Influence of Nocturnal Low-level Jets on Eddy-covariance Fluxes over a Tall Forest Canopy

Prabha, Thara V.; Leclerc, Monique Y.; Karipot, Anandakumar; Hollinger, David Y.; Mursch-Radlgruber, Erich

doi:10.1007/s10546-007-9232-3

Cited by 33 publications

(34 citation statements)

References 63 publications

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“…It is then observed a turbulence "bursting" in a lower portion of the boundary layer, occurrence also related in other works [20,21]. In [10] related the presence of a LLJ produces a great vert ical wind shear, producing upside-down mechanical turbulence.…”

Section: Low-level Jets Detecti On and Classificationsupporting

confidence: 59%

“…To higher stable profiles, TKE has its maximu m near the LLJ center. In [21] used Wavelets Transform (WT) to demonstrate that strong eddies, which interact with the turbulence scales of the forest top, contribute to the counter-gradient scalar flu x production. These contributions are present in the variance spectrum and cospectrum obtained via WT.…”

Section: Low-level Jets Detecti On and Classificationmentioning

confidence: 99%

“…In [17,21] the authors discuss the ideal conditions of man ifestation of a LLJ that does not generate upside down mixing. Reference [14] concludes that this kind of LLJ is characterized by accumu lation of CO 2 gas below velocity maximu m. So me o f the ideal conditions established by them were: a) a min imu m of wind velocity unbounded from the surface; b) this maximu m must de located in the region below temperature inversion, which maintains a concentration of gas due to the strong gradient of temperature above.…”

Section: Low-level Jets Detecti On and Classificationmentioning

confidence: 99%

“…A contrary effect is observable for the LLJ-SS, that is, LLJ-SS causes a strong shear which reaches surface and inhibits top-down eddies propagation on scales greater than that of the LLJ height, as is possible to observe in figures (2-d and 2-f). Fo r LLJ-SS, the strong shear generated by LLJ blocked the passage of greater eddies at scales higher than the LLJ height [5,16,20,21]. Effectively this means that there occurs a process of filtering of the greatest eddies, associated with the highest scales observed at surface.…”

Section: The Shear-sheltering Mechanismmentioning

confidence: 99%

“…LLJ actions were recently studied to various experimental sites and in many different perspectives [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. In this context, the p resent paper presents an aspect not yet analyzed about the action of LLJ's in NBL.…”

Section: Introductionmentioning

confidence: 99%

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Low Level Jets in the Pantanal Wetland Nocturnal Boundary Layer – Case Studies

Martins¹,

Sá²,

Moraes³

2013

AJEE

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Situated in South America midwest region, Pantanal is a unique biome, alternating dry and flooded periods. An important seasonal variability characteristic fro m Pantanal's energy balance is the occurrence of situations in which sensible heat flu x is positive (bottom-up) during night-time, when the region is flooded enough. In this study it is investigated an interesting aspect of Nocturnal Boundary Layer's (NBL) structure seasonal variability above Pantanal, that is, how Low-Level Jets (LLJ) occurrence and associated turbulent structure. For th is, scale action of different Low-Leve l Jets (LLJ) types on Pantanal's Nocturnal Boundary Layer was investigated through case studies. Six events, distributed the following way, were used: Two events without LLJ's, two events LLJ's weak shear and two events LLJ's strong shear. Fro m the two events without LLJ's, one of them is observed during the dry season and the other, during the flooded one. The same procedure was applied to other events (LLJ's weak shear and LLJ's strong shear). Vertical wind velocity and temperature variance, as well as the covariance among these variables were analyzed and investigated in scale via Wavelet Transform. Remarkab le differences were observed among turbulence in NBL characteristics during the "dry" and "flooded" periods. It was observed that LLJ weak shear acts like a forcing that generates action of top-down mechanisms in the Pantanal's Nocturnal Boundary-layer. On the other hand, LLJ strong shear causes eddies blocking situations with length scales greater than the LLJ height. The decrease of the surface roughness at the flooded season, compared to the dry season, reduces remarkably the temperature variance in the lowest length scales below 350m. Such results are useful for a better understanding of seasonal variability in the Pantanal's Nocturnal Boundary-layer, as well as to other regions with similar environmental characteristics and must be taken into consideration in nu merical simu lations of the flow structure above the region.

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Section: Low-level Jets Detecti On and Classificationsupporting

confidence: 59%

Section: Low-level Jets Detecti On and Classificationmentioning

confidence: 99%

Section: Low-level Jets Detecti On and Classificationmentioning

confidence: 99%

Section: The Shear-sheltering Mechanismmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Low Level Jets in the Pantanal Wetland Nocturnal Boundary Layer – Case Studies

Martins¹,

Sá²,

Moraes³

2013

AJEE

View full text Add to dashboard Cite

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Wavelet spectra within a forest subcanopy under different wind directions and stabilities

Russell

Lamb

2017

JGR Atmospheres

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Vertical structure of turbulence within a forest canopy is complex as a result of interactions between the flow dynamics, stability, and vegetation. It remains unclear as to how the combination of the changing stability, flow conditions, and upstream obstacles alters vertical variations in turbulence structures within canopy. Here we used data from three sonic anemometers within the forest canopy to study the interplay between these factors. The turbulence structure depended upon the wind direction and stability similarly as particular stability conditions were primarily associated with certain wind directions over the sloped terrain. The general shape of the spectra varied with the depth into the canopy, creating a perceived spectral gap near the surface that was not observed near the top of the canopy. The strength of the division between smaller scales and larger scales increased under more stable conditions as the different layers were unable to couple, limiting the passage of energy through the canopy.

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