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   

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   

Sensitivity of last glacial maximum climate to sea ice conditions in the Nordic Seas     

Øyvind Byrkjedal  Nils Gunnar Kvamstø  Marius Meland  Eystein Jansen 《Climate Dynamics》2006,26(5):473-487

Published reconstructions of last glacial maximum (LGM) sea surface temperatures and sea ice extent differ significantly. We here test the sensitivity of simulated North Atlantic climates to two different reconstructions by using these reconstructions as boundary conditions for model experiments. An atmospheric general circulation model has been used to perform two simulations of the (LGM) and a modern-day control simulation. Standard (CLIMAP) reconstructions of sea ice and sea surface temperatures have been used for the first simulation, and a set of new reconstructions in the Nordic Seas/Northern Atlantic have been used for the second experiment. The new reconstruction is based on 158 core samples, and represents ice-free conditions during summer in the Nordic Seas, with accordingly warmer sea surface temperatures and less extensive sea ice during winter as well. The simulated glacial climate is globally 5.7 K colder than modern day, with the largest changes at mid and high latitudes. Due to more intense Hadley circulation, the precipitation at lower latitudes has increased in the simulations of the LGM. Relative to the simulation with the standard CLIMAP reconstructions, reduction of the sea ice in the North Atlantic gives positive local responses in temperature, precipitation and reduction of the sea level pressure. Only very weak signatures of the wintertime Icelandic Low occur when the standard CLIMAP sea surface temperature reconstruction is used as the lower boundary condition in LGM. With reduced sea ice conditions in the Nordic Seas, the Icelandic Low becomes more intense and closer to its present structure. This indicates that thermal forcing is an important factor in determining the strength and position of the Icelandic Low. The Arctic Oscillation is the most dominant large scale variability feature on the Northern Hemisphere in modern day winter climate. In the simulation of the LGM with extensive sea ice this pattern is significantly changed and represents no systematic large scale variability over the North Atlantic. Reduction of the North Atlantic sea ice extent leads to stronger variability in monthly mean sea level pressure in winter. The synoptic variability appears at a lower level in the simulation when standard reconstructions of the sea surface in the LGM are used. A closer inspection of storm tracks in this model experiment shows that that the synoptic lows follow a narrow band along the ice edge during winter. The trajectories of synoptic lows are not constrained to the sea ice edge to the same degree when the sea ice extent is reduced. Seasonally open waters in the Nordic Seas in the new reconstruction apparently act as a moisture source, consistent with the current understanding of the rapid growth of the Fennoscandian and Barents Ice Sheets, during the LGM. The signal from the intensified thermal forcing in the North Atlantic in Boreal winter is carried zonally by upper tropospheric waves, and thus generates non-local responses to the changed sea ice cover.  相似文献   

Analyzing Changes in Urban Form and Commuting Time*     

Marie‐Hlne Vandersmissen  Paul Villeneuve  Marius Thriault 《The Professional geographer》2003,55(4):446-463

Urban work trips have changed in important ways during the last decades. In Québec City, a medium‐sized Canadian metropolitan area, commuting distances increased for both male and female workers between 1977 and 1996, while durations increased for male workers and decreased for female workers. This article seeks to identify spatial and social factors responsible for these changes. We develop a disaggregate model of trip duration estimated on the basis of large samples derived from travel surveys comparable through time. Using categorical variables to specify change, we are able to separate change effects from level effects attributable to various dimensions of urban form. Our analysis clearly indicates that, once travel mode and key social factors are controlled for, the shift from a monocentric to a dispersed city form is responsible, in the Québec metropolitan area, for increasing commuting time. This is contrary to findings in larger metropolitan areas, where, it has been argued, the suburbanization of jobs maintains stability in commuting duration.  相似文献   

Positive density gradients at the magnetopause: interpretation in the framework of the impulsive penetration mechanism     

Marius M. Echim  J. Lemaire   《Journal of Atmospheric and Solar》2002,64(18):135

  相似文献   

Complexity Phenomena and ROMA of the Earth’s Magnetospheric Cusp,Hydrodynamic Turbulence,and the Cosmic Web     

Tom Chang  Cheng-chin Wu  Marius Echim  Hervé Lamy  Mark Vogelsberger  Lars Hernquist  Debora Sijacki 《Pure and Applied Geophysics》2015,172(7):2025-2043

  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   

Isotopic offsets in throughfall and stemflow may have small effects on estimates of winter precipitation fractions     

Marius G. Floriancic  James W. Kirchner 《水文研究》2024,38(3):e15095

Forest canopies alter the amount and isotopic composition of precipitation reaching the forest floor. Thus retention, evaporation and transport processes in forest canopies, and their effects on water isotopes, are key to understanding forest water cycling. Using a two-year isotope dataset from a mixed beech/spruce forest in Zurich, Switzerland, we assessed the isotopic offsets between precipitation, throughfall and stemflow. We also analysed how these offsets affect estimates of the fraction of soil water that is derived from winter precipitation. Throughfall was typically enriched in heavy isotopes compared to precipitation, but isotopically lighter than stemflow, with average δ²H of −64.3 ‰, −59.9 ‰ and − 56.3 ‰ in precipitation, throughfall and stemflow, respectively. The differences between beech and spruce were rather small compared to the seasonal differences in precipitation isotopes. Isotopic offsets between precipitation and throughfall/stemflow were smaller during the spring and summer months (March through August) than during fall and winter (September through February). Bulk and mobile soil waters at 10 and 40 cm showed smaller seasonal variations than those in precipitation, throughfall and stemflow, and were isotopically lighter than recent precipitation, with the largest offsets occurring during the summer months (June through August) for bulk soil waters. Thus, bulk soil waters at both depths contain a mixture of precipitation from previous events and seasons, with over-representation of isotopically lighter winter precipitation. Mobile soil waters were more similar to recent precipitation than bulk soil waters were. Throughfall isotopes were slightly heavier than precipitation isotopes, resulting in different sinusoidal fits for seasonal isotopic cycles in precipitation and throughfall. These differences lead to small underestimates in the fraction of soil water originating from winter precipitation, when open-field precipitation rather than throughfall is used as the input data. Together our results highlight the importance of isotope measurements in throughfall and stemflow for the assessment of precipitation seasonality and water cycling across forested landscapes.  相似文献