scholarly journals Air and Surface Temperature Coupling in the Convective Atmospheric Boundary Layer

2011 ◽  
Vol 68 (12) ◽  
pp. 2945-2954 ◽  
Author(s):  
Anirban Garai ◽  
Jan Kleissl
Keyword(s):  
Boundary Layer ◽  
Surface Temperature ◽  
Coherent Structures ◽  
High Frequency ◽  
Spatial Scales ◽  
Temporal Correlation ◽  
Convective Boundary ◽  
Velocity Information ◽  
Thermal Signature ◽  
Practical Implications

Abstract In a convective boundary layer, coherent structures were detected through their thermal signature on an artificial turf surface using high-frequency thermal infrared (TIR) imagery and surface layer turbulence measurements. The coherent structures cause surface temperature variations over tens of seconds and spatial scales of tens to a few hundred meters. Evidence of processes similar to those in a renewal event was observed. Spatial and temporal correlation analysis revealed the geometric and velocity information of the structures at the ground footprint of air temperature measurements. The velocity of the coherent structures was consistent with the wind speed at 6.5 m AGL. Practical implications of turbulence-driven surface temperature variability for thermal remote sensing are also discussed.

Skin friction and surface temperature of an insulated flat plate fixed in a fluctuating stream

1971 ◽  
Vol 46 (1) ◽  
pp. 165-175 ◽  
Author(s):  
Hiroshi Ishigaki
Keyword(s):  
Boundary Layer ◽  
Surface Temperature ◽  
Flat Plate ◽  
Skin Friction ◽  
High Frequency ◽  
Energy Equation ◽  
Oscillation Amplitude ◽  
Flow Oscillation ◽  
Velocity Amplitude ◽  
The Mean

The time-mean skin friction of the laminar boundary layer on a flat plate which is fixed at zero incidence in a fluctuating stream is investigated analytically. Flow oscillation amplitude outside the boundary layer is assumed constant along the surface. First, the small velocity-amplitude case is treated, and approximate formulae are obtained in the extreme cases when the frequency is low and high. Next, the finite velocity-amplitude case is treated under the condition of high frequency, and it is found that the formula obtained for the small-amplitude and high-frequency case is also valid. These results show that the increase of the mean skin friction reduces with frequency and is ultimately inversely proportional to the square of frequency.The corresponding energy equation is also studied simultaneously under the condition of zero heat transfer between the fluid and the surface. It is confirmed that the time-mean surface temperature increases with frequency and tends to be proportional to the square root of frequency. Moreover, it is shown that the timemean recovery factor can be several times as large as that without flow oscillation.

scholarly journals Turbulence fluxes and variances measured with a sonic anemometer mounted on a tethered balloon

2016 ◽  
Vol 9 (9) ◽  
pp. 4375-4386 ◽  
Author(s):  
Guylaine Canut ◽  
Fleur Couvreux ◽  
Marie Lothon ◽  
Dominique Legain ◽  
Bruno Piguet ◽  
...  
Keyword(s):  
Boundary Layer ◽  
High Frequency ◽  
Field Experiments ◽  
Sonic Anemometer ◽  
Motion Sensor ◽  
Tethered Balloon ◽  
Inertial Motion ◽  
Convective Boundary ◽  
Momentum Fluxes ◽  
Field Campaigns

Abstract. This study presents the first deployment in field campaigns of a balloon-borne turbulence probe, developed with a sonic anemometer and an inertial motion sensor suspended below a tethered balloon. This system measures temperature and horizontal and vertical wind at high frequency and allows the estimation of heat and momentum fluxes as well as turbulent kinetic energy in the lower part of the boundary layer. The system was validated during three field experiments with different convective boundary-layer conditions, based on turbulent measurements from instrumented towers and aircraft.

scholarly journals First Evidences of Methyl Chloride (CH3Cl) Transport from the Northern Italy Boundary Layer during Summer 2017

Atmosphere ◽  
2020 ◽  
Vol 11 (3) ◽  
pp. 238 ◽  
Author(s):  
Paolo Cristofanelli ◽  
Jgor Arduini ◽  
Francescopiero Calzolari ◽  
Umberto Giostra ◽  
Paolo Bonasoni ◽  
...  
Keyword(s):  
Boundary Layer ◽  
High Frequency ◽  
Stratospheric Ozone ◽  
Methyl Chloride ◽  
Temporal Correlation ◽  
Northern Italy ◽  
Montreal Protocol ◽  
Anthropogenic Activity ◽  
Bivariate Analysis

Methyl Chloride (CH3Cl) is a chlorine-containing trace gas in the atmosphere contributing significantly to stratospheric ozone depletion. While the atmospheric CH3Cl emissions are predominantly caused by natural sources on the global budget, significant uncertainties still remain for the anthropogenic CH3Cl emission strengths. In summer 2007 an intensive field campaign within the ACTRIS-2 Project was hosted at the Mt. Cimone World Meteorological Organization/Global Atmosphere Watch global station (CMN, 44.17° N, 10.68° E, 2165 m a.s.l.). High-frequency and high precision in situ measurements of atmospheric CH3Cl revealed significant high-frequency variability superimposed on the seasonally varying regional background levels. The high-frequency CH3Cl variability was characterized by an evident cycle over 24 h with maxima during the afternoon which points towards a systematic role of thermal vertical transport of air-masses from the regional boundary layer. The temporal correlation analysis with specific tracers of anthropogenic activity (traffic, industry, petrochemical industry) together with bivariate analysis as a function of local wind regime suggested that, even if the role of natural marine emissions appears as predominant, the northern Italy boundary layer could potentially represent a non-negligible source of CH3Cl during summer. Since industrial production and use of CH3Cl have not been regulated under the Montreal Protocol (MP) or its successor amendments, continuous monitoring of CH3Cl outflow from the Po Basin is important to properly assess its anthropogenic emissions.

scholarly journals Characterization of a boreal convective boundary layer and its impact on atmospheric chemistry during HUMPPA-COPEC-2010

2012 ◽  
Vol 12 (19) ◽  
pp. 9335-9353 ◽  
Author(s):  
H. G. Ouwersloot ◽  
J. Vilà-Guerau de Arellano ◽  
A. C. Nölscher ◽  
M. C. Krol ◽  
L. N. Ganzeveld ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Chemistry ◽  
Convective Boundary Layer ◽  
Large Scale ◽  
Spatial Scales ◽  
Potential Temperature ◽  
Chemical Species ◽  
Convective Boundary ◽  
The Impact

Abstract. We studied the atmospheric boundary layer (ABL) dynamics and the impact on atmospheric chemistry during the HUMPPA-COPEC-2010 campaign. We used vertical profiles of potential temperature and specific moisture, obtained from 132 radio soundings, to determine the main boundary layer characteristics during the campaign. We propose a classification according to several main ABL prototypes. Further, we performed a case study of a single day, focusing on the convective boundary layer, to analyse the influence of the dynamics on the chemical evolution of the ABL. We used a mixed layer model, initialized and constrained by observations. In particular, we investigated the role of large scale atmospheric dynamics (subsidence and advection) on the ABL development and the evolution of chemical species concentrations. We find that, if the large scale forcings are taken into account, the ABL dynamics are represented satisfactorily. Subsequently, we studied the impact of mixing with a residual layer aloft during the morning transition on atmospheric chemistry. The time evolution of NOx and O3 concentrations, including morning peaks, can be explained and accurately simulated by incorporating the transition of the ABL dynamics from night to day. We demonstrate the importance of the ABL height evolution for the representation of atmospheric chemistry. Our findings underscore the need to couple the dynamics and chemistry at different spatial scales (from turbulence to mesoscale) in chemistry-transport models and in the interpretation of observational data.

scholarly journals Diagnosing Coherent Structures in the Convective Boundary Layer by Optimizing Their Vertical Turbulent Scalar Transfer

2019 ◽  
Vol 174 (1) ◽  
pp. 119-144 ◽  
Author(s):  
Georgios A. Efstathiou ◽  
John Thuburn ◽  
Robert J. Beare
Keyword(s):  
Boundary Layer ◽  
Coherent Structures ◽  
Convective Boundary Layer ◽  
Thermodynamic Characteristics ◽  
Optimization Method ◽  
Area Fraction ◽  
Optimization Approach ◽  
Turbulent Transfer ◽  
Scalar Flux ◽  
Convective Boundary

Abstract A new method is introduced to identify coherent structures in the convective boundary layer, based on optimizing the vertical scalar flux in a two-fluid representation of turbulent motions as simulated by a large-eddy simulation. The new approach partitions the joint frequency distribution (JFD) of the vertical velocity and a transported scalar into coherent structures (fluid 2) and their environment (fluid 1) by maximizing that part of the scalar flux resolved by the mean properties in fluid 2 and fluid 1. The proposed method does not rely on any a priori criteria for the partitioning of the flow nor any pre-assumptions about the shape of the JFD. Different flavours of the optimization approach are examined based on maximizing either the total (fluid 1 $$+$$+ fluid 2) or the fluid-2 resolved scalar flux, and on whether all possible partitions or only a subset are considered. These options can result in different derived area fractions for the coherent structures. The properties of coherent structures diagnosed by the optimization method are compared to the conditional sampling of a surface-emitted decaying tracer, in which coherent structures are defined as having tracer perturbation greater than some height-dependent threshold. Results show that the optimization method is able to smoothly define coherent thermal structures in both the horizontal and the vertical. Moreover, optimizing the turbulent transfer by the fluid-2 resolved flux produces very similar coherent structures to the tracer threshold method, especially in terms of their area fraction and updraft velocities. Nonetheless, further analysis of the partitioning of the JFD reveals that, even though the area fraction of coherent structures might be similar, their definition can occupy different quadrants of the JFD, implying the contribution of different physical mechanisms to the turbulent transfer in the boundary layer. Finally, the kinematic and thermodynamic characteristics of the coherent structures are examined based on their definition criteria.

scholarly journals Scalar Turbulence in Convective Boundary Layers by Changing the Entrainment Flux

2013 ◽  
Vol 70 (1) ◽  
pp. 248-265 ◽  
Author(s):  
Alessandra S. Lanotte ◽  
Irene M. Mazzitelli
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Spatial Scales ◽  
Surface Flux ◽  
Scalar Fields ◽  
Temperature Inversion ◽  
Trace Gas ◽  
Free Atmosphere ◽  
Convective Boundary ◽  
Homogeneous Surface

Abstract A large-eddy simulation model is adopted to investigate the evolution of scalars transported by atmospheric cloud-free convective boundary layer flows. Temperature fluctuations due to the ground release of sensible heat and concentration fluctuations of a trace gas emitted at the homogeneous surface are mixed by turbulence within the unstable boundary layer. On the top, the entrainment zone is varied to obtain two distinct situations: (i) the temperature inversion is strong and the trace gas increment across the entrainment region is small, yielding to a small top flux with respect to the surface emission; (ii) the temperature inversion at the top of the convective boundary layer is weak, and the scalar increment large enough to achieve a concentration flux toward the free atmosphere that overwhelms the surface flux. In both cases, an estimation of the entrainment flux is obtained within a simple model, and it is tested against numerical data. The evolution of the scalar profiles is discussed in terms of the different entrainment–surface flux ratios. Results show that, when entrainment at the top of the boundary layer is weak, temperature and trace gas scalar fields are strongly correlated, particularly in the lower part of the boundary layer. This means that they exhibit similar behavior from the largest down to the smallest spatial scales. However, when entrainment is strong, as moving from the surface, differences in the transport of the two scalars arise. Finally, it is shown that, independently of the scalar regime, the temperature field exhibits more intermittent fluctuations than the trace gas.

scholarly journals Surface Temperature and Surface-Layer Turbulence in a Convective Boundary Layer

2013 ◽  
Vol 148 (1) ◽  
pp. 51-72 ◽  
Author(s):  
Anirban Garai ◽  
Eric Pardyjak ◽  
Gert-Jan Steeneveld ◽  
Jan Kleissl
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Surface Temperature ◽  
Convective Boundary Layer ◽  
Convective Boundary

scholarly journals A Simple Model of a Balanced Boundary Layer Coupled to a Large-Scale Convective Circulation

2019 ◽  
Vol 76 (3) ◽  
pp. 837-849
Author(s):  
Robert J. Beare ◽  
Michael J. P. Cullen
Keyword(s):  
Boundary Layer ◽  
Simple Model ◽  
Surface Temperature ◽  
Mass Flux ◽  
Time Scale ◽  
Large Scale ◽  
Climate Models ◽  
Convective Boundary ◽  
Convective Circulation ◽  
Convective Mass Flux

Abstract Many simple models of large-scale tropical circulations do not include a frictional boundary layer. A simple model is presented where the convective circulation is coupled to the boundary layer convergence. In the free troposphere, convection and boundary layer heating try to relax to a moist adiabat from the local sea surface temperature with a time scale τc, but other processes act to maintain a weak temperature gradient. There is a mass balance between radiatively driven subsidence and the large-scale convective mass flux. For a prescribed Gaussian surface temperature, the model predicts a mass flux that varies as and a convective width proportional to its reciprocal. In the boundary layer, there can be significant horizontal temperature gradients and a balance between the pressure gradient and drag is assumed. Coupling between the two layers is mediated by the vertical velocity at the top of the boundary layer. The boundary layer constrains the circulation in three ways. First, it may lengthen the relaxation time scale compared to deep convection. Second, the evaporation in the nonconvecting region constrains the horizontal moisture advection. Third, it maintains a convective boundary layer where there is a convective mass flux; this condition cannot be satisfied if τc is too small or if the drag is too large, thus showing that such values are physically impossible. These results provide testable hypotheses concerning the physics and large-scale dynamics in weather and climate models.

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