Some aspects of the decay of convective turbulence

Cole, Gerald S.; Fernando, H. J. S.

doi:10.1016/s0169-5983(97)00051-8

Cited by 21 publications

(13 citation statements)

References 28 publications

(48 reference statements)

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“…Monin and Yaglom, 1975;Cole and Fernando, 1998). The first LES study of the decaying atmospheric convective mixed layer was performed by Nieuwstadt and Brost (1986).…”

Section: Turbulence Kinetic Energy (Tke) Decaymentioning

confidence: 99%

The BLLAST field experiment: Boundary-Layer Late Afternoon and Sunset Turbulence

Lothon¹,

Pino²,

Couvreux³

et al. 2014

Atmos. Chem. Phys.

168

226

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Abstract. Due to the major role of the sun in heating the earth's surface, the atmospheric planetary boundary layer over land is inherently marked by a diurnal cycle. The afternoon transition, the period of the day that connects the daytime dry convective boundary layer to the night-time stable boundary layer, still has a number of unanswered scientific questions. This phase of the diurnal cycle is challenging from both modelling and observational perspectives: it is transitory, most of the forcings are small or null and the turbulence regime changes from fully convective, close to homogeneous and isotropic, toward a more heterogeneous and intermittent state.These issues motivated the BLLAST (Boundary-Layer Late Afternoon and Sunset Turbulence) field campaign that was conducted from 14 June to 8 July 2011 in southern France, in an area of complex and heterogeneous terrain. A wide range of instrumented platforms including full-size aircraft, remotely piloted aircraft systems, remote-sensing instruments, radiosoundings, tethered balloons, surface flux stations and various meteorological towers were deployed over different surface types. The boundary layer, from the earth's surface to the free troposphere, was probed during the entire day, with a focus and intense observation periods that were conducted from midday until sunset. The BLLAST field campaign also provided an opportunity to test innovative measurement systems, such as new miniaturized sensors, and a new technique for frequent radiosoundings of the low troposphere.Twelve fair weather days displaying various meteorological conditions were extensively documented during the field experiment. The boundary-layer growth varied from one day to another depending on many contributions including stability, advection, subsidence, the state of the previous day's residual layer, as well as local, meso-or synoptic scale conditions.Ground-based measurements combined with tetheredballoon and airborne observations captured the turbulence decay from the surface throughout the whole boundary layer and documented the evolution of the turbulence characteristic length scales during the transition period.Closely integrated with the field experiment, numerical studies are now underway with a complete hierarchy of models to support the data interpretation and improve the model representations.

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“…Monin and Yaglom, 1975;Cole and Fernando, 1998). The first LES study of the decaying atmospheric convective mixed layer was performed by Nieuwstadt and Brost (1986).…”

Section: Turbulence Kinetic Energy (Tke) Decaymentioning

confidence: 99%

The BLLAST field experiment: Boundary-Layer Late Afternoon and Sunset Turbulence

Lothon¹,

Pino²,

Couvreux³

et al. 2014

Atmos. Chem. Phys.

168

226

View full text Add to dashboard Cite

show abstract

“…However, different results were obtained if a slower decrease in the forcing surface buoyancy flux is considered with an external timescale τ f (Sorbjan, 1997;Rizza et al, 2013a, b;Nadeau et al, 2011). If τ f is large relative to t * , the turbulence can adjust to the forcing change, in quasi-equilibrium, as noted by Cole and Fernando (1998). This is the case in the mid-afternoon PBL, when t * is around 10 or 15 min and τ f is around 2 or 3 h. Sorbjan (1997) found that the TKE decay scales with τ f /t * , with t * estimated at the start of the decay.…”

Section: Introductionmentioning

confidence: 98%

“…Monin and Yaglom, 1975;Cole and Fernando, 1998), theoretical models (Goulart et al, 2003), numerical studies with large-eddy simulations (LESs) (e.g. Nieuwstadt and Brost, 1986;Sorbjan, 1997;Rizza et al, 2013a) and observations (e.g.…”

Section: Introductionmentioning

confidence: 99%

Turbulence vertical structure of the boundary layer during the afternoon transition

et al. 2015

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Abstract.We investigate the decay of planetary boundary layer (PBL) turbulence in the afternoon, from the time the surface buoyancy flux starts to decrease until sunset. Dense observations of mean and turbulent parameters were acquired during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field experiment by several meteorological surface stations, sounding balloons, radars, lidars and two aircraft during the afternoon transition. We analysed a case study based on some of these observations and largeeddy simulation (LES) data focusing on the turbulent vertical structure throughout the afternoon transition.The decay of turbulence is quantified through the temporal and vertical evolution of (1) the turbulence kinetic energy (TKE), (2) the characteristic length scales of turbulence and (3) the shape of the turbulence spectra. A spectral analysis of LES data, airborne and surface measurements is performed in order to characterize the variation in the turbulent decay with height and study the distribution of turbulence over eddy size.This study highlights the LES ability to reproduce the turbulence evolution throughout the afternoon. LESs and observations agree that the afternoon transition can be divided in two phases: (1) a first phase during which the TKE decays at a low rate, with no significant change in turbulence characteristics, and (2) a second phase characterized by a larger TKE decay rate and a change in spectral shape, implying an evolution of eddy size distribution and energy cascade from low to high wave number.The changes observed either in TKE decay (during the first phase) or in the vertical wind spectra shape (during the second phase of the afternoon transition) occur first in the upper region of the PBL. The higher within the PBL, the stronger the spectra shape changes.

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“…These two periods are difficult to study due to their rapid variability. The afternoon transition has been studied by using observations and/or numerical simulations (Sorbjan, 1997;Cole and Fernando, 1998;Edwards et al, 2006;Pino et al, 2006a;Angevine, 2007;Nadeau et al, 2011). However, there are still many unknowns during this period: the presence of significant vertical movements in late afternoon, which appear even with very small surface heat flux; the influence of boundary layer processes in the turbulence decay; and what the processes are that govern the decrease of the boundary-layer depth .…”

Section: Introductionmentioning

confidence: 99%

Role of the residual layer and large-scale subsidence on the development and evolution of the convective boundary layer

et al. 2014

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Abstract. Observations, mixed-layer theory and the DutchLarge-Eddy Simulation model (DALES) are used to analyze the dynamics of the boundary layer during an intensive operational period (1 July 2011) of the Boundary Layer Late Afternoon and Sunset Turbulence campaign. Continuous measurements made by remote sensing and in situ instruments in combination with radio soundings, and measurements done by remotely piloted aircraft systems and two manned aircrafts probed the vertical structure and the temporal evolution of the boundary layer during the campaign. The initial vertical profiles of potential temperature, specific humidity and wind, and the temporal evolution of the surface heat and moisture fluxes prescribed in the models runs are inspired by some of these observations. The research focuses on the role played by the residual layer during the morning transition and by the large-scale subsidence on the evolution of the boundary layer. By using DALES, we show the importance of the dynamics of the boundary layer during the previous night in the development of the boundary layer at the morning. DALES numerical experiments including the residual layer are capable of modeling the observed sudden increase of the boundary-layer depth during the morning transition and the subsequent evolution of the boundary layer. These simulations show a large increase of the entrainment buoyancy flux when the residual layer is incorporated into the mixed layer. We also examine how the inclusion of the residual layer above a shallow convective boundary layer modifies the turbulent kinetic energy budget.Large-scale subsidence mainly acts when the boundary layer is fully developed, and, for the studied day, it is necessary to be considered to reproduce the afternoon observations.Finally, we also investigate how carbon dioxide (CO 2 ) mixing ratio stored the previous night in the residual layer plays a fundamental role in the evolution of the CO 2 mixing ratio during the following day.

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Some aspects of the decay of convective turbulence

Cited by 21 publications

References 28 publications

The BLLAST field experiment: Boundary-Layer Late Afternoon and Sunset Turbulence

The BLLAST field experiment: Boundary-Layer Late Afternoon and Sunset Turbulence

Turbulence vertical structure of the boundary layer during the afternoon transition

Role of the residual layer and large-scale subsidence on the development and evolution of the convective boundary layer

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