237 research outputs found
Turbulent dispersion in cloud-topped boundary layers
No full textCompared to dry boundary layers, dispersion in cloud-topped boundary layers has received less attention. In this LES based numerical study we investigate the dispersion of a passive tracer in the form of Lagrangian particles for four kinds of atmospheric boundary layers: 1) a dry convective boundary layer (for reference), 2) a "smoke" cloud boundary layer in which the turbulence is driven by radiative cooling, 3) a stratocumulus topped boundary layer and 4) a shallow cumulus topped boundary layer. We show that the dispersion characteristics of the smoke cloud boundary layer as well as the stratocumulus situation can be well understood by borrowing concepts from previous studies of dispersion in the dry convective boundary layer. A general result is that the presence of clouds enhances mixing and dispersion – a notion that is not always reflected well in traditional parameterization models, in which clouds usually suppress dispersion by diminishing solar irradiance. The dispersion characteristics of a cumulus cloud layer turn out to be markedly different from the other three cases and the results can not be explained by only considering the well-known top-hat velocity distribution. To understand the surprising characteristics in the shallow cumulus layer, this case has been examined in more detail by 1) determining the velocity distribution conditioned on the distance to the nearest cloud and 2) accounting for the wavelike behaviour associated with the stratified dry environment.Infrastructures, Systems and ServicesTechnology, Policy and Managemen
Dynamics of subsiding shells in actively growing shallow cumulus clouds
No full textThe data in this upload has been used to generate the results published in
Nair, V., Heus, T., & van Reeuwijk, M. (2020). Dynamics of Subsiding Shells in Actively Growing Clouds with Vertical Updrafts, Journal of the Atmospheric Sciences, 77(4), 1353-1369
On the edge of a cloud
No full textCumulus clouds have since long been one of the greatest challenges in the atmospheric sciences. For a correct representation of clouds in weather and climate models, where they are the largest unknowns, a good understanding of interaction between cloud and environment is of prime importance. In this thesis, this problem is attacked with a combination of detailed numerical simulations and air-plane observations. While the traditional view states that air inside the cloud goes up, and all the air outside goes down in compensation, it is found here that on average, the air far away from the cloud hardly moves. Most of the compensating downward motion happens in the direct vicinity of the cloud, in a subsiding shell. This shell is shown to be due to cloudy air that evaporates, cools, and therefore sinks. Interaction between cloud and environment only happens through the buffer layer created by the shell. The shell is especially strong due to the horizontal mixing that is dominant in the cloud-environment interaction: processes that happen at the top of the cloud have little or no influence at lower levels. As a function of time, the cloud is not behaving like a continuous upward moving thermal, but consists of several bubble like pulses. Again, horizontal mixing is important in understanding the physics of these pulses.Applied Science
The International Classroom: How to transform an international educational practice into an Intercultural Classroom?
No full textNot peer reviewe
The International Classroom: How to transform an international educational practice into an Intercultural Classroom?
No full textNot peer reviewe
The implementation of a Lagrangian Particle Dispersion Model in Large Eddy Simulations of the Atmospheric Boundary Layer
No full textApplied SciencesKramers Laboratorium voor Fysische Technologi
The units of rate constants in chemical kinetics
No full textThis short article discusses the units of rate constants as used in chemical kinetics and, in particular, the aspect of non-integral powers of base units, which some might find unusual for units in the SI system. In many ways the fact that the units of the rate constants as usually defined convey information about the order of the reaction or reactions involved is very useful, but in other ways having the same (or at least very similar) quantity that has different units under different conditions is not so desirable. Furthermore, just as with chemical equilibrium constants, taking functions of the rate constant (such as the logarithm when representing the Arrhenius equation in the form ln kvs.1/T) needs special attention. Here we examine a possible alternative definition of rate constants in terms of an explicit ratio to the concentration standard state and although we acknowledge that this approach unlikely to be adopted by the community, it serves as a basis to discuss the meaning of rate constants
Precisie analyse van regelmatige netten
No full textPrecisie-analyse valt uiteen in precisie-beheersinq (het stellen van kriteria aan de precisie) en precisiebeschrijving (het met behulp van parameters samenvatten van de precisie). Beide kunnen zich toespitsen op of puntsbepaling ten behoeve van specifieke toepassingen , waarbij een a priori bekende deelfunctie aanwezig is, pf puntsbepaling ten behoeve van algemeen gebruik, waarbij verschillende toepassingen in de toekomst mogelijk moeten zijn. Precisie-analyse ten behoeve van specifieke toepassingen wordt hier buiten beschouwing gelaten omdat het de bij dit onderzoek onderzochte problemen niet kent.Civil Engineering and Geoscience
Bodembeweging in Zuid-Limburg ten gevolge van de mijnbouw: Treedt er in Voerendaal nog zakking op?
No full textCivil Engineering and Geoscience
Een analyse van de stralenbundelmethode
No full textHoofdstuk 1 behandelt een aantal algemene aspecten van de blind el ve^- effening. Definitie: driedimensionale puntsbepaling met gemeten fotocoördinaten m.b.v. een stereo- of monocomparator. Gegeven zijn de inwendige oriëntering van alle bundels en paspunten in een terrestrisch stelsel. Het mathematisch model is, dat fotopunt, projectiecentrum en objectpunt op één lijn liggen: collinariteitsvoorwaarde. De stralenbundelmethode wordt in Nederland niet produktief toegepast. Eén van de redenen is de beperkte toepassing: puntsgewijze uitwerking. De onafhankelijke modellentriangulatie is voor gangbare kaarteringsdoel— einden voldoende precies gebleken, zodat het vanuit dit gezichtspunt ook niet zinvol is om slechts de triangulering met de bundelmethode uit te voeren.Civil Engineering and Geoscience
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