343 research outputs found
CMIP6 Models Underestimate the Holton‐Tan Effect
No full textThis is data from four of the experiments that we use to learn about the teleconnections forced by the Quasi-Biennial Oscillation (QBO). Details and results from each data set can be found in the submitted manuscript 'CMIP6 models underestimate the Holton-Tan effect' or in the accepted manuscript 'Variation in the Holton-Tan effect by longitude' (https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/qj.3993).
A blurb of metadata has been added to each of the netcdf files explaining what is in the data set and briefly how it was made. For further questions, please email [email protected]
Characteristics of colliding sea breeze gravity current fronts: a laboratory study
No full textAuthor Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Quarterly Journal of the Royal Meteorological Society 143 (2017): 1434–1441, doi:10.1002/qj.3015.Sea and land breeze circulations driven by surface temperature differences between
land and sea often evolve into gravity currents with sharp fronts. Along narrow
peninsulas, islands and enclosed seas, sea/land breeze fronts from opposing shorelines
may converge and collide and may initiate deep convection and heavy precipitation.
Here we investigate the collision of two sea breeze gravity current fronts in an
analogue laboratory setting. We examine these collisions by means of ‘lock-exchange’
experiments in a rectangular channel. The effects of differences in gravity current
density and height are studied. Upon collision, a sharp front separating the two currents
develops. For symmetric collisions (the same current densities and heights) this front is
vertical and stationary. For asymmetric collisions (density differences, similar heights)
the front is tilted, changes shape in time and propagates in the same direction as the
heavier current before the collision. Both symmetric and asymmetric collisions lead to
upward displacement of fluid from the gravity currents and mixing along the plane
of contact. The amount of mixing along the collision front decreases with asymmetry.
Height differences impact post-collision horizontal propagation: there is significant
propagation in the same direction as the higher current before collision, independent
of density differences. Collisions of two gravity current fronts force sustained ascending
motions which increase the potential for deep convection. From our experiments we
conclude that this potential is larger in stationary collision fronts from symmetric
sea breeze collisions than in propagating collision fronts from asymmetric sea breeze
collisions.National Science Foundation Grant Number: OCE-0824636;
Office of Naval Research Grant Number: N00014-09-1-0844;
National Aeronautics and Space Administration Grant Number: NASA NNX14A078
Spin correlations in top quark pair production near threshold at the e(+)e(-) linear collider
No full textWe investigate the spin correlations in top quark pair production near the threshold at the e(+)e(-) linear collider. Comparing with the results above the threshold region, we find that near the threshold region the off-diagonal basis, the optimized decomposition of the top quark spins above the threshold region, does not exist, and the beamline basis is the optimal basis, in which there are the dominant spin components: the up-down (UD) component for e(L)- e(+) scattering and the down-up (DU) component for e(R)(-)e(+) scattering can make up more than 50% of the total cross section, respectively.Physics, MultidisciplinarySCI(E)中国科学引文数据库(CSCD)0ARTICLE6687-6924
Joint Probability Distribution and the Minimum of a Set of Normalized Random Variables
No full textAbstractSuppose that n types of components M1, M2… Mn are combined to form and integrated object I and suppose that y units of the integrated object are required to be formed. Assuming that not all components can be used in forming the integrated objects, let qj be the percentage of usable components of the jth type, a random variable having a probability density function fj(qj). Let wj be the normalized random variable obtained from qj by wj = qj/μj, where μj is the expected value of qj. Consider the random variable W=Min{wj, 1 ≤ j ≤ n}. This paper describes the joint probability distribution of the set of the normalized random variables and determines the probability distribution of the minimum W of this set. The expected value of W is key to determining the number of components needed to form the y integrated objects. A special case is presented where the percentages of usable components are uniformly distributed. The problem is applied to a production model
Producción de bosones de Higgs cargados en la colisión inelástica profunda pp (LHC)
No full text“En este trabajo estamos interesados en calcular la producción de bosones de Higgs cargados en la dispersión inelástica profunda protón-protón (pp) en el contexto del Modelo de Dos Dobletes de Higgs tipo-III a energías del LHC (14 TeV), esto es, p + p −→ H± + X, utilizando el Modelo de Partones. Específicamente, calculamos las secciones eficaces diferenciales de los procesos involucrados, qi + qj → H±x + X con x = W±, Z0 , H±, γ, g, q, ϕ0 , así como la sección eficaz diferencial del proceso qi+qj → H±. Además, calculamos la sección eficaz hadrónica total de la producción directa p + p → H± + X, tanto analítica como numéricamente, comparando los resultados con la sección eficaz de la producción directa del bosón W+. Se presenta el cálculo analítico y numérico de estas, considerando diferentes regiones del espacio de parámetros (mH+ , tan β, χ˜ u,d). Finalmente, se estudian los procesos con cambio de sabor que aparecen en la producción directa del bosón H+”
An evaluation of surface meteorology and fluxes over the Iceland and Greenland Seas in ERA5 reanalysis: the impact of sea ice distribution
No full text© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Renfrew, I. A., Barrell, C., Elvidge, A. D., Brooke, J. K., Duscha, C., King, J. C., Kristiansen, J., Cope, T. L., Moore, G. W. K., Pickart, R. S., Reuder, J., Sandu, I., Sergeev, D., Terpstra, A., Vage, K., & Weiss, A. An evaluation of surface meteorology and fluxes over the Iceland and Greenland Seas in ERA5 reanalysis: the impact of sea ice distribution. Quarterly Journal of the Royal Meteorological Society, (2020): 1-22, doi:10.1002/qj.3941.The Iceland and Greenland Seas are a crucial region for the climate system, being the headwaters of the lower limb of the Atlantic Meridional Overturning Circulation. Investigating the atmosphere–ocean–ice processes in this region often necessitates the use of meteorological reanalyses—a representation of the atmospheric state based on the assimilation of observations into a numerical weather prediction system. Knowing the quality of reanalysis products is vital for their proper use. Here we evaluate the surface‐layer meteorology and surface turbulent fluxes in winter and spring for the latest reanalysis from the European Centre for Medium‐Range Weather Forecasts, i.e., ERA5. In situ observations from a meteorological buoy, a research vessel, and a research aircraft during the Iceland–Greenland Seas Project provide unparalleled coverage of this climatically important region. The observations are independent of ERA5. They allow a comprehensive evaluation of the surface meteorology and fluxes of these subpolar seas and, for the first time, a specific focus on the marginal ice zone. Over the ice‐free ocean, ERA5 generally compares well to the observations of surface‐layer meteorology and turbulent fluxes. However, over the marginal ice zone, the correspondence is noticeably less accurate: for example, the root‐mean‐square errors are significantly higher for surface temperature, wind speed, and surface sensible heat flux. The primary reason for the difference in reanalysis quality is an overly smooth sea‐ice distribution in the surface boundary conditions used in ERA5. Particularly over the marginal ice zone, unrepresented variability and uncertainties in how to parameterize surface exchange compromise the quality of the reanalyses. A parallel evaluation of higher‐resolution forecast fields from the Met Office's Unified Model corroborates these findings.This study was part of the Iceland Greenland Seas Project. Funding was from the NERC AFIS grant (NE/N009754/1), the ALERTNESS (Advanced models and weather prediction in the Arctic: enhanced capacity from observations and polar process representations) project (Research Council of Norway project number 280573), the Trond Mohn Foundation (BFS2016REK01), and the National Science Foundation grant OCE‐1558742. The Leosphere WindCube v2 and the Wavescan buoy are part of the OBLO (Offshore Boundary Layer Observatory) infrastructure funded by the Research Council of Norway (project number 227777)
Composite hodographs and inertial oscillations in the nocturnal boundary layer
No full textIn this work the dynamic behaviour of the wind in the nocturnal boundary layer is studied, with a particular focus on systematic behaviour of the near-surface wind. Recently, an extension of the well-known Blackadar model for frictionless inertial oscillations above the nocturnal boundary layer was proposed by Van deWiel et al., which accounts for frictional effects within the nocturnal boundary layer. It appears that the nocturnal wind velocity profile tends to perform an inertial oscillation around an equilibrium wind profile, rather than around the geostrophic wind vector (as in the Blackadar model). In the present studywe propose the concept of ‘composite hodographs’ to evaluate the ideas and assumptions of the aforementioned analytical model. Composite hodographs are constructed based on a large observational dataset from the Cabauw observatory. For comparison and deeper analysis, this method is also applied to single-column model simulations that represent the same dataset. From this, it is shown that winds in the middle and upper part of the nocturnal boundary layer closely follow the dynamics predicted by the model by Van de Wiel et al. In contrast, the near-surface wind shows more complex behaviour that can be described by two different stages: (1) a decelerating phase where the wind decreases rapidly in magnitude due to enlarged stress divergence in the transition period near sunset (an aspect not included in the analytical model), and (2) a regular type of inertial oscillation, but with relatively small amplitude as compared to the oscillations in the middle and upper parts of the nocturnal boundary laye
Displacement of a two-dimensional immiscible droplet in a channel
No full textWe used the lattice Boltzmann method to study the displacement of a two-dimensional immiscible droplet subject to gravitational forces in a channel. The dynamic behavior of the droplet is shown, and the effects of the contact angle, Bond number (the ratio of gravitational to surface forces), droplet size, and density and viscosity ratios of the droplet to the displacing fluid are investigated. For the case of a contact angle less than or equal to 90degrees, at a very small Bond number, the wet length between the droplet and the wall decreases with time until a steady shape is reached. When the Bond number is large enough, the droplet first spreads and then shrinks along the wall before it reaches steady state. Whether the steady-state value of the wet length is greater or less than the static value depends on the Bond number. When the Bond number exceeds a critical value, a small portion of the droplet pinches off from the rest of the droplet for a contact angle less than 90degrees; a larger portion of the droplet is entrained into the bulk for a contact angle equal to 90degrees. For the nonwetting case, however, for any Bond number less than a critical value, the droplet shrinks along the wall from its static state until reaching the steady state. For any Bond number above the critical value, the droplet completely detaches from the wall. Either increasing the contact angle or viscosity ratio or decreasing the density ratio decreases the critical Bond number. Increasing the droplet size increases the critical Bond number while it decreases the critical capillary number. (C) 2002 American Institute of Physics.MechanicsPhysics, Fluids & PlasmasSCI(E)101ARTICLE93203-32141
Characteristics of inertial gravity waves over Southern Africa as simulated with CAM-EULAG
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