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  • 1.
    Carlund, Thomas
    SMHI, Core Services.
    Upgrade of SMHI's meteorological radiation network 2006-2007: Effects on direct and global solar radiation2011Report (Other academic)
    Abstract [en]

    The radiation network of SMHI was modernized in 2006-2007. Old measurements were closed down after 6-18 months of parallel operation of new and old measurements. This study reports the results of the comparison mainly between the old and new global and direct solar radiation measurements.On average the agreement between old and new measurements was good. The network average of ratios of whole period values was for global radiation 0.997 and for direct radiation 1.009. None of these results are significantly different from one at a level of confidence of 90 %.Despite the fairly good agreement some systematic differences between the old and new measurements were found. The differences are mainly thought to be caused by a difference in the apparent directional response between the old and new pyranometers and different viewing geometries in the old and new pyrheliometers. Functions to correct old global and direct radiation have been developed. These should be used to increase the homogeneity in Swedish solar radiation data from 1983and onwards, especially for monthly data.A new measurement method and new instruments for determination of sunshine duration were introduced in the upgraded network. A more detailed study comparing sunshine duration measurements by pyrheliometers in the old network and by contrast sensors in the modernized network, probably based on 1-minute or even instantaneous data, needs to be done in the future.

  • 2.
    Carlund, Thomas
    et al.
    SMHI, Core Services.
    Håkansson, Bertil
    SMHI, Research Department, Oceanography.
    Land, P
    Aerosol optical depth over the Baltic Sea derived from AERONET and SeaWiFS measurements2005In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 26, no 2, p. 233-245Article in journal (Refereed)
    Abstract [en]

    Three years of data on aerosol optical depth (tau(a)) from the Aerosol Robotic Network (AERONET) station on the island of Gotland in the Baltic Sea have been analysed and compared with Sea-viewing Wide Field of view Sensor (SeaWiFS) data. Normally, the atmosphere over Gotland could be considered as clear, with a daily median value Of tau(a) at 500 nm of about 0.08. The median value of Angstrom's wavelength exponent (alpha) for wavelengths between 440 nm and 870 nm was 1.37, indicating that the dominant aerosol is more of a continental than of a pure maritime type. SeaWiFS GAC level 2 data on tau(a) and alpha were compared to data from the ground-based AERONET station. For the 37 cases of simultaneous satellite and ground-based measurements under cloud-free skies it was found that, on average, the value of tau(a)(865 nm) from SeaWiFS was about 0.02 higher than tau(a)(870 nm) from the AERONET station. At the same time approximate tau(a)(440 nm) from SeaWiFS was about 0.03 lower than tau(a)(440 nm) of AERONET. alpha(510, 865) from SeaWiFS was, on average, 1.2 lower than alpha(500, 870) from the AERONET measurements. These results cannot explain the very frequent occurences of negative values of normalized water-leaving radiance at 412 nm and 443 nm in the SeaWiFS reprocessing #3 data.

  • 3.
    Carlund, Thomas
    et al.
    SMHI, Core Services.
    Kouremeti, Natalia
    Kazadzis, Stelios
    Grobner, Julian
    Aerosol optical depth determination in the UV using a four-channel precision filter radiometer2017In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 10, no 3, p. 905-923Article in journal (Refereed)
  • 4.
    Carlund, Thomas
    et al.
    SMHI, Core Services.
    Landelius, Tomas
    SMHI, Research Department, Atmospheric remote sensing.
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Comparison and uncertainty of aerosol optical depth estimates derived from spectral and broadband measurements2003In: Journal of applied meteorology (1988), ISSN 0894-8763, E-ISSN 1520-0450, Vol. 42, no 11, p. 1598-1610Article in journal (Refereed)
    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.

  • 5. Kazadzis, Stelios
    et al.
    Kouremeti, Natalia
    Diemoz, Henri
    Grobner, Julian
    Forgan, Bruce W.
    Campanelli, Monica
    Estelles, Victor
    Lantz, Kathleen
    Michalsky, Joseph
    Carlund, Thomas
    SMHI, Core Services.
    Cuevas, Emilio
    Toledano, Carlos
    Becker, Ralf
    Nyeki, Stephan
    Kosmopoulos, Panagiotis G.
    Tatsiankou, Viktar
    Vuilleumier, Laurent
    Denn, Frederick M.
    Ohkawara, Nozomu
    Ijima, Osamu
    Goloub, Philippe
    Raptis, Panagiotis I.
    Milner, Michael
    Behrens, Klaus
    Barreto, Africa
    Martucci, Giovanni
    Hall, Emiel
    Wendell, James
    Fabbri, Bryan E.
    Wehrli, Christoph
    Results from the Fourth WMO Filter Radiometer Comparison for aerosol optical depth measurements2018In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 18, no 5, p. 3185-3201Article in journal (Refereed)
  • 6.
    Landelius, Tomas
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Andersson, Sandra
    SMHI, Core Services.
    Carlund, Thomas
    SMHI, Core Services.
    Josefsson, Weine
    SMHI, Core Services. SMHI, Research Department, Atmospheric remote sensing.
    Karteringen av solstrålningen i Sverige2018In: Polarfront, no 168, p. 31-40Article in journal (Other academic)
  • 7. Lopez-Solano, Javier
    et al.
    Redondas, Alberto
    Carlund, Thomas
    SMHI, Core Services.
    Rodriguez-Franco, Juan J.
    Diemoz, Henri
    Leon-Luis, Sergio F.
    Hernandez-Cruz, Bentorey
    Guirado-Fuentes, Carmen
    Kouremeti, Natalia
    Grobner, Julian
    Kazadzis, Stelios
    Carreno, Virgilio
    Berjon, Alberto
    Santana-Diaz, Daniel
    Rodriguez-Valido, Manuel
    De Bock, Veerle
    Moreta, Juan R.
    Rimmer, John
    Smedley, Andrew R. D.
    Boulkelia, Lamine
    Jepsen, Nis
    Eriksen, Paul
    Bais, Alkiviadis F.
    Shirotov, Vadim
    Vilaplana, Jose M.
    Wilson, Keith M.
    Karppinen, Tomi
    Aerosol optical depth in the European Brewer Network2018In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 18, no 6, p. 3885-3902Article in journal (Refereed)
  • 8. Melin, Frederic
    et al.
    Zibordi, Giuseppe
    Carlund, Thomas
    SMHI, Core Services.
    Holben, Brent N.
    Stefan, Sabina
    Validation of SeaWiFS and MODIS Aqua/Terra aerosol products in coastal regions of European marginal seas2013In: Oceanologia, ISSN 0078-3234, Vol. 55, no 1, p. 27-51Article in journal (Refereed)
    Abstract [en]

    The aerosol products associated with the ocean colour missions SeaWiFS and MODIS (both Aqua and Terra) are assessed with AERONET field measurements collected in four European marginal seas for which fairly large uncertainties in ocean colour in-water products have been documented: the northern Adriatic, the Baltic, Black and North Seas. On average, more than 500 match-ups are found for each basin and satellite mission, showing an overall consistency of validation statistics across the three missions. The median absolute relative difference between satellite and field values of aerosol optical thickness tau(a) at 443 nm varies from 12% to 15% for the three missions at the northern Adriatic and Black Sea sites, and from 13% to -26% for the Baltic and North Sea sites. It is in the interval 16-31% for the near-infrared band. The spectral shape of tau(a) is well reproduced with a median bias of the Angstrom exponent varying between -15% and +14%, which represents a clear improvement with respect to previous versions of the atmospheric correction scheme. These results show that the uncertainty associated with tau(a) in the considered coastal waters of the European marginal seas is comparable to global validation statistics.

  • 9. Michalsky, Joseph
    et al.
    Dutton, Ellsworth G.
    Nelson, Donald
    Wendell, James
    Wilcox, Stephen
    Andreas, Afshin
    Gotseff, Peter
    Myers, Daryl
    Reda, Ibrahim
    Stoffel, Thomas
    Behrens, Klaus
    Carlund, Thomas
    SMHI, Core Services.
    Finsterle, Wolfgang
    Halliwell, David
    An Extensive Comparison of Commercial Pyrheliometers under a Wide Range of Routine Observing Conditions2011In: Journal of Atmospheric and Oceanic Technology, ISSN 0739-0572, E-ISSN 1520-0426, Vol. 28, no 6, p. 752-766Article in journal (Refereed)
    Abstract [en]

    In the most comprehensive pyrheliometer comparison known to date, 33 instruments were deployed to measure direct normal solar radiation over a 10-month period in Golden, Colorado. The goal was to determine their performance relative to four electrical-substitution cavity radiometers that were calibrated against the World Radiometric Reference (WRR) that is maintained at the World Radiation Center in Davos, Switzerland. Because of intermittent cabling problems with one of the cavity radiometers, the average of three windowed, electrical-substitution cavity radiometers served as the reference irradiance for 29 test instruments during the 10-month study. To keep the size of this work manageable, comparisons are limited to stable sunny conditions, passing clouds, calm and windy conditions, and hot and cold temperatures. Other variables could have been analyzed, or the conditions analyzed could have employed higher resolution. A more complete study should be possible now that the instruments are identified; note that this analysis was performed without any knowledge on the part of the analyst of the instruments' manufacturers or models. Apart from the windowed cavities that provided the best measurements, two categories of performance emerged during the comparison. All instruments exceeded expectations in that they measured with lower uncertainties than the manufacturers' own specifications. Operational 95% uncertainties for the three classes of instruments, which include the uncertainties of the open cavities used for calibration, were about 0.5%, 0.8%, and 1.4%. The open cavities that were used for calibration of all pyrheliometers have an estimated 95% uncertainty of 0.4%-0.45%, which includes the conservative estimate of 0.3% uncertainty for the WRR.

  • 10. Riihela, Aku
    et al.
    Carlund, Thomas
    SMHI, Core Services.
    Trentmann, Joerg
    Mueller, Richard
    Lindfors, Anders V.
    Validation of CM SAF Surface Solar Radiation Datasets over Finland and Sweden2015In: Remote Sensing, ISSN 2072-4292, E-ISSN 2072-4292, Vol. 7, no 6, p. 6663-6682Article in journal (Refereed)
    Abstract [en]

    Accurate determination of the amount of incoming solar radiation at Earth's surface is important for both climate studies and solar power applications. Satellite-based datasets of solar radiation offer wide spatial and temporal coverage, but careful validation of their quality is a necessary prerequisite for reliable utilization. Here we study the retrieval quality of one polar-orbiting satellite-based dataset (CLARA-A1) and one geostationary satellite-based dataset (SARAH), using in situ observations of solar radiation from the Finnish and Swedish meteorological measurement networks as reference. Our focus is on determining dataset quality over high latitudes as well as evaluating daily mean retrievals, both of which are aspects that have drawn little focus in previous studies. We find that both datasets are generally capable of retrieving the levels and seasonal cycles of solar radiation in Finland and Sweden well, with some limitations. SARAH exhibits a slight negative bias and increased retrieval uncertainty near the coverage edge, but in turn offers better precision (less scatter) in the daily mean retrievals owing to the high sampling rate of geostationary imaging.

  • 11. Toledano, C.
    et al.
    Cachorro, V. E.
    Gausa, M.
    Stebel, K.
    Aaltonen, V.
    Berjon, A.
    Ortiz de Galisteo, J. P.
    de Frutos, A. M.
    Bennouna, Y.
    Blindheim, S.
    Myhre, C. L.
    Zibordi, G.
    Wehrli, C.
    Kratzer, S.
    Håkansson, Bertil
    SMHI, Research Department, Oceanography.
    Carlund, Thomas
    SMHI, Core Services.
    de Leeuw, G.
    Herber, A.
    Torres, B.
    Overview of sun photometer measurements of aerosol properties in Scandinavia and Svalbard2012In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 52, p. 18-28Article in journal (Refereed)
    Abstract [en]

    An overview on the data of columnar aerosol properties measured in Northern Europe is provided. Apart from the necessary data gathered in the Arctic, the knowledge of the aerosol loading in nearby areas (e.g. sub-Arctic) is of maximum interest to achieve a correct analysis of the Arctic aerosols and transport patterns. This work evaluates data from operational sites with sun photometer measurements belonging either to national or international networks (AERONET, GAW-PFR) and programs conducted in Scandinavia and Svalbard. We enumerate a list of sites, measurement type and periods together with observed aerosol properties. An evaluation and analysis of aerosol data was carried out with a review of previous results as well. Aerosol optical depth (AOD) and Angstrom exponent (AE) are the current parameters with sufficient long-term records for a first evaluation of aerosol properties. AOD (500 nm) ranges from 0.08 to 0.10 in Arctic and sub-Arctic sites (Ny-Alesund: 0.09; Andenes: 0.10; Sodankyla: 0.08), and it is somewhat higher in more populated areas in Southern Scandinavia (AOD about 0.10-0.12 at 500 nm). On the Norwegian coast, aerosols show larger mean size (AE = 1.2 at Andenes) than in Finland, with continental climate (AE = 1.5 at Sodankyla). Columnar particle size distributions and related parameters derived from inversion of sun/sky radiances were also investigated. This work makes special emphasis in the joint and collaborative effort of the various groups from different countries involved in this study. Part of the measurements presented here were involved in the IPY projects Polar-AOD and POLARCAT. (C) 2011 Elsevier Ltd. All rights reserved.

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