A new large-eddy simulation model for simulating air flow and warm clouds above highly complex terrain. Part I: The dry model     

Daniel Reinert  Volkmar Wirth  Joachim Eichhorn  Walter-Georg Panhans 《Boundary-Layer Meteorology》2007,125(1):109-132

This paper presents the dry version of a new large-eddy simulation (LES) model, which is designed to simulate air flow and clouds above highly complex terrain. The model is three-dimensional and nonhydrostatic, and the governing equations are sound filtered by use of the anelastic approximation. A fractional step method is applied to solve the equations on a staggered Cartesian grid. Arbitrarily steep and complex orography can be accounted for through the method of viscous topography. The dynamical model core is validated by comparing the results for a spreading density current against a benchmark solution. The model accuracy is further assessed through the simulation of turbulent flow across a quasi two-dimensional ridge. The results are compared with wind-tunnel data. The method of viscous topography is not restricted to moderately sloped terrain. Compared to models using curvilinear grids, it allows this model to be applied to a much wider range of flows. This is illustrated through the simulation of an atmospheric boundary-layer flow over a surface mounted cube. The results show that the dry model version is able to accurately represent the complex flow in the vicinity of three-dimensional obstacles. It is concluded that the method of viscous topography was successfully implemented into a micrometeorological LES model. As will be shown in Part II, this allows the detailed study of clouds in highly complex terrain.  相似文献   

An analytic solution to the wave bottom boundary layer governing equation under arbitrary wave forcing     

Diane L. Foster  Ronald A. Guenther  Robert A. Holman 《Ocean Engineering》1999,26(7):48

Existing models of the wave bottom boundary layer have focused on the vertical and temporal dynamics associated with monochromatic forcing. While these models have made significant advances, they do not address the more complicated dynamics of random wave forcing, commonly found in natural environments such as the surf zone. In the closed form solution presented here, the eddy viscosity is assumed to vary temporally with the bed shear velocity and linearly with depth, however, the solution technique is valid for any eddy viscosity which is separable in time and space. A transformation of the cross-shore velocity to a distorted spatial domain leads to time-independent boundary conditions, allowing for the derivation of an analytic expression for the temporal and vertical structure of the cross-shore velocity under an arbitrary wave field. The model is compared with two independent laboratory observations. Model calculations of the bed shear velocity are in good agreement with laboratory measurements made by Jonsson and Carlsen (1976, J. Hydraul. Res., 14, 45–60). A variety of monochromatic, skewed, and asymmetric wave forcing conditions, characteristic of those found in the surf zone, are used to evaluate the relative effects on the bed shear. Because the temporal variation of the eddy viscosity is assumed proportional to the bottom shear, a weakly nonlinear interaction is created, and a fraction of the input monochromatic wave energy is transferred to the odd harmonics. For a monochromatic input wave, the ratio of the third harmonic of velocity at the bed to the first is <10%. However, for a skewed and asymmetric input wave, this ratio can be as large as 30% and is shown to increase with increasing root-mean-square input wave acceleration. The work done by the fluid on the bed is shown to be a maximum under purely skewed waves and is directed onshore. Under purely asymmetric waves, the work done is significantly smaller and directed offshore.  相似文献   

RCP 8.5��A scenario of comparatively high greenhouse gas emissions     

Keywan Riahi  Shilpa Rao  Volker Krey  Cheolhung Cho  Vadim Chirkov  Guenther Fischer  Georg Kindermann  Nebojsa Nakicenovic  Peter Rafaj 《Climatic change》2011,109(1-2):33-57

This paper summarizes the main characteristics of the RCP8.5 scenario. The RCP8.5 combines assumptions about high population and relatively slow income growth with modest rates of technological change and energy intensity improvements, leading in the long term to high energy demand and GHG emissions in absence of climate change policies. Compared to the total set of Representative Concentration Pathways (RCPs), RCP8.5 thus corresponds to the pathway with the highest greenhouse gas emissions. Using the IIASA Integrated Assessment Framework and the MESSAGE model for the development of the RCP8.5, we focus in this paper on two important extensions compared to earlier scenarios: 1) the development of spatially explicit air pollution projections, and 2) enhancements in the land-use and land-cover change projections. In addition, we explore scenario variants that use RCP8.5 as a baseline, and assume different degrees of greenhouse gas mitigation policies to reduce radiative forcing. Based on our modeling framework, we find it technically possible to limit forcing from RCP8.5 to lower levels comparable to the other RCPs (2.6 to 6 W/m²). Our scenario analysis further indicates that climate policy-induced changes of global energy supply and demand may lead to significant co-benefits for other policy priorities, such as local air pollution.  相似文献   

Efficient identification of exoplanetary transit candidates from SuperWASP light curves     

A. Collier Cameron  D. M. Wilson  R. G. West  L. Hebb  X.-B. Wang  S. Aigrain  F. Bouchy  D. J. Christian  W. I. Clarkson  B. Enoch  M. Esposito  E. Guenther  C. A. Haswell  G. Hébrard  C. Hellier  K. Horne  J. Irwin  S. R. Kane  B. Loeillet  T. A. Lister  P. Maxted  M. Mayor  C. Moutou  N. Parley  D. Pollacco  F. Pont  D. Queloz  R. Ryans  I. Skillen  R. A. Street  S. Udry  P. J. Wheatley 《Monthly notices of the Royal Astronomical Society》2007,380(3):1230-1244

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Three-dimensional convection simulations of the outer layers of the Sun using realistic physics     

F. J. Robinson  P. Demarque  L. H. Li  S. Sofia  Y.-C. Kim  K. L. Chan  D. B. Guenther 《Monthly notices of the Royal Astronomical Society》2003,340(3):923-936

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The power of low‐resolution spectroscopy: On the spectral classification of planet candidates in the ground‐based CoRoT follow‐up     

M. Ammler‐von Eiff  D. Sebastian  E. W. Guenther  B. Stecklum  J. Cabrera 《Astronomische Nachrichten》2015,336(2):134-144

Planetary transits detected by the CoRoT mission can be mimicked by a low‐mass star in orbit around a giant star. Spectral classification helps to identify the giant stars and also early‐type stars which are often excluded from further follow‐up. We study the potential and the limitations of low‐resolution spectroscopy to improve the photometric spectral types of CoRoT candidates. In particular, we want to study the influence of the signal‐to‐noise ratio (SNR) of the target spectrum in a quantitative way. We built an own template library and investigate whether a template library from the literature is able to reproduce the classifications. Including previous photometric estimates, we show how the additional spectroscopic information improves the constraints on spectral type. Low‐resolution spectroscopy (R ≈ 1000) of 42 CoRoT targets covering a wide range in SNR (1–437) and of 149 templates was obtained in 2012–2013 with the Nasmyth spectrograph at the Tautenburg 2 m telescope. Spectral types have been derived automatically by comparing with the observed template spectra. The classification has been repeated with the external CFLIB library. The spectral class obtained with the external library agrees within a few sub‐classes when the target spectrum has a SNR of about 100 at least. While the photometric spectral type can deviate by an entire spectral class, the photometric luminosity classification is as close as a spectroscopic classification with the external library. A low SNR of the target spectrum limits the attainable accuracy of classification more strongly than the use of external templates or photometry. Furthermore we found that low‐resolution reconnaissance spectroscopy ensures that good planet candidates are kept that would otherwise be discarded based on photometric spectral type alone. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Generalized least-squares adjustment,a timely but much neglected tool     

Heinrich Eichhorn 《Celestial Mechanics and Dynamical Astronomy》1993,56(1-2):337-351

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Nachweis von Huminstoffen mit der Alcianblaumethode     

R. Klckin  U. Eichhorn 《洁净——土壤、空气、水》1978,6(1):63-68

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Evaluating a New Deposition Velocity Module in the Noah Land-Surface Model     

U. Charusombat  D. Niyogi  A. Kumar  X. Wang  F. Chen  A. Guenther  A. Turnipseed  K. Alapaty 《Boundary-Layer Meteorology》2010,137(2):271-290

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Introduction and welcome     

Heinrich Eichhorn 《Astrophysics and Space Science》1991,177(1-2):1-2

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