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Recent Submissions

  • Pfau-Kempf, Yann (Finnish Meteorological Institute, 2016)
    Vlasiator – From local to global magnetospheric hybrid-Vlasov simulations Contributions 127
    The Sun is the source of the solar wind, a continuous stream of electrically charged particles and magnetic fields pervading the Solar system. Its interaction with the magnetic field of the Earth, in and around the region called the magnetosphere, controls the flow of matter and energy in near-Earth space. A fundamental understanding of the physical processes at play is crucial for the building of forecasting and warning systems, as the influence of the solar wind during space storms can harm life and technology in space and on the ground. These effects, collectively known as space weather, are one of the biggest albeit least understood natural threats to society. The research effort needed includes the development of observational methods as well as theories and models, to first describe and later predict the mechanisms and consequences of space weather. This doctoral thesis, comprising an introduction and four peer-reviewed articles, presents the hybrid-Vlasov model Vlasiator developed at the Finnish Meteorological Institute. Based on a detailed description of proton physics in space plasmas, Vlasiator allows to simulate both local contexts and the Earth’s magnetosphere on global scales. This unprecedented capability is only accessible by harnessing the power of modern supercomputers. The aim of this work is threefold. The current version of Vlasiator is documented considering physical and computational aspects, the correctness of the simulations is demonstrated by comparing to analytical theories and spacecraft observations, and new scientific results gained with this model are presented.
  • Vira, Julius (Finnish Meteorological Institute, 2017)
    Finnish Meteorological Institute Contributions 130
    Atmospheric chemistry and transport models are used for a wide range of applications which include predicting dispersion of a hazardous pollutants, forecasting regional air quality, and modelling global distribution of aerosols and reactive gases. However, any such prediction is uncertain due to inaccuracies in input data, model parametrisations and lack of resolution. This thesis studies methods for integrating remote sensing and in-situ observations into atmospheric chemistry models with the aim of improving the predictions. Techniques of data assimilation, originally developed for numerical weather prediction, are evaluated for improving regional-scale predictions in two forecast experiments, one targeting the photochemical pollutants ozone (O3) and nitrogen dioxide (NO2), the other targeting sulphur dioxide (SO2). In both cases, assimilation of surface-based air quality monitoring data is found to initially improve the forecast when assessed on monitoring stations not used in assimilation. However, as the forecast length increased, the forecast converged towards the reference simulations where no data assimilation was used. The relaxation time was 6-12 hours for SO2 and NO2 and about 24 hours for O3. An alternative assimilation scheme was tested for SO2. In addition to the initial state of the forecast, the scheme adjusted the gridded emission fluxes based on the observations within the last 24 hours. The improvements due to adjustment of emissions were generally small but, where observed, the improvements persisted throughout the 48 hour forecast. The assimilation scheme was further adapted for estimating emission fluxes in volcanic eruptions. Assimilating retrievals of the Infrared Atmospheric Sounding Interferometer (IASI) instrument allowed reconstructing both the vertical and horizontal profile of SO2 emissions during the 2010 eruption of Eyjafjallaj¨okull in Iceland. As a novel feature, retrievals of plume height were assimilated in addition to the commonly used column density retrievals. The results for Eyjafjallaj¨okull show that the plume height retrievals provide a useful additional constraint in conditions where the vertical distribution would otherwise remain ambiguous. Finally, the thesis presents a rigorous description and evaluation of a numerical scheme for solving the advection equation. The scheme conserves tracer mass and non-negativity, and is therefore suitable for regional and global atmospheric chemistry models. The scheme is particularly adapted for handling discontinuous solutions; for smooth solutions, the scheme is nevertheless found to perform comparably to other state-of-art schemes used in atmospheric models.
  • Kaipiainen, Heidi; Kemppainen, Eija; Bonn, Thomas (Suomen ympäristökeskus, 1997)
    Suomen ympäristö 78
  • Mäkinen, Irma; Huhtala, Sami; Korhonen, Kaija; Saares, Riitta; Salonen, Pasi; Vänni, Timo (Suomen ympäristökeskus, 2001)
    Suomen ympäristökeskuksen moniste 214
  • Penttinen, Riina; Kauppila, Jussi (Suomen ympäristökeskus, 2001)
    Suomen ympäristökeskuksen moniste 213
  • Mäkinen, Irma; Huhtala, Sami; Järvinen, Olli; Saares, Riitta; Vänni, Timo (Suomen ympäristökeskus, 2000)
    Suomen ympäristökeskuksen moniste 208
  • Tenhunen, Jyrki; Oinonen, Jaana; Seppälä, Jyri (Suomen ympäristökeskus, 2000)
    Suomen ympäristö 434
  • Raassina, Sami; Suokas, Tuomo (Suomen ympäristökeskus, 2001)
    Suomen ympäristökeskuksen moniste 207
  • Luntinen, Marita; Seppälä, Timo; Tuomainen, Jouko; Lapveteläinen, Tiina (Suomen ympäristökeskus, 2000)
    Suomen ympäristökeskuksen moniste 206
  • Hevonoja, Irma; Kleemola, Pauli; Soinisalo, Oili (Suomen ympäristökeskus, 2000)
    Suomen ympäristökeskuksen moniste 204
  • Forsius, Kaj (Suomen ympäristökeskus, 2000)
    Suomen ympäristökeskuksen moniste 203
  • Saarikoski, Heli (Suomen ympäristökeskus, 2000)
    Suomen ympäristökeskuksen moniste 202
  • Vaalasranta, Anna; Jaakkola, Mauri (Suomen ympäristökeskus, 2000)
    Suomen ympäristökeskuksen moniste 199