Analysis of 2 meter temperature and relative humidity

This note documents the recent installation of the analysis of the near surface parameters into the HIRLAM system. It is intended to explain why this analysis is primarely needed for the new surface parameterization that is being developed, although a version able to run within the old surface parameterization context has been prepared also. A procedure for the vertical reduction of the first guess fields to the station height has been introduced, and is specially useful in complex terrain. Since the method of analysis is Optimum Interpolation, a re-evaluation of the statistics of the first guess errors was necessary. First guess error covariances have been obtained for a selection of stations in Spain and in Scandinavia for winter and summer, in order to study the possible dependence on season and latitude. The effect of the orography as source of anisotropy, both because to the coastline and the inland topography, is included in the formulation of a new structure function

Perturbations in Hybrid Loop Quantum Cosmology: Continuum Limit in Fourier Space

We analyze the passage to a continuum limit of the mode spectrum of primordial perturbations around flat cosmological spacetimes in hybrid Loop Quantum Cosmology, showing that this limit can be reached even if one starts by considering a finite fiducial cell as spatial slice. We focus our attention on regimes in which the background cosmology follows the effective dynamics of Loop Quantum Cosmology, although we comment on extensions of our arguments beyond this regime, as well as to some formalisms other than the hybrid approach. Whereas the perturbed system can be described in an invariant way under changes of the fiducial volume using the standard variables of the improved prescription for Loop Quantum Cosmology, we show that the desired continuum limit can be established by means of scaling transformations of the physical volume when this volume grows unboundedly. These transformations lead to a model with a continuum of modes and independent of any scale of reference for the physical volume. For the sake of comparison, we also consider an alternative road to the continuum in Fourier space that has been employed in geometrodynamics and is based on the use of scaling transformations of the fiducial volume, together with variables that are independent of them.Comment: 13 page

On the evolution of the volume in Loop Quantum Cosmology

The dynamics of the expectation value of the volume is one of the key ingredients behind the replacement of the Big Bang singularity by a bounce in Loop Quantum Cosmology. As such, it is of great importance that this quantity is mathematically well-defined in the space of physical states of the theory. A number of caveats have been raised about such a definition entering in conflict with the quantum evolution of states, motivated by the situation found in quantum geometrodynamics. We show that there are ways around these caveats, all of which are related to the existence of quantization prescriptions leading to a nondegenerate curvature operator in Loop Quantum Cosmology. Furthermore, we explicitly check that there exist families of physical states for which the expectation value of the volume is actually finite under evolution. These include the Gaussian states traditionally used in investigations of the quantum bounce. Interestingly, the properties of the curvature operator that allow for such a good behavior of the volume are only possible thanks to the discreteness of the geometry characteristic of the loop quantization procedure.Comment: 13 page

Usage of satellite data in the HIRLAM new snow depth analysis

Comunicación presentada en: 4th SRNWP/HIRLAM workshop on surface processes and assimilation of surface variables celebrado en Norrköping, Suecia, del 15 al 17 de septiembre de 2004.New Optimum Interpolation Snow Depth Analysis has been recently developed for HIRLAM. Now, SSMI derived NESDIS snow cover weekly product and MODIS TERRA daily 0.05º snow cover data have been tested as information supply for this analysis. Some conclusions are drawn from them. Additionally, we tested the differences found in the snow cover field depending on the spatial resolution of the experiments

Usage of SYNOP 10 meters wind observations in HIRLAM

It is not easy to deal with 10 meters wind observations oven land in NWP models. This is due mainly to the difficulty of the models to represent the real orography and physiography and the high degree of dependence of near surface wind observations with both, physiography and orography. Other source of errors in the analyzed 10 meters wind field is the usage of observations which are not representative of the neighbouring terrain. Here, we describe the method we used to, subjectively, identify good and bad wind stations, the way to introduce SYNOP 10 meters wind observations in HIRLAM using whitelists and the analysis of the experiments and case studies carried out

Fermions in Hybrid Loop Quantum Cosmology

This work pioneers the quantization of primordial fermion perturbations in hybrid Loop Quantum Cosmology (LQC). We consider a Dirac field coupled to a spatially flat, homogeneous, and isotropic cosmology, sourced by a scalar inflaton, and treat the Dirac field as a perturbation. We describe the inhomogeneities of this field in terms of creation and annihilation variables, chosen to admit a unitary evolution if the Dirac fermion were treated as a test field. Considering instead the full system, we truncate its action at quadratic perturbative order and construct a canonical formulation. In particular this implies that, in the global Hamiltonian constraint of the model, the contribution of the homogeneous sector is corrected with a quadratic perturbative term. We then adopt the hybrid LQC approach to quantize the full model, combining the loop representation of the homogeneous geometry with the Fock quantization of the inhomogeneities. We assume a Born-Oppenheimer ansatz for physical states and show how to obtain a Schr\"odinger equation for the quantum evolution of the perturbations, where the role of time is played by the homogeneous inflaton. We prove that the resulting quantum evolution of the Dirac field is indeed unitary, despite the fact that the underlying homogeneous geometry has been quantized as well. Remarkably, in such evolution, the fermion field couples to an infinite sequence of quantum moments of the homogeneous geometry. Moreover, the evolved Fock vacuum of our fermion perturbations is shown to be an exact solution of the Schr\"odinger equation. Finally, we discuss in detail the quantum backreaction that the fermion field introduces in the global Hamiltonian constraint. For completeness, our quantum study includes since the beginning (gauge-invariant) scalar and tensor perturbations, that were studied in previous works.Comment: 29 pages. It matches published versio

Modified FRW cosmologies arising from states of the hybrid quantum Gowdy model

We construct approximate solutions of the hybrid quantum Gowdy cosmology with three-torus topology, linear polarization, and local rotational symmetry, in the presence of a massless scalar field. More specifically, we determine some families of states for which the complicated inhomogeneous and anisotropic Hamiltonian constraint operator of the Gowdy model is approximated by a much simpler one. Our quantum states follow the dynamics governed by this simpler constraint, while being at the same time also approximate solutions of the full Gowdy model. This is so thanks to the quantum correlations that the considered states present between the isotropic and anisotropic sectors of the model. Remarkably, this simpler constraint can be regarded as that of a flat Friedmann-Robertson-Walker universe filled with different kinds of perfect fluids and geometrically corrected by homogeneous and isotropic curvature-like terms. Therefore, our quantum states, which are intrinsically inhomogeneous, admit approximate homogeneous and isotropic effective descriptions similar to those considered in modified theories of gravity.Comment: Version accepted for publication in PR