Browsing by Subject "SCHEME"

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  • Zsebeházi, Gabriella; Mahó, Sándor István (2021)
    Land surface models with detailed urban parameterization schemes provide adequate tools to estimate the impact of climate change in cities, because they rely on the results of the regional climate model, while operating on km scale at low cost. In this paper, the SURFEX land surface model driven by the evaluation and control runs of ALADIN-Climate regional climate model is validated over Budapest from the aspect of urban impact on temperature. First, surface temperature of SURFEX with forcings from ERA-Interim driven ALADIN-Climate was compared against the MODIS land surface temperature for a 3-year period. Second, the impact of the ARPEGE global climate model driven ALADIN-Climate was assessed on the 2 m temperature of SURFEX and was validated against measurements of a suburban station for 30 years. The spatial extent of surface urban heat island (SUHI) is exaggerated in SURFEX from spring to autumn, because the urbanized gridcells are generally warmer than their rural vicinity, while the observed SUHI extent is more variable. The model reasonably simulates the seasonal means and diurnal cycle of the 2 m temperature in the suburban gridpoint, except summer when strong positive bias occurs. However, comparing the two experiments from the aspect of nocturnal UHI, only minor differences arose. The thorough validation underpins the applicability of SURFEX driven by ALADIN-Climate for future urban climate projections.
  • Boyd, Christopher; Vehkalahti, Roope; Tirkkonen, Olav; Laaksonen, Antti (IEEE, 2019)
    IEEE International Symposium on Information Theory
    We study medium access control layer random access under the assumption that the receiver can perform successive interference cancellation, without feedback. During recent years, a number of protocols with impressive error performance have been suggested for this channel model. However, the random nature of these protocols causes an error floor which limits their usability when targeting ultra-reliable communications. In very recent works by Paolini et al. and Boyd et. al., it was shown that if each user employs predetermined combinatorial access patterns, this error floor disappears. In this paper, we develop code design criteria for deterministic random access protocols in the ultra-reliability region, and build codes based on these principles. The suggested design methods are supported by simulations.
  • Ollinaho, Pirkka; Carver, Glenn D.; Lang, Simon T. K.; Tuppi, Lauri; Ekblom, Madeleine; Järvinen, Heikki (2021)
    Ensemble prediction is an indispensable tool in modern numerical weather prediction (NWP). Due to its complex data flow, global medium-range ensemble prediction has almost exclusively been carried out by operational weather agencies to date. Thus, it has been very hard for academia to contribute to this important branch of NWP research using realistic weather models. In order to open ensemble prediction research up to the wider research community, we have recreated all 50 + 1 operational IFS ensemble initial states for OpenIFS CY43R3. The dataset (Open Ensemble 1.0) is available for use under a Creative Commons licence and is downloadable from an https server. The dataset covers 1 year (December 2016 to November 2017) twice daily. Downloads in three model resolutions (T(L)159, T(L)399, and T(L)639) are available to cover different research needs. An open-source workflow manager, called OpenEPS, is presented here and used to launch ensemble forecast experiments from the perturbed initial conditions. The deterministic and probabilistic forecast skill of OpenIFS (cycle 40R1) using this new set of initial states is comprehensively evaluated. In addition, we present a case study of Typhoon Damrey from year 2017 to illustrate the new potential of being able to run ensemble forecasts outside of major global weather forecasting centres.
  • Solala, Eelis; Losilla, Sergio A.; Sundholm, Dage; Xu, Wenhua; Parkkinen, Pauli (2017)
    We present an integration scheme for optimizing the orbitals in numerical electronic structure calculations on general molecules. The orbital optimization is performed by integrating the Helmholtz kernel in the double bubble and cube basis, where bubbles represent the steep part of the functions in the vicinity of the nuclei, whereas the remaining cube part is expanded on an equidistant threedimensional grid. The bubbles' part is treated by using one-center expansions of the Helmholtz kernel in spherical harmonics multiplied with modified spherical Bessel functions of the first and second kinds. The angular part of the bubble functions can be integrated analytically, whereas the radial part is integrated numerically. The cube part is integrated using a similar method as we previously implemented for numerically integrating two-electron potentials. The behavior of the integrand of the auxiliary dimension introduced by the integral transformation of the Helmholtz kernel has also been investigated. The correctness of the implementation has been checked by performing Hartree-Fock self-consistent-field calculations on H-2, H2O, and CO. The obtained energies are compared with reference values in the literature showing that an accuracy of 10(-4) to 10(-7) E-h can be obtained with our approach. Published by AIP Publishing.
  • Ollinaho, P.; Bechtold, P.; Leutbecher, M.; Laine, M.; Solonen, A.; Haario, H.; Järvinen, Heikki (2013)
  • Stepanenko, Victor; Joehnk, Klaus D.; Machulskaya, Ekaterina; Perroud, Marjorie; Subin, Zack; Nordbo, Annika; Mammarella, Ivan; Mironov, Dmitri (2014)
  • Solala, Eelis; Parkkinen, Pauli; Sundholm, Dage (2018)
    Canonical decomposition methods and the Tucker decomposition method have been applied to the cube part of the orbitals in the bubbles and cube framework for numerical electronic structure calculations on molecules. The iterative process of two variants of the alternating least squares method for performing canonical decomposition is found to converge rapidly to a given accuracy, whereas the accuracy is not significantly improved by continuing the iterations, implying that the studied canonical decomposition methods are not of practical use in our approach to numerical electronic structure calculations. The Tucker decomposition method of the orbitals is on the other hand found to have relative errors that are smaller than the numerical accuracy of the orbitals. The calculations also show that the reconstruction of the orbitals leads to errors that are well below the required accuracy.