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Kjeller, Norway

Lahoz W.A.,NILU | Lahoz W.A.,Meteo - France | De Lannoy G.J.M.,NASA
Surveys in Geophysics | Year: 2014

This paper reviews the conceptual problems limiting our current knowledge of the hydrological cycle over land. We start from the premise that to understand the hydrological cycle we need to make observations and develop dynamic models that encapsulate our understanding. Yet, neither the observations nor the models could give a complete picture of the hydrological cycle. Data assimilation combines observational and model information and adds value to both the model and the observations, yielding increasingly consistent and complete estimates of hydrological components. In this review paper we provide a historical perspective of conceptual problems and discuss state-of-the-art hydrological observing, modelling and data assimilation systems. © 2013 The Author(s). Source

Diapouli E.,L.E.S.S. | Eleftheriadis K.,L.E.S.S. | Karanasiou A.A.,L.E.S.S. | Vratolis S.,L.E.S.S. | And 3 more authors.
Aerosol and Air Quality Research | Year: 2011

The scope of this work was to characterize PM mass and number concentration at typical residential microenvironments in the centre of Athens and to examine the relative contribution of the indoor and outdoor sources. Three residential flats located in densely populated residential areas were studied, during a warm and cold period of 2002. PM 10, PM 2 and black carbon (BC) mass concentrations, as well as ultrafine and accumulation mode particle number size distributions were recorded indoors and outdoors simultaneously. Outdoor concentrations of all size fractions were significant, and indicative of urban sites affected by heavy traffic. Indoor levels were generally lower than the corresponding outdoor ones. Nevertheless, elevated indoor concentrations were recorded, caused by increased ambient air penetration in the indoor microenvironments and/or indoor particle generation. The mean 24-hr indoor PM 10 concentration at all residences was 35.0 ± 10.7 μg/m 3 during the warm period and 31.8 ± 7.8 μg/m 3 during the cold period. The corresponding PM 2 concentration was 30.1 ± 11.1 μg/m 3 and 27.2 ± 3.6 μg/m 3 during warm and cold periods, respectively. Regression analysis of indoor and outdoor concentration data revealed that indoor BC may be considered mainly of outdoor origin. A large fraction of the outdoor-generated PM 2 and ultrafine and accumulation mode particles also seems to penetrate indoors, causing elevated indoor levels. Regarding indoor particle generation, cooking was the strongest contributor in residential microenvironments. © Taiwan Association for Aerosol Research. Source

Thomas H.E.,Michigan Technological University | Watson I.M.,Michigan Technological University | Watson I.M.,University of Bristol | Carn S.A.,Michigan Technological University | And 2 more authors.
Geomatics, Natural Hazards and Risk | Year: 2011

Volcanic degassing is a major contributor to the global sulphur dioxide (SO 2) budget, characterized by quiescent emissions in the lower troposphere with sporadic, spatially variable explosive eruptions into the upper troposphere and lower stratosphere (UTLS). The volcanic input of SO 2 to the atmosphere can be quantified using a suite of satellite-based instruments with a range of orbits and resolutions, resulting in differing estimates of SO 2 extent and concentration from eruptions. We compare near-coincident retrievals of SO 2 from the Moderate Resolution Imaging Spectroradiometer (MODIS), Atmospheric Infrared Radiation Sounder (AIRS) and OzoneMonitoring Instrument (OMI) at four eruptive settings. The OMI instrument is the most sensitive, with the ability to detect both low and high altitude clouds, but as an ultraviolet sensor, retrievals are limited to daytime, unlike the infrared sensors. AIRS retrievals are up to an order of magnitude less sensitive than OMI, restricted to water-free clouds in the upper troposphere. MODIS has the lowest sensitivity and is therefore constrained to the largest eruptions. Total tonnages from each sensor reflect these varying sensitivities along with potential calibration discrepancies. Results suggest that by using a number of instruments in synergy a more complete method of eruption detection is achieved. © 2011 Taylor & Francis. Source

Barre J.,U.S. National Center for Atmospheric Research | Edwards D.,U.S. National Center for Atmospheric Research | Worden H.,U.S. National Center for Atmospheric Research | Da Silva A.,NASA | Lahoz W.,NILU
Atmospheric Environment | Year: 2015

By the end of the current decade, there are plans to deploy several geostationary Earth orbit (GEO) satellite missions for atmospheric composition over North America, East Asia and Europe with additional missions proposed. Together, these present the possibility of a constellation of geostationary platforms to achieve continuous time-resolved high-density observations over continental domains for mapping pollutant sources and variability at diurnal and local scales. In this paper, we use a novel approach to sample a very high global resolution model (GEOS-5 at 7km horizontal resolution) to produce a dataset of synthetic carbon monoxide pollution observations representative of those potentially obtainable from a GEO satellite constellation with predicted measurement sensitivities based on current remote sensing capabilities. Part 1 of this study focuses on the production of simulated synthetic measurements for air quality OSSEs (Observing System Simulation Experiments). We simulate carbon monoxide nadir retrievals using a technique that provides realistic measurements with very low computational cost. We discuss the sampling methodology: the projection of footprints and areas of regard for geostationary geometries over each of the North America, East Asia and Europe regions; the regression method to simulate measurement sensitivity; and the measurement error simulation. A detailed analysis of the simulated observation sensitivity is performed, and limitations of the method are discussed. We also describe impacts from clouds, showing that the efficiency of an instrument making atmospheric composition measurements on a geostationary platform is dependent on the dominant weather regime over a given region and the pixel size resolution. These results demonstrate the viability of the "instrument simulator" step for an OSSE to assess the performance of a constellation of geostationary satellites for air quality measurements. We describe the OSSE results in a follow up paper (Part 2 of this study). © 2015 Elsevier Ltd. Source

Burton M.R.,Italian National Institute of Geophysics and Volcanology | Prata F.,NILU | Platt U.,University of Heidelberg
Journal of Volcanology and Geothermal Research | Year: 2015

Ground-based volcanic gas and ash imaging has the potential to revolutionise the way in which volcanoes are monitored and studied. The ability to track and quantify volcanic emissions in space and time with unprecedented fidelity opens the door to integration with geophysical measurements, allowing breakthroughs in our understanding of the physical processes driving volcanic activity. In May 2013 a European Science Foundation funded Plume Imaging workshop was conducted in Stromboli, Italy, with the objective of bringing the ground-based volcanic plume imaging community together in order to examine the state of the art, and move towards a 'best-practice' for volcanic ash and gas imaging techniques. A particular focus was the development of SO2 imaging systems, or SO2 cameras, with six teams deploying and testing various designs of ultraviolet and infrared-based imaging systems capable of imagining SO2. One conclusion of the workshop was that the term 'SO2 camera' should be applied to any SO2 imaging system, regardless of wavelength of radiation used.This Special Issue on Volcanic Plume Imaging is the direct result of the Stromboli workshop, and together the papers presented here represent the state of the art of ground-based volcano plume imaging science and technology. In this work, we examine in detail the volcanological applications of the SO2 camera, reviewing previous works and placing the new research contained in this Special Issue in context. The development of the SO2 camera, and future developments extending imaging to other volcanic gases, is one of the most exciting and novel research frontiers in volcanology today. © 2014. Source

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