scholarly journals What Controls the Mean Depth of the PBL?

2005 ◽  
Vol 18 (16) ◽  
pp. 3157-3172 ◽  
Author(s):  
Brian Medeiros ◽  
Alex Hall ◽  
Bjorn Stevens
Keyword(s):  
Los Angeles ◽  
Boundary Layers ◽  
Large Scale ◽  
Static Stability ◽  
Stability Control ◽  
Surface Fluxes ◽  
Free Atmosphere ◽  
Convective Boundary ◽  
Consistent Treatment ◽  
The University

Abstract The depth of the planetary boundary layer (PBL) is a climatologically important quantity that has received little attention on regional to global scales. Here a 10-yr climatology of PBL depth from the University of California, Los Angeles (UCLA) atmospheric GCM is analyzed using the PBL mass budget. Based on the dominant physical processes, several PBL regimes are identified. These regimes tend to exhibit large-scale geographic organization. Locally generated buoyancy fluxes and static stability control PBL depth nearly everywhere, though convective mass flux has a large influence at tropical marine locations. Virtually all geographical variability in PBL depth can be linearly related to these quantities. While dry convective boundary layers dominate over land, stratocumulus-topped boundary layers are most common over ocean. This division of regimes leads to a dramatic land–sea contrast in PBL depth. Diurnal effects keep mean PBL depth over land shallow despite large daytime surface fluxes. The contrast arises because the large daily exchange of heat and mass between the PBL and free atmosphere over land is not present over the ocean, where mixing is accomplished by turbulent entrainment. Consistent treatment of remnant air from the deep, daytime PBL is necessary for proper representation of this diurnal behavior over land. Many locations exhibit seasonal shifts in PBL regime related to changes in PBL clouds. These shifts are controlled by seasonal variations in buoyancy flux and static stability.

The impact of large-scale winds on thermally driven flows and exchange processes over mountainous terrain

2020 ◽  
Author(s):  
Jan Weinkaemmerer ◽  
Ivan Bašták Ďurán ◽  
Jürg Schmidli
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Volume Effect ◽  
Turbulent Heat ◽  
Atmospheric Conditions ◽  
Free Atmosphere ◽  
Convective Boundary ◽  
Mean Values ◽  
Mountainous Regions ◽  
The Impact

<p>In the convective boundary layer over mountainous regions, the mean values and the fluxes of quantities like heat, mass, and momentum are strongly influenced by thermally induced flows. Several studies have pointed out that the enhanced warming of the air inside a valley can be explained by the valley-volume effect whereas the cross-valley circulation leads to a net export of heat to the free atmosphere. We are interested in the influence of an upper-level wind on the local circulations and the boundary-layer properties, both locally and in terms of the horizontal mean, as this aspect has not yet received much attention. LES are carried out over idealized, two-dimensional topographies using the CM1 numerical model. For the analysis, turbulent, mean-circulation, and large-scale contributions are systematically distinguished. Also, budget analyses are performed for the turbulence kinetic energy and the turbulent heat and mass flux. Based on the first results for periodic topographies, no crucial influence on the horizontally averaged heat-flux and temperature profile can be observed, even though the flow pattern of the thermal wind is qualitatively changed. In addition to that, the impact on moisture transport will be evaluated and simulations over different topographies as well as for different atmospheric conditions and surface properties will be presented.</p>

scholarly journals The Influence of Idealized Heterogeneity on Wet and Dry Planetary Boundary Layers Coupled to the Land Surface

2005 ◽  
Vol 62 (7) ◽  
pp. 2078-2097 ◽  
Author(s):  
Edward G. Patton ◽  
Peter P. Sullivan ◽  
Chin-Hoh Moeng
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Convective Boundary Layer ◽  
Land Surface ◽  
Surface Flux ◽  
Scalar Fields ◽  
Surface Fluxes ◽  
Convective Boundary ◽  
Turbulent Statistics ◽  
The Impact

Abstract This manuscript describes numerical experiments investigating the influence of 2–30-km striplike heterogeneity on wet and dry convective boundary layers coupled to the land surface. The striplike heterogeneity is shown to dramatically alter the structure of the convective boundary layer by inducing significant organized circulations that modify turbulent statistics. The impact, strength, and extent of the organized motions depend critically on the scale of the heterogeneity λ relative to the boundary layer height zi. The coupling with the land surface modifies the surface fluxes and hence the circulations resulting in some differences compared to previous studies using fixed surface forcing. Because of the coupling, surface fluxes in the middle of the patches are small compared to the patch edges. At large heterogeneity scales (λ/zi ∼18) horizontal surface-flux gradients within each patch are strong enough to counter the surface-flux gradients between wet and dry patches allowing the formation of small cells within the patch coexisting with the large-scale patch-induced circulations. The strongest patch-induced motions occur in cases with 4 < λ/zi < 9 because of strong horizontal pressure gradients across the wet and dry patches. Total boundary layer turbulence kinetic energy increases significantly for surface heterogeneity at scales between λ/zi = 4 and 9; however, entrainment rates for all cases are largely unaffected by the striplike heterogeneity. Velocity and scalar fields respond differently to variations of heterogeneity scale. The patch-induced motions have little influence on total vertical scalar flux, but the relative contribution to the flux from organized motions compared to background turbulence varies with heterogeneity scale. Patch-induced motions are shown to dramatically impact point measurements in a free-convective boundary layer. The magnitude and sign of this impact depends on the location of the measurement within the region of heterogeneity.

scholarly journals Atmospheric boundary layers in storms: advanced theory and modelling applications

2005 ◽  
Vol 2 ◽  
pp. 47-49 ◽  
Author(s):  
S. S. Zilitinkevich ◽  
I. N. Esau ◽  
A. Baklanov
Keyword(s):  
Boundary Layers ◽  
Common Knowledge ◽  
Outer Boundary ◽  
Potential Temperature ◽  
Static Stability ◽  
Free Flow ◽  
Traditional Theory ◽  
Free Atmosphere ◽  
Non Local ◽  
Neutrally Stratified

Abstract. Turbulent planetary boundary layers (PBLs) control the exchange processes between the atmosphere and the ocean/land. The key problems of PBL physics are to determine the PBL height, the momentum, energy and matter fluxes at the surface and the mean wind and scalar profiles throughout the layer in a range of regimes from stable and neutral to convective. Until present, the PBLs typical of stormy weather were always considered as neutrally stratified. Recent works have disclosed that such PBLs are in fact very strongly affected by the static stability of the free atmosphere and must be treated as factually stable (we call this type of the PBL "conventionally neutral" in contract to the "truly neutral" PBLs developed against the neutrally stratified free flow). It is common knowledge that basic features of PBLs exhibit a noticeable dependence on the free-flow static stability and baroclinicity. However, the concern of the traditional theory of neural and stable PBLs was almost without exception the barotropic nocturnal PBL, which develops at mid latitudes during a few hours in the night, on the background of a neutral or slightly stable residual layer. The latter separates this type of the PBL from the free atmosphere. It is not surprising that the nature of turbulence in such regimes is basically local and does not depend on the properties of the free atmosphere. Alternatively, long-lived neutral (in fact only conditionally neutral) or stable PBLs, which have much more time to grow up, are placed immediately below the stably stratified free flow. Under these conditions, the turbulent transports of momentum and scalars even in the surface layer - far away from the PBL outer boundary - depend on the free-flow Brunt-Väisälä frequency, N. Furthermore, integral measures of the long-lived PBLs (their depths and the resistance law functions) depend on N and also on the baroclinic shear, S. In the traditional PBL models both non-local parameters N and S were overlooked. One of possible mechanisms responsible for non-local features of the long-lived PBLs could be the radiation of internal gravity waves (IGW) from the PBL upper boundary to the free atmosphere and the IGW-induced transport of the squared fluctuations of velocity and potential temperature. The free-flow stability plays an especially important role in is the conventionally neutral PBLs (those with the zero potential-temperature flux at the surface: Fθ=0 at z=0, developed against non-zero static stability in the free atmosphere: N>0). The above reasoning obviously calls for a comprehensive revision of the traditional theory. In a series of papers (quoted below in References) an advanced theory has been proposed. It includes the following developments.

scholarly journals Characteristics of Cold Air Outbreak events and associated Polar Mesoscale Cyclogenesis over the North Atlantic region

2021 ◽  
pp. 1-52
Author(s):  
Annick Terpstra ◽  
Ian A. Renfrew ◽  
Denis E. Sergeev
Keyword(s):  
Large Scale ◽  
Static Stability ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Labrador Sea ◽  
Air Mass ◽  
Cold Air ◽  
Norwegian Sea ◽  
Air Masses ◽  
Mesoscale Cyclones

AbstractEquatorward excursions of cold polar air masses into ice-free regions, so-called Cold Air Outbreaks (CAO), are frequently accompanied by the development of severe mesoscale weather features. Focusing on two key regions, the Labrador Sea and the Greenland/Norwegian Sea, we apply objective detection for both CAO events and polar mesoscale cyclones to outline the temporal evolution of CAO events and quantify associated mesoscale cyclogenesis. We introduce a novel metric, the CAO-depth, which incorporates both the static stability and the temperature of the air mass. The large-scale atmospheric conditions during the onset of CAO events comprise a very cold upper level trough over the CAO region and a surface cyclone downstream. As the CAO matures, the cold air mass extends southeastward, accompanied by lower static stability and enhanced surface fluxes. Despite the nearly 20 degrees difference in latitude, CAO events over both regions exhibit similar evolution and characteristics including surface fluxes and thermodynamic structure. About 2/3rd of the identified CAO events are accompanied by polar mesoscale cyclogenesis, with the majority of mesoscale cyclones originating inside the cold air masses. Neither the duration nor the maturity of the CAO event seems relevant for mesoscale cyclogenesis. Mesoscale cyclogenesis conditions during CAO events over the Labrador Sea are warmer, moister, and exhibit stronger surface latent heat fluxes than their Norwegian Sea counterparts.

SOCIAL PROJECT AS A PLATFORM FOR THE IMPLEMENTATION OF PROFESSIONAL SKILLS OF FUTURE INFORMATICS TEACHERS

2019 ◽  
pp. 16-22
Author(s):  
E. V. Klimenko ◽  
N. S. Buslova
Keyword(s):  
Large Scale ◽  
Modern Society ◽  
Professional Competencies ◽  
Future Teachers ◽  
Professional Skills ◽  
Knowledge And Skills ◽  
Theoretical Reasoning ◽  
Social Project ◽  
The University

The article is devoted to the consideration of ways to solve one of the actual problems in theory and methodology of training and upbringing — the problem of developing professional skills of future informatics teacher. As a way to adapt students to the profession, the possibility of their involvement in social designing was chosen. Participation in social projects contributes to the approbation and introduction of new forms and methods in teaching informatics. Expanding the experience of future teachers in carrying out large-scale events contributes to the formation of a socially adapted personality competitive in modern society. The potential of a social project in consolidating the knowledge and skills obtained during the theoretical training at the university is indicated. In the article, theoretical reasoning is accompanied by examples of real social projects and activities aimed at the formation of professional competencies of future informatics teachers.

Dialogues

2020 ◽  
Vol 2 (3) ◽  
pp. 53-59
Keyword(s):  
Los Angeles ◽  
New Spain ◽  
American Art ◽  
Historical Trauma ◽  
State Building ◽  
University Of California ◽  
Religious Experiences ◽  
Political Space ◽  
California Missions ◽  
The University

The California missions, whose original church spaces and visual programs were produced by Iberian, Mexican, and Native artisans between 1769 and 1823, occupy an ambiguous chronological, geographical, and political space. They occupy lands that have pertained to conflicting territorialities: from Native nations, to New Spain, to Mexico, to the modern multicultural California. The physical and visual landscapes of the missions have been sites of complex and often incongruous religious experiences; historical trauma and romantic vision; Indigenous genocide, exploitation, resistance, and survivance; state building and global enterprise. This Dialogues section brings together critical voices, including especially the voices of California Indian scholars, to interrogate received models for thinking about the art historical legacies of the California missions. Together, the contributing authors move beyond and across borders and promote new decolonial strategies that strive to be responsive to the experience of California Indian communities and nations. This conversation emerges from cross-disciplinary relationships established at a two-day conference, “‘American’ Art and the Legacy of Conquest: Art at California’s Missions in the Global 18th–20th Centuries,” sponsored by the Terra Foundation for American Art and held at the University of California, Los Angeles, in November 2019.

Disruptive innovation and operationalization in local and sustainable food systems: Examining the University of Toronto-Local Food Plus partnership

2019 ◽  
Vol 6 (1) ◽  
pp. 120-139
Author(s):  
Lori Stahlbrand
Keyword(s):  
Food Systems ◽  
Large Scale ◽  
Food System ◽  
Local Food ◽  
Disruptive Innovation ◽  
Government Support ◽  
Sustainable Food ◽  
University Of Toronto ◽  
The University

This paper traces the partnership between the University of Toronto and the non-profit Local Food Plus (LFP) to bring local sustainable food to its St. George campus. At its launch, the partnership represented the largest purchase of local sustainable food at a Canadian university, as well as LFP’s first foray into supporting institutional procurement of local sustainable food. LFP was founded in 2005 with a vision to foster sustainable local food economies. To this end, LFP developed a certification system and a marketing program that matched certified farmers and processors to buyers. LFP emphasized large-scale purchases by public institutions. Using information from in-depth semi-structured key informant interviews, this paper argues that the LFP project was a disruptive innovation that posed a challenge to many dimensions of the established food system. The LFP case study reveals structural obstacles to operationalizing a local and sustainable food system. These include a lack of mid-sized infrastructure serving local farmers, the domination of a rebate system of purchasing controlled by an oligopolistic foodservice sector, and embedded government support of export agriculture. This case study is an example of praxis, as the author was the founder of LFP, as well as an academic researcher and analyst.

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