scholarly journals Study of the overturning length scales at the Spanish planetary boundary layer

2015 ◽  
Vol 2 (6) ◽  
pp. 1531-1551
Author(s):  
P. López ◽  
J. L. Cano
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Power Law ◽  
Power Laws ◽  
Data Sets ◽  
The Novel ◽  
Convective Conditions ◽  
Mixing Conditions ◽  
Thorpe Scale ◽  
Field Campaigns

Abstract. The focus of this paper is to analyze the behaviour of the maximum Thorpe displacement (dT)max and the Thorpe scale LT at the atmospheric boundary layer (ABL), extending previous research with new data and improving our studies related to the novel use of the Thorpe method applied to ABL. The maximum Thorpe displacements varies between −900 and 950 m for the different field campaigns. The Thorpe scale LT ranges between 0.2 and 680 m for the different data sets which cover different stratified mixing conditions (turbulence sher-driven and convective regions). We analyze the relation between dT)max and the Thorpe scale LT and we deduce that they verify a power law. We also deduce that there is a difference in exponents of the power laws for convective conditions and shear-driven conditions. This different power laws could identify overturns created under different mechanisms.

scholarly journals Study of the overturning length scales at the Spanish planetary boundary layer

2016 ◽  
Vol 23 (2) ◽  
pp. 75-82
Author(s):  
Pilar López ◽  
José L. Cano
Keyword(s):  
Boundary Layer ◽  
Power Law ◽  
Power Laws ◽  
Data Sets ◽  
The Novel ◽  
Convective Conditions ◽  
Mixing Conditions ◽  
Thorpe Scale ◽  
Field Campaigns ◽  
The Relationship

Abstract. The focus of this paper is to analyse the behaviour of the maximum Thorpe displacement (dT)max and the Thorpe scale LT at the atmospheric boundary layer (ABL), extending previous research with new data and improving our studies related to the novel use of the Thorpe method applied to ABL. The maximum Thorpe displacements vary between −900 and 950 m for the different field campaigns. The Thorpe scale LT ranges between 0.2 and 680 m for the different data sets which cover different stratified mixing conditions (turbulence shear-driven and convective regions). We analyse the relationship between (dT)max and the Thorpe scale LT and we deduce that they verify a power law. We also deduce that there is a difference in exponents of the power laws for convective conditions and shear-driven conditions. These different power laws could identify overturns created under different mechanisms.

scholarly journals A numerical framework for simulating episodic emissions of high-temperature marine INPs

2021 ◽  
Author(s):  
Isabelle Steinke ◽  
Paul J. DeMott ◽  
Grant Deane ◽  
Thomas C. J. Hill ◽  
Mathew Maltrud ◽  
...  
Keyword(s):  
Boundary Layer ◽  
High Temperature ◽  
Atmospheric Boundary Layer ◽  
Heterotrophic Bacteria ◽  
Sea Spray ◽  
Surface Microlayer ◽  
Partial Explanation ◽  
Sea Surface Microlayer ◽  
Sea Spray Aerosol ◽  
Field Campaigns

Abstract. We present a framework for estimating concentrations of episodically elevated high-temperature marine ice nucleating particles (INPs) in the sea surface microlayer and their subsequent emission into the atmospheric boundary layer. These episodic INPs have been observed in multiple ship-based and coastal field campaigns, but the processes controlling their ocean concentrations and transfer to the atmosphere are not yet fully understood. We use a combination of empirical constraints and simulation outputs from an Earth System Model to explore different hypotheses for explaining the variability of INP concentrations, and the occurrence of episodic INPs, in the marine atmosphere. In our calculations, we examine two proposed oceanic sources of high-temperature INPs: heterotrophic bacteria and marine biopolymer aggregates (MBPAs). Furthermore, we assume that the emission of these INPs is determined by the production of supermicron sea spray aerosol formed from jet drops, with an entrainment probability that is described by Poisson statistics. The concentration of jet drops is derived from the number concentration of supermicron sea spray aerosol calculated from model runs. We then derive the resulting number concentrations of marine high-temperature INPs (≥ 253 K) in the atmospheric boundary layer and compare their variability to atmospheric observations of INP variability. Specifically, we compare against concentrations of episodically occurring high-temperature INPs observed during field campaigns in the Southern Ocean, the Equatorial Pacific, and the North Atlantic. We find that heterotrophic bacteria and MBPAs acting as INPs provide only a partial explanation for the observed high INP concentrations. We note, however, that there are still substantial knowledge gaps, particularly concerning the identity of the oceanic INPs contributing most frequently to episodic high-temperature INPs, their specific ice nucleation activity, and the enrichment of their concentrations during the sea-air transfer process. Therefore, targeted measurements investigating the composition of these marine INPs as well as drivers for their emission are needed, ideally in combination with modeling studies focused on the potential cloud impacts of these high-temperature INPs.

Considerations of the stability of certain heterogeneous shear flows including some inflexion-free profiles

1974 ◽  
Vol 65 (1) ◽  
pp. 65-69 ◽  
Author(s):  
George Chimonas
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Shear Flows ◽  
The Novel ◽  
Rigid Boundary ◽  
Flow Shear ◽  
Flow Profiles ◽  
Neutral Mode ◽  
The Stability ◽  
Decreasing Functions

We use some well-known properties of the Taylor-Goldstein equation to generate a set of stably stratified shear flows with known singular neutral-mode solutions. The novel feature of the analysis is that it includes such solutions for flows in which, proceeding upwards from a rigid boundary, the Brunt-Väisälä frequency and the flow shear do not change sign and are monotonically decreasing functions of height. Such profiles are much closer to the conditions met in work on the atmospheric boundary layer than the more frequently used inflected flow profiles.

Turbulent Boundary Layer With Negligible Wall Stress

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Noor Afzal
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Power Law ◽  
Asymptotic Expansions ◽  
Kinematic Viscosity ◽  
Adverse Pressure Gradient ◽  
Power Laws ◽  
Outer Flow ◽  
Half Power

The turbulent boundary layer subjected to strong adverse pressure gradient near the separation region has been analyzed at large Reynolds numbers by the method of matched asymptotic expansions. The two regions consisting of outer nonlinear wake layer and inner wall layer are analyzed in terms of pressure scaling velocities Up=(νp′∕ρ)1∕3 in the wall region and Uδ=(δp′∕ρ)1∕2 in the outer wake region, where p′ is the streamwise pressure gradient and ρ is the fluid density. In this work, the variables δ, the outer boundary layer thickness, and Uδ, the outer velocity scale, are independent of ν, the molecular kinematic viscosity, which is a better model of fully developed mean turbulent flow. The asymptotic expansions have been matched by Izakson–Millikan–Kolmogorov hypothesis leading to open functional equations. The solution for the velocity distribution gives new composite log-half-power laws, based on the pressure scales, providing a better model of the flow, where the outer composite log-half-power law does not depend on the molecular kinematic viscosity. These new composite laws are better and one may be benefited from their limiting relations that for weak pressure gradient yield the traditional logarithmic laws and for strong adverse pressure gradient yield the half-power laws. During matching of the nonlinear outer layer two cases arise: One where Uδ∕Ue is small and second where Uδ∕Ue of order unity (where Ue is the velocity at the edge of the boundary layer). In the first case, the lowest order nonlinear outer flow under certain conditions shows equilibrium. The outer flow subjected to the constant eddy viscosity closure model is governed by the Falkner–Skan equation subjected to the matching condition of finite slip velocity on the surface. The jet- and wakelike solutions are presented, where the zero velocity slip implying the point of separation, which compares well with Coles traditional wake function. In the second case, higher order terms in the asymptotic solutions for nearly separating flow have been estimated. The proposed composite log-half-power law solution and the limiting half-power law have been well supported by extensive experimental and direct numerical simulation data. For moderate values of the pressure gradient the data show that the proposed composite log-half-power laws are a better model of the flow.

Power-Law Scaling of Turbulence Cospectra for the Stably Stratified Atmospheric Boundary Layer

2020 ◽  
Vol 177 (1) ◽  
pp. 1-18
Author(s):  
Yu Cheng ◽  
Qi Li ◽  
Andrey Grachev ◽  
Stefania Argentini ◽  
Harindra J. S. Fernando ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Power Law

scholarly journals Analyzing the Atmospheric Boundary Layer by high-order moments obtained from multiwavelength lidar data: impact of wavelength choice

2019 ◽  
Author(s):  
Gregori de Arruda Moreira ◽  
Fábio Juliano da Silva Lopes ◽  
Juan Luis Guerrero-Rascado ◽  
Jonatan João da Silva ◽  
Antonio Arleques Gomes ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
High Order ◽  
Molecular Signature ◽  
Mixing Conditions ◽  
Backscatter Signal ◽  
Turbulent Layer ◽  
Limited Applicability ◽  
Backscattered Signals ◽  
532 Nm

Abstract. The lowest region of the troposphere is a turbulent layer denominated Atmospheric Boundary Layer (ABL) characterized by high daily variability due to the influence of surface forcings. This is the reason why detecting systems with high spatial and temporal resolution, like lidars, have been widely applied for researching this region. In this paper, we present a comparative analysis on the use of lidar backscattered signals at three wavelengths (355, 532 and 1064 nm) to study the ABL investigating the high-order moments, which give us information about the ABL height (derived by the variance method), aerosol layers movements (skewness) and mixing conditions (kurtosis) at several heights. Previous studies have shown that 1064-nm wavelength, due to the predominance of particle signature in the total backscattered atmospheric signal, provides an appropriate description of the turbulence field and thus, in this study, it was considered as a reference. We analyze two case studies, which show us that the backscattered signal at 355 nm, even after applying some corrections, has a limited applicability for turbulence studies using the proposed methodology due to the strong contribution of the molecular signature to the total backscatter signal. This increases the noise associated to the profiles and, consequently, generates misinformation. On the other hand, the information on the turbulence field derived from the backscattered signal at 532 nm is similar to that obtained at 1064 nm due to the appropriate attenuation of the noise, generated by molecular component of backscattered signal, by the application of the corrections proposed.

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