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@MASTERSTHESIS{Rssler:256610,
      author       = {Rössler, Thomas},
      title        = {{O}ptimization and validation of atmospheric advective and
                      diffusive transport simulations},
      school       = {Fachhochschule Aachen, Campus Jülich},
      type         = {BA},
      reportid     = {FZJ-2015-06477},
      pages        = {II, 65},
      year         = {2015},
      note         = {Fachhochschule Aachen, Campus Jülich, Bachelorarbeit,
                      2015},
      abstract     = {Lagrangian particle dispersion models are indispensable
                      tools to study atmospheric transport processesbased on the
                      flow of individual air parcels.In operational uses cases
                      they are used to simulate the spread of radionuclides or
                      volcanic emissionsin emergency situations.Different
                      Lagrangian particle dispersion models have been developed
                      for those studies, like FLEXPART or HYSPLIT.It is very
                      important that the models are verified and their errors are
                      estimated so that the results are reliable.In this thesis
                      the advection and diffusion part of the new Lagrangian
                      particle dispersionmodel Massive Parallel Trajectory
                      Calculations (MPTRAC) was verified in idealized test cases
                      and inreal atmospheric conditions and optimized in terms of
                      accuracy and performance. Analytical test cases were applied
                      to the model to validate the advection.The implementation
                      and accuracy of integration schemes of different order,the
                      error caused by the linear interpolation of the wind fields
                      and the used coordinate system were discussed.All
                      implementations lead to correct and very accurate results. A
                      notable difference concerning the accuracy was only
                      determined between the first order Euler method and other
                      methods of higher order. Runge-Kutta methods of the order 2
                      to 4 and the Petterssen scheme led to very similar results,
                      indicating that an order of larger than 2 can not increase
                      the accuracy significantly.This is partly caused by the
                      linear interpolation of the meteorological data. Even if
                      tests have shown that the error caused by this linear
                      interpolation is small, higher order methods may need a
                      better interpolation to provide benefits.Tests for real
                      atmospheric conditions confirm these results, i.g., the
                      midpoint method was found to be the most performant
                      integration scheme. However, a small time step is required
                      to yieldsmall deviations from the reference solution. For
                      the tests with real atmospheric conditions the atmosphere
                      was separated into regions with similar conditions and the
                      resulting transport deviations are analyzed in detail.
                      Simulation errors in the stratosphere and in the tropics are
                      significantly smaller than in the troposphere or at high
                      latitudes.The diffusion scheme of MPTRAC consists of three
                      components, a random horizontal displacement, a random
                      vertical displacement, and a mesoscale diffusion that
                      depends on the variation of the wind field around an air
                      parcel.All three components were tested individually without
                      advection and produced results that correspond to analytical
                      solutions.However, it is difficult to predict a solution
                      under real atmospheric conditions, because the wind field
                      has a significant influence. A sensitivity test was done, to
                      get an overview of the impact of the diffusion components on
                      the transport of air parcels.The mesoscale diffusion has the
                      strongest influence, if default parameters are used,
                      followed by the vertical diffusion.The horizontal diffusion
                      has only a very small impact and does not seem to influence
                      the transport simulations significantly.In conclusion, the
                      model MPTRAC can be used to simulate the advection and
                      dispersion of air parcels correctly and
                      efficiently.Simulations with altitudes below the free
                      troposphere require relatively small time steps and the
                      diffusion model isprobably too simplistic, but the main task
                      of the model are simulations in the free troposphere and
                      stratosphere where the model shows good results.},
      cin          = {JSC},
      cid          = {I:(DE-Juel1)JSC-20090406},
      pnm          = {511 - Computational Science and Mathematical Methods
                      (POF3-511)},
      pid          = {G:(DE-HGF)POF3-511},
      typ          = {PUB:(DE-HGF)2},
      url          = {https://juser.fz-juelich.de/record/256610},
}