scholarly journals Influence of nighttime radiation fog on the development of the daily boundary layer: An large eddy simulation study

2021 ◽  
Author(s):  
Johannes Schwenkel ◽  
Björn Maronga
Keyword(s):  
Boundary Layer ◽  
Turbulent Mixing ◽  
Weather Prediction ◽  
Cloud Microphysics ◽  
Small Scale ◽  
Radiative Loss ◽  
Intermittent Turbulence ◽  
Convective Boundary ◽  
Radiation Fog ◽  
Large Eddy

<p>Apart from hazards associated with deep fog, its presence significantly alters the properties of the nocturnal boundary layer (NBL). <br>The NBL is typically characterized by a stable stratification resulting in weak or sometimes intermittent turbulence. <br>In contrast, the NBL during deep fog is often convective, as for the longwave radiation optical thick fog layer, the net radiative loss takes place at the fog top, destabilizing the atmosphere from above.<br>Therefore, processes as modified longwave cooling, shortwave absorption, turbulent mixing, reduction of the total water content through droplet settling or modified dewfall, is able to induce differences between the stable NBL (SNBL) and foggy NBL. <br>Albeit after sunrise the SNBL is quickly transformed into a convective boundary layer (CBL), properties of the NBL are transferred into the day and affect the CBL. <br>Even though fundamental and applied research have significantly improved fog forecasts and contributed to a broader and deeper understanding at the process-level in the last decades, common numerical weather prediction (NWP) models still miss a significant amount of fog events.<br>A number of complex small-scale processes (such as turbulent mixing, land-atmosphere interactions, aerosol and cloud microphysics and radiation) interacting on different scales have to be correctly resolved or parameterized.<br>Likewise, the prerequisite formation conditions must be presented precisely as they are highly sensitive to slight changes in temperature, humidity or soil moisture, entailing that even small biases in the forcing data could lead to an incorrect representation of subtle supersaturations and might result in failing to predict fog.</p><p>Thus, we will present in this talk results of idealized large eddy simulations pairs (with and without the possibility to form fog) covering the diurnal cycle based on a typical fog event observed in Cabauw considering radiative conditions between February and April. <br>As we performed several parameter studies we will demonstrate, that the CBL in cases without fog is warmer and obtain higher inversion heights than in simulations with fog during night.<br>Further, we show that this temperature deviations are mainly driven by an stronger integrated  longwave cooling during night in the foggy cases.<br>Moreover, we identified the liquid water path as a crucial parameter determining the strength of the fog impact on CBL development. </p>

scholarly journals Comparison of Convective Boundary Layer Velocity Spectra Retrieved from Large- Eddy-Simulation and Weather Research and Forecasting Model Data

2014 ◽  
Vol 53 (2) ◽  
pp. 377-394 ◽  
Author(s):  
Jeremy A. Gibbs ◽  
Evgeni Fedorovich
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Wrf Model ◽  
Velocity Fields ◽  
Weather Research And Forecasting ◽  
Small Scale ◽  
Convective Boundary ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Velocity Spectra

AbstractAs computing capabilities expand, operational and research environments are moving toward the use of finescale atmospheric numerical models. These models are attractive for users who seek an accurate description of small-scale turbulent motions. One such numerical tool is the Weather Research and Forecasting (WRF) model, which has been extensively used in synoptic-scale and mesoscale studies. As finer-resolution simulations become more desirable, it remains a question whether the model features originally designed for the simulation of larger-scale atmospheric flows will translate to adequate reproductions of small-scale motions. In this study, turbulent flow in the dry atmospheric convective boundary layer (CBL) is simulated using a conventional large-eddy-simulation (LES) code and the WRF model applied in an LES mode. The two simulation configurations use almost identical numerical grids and are initialized with the same idealized vertical profiles of wind velocity, temperature, and moisture. The respective CBL forcings are set equal and held constant. The effects of the CBL wind shear and of the varying grid spacings are investigated. Horizontal slices of velocity fields are analyzed to enable a comparison of CBL flow patterns obtained with each simulation method. Two-dimensional velocity spectra are used to characterize the planar turbulence structure. One-dimensional velocity spectra are also calculated. Results show that the WRF model tends to attribute slightly more energy to larger-scale flow structures as compared with the CBL structures reproduced by the conventional LES. Consequently, the WRF model reproduces relatively less spatial variability of the velocity fields. Spectra from the WRF model also feature narrower inertial spectral subranges and indicate enhanced damping of turbulence on small scales.

scholarly journals A Closer Look at Boundary Layer Inversion in Large-Eddy Simulations and Bulk Models: Buoyancy-Driven Case

2015 ◽  
Vol 72 (2) ◽  
pp. 728-749 ◽  
Author(s):  
Pierre Gentine ◽  
Gilles Bellon ◽  
Chiel C. van Heerwaarden
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Weather Prediction ◽  
Inversion Layer ◽  
Large Eddy Simulations ◽  
Buoyancy Flux ◽  
Convective Boundary ◽  
Strong Inversion ◽  
Wide Range ◽  
Large Eddy

Abstract The inversion layer (IL) of a clear-sky, buoyancy-driven convective boundary layer is investigated using large-eddy simulations covering a wide range of convective Richardson numbers. A new model of the IL is suggested and tested. The model performs better than previous first-order models of the entrainment and provides physical insights into the main controls of the mixed-layer and IL growths. A consistent prognostic equation of the IL growth is derived, with explicit dependence on the position of the minimum buoyancy flux, convective Richardson number, and relative stratification across the inversion G. The IL model expresses the interrelationship between the position and magnitude of the minimum buoyancy flux and inversion-layer depth. These relationships emphasize why zero-order jump models of the convective boundary layer perform well under a strong inversion and show that these models miss the additional parameter G to fully characterize the entrainment process under a weak inversion. Additionally, the position of the minimum buoyancy flux within the new IL model is shown to be a key component of convective boundary layer entrainment. The new IL model is sufficiently simple to be used in numerical weather prediction or general circulation models as a way to resolve the IL in a low-vertical-resolution model.

scholarly journals The diurnal evolution of <sup>222</sup>Rn and its progeny in the atmospheric boundary layer during the Wangara experiment

2007 ◽  
Vol 7 (3) ◽  
pp. 8895-8931
Author(s):  
J.-F. Vinuesa ◽  
S. Basu ◽  
S. Galmarini
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Turbulent Mixing ◽  
Secular Equilibrium ◽  
Convective Boundary ◽  
Large Eddy Simulation Model ◽  
Eddy Simulation ◽  
Boundary Layer Processes ◽  
Turbulent Characteristics ◽  
Large Eddy

Abstract. The diurnal atmospheric boundary layer evolution of the 222Rn decaying family is studied by using a state-of-the-art large-eddy simulation model. In particular, a diurnal cycle observed during the Wangara experiment is successfully simulated together with the effect of diurnal varying turbulent characteristics on radioactive compounds in a secular equilibrium. This study allows us to clearly analyze and identify the boundary layer processes driving the 222Rn and its progeny concentration behaviors. The activity disequilibrium observed in the nocturnal boundary layer is due to the proximity of the radon source and the trapping of fresh 222Rn close to the surface induced by the weak vertical transport. During the morning transition, the secular equilibrium is fast restored by the vigorous turbulent mixing. The evolution of 222Rn and its progeny concentration in the unsteady growing convective boundary layer depends on the strength of entrainment events.

scholarly journals The diurnal evolution of <sup>222</sup>Rn and its progeny in the atmospheric boundary layer during the Wangara experiment

2007 ◽  
Vol 7 (18) ◽  
pp. 5003-5019 ◽  
Author(s):  
J.-F. Vinuesa ◽  
S. Basu ◽  
S. Galmarini
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Turbulent Mixing ◽  
Secular Equilibrium ◽  
Convective Boundary ◽  
Large Eddy Simulation Model ◽  
Eddy Simulation ◽  
Boundary Layer Processes ◽  
Turbulent Characteristics ◽  
Large Eddy

Abstract. The diurnal atmospheric boundary layer evolution of the 222Rn decaying family is studied using a state-of-the-art large-eddy simulation model. In particular, a diurnal cycle observed during the Wangara experiment is successfully simulated together with the effect of diurnal varying turbulent characteristics on radioactive compounds initially in a secular equilibrium. This study allows us to clearly analyze and identify the boundary layer processes driving the behaviour of 222Rn and its progeny concentrations. An activity disequilibrium is observed in the nocturnal boundary layer due to the proximity of the radon source and the trapping of fresh 222Rn close to the surface induced by the weak vertical transport. During the morning transition, the secular equilibrium is fast restored by the vigorous turbulent mixing. The evolution of 222Rn and its progeny concentrations in the unsteady growing convective boundary layer depends on the strength of entrainment events.

scholarly journals Representation of the grey zone of turbulence in the atmospheric boundary layer

2016 ◽  
Vol 13 ◽  
pp. 63-67 ◽  
Author(s):  
Rachel Honnert
Keyword(s):  
Boundary Layer ◽  
Weather Prediction ◽  
Numerical Weather Prediction Model ◽  
Grey Zone ◽  
Shallow Convection ◽  
Convective Boundary ◽  
Boundary Layer Height ◽  
Eddy Simulation ◽  
Layer Structures ◽  
Large Eddy

Abstract. Numerical weather prediction model forecasts at horizontal grid lengths in the range of 100 to 1 km are now possible. This range of scales is the "grey zone of turbulence". Previous studies, based on large-eddy simulation (LES) analysis from the MésoNH model, showed that some assumptions of some turbulence schemes on boundary-layer structures are not valid. Indeed, boundary-layer thermals are now partly resolved, and the subgrid remaining part of the thermals is possibly largely or completely absent from the model columns. First, some modifications of the equations of the shallow convection scheme have been tested in the MésoNH model and in an idealized version of the operational AROME model at resolutions coarser than 500 m. Secondly, although the turbulence is mainly vertical at mesoscale (>  2 km resolution), it is isotropic in LES (<  100 m resolution). It has been proved by LES analysis that, in convective boundary layers, the horizontal production of turbulence cannot be neglected at resolutions finer than half of the boundary-layer height. Thus, in the grey zone, fully unidirectional turbulence scheme should become tridirectional around 500 m resolution. At Météo-France, the dynamical turbulence is modelled by a K-gradient in LES as well as at mesoscale in both MésoNH and AROME, which needs mixing lengths in the formulation. Vertical and horizontal mixing lengths have been calculated from LES of neutral and convective cases at resolutions in the grey zone.

LESbrary: A library of large eddy simulation data for the calibration and uncertainty quantification of ocean surface boundary layer turbulence parameterizations

2021 ◽  
Author(s):  
Gregory Wagner ◽  
Andre Souza ◽  
Adeline Hillier ◽  
Ali Ramadhan ◽  
Raffaele Ferrari
Keyword(s):  
Boundary Layer ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Ocean Surface ◽  
Limited Area ◽  
Surface Boundary ◽  
Model Errors ◽  
Surface Boundary Layer ◽  
Large Eddy ◽  
Free Parameters

&lt;p&gt;Parameterizations of turbulent mixing in the ocean surface boundary layer (OSBL) are key Earth System Model (ESM) components that modulate the communication of heat and carbon between the atmosphere and ocean interior. OSBL turbulence parameterizations are formulated in terms of unknown free parameters estimated from observational or synthetic data. In this work we describe the development and use of a synthetic dataset called the &amp;#8220;LESbrary&amp;#8221; generated by a large number of idealized, high-fidelity, limited-area large eddy simulations (LES) of OSBL turbulent mixing. We describe how the LESbrary design leverages a detailed understanding of OSBL conditions derived from observations and large scale models to span the range of realistically diverse physical scenarios. The result is a diverse library of well-characterized &amp;#8220;synthetic observations&amp;#8221; that can be readily assimilated for the calibration of realistic OSBL parameterizations in isolation from other ESM model components. We apply LESbrary data to calibrate free parameters, develop prior estimates of parameter uncertainty, and evaluate model errors in two OSBL parameterizations for use in predictive ESMs.&lt;/p&gt;

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