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  • 161. Hultgren, Pia
    et al.
    Dybbroe, Adam
    SMHI, Samhälle och säkerhet.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    SCANDIA -its accuracy in classifying LOW CLOUD1999Rapport (Övrigt vetenskapligt)
  • 162.
    Josefsson, Weine
    et al.
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Karlsson, Jan-Erik
    Measurements of total ozone 1994-19961997Rapport (Övrigt vetenskapligt)
  • 163.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Cloud climate investigations in the Nordic region using NOAA AVHRR data1997Ingår i: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 57, nr 3-4, s. 181-195Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A method to estimate monthly cloud conditions (monthly cloud frequencies) from multispectral satellite imagery is described. The operational cloud classification scheme SCANDIA (the SMHI Cloud ANalysis model using DIgital AVHRR data), based on high resolution imagery from the polar orbiting NOAA-satellites, has been used to produce monthly cloud frequencies for the entire year of 1993 and some additional months in 1991, 1992, 1994 and 1995. Cloud analyses were made for an area covering the Nordic countries with a horizontal resolution of four km. Examples of seasonal, monthly and diurnal variation in cloud conditions are given and an annual mean for 1993 is presented. Comparisons with existing surface observations showed very good agreement for horizontal cloud distributions but approximately 5% smaller cloud amounts were found in the satellite estimations. The most evident problems were encountered in the winter season due to difficulties in identifying low-level cloudiness at very low sun elevations. The underestimation in the summer season was partly fictious and caused by the overestimation of convective cloud cover by surface observers. SCANDIA results were compared to ISCCP (International Satellite Cloud Climatology Project) cloud climatologies for two selected months in 1991 and 1992. ISCCP cloudiness was indicated to be higher, especially during the month with anticyclonic conditions where a cloudiness excess of more than 10% were found. The regional variation of cloud conditions in the area was found to be inadequately described by ISCCP cloud climatologies. An improvement of the horizontal resolution of ISCCP data seems necessary to enable use for regional applications. The SCANDIA model is proposed as a valuable tool for local and regional monitoring of the cloud climatology at high latitudes. More extensive comparisons with ISCCP cloud climatologies are suggested as well as comparisons with modelled cloudiness from atmospheric general circulation models and climate models. Special studies of cloud conditions in the Polar areas are also proposed.

  • 164.
    Josefsson, Weine
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Solar UV-radiation monitoring 19961996Rapport (Övrigt vetenskapligt)
  • 165.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Cloud classifications with the SCANDIA model1996Rapport (Övrigt vetenskapligt)
  • 166.
    Josefsson, Weine
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Five years of solar UV-radiation monitoring in Sweden1996Rapport (Övrigt vetenskapligt)
  • 167.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Validation of modelled cloudiness using satellite-estimated cloud climatologies1996Ingår i: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 48, nr 5, s. 767-785Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A method to evaluate forecasts of total fractional cloud cover using satellite measurements is demonstrated. Cloud analyses in the form of monthly cloud climatologies are extracted from NOAA. AVHRR data which are compared to corresponding cloud forecast information from the HIRLAM and ECMWF numerical weather prediction models. The satellite-based cloud information is extracted for a summer month in 1994 and a winter month in 1995 by use of the SMHI cloud classification model SCANDIA. Cloud analyses are conducted for an area covering a substantial part of northern Europe. Deficiencies in forecasted cloud amounts are found for both models, especially the underestimation of cloudiness for short forecast lengths with the HIRLAM model. Forecast improvements using the HIRLAM model are indicated when introducing a cloud initialisation technique using cloud fields from initial 6-hour forecasts (first-guess fields). Future systematic validations using this technique are, however, needed to make firm conclusions on the general model behaviour. SCANDIA-derived cloud information is proposed as a valuable complement to other datasets used for cloud forecast validation (e.g., the SSM/I- and ISCCP data sets).

  • 168.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    ESTIMATION OF CLOUDINESS AT HIGH-LATITUDES FROM MULTISPECTRAL SATELLITE MEASUREMENTS1995Ingår i: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 24, nr 1, s. 33-40Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Clouds play an important role in the climate system, and strongly modify radiation conditions in the atmosphere and at the earth's surface. Present estimations show that the net impact of clouds in the atmosphere results in a cooling several times larger than the expected warming that would result from a doubling of the CO2-concentration in the atmosphere. Regional and global monitoring of cloud conditions is therefore necessary for studying the role of clouds in possible climate feedback mechanisms. This paper presents a method to estimate cloud conditions (cloud cover) in the Nordic region, from multispectral satellite data. A cloud classification scheme, based on high-resolution imagery data from polar orbiting NOAA-satellites, was used to produce monthly cloud frequencies for the summer of 1993. Comparisons with existing surface observations have shown very good agreement. Cloud conditions are shown to be highly sensitive to characteristics of the earth's surface. Large differences between land and sea areas were found, especially in the beginning of summer. Cloud frequencies were significantly lower over the Baltic Sea compared to surrounding land areas. Mountainous areas showed, on the contrary, much higher cloud frequencies than surrounding areas.

  • 169.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Satellite-estimated cloudiness from NOAA AVHRR data in the Nordic are during 19931994Rapport (Övrigt vetenskapligt)
  • 170.
    Josefsson, Weine
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Normalvärden för perioden 1961-90 av globalstrålning och solskenstid i Sverige1993Rapport (Övrigt vetenskapligt)
  • 171.
    Andersson, Tage
    et al.
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Lindgren, Bo
    SMHI.
    A SEA-BREEZE FRONT SEEN BY RADAR1992Ingår i: METEOROLOGICAL MAGAZINE, ISSN 0026-1149, Vol. 121, nr 1443, s. 239-241Artikel i tidskrift (Refereegranskat)
  • 172.
    Josefsson, Weine
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    FOCUSED SUN OBSERVATIONS USING A BREWER OZONE SPECTROPHOTOMETER1992Ingår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 97, nr D14, s. 15813-15817Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Accurate measurements of total ozone at high latitudes during winter have become increasingly important for studies of polar ozone depletion. The direct Sun measurements are the most direct and physically well defined type of measurement of total ozone with Dobson and Brewer spectrophotometers along with the focused Sun measurements. The direct Sun and focused Sun method are influenced by many sources of error at low solar elevations. A large error arises from the addition of radiation scattered from air along the path of the solar beam. A method to correct for this error using the Brewer instrument is described. The method gives reasonably accurate values down to solar elevations of 5-degrees compared to 10-degrees-20-degrees without corrections. This is especially important for high-latitude stations, where the low solar elevations are a limiting factor for accurate measurements of the total ozone particularly during the winter.

  • 173.
    Andersson, Tage
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    A HEAVY MESOSCALE SNOWFALL EVENT IN NORTHERN GERMANY1991Ingår i: METEOROLOGICAL MAGAZINE, ISSN 0026-1149, Vol. 120, nr 1425, s. 67-68Artikel i tidskrift (Refereegranskat)
  • 174.
    Andersson, Tage
    et al.
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Ivarsson, Karl-Ivar
    SMHI.
    A MODEL FOR PROBABILITY NOWCASTS OF ACCUMULATED PRECIPITATION USING RADAR1991Ingår i: Journal of applied meteorology (1988), ISSN 0894-8763, E-ISSN 1520-0450, Vol. 30, nr 1, s. 135-141Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new model for making probability forecasts of accumulated spot precipitation from weather radar data is presented. The model selects a source region upwind of the forecast spot. All pixels (horizontal size 2 x 2 km2) within the source region are considered, having the same probability of hitting the forecast spot. A pixel hitting the forecast spot is supposed to precipitate there a short time (about 10 min.). A drawing is performed, and a frequency distribution of accumulated precipitation during the first time step of the forecast is obtained. A second drawing gives the frequency distribution of accumulated precipitation during the first to second time step, a third one during the first to third, and so on until the end of the forecast period is reached. A number of forecasts for 1-h accumulated precipitation, with lead times of 0, 1, and 2 h, have been performed and verified. The forecasts for 0-h lead time got the highest Brier skill scores, +50% to 60% relative to climatological forecasts for accumulated precipitation below 1 mm.

  • 175.
    Andersson, Tage
    et al.
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Nilsson, Stefan
    SMHI, Samhälle och säkerhet.
    TOPOGRAPHICALLY INDUCED CONVECTIVE SNOWBANDS OVER THE BALTIC SEA AND THEIR PRECIPITATION DISTRIBUTION1990Ingår i: Weather and forecasting, ISSN 0882-8156, E-ISSN 1520-0434, Vol. 5, nr 2, s. 299-312Artikel i tidskrift (Refereegranskat)
  • 176.
    Josefsson, Weine
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Computed global radiation using interpolated, gridded cloudiness from the MESA-BETA analysis compared to measured global radiation1989Rapport (Övrigt vetenskapligt)
  • 177.
    Andersson, Tage
    et al.
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Andersson, M
    SMHI.
    Jacobsson, Caje
    SMHI.
    Nilsson, Stefan
    SMHI.
    THERMODYNAMIC INDEXES FOR FORECASTING THUNDERSTORMS IN SOUTHERN SWEDEN1989Ingår i: METEOROLOGICAL MAGAZINE, ISSN 0026-1149, Vol. 118, nr 1404, s. 141-146Artikel i tidskrift (Refereegranskat)
  • 178.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    DEVELOPMENT OF AN OPERATIONAL CLOUD CLASSIFICATION MODEL1989Ingår i: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 10, nr 4-5, s. 687-693Artikel i tidskrift (Refereegranskat)
  • 179.
    Josefsson, Weine
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Solar ultraviolet radiation in Sweden1986Rapport (Övrigt vetenskapligt)
  • 180.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Information från Meteosat - forskningsrön och operationell tillämpning1985Rapport (Övrigt vetenskapligt)
6789 161 - 180 av 180
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  • sv-SE
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