Resolving frontal structures: on the payoff using a less diffusive but computationally more expensive advection scheme     

Knut Barthel  Ute Daewel  Dhanya Pushpadas  Corinna Schrum  Marius ?rthun  Henning Wehde 《Ocean Dynamics》2012,62(10-12):1457-1470

This article presents some advantages using a shape-preserving total variation diminishing (TVD) advection scheme in an ecosystem model. The superbee flux-limiter has been used to the second-order Lax–Wendroff advection scheme to make it TVD. We performed simulations for three shelf sea regions with different characteristic time scales, namely, the North Sea, the Barents Sea, and the Baltic Sea. To explore the advantages, we also performed reference runs with the much simpler and computationally cheaper upwind advection scheme. Frontal structures are much better resolved with the TVD scheme. The bottom salinity in the Baltic Sea stays at realistic values throughout the 10-year simulation with the TVD scheme, while with the upwind scheme, it drifts towards lower values and the permanent haline stratification in the Baltic is almost completely eroded within one seasonal cycle. Only when applying TVD for both the vertical and horizontal advections the model succeeded to preserve haline stratification in the decadal simulation. Lower trophic level patterns are far better reproduced with the TVD scheme, and for the estimated cod larval survival, the advantages seem to be even stronger. Simulations using the TVD-derived prey fields identified distinct regions such as Dogger Bank to favor potential larvae survival (PLS), which did not appear as particularly favorable in the upstream simulations. The TVD scheme needs about 25?% more time on the central processing unit (CPU) in case of a pure hydrodynamic setup with only two scalar state variables (Barents Sea application). The additional CPU time cost increases for a coupled physical–biological model application with a large number of state variables. However, this is more than compensated by all the advantages found, and, hence, we conclude that it is worthwhile to use the TVD scheme in our ecosystem model.  相似文献   

The Small Unmanned Meteorological Observer SUMO: Recent developments and applications of a micro-UAS for atmospheric boundary layer research   总被引：1，自引：0，他引：1  

Joachim Reuder  Marius O. Jonassen  Haraldur Ólafsson 《Acta Geophysica》2012,60(5):1454-1473

During the last 5 years, the Small Unmanned Meteorological Observer SUMO has been developed as a flexible tool for atmospheric boundary layer (ABL) research to be operated as sounding system for the lowest 4 km of the atmosphere. Recently two main technical improvements have been accomplished. The integration of an inertial measurement unit (IMU) into the Paparazzi autopilot system has expanded the environmental conditions for SUMO operation. The implementation of a 5-hole probe for determining the 3D flow vector with 100 Hz resolution and a faster temperature sensor has enhanced the measurement capabilities.  相似文献   

Estimating aquifer channel recharge using optical data interpretation     

Walter GR  Necsoiu M  McGinnis R 《Ground water》2012,50(1):68-76

Recharge through intermittent and ephemeral stream channels is believed to be a primary aquifer recharge process in arid and semiarid environments. The intermittent nature of precipitation and flow events in these channels, and their often remote locations, makes direct flow and loss measurements difficult and expensive. Airborne and satellite optical images were interpreted to evaluate aquifer recharge due to stream losses on the Frio River in south-central Texas. Losses in the Frio River are believed to be a major contributor of recharge to the Edwards Aquifer. The results of this work indicate that interpretation of readily available remote sensing optical images can offer important insights into the spatial distribution of aquifer recharge from losing streams. In cases where upstream gauging data are available, simple visual analysis of the length of the flowing reach downstream from the gauging station can be used to estimate channel losses. In the case of the Frio River, the rate of channel loss estimated from the length of the flowing reach at low flows was about half of the loss rate calculated from in-stream gain-loss measurements. Analysis based on water-surface width and channel slope indicated that losses were mainly in a reach downstream of the mapped recharge zone. The analysis based on water-surface width, however, did not indicate that this method could yield accurate estimates of actual flow in pool and riffle streams, such as the Frio River and similar rivers draining the Edwards Plateau.  相似文献   

Response of braiding channel morphodynamics to peak discharge changes in the Upper Yellow River          下载免费PDF全文

Filip Schuurman  Wanquan Ta  Sander Post  Marius Sokolewicz  Marcela Busnelli  Maarten Kleinhans 《地球表面变化过程与地形》2018,43(8):1648-1662

The braiding intensity and dynamics in large braiding rivers are well known to depend on peak discharges, but the response in braiding and channel–floodplain transformations to changes in discharge regime are poorly known. This modelling study addresses the morphodynamic effects of increasing annual peak discharges in braiding rivers. The study site is a braiding reach of the Upper Yellow River. We estimated the effects on the larger‐scale channel pattern, and on the smaller‐scale bars, channel branches and floodplains. Furthermore, we determined the sensitivity of the channel pattern to model input parameters. The results showed that the dominant effect of a higher peak discharge is the development of chute channels on the floodplains, formed by connecting head‐cut channels and avulsive channels. Widening of the main channel by bank erosion was found to be less dominant. In addition, sedimentation on the bars and floodplains increased with increasing peak discharge. The model results also showed that the modelled channel pattern is especially sensitive to parametrization of the bed slope effect, whereas the effect of median grain size was found to be relatively small. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

The end of the Great Khersonian Drying of Eurasia: Magnetostratigraphic dating of the Maeotian transgression in the Eastern Paratethys     

Dan Valentin Palcu  Iuliana Vasiliev  Marius Stoica  Wout Krijgsman 《Basin Research》2019,31(1):33-58

Central Eurasia underwent significant palaeoclimatic and palaeogeographic transformations during the middle to late Miocene. The open marine ecosystems of the Langhian and Serravallian seas progressively collapsed and were replaced in the Tortonian by large endorheic lakes. These lakes experienced major fluctuations in water level, directly reflecting the palaeoclimatic conditions of the region. An extreme lowstand of the Eastern Paratethys lake (?300 m) during the regional Khersonian stage reveals a period of intensely dry conditions in Central Eurasia causing a fragmentation of the Paratethys region. This period of “Great Drying” ended by a climate change towards more humid conditions at the base of the Maeotian stage, resulting in a large transgressive event that reconnected most of the Paratethyan basins. The absence of a robust time frame for the Khersonian–Maeotian interval hampers a direct correlation with the global records and complicates a thorough understanding of the underlying mechanisms. Here we present a new chronostratigraphic framework for the Khersonian and Maeotian deposits of the Dacian Basin of Romania, based on integrated magneto‐biostratigraphic studies on long and continuous sedimentary successions. We show the dry climate conditions in the Khersonian start at 8.6–8.4 Ma. The Khersonian/Maeotian transition is dated at 7.65–7.5 Ma, several million years younger than previous estimates. The Maeotian transgression occurs later (7.5–7.4 Ma) in more marginal and shallower basins, in agreement with the time transgressive character of the flooding. In addition, we date a sudden water level drop of the Eastern Paratethys lake, the Intra‐Maeotian Event (IME), at 6.9 Ma, and hypothesize that this corresponds to a reconnection phase with the Aegean basin of the Mediterranean. Finally, we discuss the potential mechanisms explaining the particularities of the Maeotian transgression and conclude that the low salinity and the seemingly “marine influxes” most likely correspond to episodes of intrabasinal mixing in a gradual and pulsating transgressive setting.  相似文献   

Modeling propensity to move after job change using event history analysis and temporal GIS     

Marie-Hélène Vandersmissen  Anne-Marie Séguin  Marius Thériault  Christophe Claramunt 《Journal of Geographical Systems》2009,11(1):37-65

The research presented in this paper analyzes the emergent residential behaviors of individual actors in a context of profound social changes in the work sphere. It incorporates a long-term view in the analysis of the relationships between social changes in the work sphere and these behaviors. The general hypothesis is that social changes produce complex changes in the long-term dynamics of residential location behavior. More precisely, the objective of this paper is to estimate the propensity for professional workers to move house after a change of workplace. Our analysis draws on data from a biographical survey using a retrospective questionnaire that enables a posteriori reconstitution of the familial, professional and residential lifelines of professional workers since their departure from their parents’ home. The survey was conducted in 1996 in the Quebec City Metropolitan Area, which, much like other Canadian cities, has experienced a substantial increase in “unstable” work, even for professionals. The approach is based on event history analysis, a Temporal Geographic Information System and exploratory spatial analysis of model’s residuals. Results indicate that 48.9% of respondents moved after a job change and that the most important factors influencing the propensity to move house after a job change are home tenure (for lone adults as for couple) and number of children (for couples only). We also found that moving is associated with changing neighborhood for owners while tenants or co-tenants tend to stay in the same neighborhood. The probability of moving 1 year after a job change is 0.10 for lone adults and couples while after 2 years, the household structure seems to have an impact: the probability increased to 0.23 for lone adults and to 0.21 for couples. The outcome of this research contributes to furthering our understanding of a familial decision (to move) following a professional event (change of job), controlling for household structure, familial, professional and spatial contexts.

Marius ThériaultEmail:

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Atmospheric profiling with the UAS SUMO: a new perspective for the evaluation of fine-scale atmospheric models   总被引：1，自引：0，他引：1  

Stephanie Mayer  Anne Sandvik  Marius O. Jonassen  Joachim Reuder 《Meteorology and Atmospheric Physics》2012,116(1-2):15-26

For the first time, unmanned aerial system measurements collected by the small unmanned meteorological observer (SUMO) are used to evaluate atmospheric boundary layer (ABL) parameterization schemes embedded in the Advanced Weather Research and Forecasting model (AR-WRF). Observation sites were located in the vicinity of the almost idealized shaped mountain Hofsj?kull, Central Iceland. SUMO profiles provided temperature, relative humidity and wind data to maximum heights of 3?km above ground. Two cases are investigated, one with calm wind conditions and development of a convective ABL and one with moderate winds and gravity waves over Hofsj?kull. For the high-resolution simulation with AR-WRF, three two-way nested domains are chosen with a grid size of 9, 3 and 1?km. During its first meteorological test, SUMO has proved its great value for the investigation of the diurnal evolution of the ABL and the identification of mesoscale features residing above the ABL, such as subsidence.  相似文献   

Nowcasting sunshine number using logistic modeling     

Marek Brabec  Viorel Badescu  Marius Paulescu 《Meteorology and Atmospheric Physics》2013,120(1-2):61-71

In this paper, we present a formalized approach to statistical modeling of the sunshine number, binary indicator of whether the Sun is covered by clouds introduced previously by Badescu (Theor Appl Climatol 72:127–136, 2002). Our statistical approach is based on Markov chain and logistic regression and yields fully specified probability models that are relatively easily identified (and their unknown parameters estimated) from a set of empirical data (observed sunshine number and sunshine stability number series). We discuss general structure of the model and its advantages, demonstrate its performance on real data and compare its results to classical ARIMA approach as to a competitor. Since the model parameters have clear interpretation, we also illustrate how, e.g., their inter-seasonal stability can be tested. We conclude with an outlook to future developments oriented to construction of models allowing for practically desirable smooth transition between data observed with different frequencies and with a short discussion of technical problems that such a goal brings.  相似文献   

Impact of Assimilation of Radiosonde and UAV Observations from the Southern Ocean in the Polar WRF Model     

Qizhen SUN  Timo VIHMA  Marius OJONASSEN  Zhanhai ZHANG 《大气科学进展》2020,37(5):441-454

Weather forecasting in the Southern Ocean and Antarctica is a challenge above all due to the rarity of observations to be assimilated in numerical weather prediction(NWP)models.As observations are expensive and logistically challenging,it is important to evaluate the benefit that additional observations could bring to NWP.Atmospheric soundings applying unmanned aerial vehicles(UAVs)have a large potential to supplement conventional radiosonde sounding observations.Here,we applied UAV and radiosonde sounding observations from an RV Polarstern cruise in the ice-covered Weddell Sea in austral winter 2013 to evaluate the impact of their assimilation in the Polar version of the Weather Research and Forecasting(Polar WRF)model.Our experiments revealed small to moderate impacts of radiosonde and UAV data assimilation.In any case,the assimilation of sounding data from both radiosondes and UAVs improved the analyses of air temperature,wind speed,and humidity at the observation site for most of the time.Further,the impact on the results of 5-day-long Polar WRF experiments was often felt over distances of at least 300 km from the observation site.All experiments succeeded in capturing the main features of the evolution of near-surface variables,but the effects of data assimilation varied between different cases.Due to the limited vertical extent of the UAV observations,the impact of their assimilation was limited to the lowermost 1?2-km layer,and assimilation of radiosonde data was more beneficial for modeled sea level pressure and near-surface wind speed.  相似文献   

Assessing the use of global land cover data for guiding large area population distribution modelling     

Catherine Linard  Marius Gilbert  Andrew J. Tatem 《GeoJournal》2011,76(5):525-538

Gridded population distribution data are finding increasing use in a wide range of fields, including resource allocation, disease burden estimation and climate change impact assessment. Land cover information can be used in combination with detailed settlement extents to redistribute aggregated census counts to improve the accuracy of national-scale gridded population data. In East Africa, such analyses have been done using regional land cover data, thus restricting application of the approach to this region. If gridded population data are to be improved across Africa, an alternative, consistent and comparable source of land cover data is required. Here these analyses were repeated for Kenya using four continent-wide land cover datasets combined with detailed settlement extents and accuracies were assessed against detailed census data. The aim was to identify the large area land cover dataset that, combined with detailed settlement extents, produce the most accurate population distribution data. The effectiveness of the population distribution modelling procedures in the absence of high resolution census data was evaluated, as was the extrapolation ability of population densities between different regions. Results showed that the use of the GlobCover dataset refined with detailed settlement extents provided significantly more accurate gridded population data compared to the use of refined AVHRR-derived, MODIS-derived and GLC2000 land cover datasets. This study supports the hypothesis that land cover information is important for improving population distribution model accuracies, particularly in countries where only coarse resolution census data are available. Obtaining high resolution census data must however remain the priority. With its higher spatial resolution and its more recent data acquisition, the GlobCover dataset was found as the most valuable resource to use in combination with detailed settlement extents for the production of gridded population datasets across large areas.  相似文献