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  • 121.
    Johansson, Barbro
    et al.
    SMHI, Affärsverksamhet.
    Lindström, Göran
    SMHI, Forskningsavdelningen, Hydrologi.
    Olsson, Jonas
    SMHI, Forskningsavdelningen, Hydrologi.
    Yacoub, Tahsin
    SMHI, Samhälle och säkerhet.
    Haase, Günther
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Jacobsson, Karin
    SMHI, Affärsverksamhet.
    Sanner, Håkan
    SMHI, Samhälle och säkerhet.
    Översvämningsprognoser i områden med ofullständiga data: Metodutveckling och utvärdering2007Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    Rapporten redovisar slutresultat från projektet ”Översvämningsprognoser Utveckling av metoder för ett rikstäckande system för vattenförings- och vattenståndsprognoser”. Projektet har i huvudsak varit finansierat av Räddningsverket, numera MSB, (Myndigheten för Samhällsskydd och Beredskap), men har även utnyttjat resultat från näraliggande projekt finansierade av Elforsk, SMHI och EU.I ett rikstäckande system måste prognoser göras för vattendrag där det saknas detaljerad information om avrinningsområdets och älvfårans egenskaper. Modeller kan inte tillämpas och verifieras på samma sätt som i områden med god datatillgång och tillgång till tidsserier med observerad vattenföring. Eftersom beräkningarna inte kan verifieras mot observationer blir det extra viktigt med bra nederbördsinformation och att kunna ge ett mått på osäkerheten i prognosen. Projektet har dels arbetat med metodutveckling, dels med en omfattande utvärdering av data och beräkningsresultat. En pilotstudie gjordes för flödet sommaren 2004 i Lagan/Ljungby. Fokus har varit på följande områden:- Utveckling och utvärdering av en metodik för att utnyttja meteorologiska och hydrologiska sannolikhetsprognoser- Utvärdering och minimering av osäkerheten i hydrologiska (vattenföring) och hydrauliska (vattenstånd) prognosmodeller.- Utveckling och utvärdering av metoder för att utnyttja radarobservationer av nederbörd.Projektet har visat att det är möjligt att göra vattenståndsprognoser med rimlig noggrannhet, utgående från data som finns tillgängliga i ett rikstäckande system. Tillgång till bra nederbördsinformation för dagarna före prognosen är viktig, speciellt i sjörika system med ett långsamt förlopp. För att kunna göra sannolikhetsprognoser räcker det inte att ta hänsyn till osäkerheten i den meteorologiska prognosen genom att direkt utnyttja meteorologiska ensembleprognoser. Spridningen i de meteorologiska nederbördsprognoserna är inte tillräcklig och osäkerheten i den hydrologiska modellen måste beaktas.De projektresultat som inom det närmaste året kommer att utnyttjas i ett rikstäckande system är de som är relaterade till hydrologisk modellering och sannolikhetsprognoser. Arbetet med att utveckla metoder för att utnyttja radarinformation i operationell skattning av arealnederbörd fortgår. Fallstudier har visat att vattenståndsprognoser kan göras med modeller baserad på översiktlig information om topografi och tvärsektioner i vattendragen. Däremot är det tidsödande att sätta upp en hydraulisk modell för en godtycklig älvsträcka. Tills vidare är det realistiskt att anta att vattenståndsprognoser främst kommer att göras i vattendrag som ingått i den översiktliga översvämningskarteringen.

  • 122. Zhang, Jianzhong
    et al.
    Kuenzer, Claudia
    Tetzlaff, Anke
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Oertel, Dieter
    Zhukov, Boris
    Wagner, Wolfgang
    Thermal characteristics of coal fires 2: Results of measurements on simulated coal fires2007Ingår i: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 63, nr 3-4, s. 135-147Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper we present thermal characteristics of coal fires as measured during simulated fires under an experimental setting in Germany in July 2002. It is thus a continuation of the previously published paper "Thermal surface characteristics of coal fire 1: Results of in-situ measurement", in which we presented temperature measurements of real subsurface coal fires in China [Zhang, J., Kuenzer, C., accepted for publication. Thermal Surface Characteristics of Coal Fires 1: Results of in-situ measurements. Accepted for publication at Journal of Applied Geophysics.]. The focus is on simulated coal fires, which are less complex in nature than fires under natural conditions. In the present study we simulated all the influences usually occurring under natural conditions in a controllable manner (uniform background material of known thermal properties, known ventilation pathways, homogeneous coal substrate), creating two artificial outdoor coal fires under simplified settings. One surface coal fire and one subsurface coal fire were observed over the course of 2 days. The set up of the fires allowed for measurements not always feasible under "real" in-situ conditions: thus compared to the in-situ investigations presented in paper one we could retrieve numerous temperature measurements inside of the fires. Single temperature measurements, diurnal profiles and airborne thermal surveying present the typical temperature patterns of a small surface-and a subsurface fire under undisturbed conditions (easily accessible terrain, 24 hour measurements period, homogeneous materials). We found that the outside air temperature does not influence the fire's surface temperature (up to 900 degrees C), while fire centre temperatures of up to 1200 degrees C strongly correlate with surface temperatures of the fire. The fires could heat their surrounding up to a distance of 4.5 m. However, thermal anomalies on the background surface only persist as long as the fire is burning and disappear very fast if the heat source is removed. Furthermore, heat outside of the fires is transported mainly by convection and not by radiation. In spatial thermal line scanner data the diurnal thermal patterns of the coal fire are clearly represented. Our experiments during that data collection also visualize the thermal anomaly differences between covered (underground) and uncovered (surface) coal fires. The latter could not be observed in-situ in a real coal fire area. Subsurface coal fires express a much weaker signal than open surface fires and contrast only by few degrees against the background. In airborne thermal imaging scanner data the fires are also well represented. Here we could show that the mid-infrared domain (3.8 mu m) is more suitable to pick up very hot anomalies, compared to the common thermal (8.8 mu m) domain. Our results help to understand coal fires and their thermal patterns as well as the limitations occurring during their analysis. We believe that the results presented here can practicably help for the planning of coal fire thermal mapping campaigns - including remote sensing methods and the thermal data can be included into numerical coal fire modelling as initial or boundary conditions. (c) 2007 Elsevier B.V. All rights reserved.

  • 123. Lindfors, Anders
    et al.
    Kaurola, Jussi
    Arola, Antti
    Koskela, Tapani
    Lakkala, Kaisa
    Josefsson, Weine
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Olseth, Jan Asle
    Johnsen, Bjorn
    A method for reconstruction of past UV radiation based on radiative transfer modeling: Applied to four stations in northern Europe2007Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 112, nr D23, artikel-id D23201Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A method for reconstruction of past UV radiation has been developed. The idea of the method is to use measurements of global radiation (300 - 3000 nm) for determining the influence of clouds on UV radiation. In order to transfer the information contained in the global radiation data into a cloud effect in the UV range, a so-called cloud modification table was developed, which is based on physical relationships determined through radiative transfer calculations. The method was given as input the measured global radiation and total ozone column, the total water vapor column from the ERA-40 data set, the surface albedo as estimated from snow depth, and the altitude of the location. Using this method, erythemally weighted UV irradiances were reconstructed back to the early 1980s at four stations in northern Europe: Bergen in Norway, Norrkoping in Sweden, and Jokioinen and Sodankyla in Finland. The reconstructed daily UV doses are in good agreement with measurements. For the summer season, the systematic error was found to vary between 0% at Bergen and 4% at Jokioinen, and the correlation coefficient was 0.99 at all stations. The summer root-mean-square error was 5% at all stations except Jokioinen, where it was 9%. The method performs well also for spring and autumn, whereas for winter conditions of low Sun, a systematical underestimation was found. A large part of this underestimation was found to be due to the plane-parallel approximation used in the radiative transfer calculations. The time series of reconstructed UV exhibit a clear increase since the early 1980s at both Sodankyla " (4.1%/decade; statistically significant) and Norrkoping (3.3%/decade; not significant). At Jokioinen, a weak increase was found, while at Bergen there was no considerable overall change. At both Sodankyla and Norrkoping, the increase in the reconstructed UV radiation was primarily driven by an increase in the global radiation, that is, by decreased cloudiness. The method is general in the sense that it can be applied also to other stations.

  • 124. Bech, J.
    et al.
    Gjertsen, U.
    Haase, Gunther
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Modelling weather radar beam propagation and topographical blockage at northern high latitudes2007Ingår i: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 133, nr 626, s. 1191-1204Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper describes a study to evaluate the variability of radio-propagation conditions and to assess their effects upon weather-radar beam blockage corrections for precipitation estimates. Radiosonde observations are examined in order to analyse the propagation conditions at several locations covered by the Nordic Weather Radar Network (NORDRAD). A beam-propagation model is used to simulate the interaction between the radar beam and the topography and to derive correction factors. The model is applied to correct yearly accumulations, assuming standard radio-propagation conditions, and is also used to examine case studies in detail under various propagation conditions. The correction reduces the bias between yearly radar precipitation estimates and gauge records by 1 dB for moderate blockages (1% to 50%), and by up to 3 dB for severe blockages (50% to 70%). The case studies indicate that HIRLAM forecasts show potential to predict the radar coverage and the associated ground- and sea-clutter patterns. This research aims at determining a beam-blockage-correction algorithm to be used within the NORDRAD quality-control system. This is particularly useful for obtaining radar precipitation estimates in environments with complex topography. Copyright (C) 2007 Royal Meteorological Society.

  • 125. Kuenzer, Claudia
    et al.
    Zhang, Jianzhong
    Tetzlaff, Anke
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    van Dijk, Paul
    Voigt, Stefan
    Mehl, Harald
    Wagner, Wolfgang
    Uncontrolled coal fires and their environmental impacts: Investigating two arid mining regions in north-central China2007Ingår i: Applied Geography, ISSN 0143-6228, E-ISSN 1873-7730, Vol. 27, nr 1, s. 42-62Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Uncontrolled coal fires occur worldwide and pose a great threat to the environment. This paper introduces the problem of coal fires referring to two coalfields in north-central China. These areas were regularly investigated during numerous fieldwork campaigns between 2002 and 2005. Emphasis is put on the environmental impacts of the fires, such as atmospheric influences, land subsidence, landscape degradation, as well as the danger for water resources and human health. New approaches for coal fire research are undertaken in numerous national and multi-lateral projects. Research disciplines, addressing the problem of coal fires, include geography, geology, geo-physics, mining-engineering, and remote sensing. In combination, they lead the direction towards a holistic approach to detect, monitor, quantify, and finally extinguish the coal fires. (c) 2006 Elsevier Ltd. All rights reserved.

  • 126.
    Josefsson, Weine
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    UV-radiation 1983-2003 measured at Norrkoping, Sweden2006Ingår i: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 83, nr 1-4, s. 59-76Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Total ozone has been monitored with high accuracy at many sites for a relative long period of time. This is not the case for UV. The main reason is that UV is difficult to measure accurately. Extensive monitoring started first during the 1990s. However, there are some data series still in operation that were initiated at earlier dates. This paper will discuss one such series from Norrkoping, Sweden that began in March 1983. The instruments used to measure UV radiation have some characteristics producing an output signal that is not directly related to the UV. Here, these problems are discussed and corrections are applied. The goal is to produce a homogenous and an accurate set of UV data as is possible. An analysis of the various sources of uncertainty is done and summarised as total uncertainty. This was found to be about 6% for the yearly values of CIE weighted UV. However, the precision is much better at about 0.6%. Finally, some results are shown for yearly and seasonal UV. The trends for the full period 1983-2003 are tested for significance. The spring, summer, autumn and yearly data showed a significant increase in UV of respectively 0.8, 0.3, 0.8 and 0.5% per year. To get some indication of the cause of the variation of global radiation (indicator of cloudiness) and total ozone measured at the same site were also processed. A small, but insignificant, decrease of total ozone was found, whilst global radiation showed an increase. It seems that cloudiness is the major factor for the observed variation in UV for this period. The data are available on the internet.

  • 127. Cheymol, Anne
    et al.
    De Backer, Hugo
    Josefsson, Weine
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Stuebi, Rene
    Comparison and validation of the aerosol optical depth obtained with the Langley plot method in the UV-B from Brewer Ozone Spectrophotometer measurements2006Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 111, nr D16, artikel-id D16202Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    [ 1] The Aerosol Optical Depths (AODs) retrieved from Brewer Ozone Spectrophotometer measurements with a method previously developed (Cheymol and De Backer, 2003) are now validated by comparisons between AODs from six Brewer spectrophotometers and two CSEM SPM2000 sunphotometers: two Brewer spectrophotometers 016 and 178 at Uccle in Belgium; one Brewer spectrophotometer 128 and one sunphotometer CSEM SPM2000 at Norrkoping in Sweden; and three Brewer instruments 040, 072, 156 at Arosa and one CSEM SPM2000 sunphotometer at Davos in Switzerland. The comparison between AODs from Brewer spectrophotometer 128 at 320.1 nm and sunphotometer SPM2000 at 368 nm at Norrkoping shows that the AODs obtained from the Brewer measurements with the Langley Plot Method (LPM) are very accurate if the neutral density filter spectral transmittances are well known: with the measured values of these filters, the correlation coefficient, the slope, and the intercept of the regression line are 0.98, 0.85 +/- 0.004, and 0.02 +/- 0.0014, respectively. The bias observed is mainly owing to the wavelength difference between the two instruments. The comparison between AODs from different Brewer spectrophotometers confirm that AODs will be in very good agreement if they are measured with several Brewer instruments at the same place: At Uccle, the correlation coefficient, slope, and intercept of the regression line are 0.98, 1.02 +/- 0.003, and 0.06 +/- 0.001, respectively; at Arosa, the comparisons between the AODs from three Brewer spectrophotometers 040, 072, and 156 give a correlation coefficient, a slope, and an intercept of the regression line above 0.94, 0.98 and below 0.04, respectively.

  • 128. Meinander, O.
    et al.
    Kazadzis, S.
    Blumthaler, M.
    Ylianttila, L.
    Johnsen, B.
    Lakkala, K.
    Koskela, T.
    Josefsson, Weine
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Diurnal discrepancies in spectral solar UV radiation measurements2006Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 45, nr 21, s. 5346-5357Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Unexpected diurnal discrepancies between high-quality spectroradiometers were observed during the 2000 Nordic Ozone Group Intercomparison campaign. The spectral ratios of the irradiances showed a diurnal variation of similar to 2-9%. This cannot be explained by the nonideal angular response of the instruments' input optics in one plane (cosine effect). Instead, by using a radiative transfer model, we show that differences in the angular response in four azimuth planes have the potential to bias the measured data by up to 4.4% (azimuth effect). Other relevant factors are also discussed and quantified and are shown to be significant when diurnal changes in radiation are explained by environmental factors, or when measured data are compared with model or satellite data. Again, intercomparison campaigns have the potential to reveal errors that would otherwise remain undetected. (c) 2006 Optical Society of America.

  • 129. Hedfors, J
    et al.
    Aldahan, A
    Kulan, A
    Possnert, G
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Vintersved, I
    Clouds and Be-7: Perusing connections between cosmic rays and climate2006Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 111, nr D2, artikel-id D02208Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    [1] Time series data on Be-7, precipitation, temperature, and satellite imagery of cloud cover over Scandinavia, together with cosmic ray and sunspot activity, were used to elucidate the relationship between cosmic rays and clouds, and ultimately climate change. The results indicate a coherent negative correlation between total cloud cover and Be-7 on intraseasonal, seasonal, and decadal scales. Although the reasons behind this correlation are unclear, a full-scale implication of this feature is in the possible use of Be-7 and Be-10 records for proxy paleo-reconstruction of total cloud cover. This is a strongly needed, but generally difficult to quantify parameter in climate models.

  • 130.
    Trolez, Matthieu
    et al.
    SMHI.
    Tetzlaff, Anke
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    CM-SAF Validating the Cloud Top Height product using LIDAR data2005Rapport (Övrigt vetenskapligt)
  • 131.
    Michelson, Daniel
    et al.
    SMHI, Samhälle och säkerhet.
    Jones, Colin
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Landelius, Tomas
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Collier, C G
    Haase, Gunther
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Heen, M
    'Down-to-Earth' modelling of equivalent surface precipitation using multisource data and radar2005Ingår i: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 131, nr 607, s. 1093-1112Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The estimation of surface rainfall from reflectivity data derived from weather radar has been much studied over many years. It is now clear that central to this problem is the adjustment of these data for the impacts of vertical variations in the reflectivity. In this paper a new procedure (known as Down-to-Earth, DTE) is proposed and tested for combining radar measurements aloft with information from a numerical weather-prediction (NWP) model and an analysis system. The procedure involves the exploitation of moist cloud physics in an attempt to account for physical processes impacting on precipitation during its descent from the height of radar echo measurements to the surface. The application of DTE leads to increased underestimation in the radar measurements compared to precipitation gauge observations at short and intermediate radar ranges (0-120 km), but is successful at reducing the bias at further ranges. However the application of DTE does not lead to significant decreases in the random error of the surface rain rate estimate. No improvement is made when attempting to account for the precipitation phase measured by radar. It is concluded that further work on radar data quality control, along with improvements to the NWP model, are essential to improve upon results using such a physically based procedure.

  • 132.
    Dybbroe, Adam
    et al.
    SMHI, Samhälle och säkerhet.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Thoss, Anke
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    NWCSAF AVHRR cloud detection and analysis using dynamic thresholds and radiative transfer modeling. Part I: Algorithm description2005Ingår i: Journal of applied meteorology (1988), ISSN 0894-8763, E-ISSN 1520-0450, Vol. 44, nr 1, s. 39-54Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    New methods and software for cloud detection and classification at high and midlatitudes using Advanced Very High Resolution Radiometer (AVHRR) data are developed for use in a wide range of meteorological, climatological, land surface, and oceanic applications within the Satellite Application Facilities (SAFs) of the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), including the SAF for Nowcasting and Very Short Range Forecasting Applications (NWCSAF) project. The cloud mask employs smoothly varying (dynamic) thresholds that separate fully cloudy or cloud-contaminated fields of view from cloud-free conditions. Thresholds are adapted to the actual state of the atmosphere and surface and the sun-satellite viewing geometry using cloud-free radiative transfer model simulations. Both the cloud masking and the cloud-type classification are done using sequences of grouped threshold tests that employ both spectral and textural features. The cloud-type classification divides the cloudy pixels into 10 different categories: 5 opaque cloud types, 4 semitransparent clouds, and 1 subpixel cloud category. The threshold method is fuzzy in the sense that the distances in feature space to the thresholds are stored and are used to determine whether to stop or to continue testing. They are also used as a quality indicator of the final output. The atmospheric state should preferably be taken from a short-range NWP model, but the algorithms can also run with climatological fields as input.

  • 133.
    Dybbroe, Adam
    et al.
    SMHI, Samhälle och säkerhet.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Thoss, Anke
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    NWCSAF AVHRR cloud detection and analysis using dynamic thresholds and radiative transfer modeling. Part II: Tuning and validation2005Ingår i: Journal of applied meteorology (1988), ISSN 0894-8763, E-ISSN 1520-0450, Vol. 44, nr 1, s. 55-71Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Algorithms for cloud detection (cloud mask) and classification (cloud type) at high and midlatitudes using data from the Advanced Very High Resolution Radiometer (AVHRR) on board the current NOAA satellites and future polar Meteorological and Operational Weather Satellites (METOP) of the European Organisation for the Exploitation of Meteorological Satellites have been extensively validated over northern Europe and the adjacent seas. The algorithms have been described in detail in Part I and are based on a multispectral grouped threshold approach, making use of cloud-free radiative transfer model simulations. The thresholds applied in the algorithms have been validated and tuned using a database interactively built up over more than 1 yr of data from NOAA-12, -14, and -15 by experienced nephanalysts. The database contains almost 4000 rectangular (in the image data)-sized targets (typically with sides around 10 pixels), with satellite data collocated in time and space with atmospheric data from a short-range NWP forecast model, land cover characterization, elevation data, and a label identifying the given cloud or surface type as interpreted by the nephanalyst. For independent and objective validation, a large dataset of nearly 3 yr of collocated surface synoptic observation (Synop) reports, AVHRR data, and NWP model output over northern and central Europe have been collected. Furthermore, weather radar data were used to check the consistency of the cloud type. The cloud mask performs best over daytime sea and worst at twilight and night over land. As compared with Synop, the cloud cover is overestimated during night (except for completely overcast situations) and is underestimated at twilight. The algorithms have been compared with the more empirically based Swedish Meteorological and Hydrological Institute (SMHI) Cloud Analysis Model Using Digital AVHRR Data (SCANDIA), operationally run at SMHI since 1989, and results show that performance has improved significantly.

  • 134.
    Karlsson, Karl-Göran
    et al.
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Jones, Colin
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Willén, Ulrika
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Wyser, Klaus
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    USE OF A HIGH-RESOLUTION CLOUD CLIMATE DATA SET FOR VALIDATION OF ROSSBY CENTRE CLIMATE SIMULATIONS2004Ingår i: 2004 EUMETSAT METEOROLOGICAL SATELLITE CONFERENCE: Ocean and Climate Observations, EUMETSAT , 2004, s. 465-473Konferensbidrag (Övrigt vetenskapligt)
  • 135.
    Josefsson, Weine
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    UV-radiation measured in Norrköping 1983-20032004Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The purpose of this work is to homogenise a number of different data sets of daily values of UV-radiation to enable studies of the temporal variation of UV-radiation and atmospheric processes. Efforts are concentrated on the longest series measured using a Robertson-Berger and a Solar Light Model 501 radiometer. The lack of practical and reliable calibration standards have made measurements of UV uncertain. There are also several sources of uncertainty inherited in the designs of the instruments as well as uncertainties in the input data to the models used for corrections and for filling gaps of missing data.The primary goal is to achieve a homogenous data set. The second goal is to mimic a true CIE-weighted irradiation, McKinley and Diffey (1987). The third goal is to be as close as possible to an absolute irradiance scale.There are some factors that will prevent the achievement of these goals. These factors will introduce uncertainty in various fashions and affect the data differently. The applied corrections are assumed to remove systematic differences in a statistical sense. However, as will be discussed below, large differences may still remain in the hourly data.For those not familiar with measurements in the UV spectral range it may seem surprising that UV data recorded by different instruments differ so much. This is partly due to the very large change (several orders of magnitude) in the solar spectrum combined with small differences in the spectral responsivity of the instruments in this range. Apparently small differences in spectral responsivity will produce relatively large variable differences in the output only by changing the solar elevation during the day or during the year. The yearly effect will be seen in the results below.

  • 136.
    Michelson, Daniel
    et al.
    SMHI, Samhälle och säkerhet.
    Landelius, Tomas
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Jones, Colin
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Collier, C. G.
    Attempts to parameterize cloud water profiles using a neural network2004Ingår i: Atmospheric Science Letters, ISSN 1530-261X, E-ISSN 1530-261X, Vol. 5, nr 7, s. 141-145Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Atmospheric state variables from a Numerical Weather Prediction (NWP) model are combined with analyzed cloud base heights in a neural network, with the objective to model corresponding cloud water profiles. It was found that the neural network was incapable of resolving the inherently non-linear vertical cloud water distributions. Copyright (C) 2004 Royal Meteorological Society

  • 137.
    Haase, Gunther
    et al.
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Landelius, Tomas
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Dealiasing of Doppler radar velocities using a torus mapping2004Ingår i: Journal of Atmospheric and Oceanic Technology, ISSN 0739-0572, E-ISSN 1520-0426, Vol. 21, nr 10, s. 1566-1573Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A novel dealiasing algorithm for Doppler radar velocity data has been developed at the Swedish Meteorological and Hydrological Institute (SMHI). Unlike most other methods, it does not need independent wind information from other instruments (e.g., nearby radiosonde or wind profiler) or numerical weather prediction (NWP) models. The innovation of the new technique is that it maps the measurements onto the surface of a torus. Dealiased volume radar data can be used in variational assimilation schemes for NWP models through the generation of so-called superobservations. Their use is expected to improve with the introduction of the proposed dealiasing method.

  • 138.
    Carlund, Thomas
    et al.
    SMHI, Samhälle och säkerhet.
    Landelius, Tomas
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Josefsson, Weine
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Comparison and uncertainty of aerosol optical depth estimates derived from spectral and broadband measurements2003Ingår i: Journal of applied meteorology (1988), ISSN 0894-8763, E-ISSN 1520-0450, Vol. 42, nr 11, s. 1598-1610Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An experimental comparison of spectral aerosol optical depth tau(a,lambda) derived from measurements by two spectral radiometers [a LI-COR, Inc., LI-1800 spectroradiometer and a Centre Suisse d'Electronique et de Microtechnique (CSEM) SPM2000 sun photometer] and a broadband field pyrheliometer has been made. The study was limited to three wavelengths ( 368, 500, and 778 nm), using operational calibration and optical depth calculation procedures. For measurements taken on 32 days spread over 1 yr, the rms difference in tau(a,lambda) derived from the two spectral radiometers was less than 0.01 at 500 and 778 nm. For wavelengths shorter than 500 nm and longer than 950 nm, the performance of the LI-1800 in its current configuration did not permit accurate determinations of tau(a,lambda). Estimates of spectral aerosol optical depth from broadband pyrheliometer measurements using two models of the Angstromngstrom turbidity coefficient were examined. For the broadband method that was closest to the sun photometer results, the mean (rms) differences in tau(a,lambda) were 0.014 (0.028), 0.014 (0.019), and 0.013 ( 0.014) at 368, 500, and 778 nm. The mean differences are just above the average uncertainties of the sun photometer tau(a,lambda) values (0.012, 0.011, and 0.011) for the same wavelengths, as determined through a detailed uncertainty analysis. The amount of atmospheric water vapor is a necessary input to the broadband methods. If upper-air sounding data are not available, water vapor from a meteorological forecast model yields significantly better turbidity results than does using estimates from surface measurements of air temperature and relative humidity.

  • 139.
    Josefsson, Weine
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Quality of total ozone measured by the focused sun method using a Brewer spectrophotometer2003Ingår i: Journal of applied meteorology (1988), ISSN 0894-8763, E-ISSN 1520-0450, Vol. 42, nr 1, s. 74-82Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Strong ozone depletions and large natural variations in total ozone have been observed at high latitudes. Accurate measurements of total ozone are important so as not to misinterpret the involved processes and to track correctly the variations. The primary basis for ground-based monitoring of total ozone is the network of Dobson and Brewer ozone spectrophotometers. However, these instruments have limitations. At high latitudes, the fundamental direct sun observation used by these instruments is not possible during large parts of the year. In particular, the low sun and the resulting weak signals present a challenge. The focused sun observation method can extend the possible range of measurements using the Brewer instrument. Here, this method is discussed from the point of accuracy. Direct (synchronized) validation against the fundamental direct sun method is not possible with the current instrument configuration. Alternative methods to overcome the obstacle of nonsynchronous observations are applied. An estimate of the uncertainty of the validation is provided. The results show that the focused sun method gives data that are in line with the estimated uncertainty of the validation. No major additional uncertainty is needed to explain the observed scatter. The main conclusion is that the focused sun observation method can have an uncertainty close to the fundamental direct sun method and thus can be used to extend the possible range of observation for the Brewer ozone spectrophotometer.

  • 140.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    A 10 year cloud climatology over Scandinavia derived from NOAA advanced very high resolution radiometer imagery2003Ingår i: International Journal of Climatology, ISSN 0899-8418, E-ISSN 1097-0088, Vol. 23, nr 9, s. 1023-1044Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Results from a satellite-based method to compile regional cloud climatologies covering the Scandinavian region are presented. Systematic processing of multispectral image data from the NOAA Advanced Very High Resolution Radiometer (AVHRR) instrument has been utilized to provide monthly cloud climatologies covering the period 1991-2000. Considerable local-scale variation of cloud amounts was found in the region. The inland Baltic Sea and adjacent land areas exhibited a large-amplitude annual cycle in cloudiness (high cloud amounts in winter, low cloud amounts in summer) whereas a weak-amplitude reversed annual cycle (high cloud amounts with a weak maximum in summer) was found for the Scandinavian mountain range. As a contrast, conditions over the Norwegian Sea showed high and almost unchanged cloud amounts during the course of the year. Some interesting exceptions to these patterns were also seen locally. The quality of the satellite-derived cloud climatology was examined through comparisons with climatologies derived from surface cloud observations, from the International Satellite Cloud Climatology Project (ISCCP) and from the European Centre for Medium-range Weather Forecasts ERA-40 data set. In general, cloud amount deviations from surface observations were smaller than 10% except for some individual winter months, when the separability between clouds and snow-covered cold land surfaces is often poor. The ISCCP data set showed a weaker annual cycle in cloudiness, generally caused by higher summer-time cloud amounts in the region. Very good agreement was found with the ERA-40 data set, especially for the summer season. However, ERA-40 showed higher cloud amounts than SCANDIA and ISCCP during the winter season. The derived cloud climatology is affected by errors due to temporal AVHRR sensor degradation, but they appear to be small for this particular study. The data set is proposed as a valuable data set for validation of cloud description in numerical weather prediction and regional climate simulation models. Copyright (C) 2003 Royal Meteorological Society.

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