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Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Lindskog, Magnus
    et al.
    SMHI, Forskningsavdelningen, Meteorologi.
    Ridal, Martin
    SMHI, Forskningsavdelningen, Meteorologi.
    Thorsteinsson, Sigurdur
    Icelandic Meteorological Office, Reykjavík, Iceland.
    Ning, Tong
    Lantmäteriet.
    Data assimilation of GNSS zenith total delays from a Nordic processing centre2017Ingår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 17, nr 22, s. 13983-13998Artikel i tidskrift (Refereegranskat)
  • 2. Mueller, Malte
    et al.
    Homleid, Mariken
    Ivarsson, Karl-Ivar
    SMHI, Samhälle och säkerhet.
    Koltzow, Morten A. O.
    Lindskog, Magnus
    SMHI, Forskningsavdelningen, Meteorologi.
    Midtbo, Knut Helge
    Andrae, Ulf
    SMHI, Forskningsavdelningen, Meteorologi.
    Aspelien, Trygve
    Berggren, Lars
    SMHI, Samhälle och säkerhet.
    Bjorge, Dag
    Dahlgren, Per
    SMHI, Forskningsavdelningen, Meteorologi.
    Kristiansen, Jorn
    Randriamampianina, Roger
    Ridal, Martin
    SMHI, Forskningsavdelningen, Meteorologi.
    Vignes, Ole
    AROME-MetCoOp: A Nordic Convective-Scale Operational Weather Prediction Model2017Ingår i: Weather and forecasting, ISSN 0882-8156, E-ISSN 1520-0434, Vol. 32, nr 2, s. 609-627Artikel i tidskrift (Refereegranskat)
  • 3.
    Olsson, Jonas
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Simonsson, Lennart
    SMHI, Forskningsavdelningen, Hydrologi.
    Ridal, Martin
    SMHI, Forskningsavdelningen, Meteorologi.
    Rainfall nowcasting: predictability of short-term extremes in Sweden2015Ingår i: Urban Water Journal, ISSN 1573-062X, Vol. 12, nr 1, s. 3-13Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Our current knowledge of the character of rainfall events in Sweden associated with extreme short-term accumulations and their predictability by forecasting, is very limited. In this study, observations from automatic stations and weather radars in Sweden were analysed to identify and characterise extreme short-term events. Often shorter-duration (1-6 h) extreme events were associated with small-scale structures, dominated by single cells, and longer-duration (12-24 h) events with less variable, larger-scale fields. For lead time 3 h, similar to 20% of the events were forecasted at the correct place with an error of <25% by the operational Swedish nowcasting system. If allowing for a 25 km displacement of the forecasted events, the hit rate increased by 10-15 percentage points. Some predictability was found for lead time 8 h but not for 24 h. The results suggest a potential added gain of increasing the temporal resolution of the Swedish flood forecasting system to sub-daily steps.

  • 4.
    Olsson, Jonas
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Simonsson, Lennart
    SMHI, Forskningsavdelningen, Hydrologi.
    Ridal, Martin
    SMHI, Forskningsavdelningen, Meteorologi.
    Rainfall nowcasting: predictability of short-term extremes in Sweden2014Ingår i: Urban Water Journal, ISSN 1573-062X, Vol. 11, nr 7, s. 605-615Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Our current knowledge of the character of rainfall events in Sweden associated with extreme short-term accumulations and their predictability by forecasting, is very limited. In this study, observations from automatic stations and weather radars in Sweden were analysed to identify and characterise extreme short-term events. Often shorter-duration (1-6 h) extreme events were associated with small-scale structures, dominated by single cells, and longer-duration (12-24 h) events with less variable, larger-scale fields. For lead time 3 h,,20% of the events were forecasted at the correct place with an error of <25% by the operational Swedish nowcasting system. If allowing for a 25 km displacement of the forecasted events, the hit rate increased by 10-15 percentage points. Some predictability was found for lead time 8 h but not for 24 h. The results suggest a potential added gain of increasing the temporal resolution of the Swedish flood forecasting system to sub-daily steps.

  • 5.
    Ridal, Martin
    SMHI, Forskningsavdelningen, Meteorologi.
    Isotopic ratios of water vapor and methane in the stratosphere: Comparison between ATMOS measurements and a one-dimensional model2002Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, ISSN 0747-7309, Vol. 107, nr D16, artikel-id 4285Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    [1] A one-dimensional model simulating the transport and chemistry of methane and water vapor including their isotopic ratios in the tropical stratosphere is compared to measurements by the Atmospheric Trace Molecule Spectroscopy experiment (ATMOS) instrument. The model and measurements show good agreement in the isotopic ratio profiles. The deltaD depletion for water vapor is -600parts per thousand to -500parts per thousand at the tropopause with a small increase up to similar to10 hPa. Above this altitude the modeled isotopic ratio shows a strong increase due to methane oxidation. The measured profiles are rather noisy above 10 hPa but give an indication of a stronger increase in the isotopic ratio than modeled. If the isotopic ratio of water vapor is allowed to vary at the tropopause simulating an annual cycle in the input values, a wave pattern that is transported upwards arises on the vertical profile. This is a similar effect as the "tape recorder'' for water vapor. A wave pattern can also be detected in the tropical deltaD profiles from ATMOS. The methane isotopic ratio shows behavior similar to that of water vapor but without the wave pattern. The increase in methane deltaD above 10 hPa is very strong. The measured profiles are again rather noisy above this altitude, but measurements from inside the polar vortex show that the methane isotopic ratio in the upper stratosphere is very high. The deltaD values are in the range of +300parts per thousand to +500parts per thousand at altitudes as low as 40 hPa (similar to25 km) in the polar vortex.

  • 6.
    Ridal, Martin
    et al.
    SMHI, Forskningsavdelningen, Meteorologi.
    Dahlbom, Mats
    Assimilation of Multinational Radar Reflectivity Data in a Mesoscale Model: A Proof of Concept2017Ingår i: Journal of Applied Meteorology and Climatology, ISSN 1558-8424, E-ISSN 1558-8432, Vol. 56, nr 6, s. 1739-1751Artikel i tidskrift (Refereegranskat)
  • 7.
    Ridal, Martin
    et al.
    SMHI, Forskningsavdelningen, Meteorologi.
    Lindskog, Magnus
    SMHI, Forskningsavdelningen, Meteorologi.
    Gustafsson, Nils
    SMHI, Forskningsavdelningen, Meteorologi.
    Haase, Günther
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Optimized advection of radar reflectivities2011Ingår i: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 100, nr 2-3, s. 213-225Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A nowcasting system for generation of short-range precipitation forecasts has been developed at the Swedish Meteorological and Hydrological Institute (SMHI). The methodology consists of utilising a time-series of radar reflectivity composites for deriving an advection field, which will give a better representation of the motion of the precipitation pattern compared to a model wind field. The advection field is derived applying a 4-dimensional variational data assimilation technique. The resulting field is then used for a semi-Lagrangian advection of the latest available reflectivity field forward in time. During the forecast, the advected field is gradually replaced by a numerical weather prediction forecast in order to include the onset of convection and advection into the radar coverage area. In an idealised example with simulated observations the functionality of the method is demonstrated. For a case study of a full scale example the resulting precipitation forecast shows large improvements compared to the operational numerical weather prediction model used at SMHI, especially for forecasts up to three hours, where the largest influence from the radar advection occurs. In an objective validation of the structure, amplitude and location of modelled precipitation, where the forecasts are compared to radar observations, these findings are confirmed. The same validation of model runs over a longer time period also clearly indicates that the amplitude, structure and location of the precipitation patterns are significantly improved as compared to a short-range forecast from the operational forecast model used at SMHI. (C) 2010 Elsevier B.V. All rights reserved.

  • 8.
    Ridal, Martin
    et al.
    SMHI, Forskningsavdelningen, Meteorologi.
    Murtagh, D P
    Merino, F
    Pardo, J R
    Pagani, L
    Microwave temperature and pressure measurements with the Odin satellite: II. Retrieval method2002Ingår i: Canadian journal of physics (Print), ISSN 0008-4204, E-ISSN 1208-6045, Vol. 80, nr 4, s. 455-467Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The millimetre receiver on the Swedish satellite Odin, will be used for detection of the 118.750 GHz oxygen line. The temperature and pressure will be determined from the output of a three-channel filter bank measurement. One frequency bin is centred over the emission-line frequency while the other two cover parts of the line wing, where the opacity is less, providing a useful signal at lower altitudes. The bandwidth of each channel is 40 MHz. The signal in the frequency bin covering the line centre is modeled by a high-resolution model including the Zeeman effect, developed by the Observatoire de Paris-Meudon. The other two 40 MHz bins are modeled using the much faster standard Odin forward model, developed at the Department of Meteorology at Stockholm University together with Chalmers University of Technology. The operational retrievals employ an iterative method that uses simulated signals from a reference atmosphere as a lookup table for the pressure. The temperature is then calculated from the equation of hydrostatic equilibrium, and a new lookup table computed. This process is repeated until a convergence criterion is reached. Simulations, including known error sources, show that the temperature can be retrieved with a root mean square (rms) around 3 K, in the altitude range similar to25-90 km using the operational temperature retrieval method (the filter bank method). A sub-millimetre receiver on board Odin will also be used to observe the oxygen line at 487.249 GHz. Both this line and the 118.750 GHz line can be observed in high resolution (150 kHz) for detailed studies of the Zeeman splitting. Retrievals from the high-resolution measurements are expected to give a precision of +/-2 K rms at that resolution. However, this kind of observation will occupy an entire spectrometer and will not be made on a regular basis.

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