mixing and lower temperature at the surface followed by increasing wind speed, increased mixing, and higher temperatures. The flow may continue to switch back and forth between these two states for much of the night. These non-stationary motions interact with motions induced by the gentle local topography, leading to intermittent local drainage flows, transient cold pools, and both propagating and semi-stationary microfronts.

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“…Interaction between submeso motions and surface heterogeneity/terrain is complex and requires detailed observations in the space-time domain (Pfister et al, 2019). The surface heterogeneity includes variability of land use (Pfister et al, 2017) and sheltering by nearby higher vegetation and buildings, in addition to local topography (Acevedo and Fitzjarrald, 2003;Bodine et al, 2009;Medeiros and Fitzjarrald, 2015;Guerra et al, 2018). Acevedo and Fitzjarrald (2001) observed maximum spatial variability of airflow during the early evening transition.…”

Section: Introductionmentioning

confidence: 99%

Time–space variations of temperature in the nocturnal boundary layer

Mahrt

2020

Quart J Royal Meteoro Soc

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This study examines nocturnal temperature changes on time‐scales of 5–60 min over gentle terrain. Such temperature variations are often important after the early evening period of rapid cooling and can lead to large temporary warming or enhanced cooling. The time–space structure of temperature changes is examined statistically with a network of flux stations over gentle topography. Large temperature changes are often associated with coherent propagating modes and associated temporary reduction or elimination of the valley cold pool, local drainage flows, and lee turbulence. The largest variations of temperature with time occur for intermediate wind speeds. Low wind speeds correspond to greater spatial variability of temperature but less time dependence. Two nondimensional ratios are developed to represent the relative importance of temporal and spatial variability.

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Small-Scale Horizontal Variability of Mean and Turbulent Quantities in the Nocturnal Boundary Layer

Cited by 12 publications

References 33 publications

The nocturnal boundary layer transition from weakly to very stable. Part II: Numerical simulation with a second‐order model

The nocturnal boundary layer transition from weakly to very stable. Part II: Numerical simulation with a second‐order model

Small-Scale Variability in the Nocturnal Boundary Layer

Time–space variations of temperature in the nocturnal boundary layer

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