Mass exchange in the stable boundary layer by coherent structures

Cooper, D. I.; Leclerc, Monique Y.; Archuleta, J.; Coulter, R. L.; Eichinger, W. E.; Kao, C.Y.J.; Nappo, Carmen J.

doi:10.1016/j.agrformet.2004.12.012

Cited by 17 publications

(19 citation statements)

References 44 publications

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“…Additional supporting instruments whose locations are shown in Figs. 2 and 3 include automatic weather stations WS1 and WS2 near TS1 and TS4 and a scanning water vapor lidar between TS3 and TS4 (Cooper et al 2006). Gasoline-powered generators were used for power at the tethersonde sites, and batteries and solar panels were used at the automatic weather stations.…”

Section: A Experiments Designmentioning

confidence: 99%

Downslope Flows on a Low-Angle Slope and Their Interactions with Valley Inversions. Part I: Observations

Whiteman

Zhong

2008

Journal of Applied Meteorology and Climatology

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Thermally driven downslope flows were investigated on a low-angle (1.6°) slope on the west side of the floor of Utah’s Salt Lake Valley below the Oquirrh Mountains using data from a line of four tethered balloons running down the topographic gradient and separated by about 1 km. The study focused on the evolution of the temperature and wind structure within and above the slope flow layer and its variation with downslope distance. In a typical situation, on clear, undisturbed October nights a 25-m-deep temperature deficit of 7°C and a 100–150-m-deep downslope flow with a jet maximum speed of 5–6 m s−1 at 10–15 m AGL developed over the slope during the first 2 h following sunset. The jet maximum speed and the downslope volume flux increased with downslope distance. The downslope flows weakened in the late evening as the stronger down-valley flows expanded to take up more of the valley atmosphere and as ambient stability increased in the lower valley with the buildup of a nocturnal temperature inversion. Downslope flows over this low-angle slope were deeper and stronger than has been reported previously by other investigators, who generally investigated steeper slopes and, in many cases, slopes on the sidewalls of isolated mountains where the downslope flows are not subject to the influence of nighttime buildup of ambient stability within valleys.

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Section: A Experiments Designmentioning

confidence: 99%

Downslope Flows on a Low-Angle Slope and Their Interactions with Valley Inversions. Part I: Observations

Whiteman

Zhong

2008

Journal of Applied Meteorology and Climatology

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“…slopes in rather homogeneous terrain (Mahrt, 1999;Aubinet, 2008), while gravity waves are usually caused by topographic changes or irregularities of the canopy top (Lee et al, 1997). In complex terrain, all of these processes may occur, and a large effort has been made within projects like T-REX (T-REX stands for Terrain-induced Rotor EXperiment; Grubisic et al, 2008) and VTMX 2000 (Vertical Transport and MiXing; Doran et al, 2002) to understand the physics behind such (nocturnal) flows and how they influence transport of matter and energy (Cooper et al, 2006;Pinto et al, 2006;Reinecke and Durran, 2009;Choukulkar et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

Low-level jets and above-canopy drainage as causes of turbulent exchange in the nocturnal boundary layer

El-Madany¹,

Duarte

Durden

et al. 2014

Biogeosciences

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Abstract. Sodar (SOund Detection And Ranging), eddycovariance, and tower profile measurements of wind speed and carbon dioxide were performed during 17 consecutive nights in complex terrain in northern Taiwan. The scope of the study was to identify the causes for intermittent turbulence events and to analyze their importance in nocturnal atmosphere-biosphere exchange as quantified with eddycovariance measurements. If intermittency occurs frequently at a measurement site, then this process needs to be quantified in order to achieve reliable values for ecosystem characteristics such as net ecosystem exchange or net primary production.Fourteen events of intermittent turbulence were identified and classified into above-canopy drainage flows (ACDFs) and low-level jets (LLJs) according to the height of the wind speed maximum. Intermittent turbulence periods lasted between 30 and 110 min. Towards the end of LLJ or ACDF events, positive vertical wind velocities and, in some cases, upslope flows occurred, counteracting the general flow regime at nighttime. The observations suggest that the LLJs and ACDFs penetrate deep into the cold air pool in the valley, where they experience strong buoyancy due to density differences, resulting in either upslope flows or upward vertical winds.Turbulence was found to be stronger and better developed during LLJs and ACDFs, with eddy-covariance data presenting higher quality. This was particularly indicated by spectral analysis of the vertical wind velocity and the steady-state test for the time series of the vertical wind velocity in combination with the horizontal wind component, the temperature, and carbon dioxide.Significantly higher fluxes of sensible heat, latent heat, and shear stress occurred during these periods. During LLJs and ACDFs, fluxes of sensible heat, latent heat, and CO 2 were mostly one-directional. For example, exclusively negative sensible heat fluxes occurred while intermittent turbulence was present. Latent heat fluxes were mostly positive during LLJs and ACDFs, with a median value of 34 W m −2 , while outside these periods the median was 2 W m −2 . In conclusion, intermittent turbulence periods exhibit a strong impact on nocturnal energy and mass fluxes.

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“…Ducted waves are bound between the ground surface and some atmospheric reflecting layer above or two reflecting critical layers aloft (Cooper et al, 2006;Fritts et al, 2003;Newsom and Banta, 2003;Rees and Mobbs, 1988), thus producing a wave guide allowing propagation to occur over long distances and time periods. This implies a large-amplitude wave-like event could have wideranging impacts.…”

Section: Introductionmentioning

confidence: 99%

On the impact of wave-like disturbances on turbulent fluxes and turbulence statistics in nighttime conditions: a case study

Durden

Nappo²,

Leclerc

et al. 2013

Biogeosciences

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Abstract. The interpretation of flux measurements in nocturnal conditions is typically fraught with challenges. This paper reports on how the presence of wave-like disturbances in a time series, can lead to an overestimation of turbulence statistics, errors when calculating the stability parameter, erroneous estimation of the friction velocity u * used to screen flux data, and errors in turbulent flux calculations. Using time series of the pressure signal from a microbarograph, wavelike disturbances at an AmeriFlux site are identified. The wave-like disturbances are removed during the calculation of turbulence statistics and turbulent fluxes. Our findings suggest that filtering eddy-covariance data in the presence of wave-like events prevents both an overestimation of turbulence statistics and errors in turbulent flux calculations. Results show that large-amplitude wave-like events, events surpassing three standard deviations, occurred on 18 % of the nights considered in the present study. Remarkably, on flux towers located in a very stably stratified boundary-layer regime, the presence of a gravity wave can enhance turbulence statistics more than 50 %. In addition, the presence of the disturbance modulates the calculated turbulent fluxes of CO 2 resulting in erroneous turbulent flux calculations of the order of 10 % depending on averaging time and pressure perturbation threshold criteria. Furthermore, the friction velocity u * was affected by the presence of the wave, and in at least one case, a 10 % increase caused u * to exceed the arbitrary 0.25 m s −1 threshold used in many studies. This results in an unintended bias in the data selected for analysis in the flux calculations. The impact of different averaging periods was also examined and found to be variable specific. These early case study results provide an insight into errors introduced when calculating "purely" turbulent fluxes. These results could contribute to improving modeling efforts by providing more accurate inputs of both turbulent kinetic energy, and isolating the turbulent component of u * for flux selection in the stable nocturnal boundary layer.

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Mass exchange in the stable boundary layer by coherent structures

Cited by 17 publications

References 44 publications

Downslope Flows on a Low-Angle Slope and Their Interactions with Valley Inversions. Part I: Observations

Downslope Flows on a Low-Angle Slope and Their Interactions with Valley Inversions. Part I: Observations

Low-level jets and above-canopy drainage as causes of turbulent exchange in the nocturnal boundary layer

On the impact of wave-like disturbances on turbulent fluxes and turbulence statistics in nighttime conditions: a case study

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