An Urban Surface Exchange Parameterisation for Mesoscale Models   总被引：9，自引：11，他引：9  

Alberto Martilli  Alain Clappier  Mathias W. Rotach 《Boundary-Layer Meteorology》2002,104(2):261-304

A scheme to represent the impact of urban buildings on airflow in mesoscale atmospheric models is presented. In the scheme, the buildings are not explicitly resolved, but their effects on the grid-averaged variables are parameterised. An urban quarter is characterised by a horizontal building size, a street canyon width and a building density as a function of height. The module computes the impact of the horizontal (roof and canyon floor) and vertical (walls) surfaces on the wind speed, temperature and turbulent kinetic energy. The computation of the shortwave and longwave radiation, needed to compute the temperature of the urban surfaces, takes into account the shadowing and radiation trapping effects induced by the urban canyons. The computation of the turbulent length scales in the TKE equation is also modified to take into account the presence of the buildings.The parameterisation is introduced into a mesoscale model and tested in a bidimensional case of a city over flat terrain. The new parameterisation is shown to be able to reproduce the most important features observed in urban areas better than the traditional approach which is based only on the modification of the roughness length, thereby retaining the Monin–Obukhov similarity theory. The new surface exchange parameterisation is furthermore shown to have a strong impact on the dispersion characteristics of air pollutants in urban areas.  相似文献   

30-year response to damming of a Mediterranean river in California,USA     

Fernando Magdaleno  Carlo Donadio  G. Mathias Kondolf 《自然地理学》2018,39(3):197-215

Dry Creek is a major tributary of the Russian River in Northern California (USA) that has experienced hydrologic and morphologic alterations after the closure of Warm Springs Dam in 1983. Our objective is to present a detailed diagnosis of the modification of the creek’s flow and sediment regimes, and interpret the alterations regarding the ecomorphologic evolution previously observed in the creek. Statistical analysis of the river’s flow and sediment series indicates that dam operation has had significant impacts on the magnitude and frequency of occurrence of the highest floods, and the magnitude, variability, and duration of low and very low flows. Similarly, sediment concentration and discharge have also experienced major alterations. Loss of habitat complexity for native flora and fauna (especially endangered salmonids), channel incision, and vegetation encroachment are some of the negative trends found for the creek over the last 30 years, since river regulation began. We discuss the present dynamics of the river and propose, on that basis, the improvement of its hydromorphic functioning as part of future large-scale restoration initiatives.  相似文献   

A novel model and estimation method for the individual random component of earthquake ground-motion relations     

Mathias Raschke 《Journal of Seismology》2017,21(1):21-34

In this paper, I introduce a novel approach to modelling the individual random component (also called the intra-event uncertainty) of a ground-motion relation (GMR), as well as a novel approach to estimating the corresponding parameters. In essence, I contend that the individual random component is reproduced adequately by a simple stochastic mechanism of random impulses acting in the horizontal plane, with random directions. The random number of impulses was Poisson distributed. The parameters of the model were estimated according to a proposal by Raschke J Seismol 17(4):1157–1182, (2013a), with the sample of random difference ξ?=?ln(Y ₁ )-ln(Y ₂ ), in which Y ₁ and Y ₂ are the horizontal components of local ground-motion intensity. Any GMR element was eliminated by subtraction, except the individual random components. In the estimation procedure, the distribution of difference ξ was approximated by combining a large Monte Carlo simulated sample and Kernel smoothing. The estimated model satisfactorily fitted the difference ξ of the sample of peak ground accelerations, and the variance of the individual random components was considerably smaller than that of conventional GMRs. In addition, the dependence of variance on the epicentre distance was considered; however, a dependence of variance on the magnitude was not detected. Finally, the influence of the novel model and the corresponding approximations on PSHA was researched. The applied approximations of distribution of the individual random component were satisfactory for the researched example of PSHA.  相似文献   

Fish assemblages in Tanzanian mangrove creek systems influenced by solar salt farm constructions     

Augustine W. Mwandya  Martin Gullström  Marcus C. Öhman  Mathias H. Andersson  Yunus D. Mgaya 《Estuarine, Coastal and Shelf Science》2009

Deforestation of mangrove forests is common occurrence worldwide. We examined fish assemblage composition in three mangrove creek systems in Tanzania (East Africa), including two creeks where the upper parts were partly clear-cut of mangrove forest due to the construction of solar salt farms, and one creek with undisturbed mangrove forest. Fish were caught monthly for one year using a seine net (each haul covering 170 m²) within three locations in each creek, i.e. at the upper, intermediate and lower reaches. Density, biomass and species number of fish were lower in the upper deforested sites compared to the mangrove-fringed sites at the intermediate and lower parts in the two creeks affected by deforestation, whereas there were no differences among the three sites in the undisturbed mangrove creek system. In addition, multivariate analyses showed that the structure of fish assemblages varied between forested and clear-cut sites within the two disturbed creeks, but not within the undisturbed creek. Across the season, we found no significant differences except for a tendency of a minor increase in fish densities during the rainy season. At least 75% of the fishes were juveniles and of commercial interest for coastal fisheries and/or aquaculture. Mugil cephalus, Gerres oyena and Chanos chanos were the most abundant species in the forested sites. The dominant species in the clear-cut areas were M. cephalus and Elops machnata, which were both found in relatively low abundances compared to the undisturbed areas. The conversion of mangrove forests into solar salt farms not only altered fish assemblage composition, but also water and sediment conditions. In comparison with undisturbed areas, the clear-cut sites showed higher salinity, water temperature as well as organic matter and chlorophyll a in the sediments. Our results suggest that mangrove habitat loss and changes in environmental conditions caused by salt farm developments will decrease fish densities, biomass and species numbers as well as alter the overall fish assemblage composition in the salt farm area but not downstream in the creek.  相似文献   

Quality of reprocessed GPS satellite orbits   总被引：4，自引：2，他引：2  

Peter Steigenberger  Markus Rothacher  Mathias Fritsche  Axel Rülke  Reinhard Dietrich 《Journal of Geodesy》2009,83(3-4):241-248

High-precision Global Positioning System (GPS) satellite orbits are one of the core products of the International GNSS Service (IGS). Since the establishment of the IGS in 1994, the quality and consistency of the IGS orbits has steadily been improved by advances in the modeling of GPS observations. However, due to these model improvements and reference frame changes, the time series of operational orbits are inhomogeneous and inconsistent. This problem can only be overcome by a complete reprocessing starting with the raw observation data. The quality of reprocessed GPS satellite orbits for the time period 1994–2005 will be assessed in this paper. Orbit fits show that the internal consistency of the orbits could be improved by a factor of about two in the early years. Comparisons with the operational IGS orbits show clear discontinuities whenever the reference frame was changed by the IGS. The independent validation with Satellite Laser Ranging (SLR) residuals shows an improvement of up to 30% whereas a systematic bias of 5 cm still persists.  相似文献   

Asteroseismology and interferometry     

M. S. Cunha  C. Aerts  J. Christensen-Dalsgaard  A. Baglin  L. Bigot  T. M. Brown  C. Catala  O. L. Creevey  A. Domiciano de Souza  P. Eggenberger  P. J. V. Garcia  F. Grundahl  P. Kervella  D. W. Kurtz  P. Mathias  A. Miglio  M. J. P. F. G. Monteiro  G. Perrin  F. P. Pijpers  D. Pourbaix  A. Quirrenbach  K. Rousselet-Perraut  T. C. Teixeira  F. Thévenin  M. J. Thompson 《Astronomy and Astrophysics Review》2007,14(3-4):217-360

Asteroseismology provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Recent developments, including the first systematic studies of solar-like pulsators, have boosted the impact of this field of research within astrophysics and have led to a significant increase in the size of the research community. In the present paper we start by reviewing the basic observational and theoretical properties of classical and solar-like pulsators and present results from some of the most recent and outstanding studies of these stars. We centre our review on those classes of pulsators for which interferometric studies are expected to provide a significant input. We discuss current limitations to asteroseismic studies, including difficulties in mode identification and in the accurate determination of global parameters of pulsating stars, and, after a brief review of those aspects of interferometry that are most relevant in this context, anticipate how interferometric observations may contribute to overcome these limitations. Moreover, we present results of recent pilot studies of pulsating stars involving both asteroseismic and interferometric constraints and look into the future, summarizing ongoing efforts concerning the development of future instruments and satellite missions which are expected to have an impact in this field of research.  相似文献   

Simulation Of Urban-Scale Dispersion Using A Lagrangian Stochastic Dispersion Model   总被引：4，自引：1，他引：3  

Mathias W. Rotach 《Boundary-Layer Meteorology》2001,99(3):379-410

  相似文献   

Current state and future challenges in stable isotope applications of the tropical hydrologic cycle (Invited Commentary)          下载免费PDF全文

Mathias Vuille 《水文研究》2018,32(9):1313-1317

  相似文献   

Climate change effects on snow melt and discharge of a partly glacierized watershed in Central Switzerland (SoilTrec Critical Zone Observatory)     

Florian Kobierska  Tobias Jonas  Jan Magnusson  Massimiliano Zappa  Mathias Bavay  Thomas Bosshard  Frank Paul  Stefano M. Bernasconi 《Applied Geochemistry》2011

A comprehensive hydrological modeling study in the drainage area of a hydropower reservoir in central Switzerland is presented. Two models were tested to reproduce the measured discharge dynamics: (1) a detailed energy-balance model (ALPINE3D) primarily designed for snow simulations; (2) a conceptual runoff model system (PREVAH), including a distributed temperature-index snow and ice melt model. Considerable effort was put into distributing available meteorological station data to the model grids as forcing data. The recent EU regional climate modeling initiative ENSEMBLES provided up-to-date climate predictions for two 30-a periods in mid and late 21st century. These were used to estimate evolutions in the water supply of the hydropower reservoir in response to expected climate changes. The simulations suggest a shift of spring peak-flow by almost two months for the end of the century. Warmer winter temperatures will cause higher winter base-flow. Due to glacier retreat, late-summer flow will decrease at the end of the century.  相似文献   

Impact of chemical and meteorological boundary and initial conditions on air quality modeling: WRF-Chem sensitivity evaluation for a European domain     

Mathias Ritter  Mathias D. Müller  Oriol Jorba  Eberhard Parlow  L.-J. Sally Liu 《Meteorology and Atmospheric Physics》2013,119(1-2):59-70

This study evaluates the impact of different chemical and meteorological boundary and initial conditions on the state-of-the-art Weather Research and Forecasting (WRF) model with its chemistry extension (WRF-Chem). The evaluation is done for July 2005 with 50 km horizontal resolution. The effect of monthly mean chemical boundary conditions derived from the chemical transport model LMDZ-INCA on WRF-Chem is evaluated against the effect of the preset idealized profiles. Likewise, the impact of different meteorological initial and boundary conditions (GFS and Reanalysis II) on the model is evaluated. Pearson correlation coefficient between these different runs range from 0.96 to 1.00. Exceptions exists for chemical boundary conditions on ozone and for meteorological boundary conditions on PM₁₀, where coefficients of 0.90 were obtained. Best results were achieved with boundary and initial conditions from LMDZ-INCA and GFS. Overall, the European simulations show encouraging results for observed air pollutant, with ozone being the most and PM₁₀ being the least satisfying.  相似文献