Downscaling heavy rainfall in the subtropics ? a simple approach for dynamical nesting

International audienceThe simulation of local scale precipitation with nested models often suffers from large errors in the boundary rows. Advection of precipitation into the model domain of the small scale model can lead to an overestimation of precipitation in the boundary grid cells of the nested model and a drying of the interior grid area. Consequently, the finer scale structure of rainfall events of the small scale model can not evolve. These errors result from three main sources: "dynamical", "scale", and "parameterization" problems. As a first step to reduce the "parameterization" boundary errors, we propose a nesting procedure where rainwater from the driving larger scale model is converted to cloud water in the smaller scale model. The nesting method is applied to a case study of heavy rainfall in semi-arid southern Morocco. The results show the elimination of erroneous excessive rainfall in the boundary rows and slightly enhanced rainfall in the interior of the nested model domain. Additionally, fine scale structures in the precipitation patterns develop. The excessive surface runoff is clearly diminished in comparison to the standard nesting procedure. The proposed approach enables scale consistent precipitation patterns resulting from model physics and grid-resolution of the smaller scale model for the complete model domain

Observation of Andreev bound states in YBaCuO/Au/Nb ramp-type Josephson junctions

We report on Josephson and quasiparticle tunneling in YBa2Cu3O7-x(YBCO)/Au/Nb ramp junctions of several geometries. Macroscopically, tunneling occurs in the ab-plane of YBCO either in the (100) and (010) direction, or in the (110) direction. These junctions have a stable and macroscopically well defined geometry. This allows systematic investigations of both quasiparticle and Josephson tunneling over a wide range of temperature and magnetic field. With Nb superconducting, its gap appears in the quasiparticle conductance spectra as Nb coherence peaks and a dip at the center of a broadened zero-bias conductance peak (ZBCP). As we increase the temperature or an applied magnetic field both the Nb coherence peaks and the dip get suppressed and the ZBCP fully develops, while states are conserved. With Nb in the normal state the ZBCP is observed up to about 77 K and is almost unaffected by an increasing field up to 7 T. The measurements are consistent with a convolution of density of states with broadened Andreev bound states formed at the YBCO/Au/Nb junction interfaces. Since junctions with different geometries are fabricated on the same substrate under the same conditions one expects to extract reliable tunneling information that is crystallographic direction sensitive. In high contrast to Josephson tunneling, however, the quasiparticle conductance spectra are crystallographic orientation insensitive: independent whether the tunneling occurs in the (100) or (110) directions, a pronounced ZBCP is always observed, consistent with microscopic roughness of the junction interfaces. Qualitatively, all these particularities regarding quasiparticle spectra hold regardless whether the YBCO thin film is twinned or untwinned.Comment: 13 pages, 10 figure

Numerical simulations of two dimensional magnetic domain patterns

I show that a model for the interaction of magnetic domains that includes a short range ferromagnetic and a long range dipolar anti-ferromagnetic interaction reproduces very well many characteristic features of two-dimensional magnetic domain patterns. In particular bubble and stripe phases are obtained, along with polygonal and labyrinthine morphologies. In addition, two puzzling phenomena, namely the so called `memory effect' and the `topological melting' observed experimentally are also qualitatively described. Very similar phenomenology is found in the case in which the model is changed to be represented by the Swift-Hohenberg equation driven by an external orienting field.Comment: 8 pages, 8 figures. Version to appear in Phys. Rev.

Current-induced vortex dynamics in Josephson-junction arrays: Imaging experiments and model simulations

We study the dynamics of current-biased Josephson-junction arrays with a magnetic penetration depth smaller than the lattice spacing. We compare the dynamics imaged by low-temperature scanning electron microscopy to the vortex dynamics obtained from model calculations based on the resistively-shunted junction model, in combination with Maxwell's equations. We find three bias current regions with fundamentally different array dynamics. The first region is the subcritical region, i.e. below the array critical current I_c. The second, for currents I above I_c, is a "vortex region", in which the response is determined by the vortex degrees of freedom. In this region, the dynamics is characterized by spatial domains where vortices and antivortices move across the array in opposite directions in adjacent rows and by transverse voltage fluctuations. In the third, for still higher currents, the dynamics is dominated by coherent-phase motion, and the current-voltage characteristics are linear.Comment: 10 pages, with eps figures. To appear in Phys. Rev.

A smooth cascade of wrinkles at the edge of a floating elastic film

The mechanism by which a patterned state accommodates the breaking of translational symmetry by a phase boundary or a sample wall has been addressed in the context of Landau branching in type-I superconductors, refinement of magnetic domains, and compressed elastic sheets. We explore this issue by studying an ultrathin polymer sheet floating on the surface of a fluid, decorated with a pattern of parallel wrinkles. At the edge of the sheet, this corrugated profile meets the fluid meniscus. Rather than branching of wrinkles into generations of ever-smaller sharp folds, we discover a smooth cascade in which the coarse pattern in the bulk is matched to fine structure at the edge by the continuous introduction of discrete, higher wavenumber Fourier modes. The observed multiscale morphology is controlled by a dimensionless parameter that quantifies the relative strength of the edge forces and the rigidity of the bulk pattern.Comment: 4 pages, 4 figure

Behavior of vortices near twin boundaries in underdoped Ba(Fe1−xCox)2As2Ba(Fe_{1-x}Co_{x})_{2}As_{2}

We use scanning SQUID microscopy to investigate the behavior of vortices in the presence of twin boundaries in the pnictide superconductor Ba(Fe1-xCox)2As2. We show that the vortices avoid pinning on twin boundaries. Individual vortices move in a preferential way when manipulated with the SQUID: they tend to not cross a twin boundary, but rather to move parallel to it. This behavior can be explained by the observation of enhanced superfluid density on twin boundaries in Ba(Fe1-xCox)2As2. The observed repulsion from twin boundaries may be a mechanism for enhanced critical currents observed in twinned samples in pnictides and other superconductors

Type-1.5 Superconductors

We demonstrate the existence of a novel superconducting state in high quality two-component MgB2 single crystalline superconductors where a unique combination of both type-1 (kappa_1 0.707) superconductor conditions is realized for the two components of the order parameter. This condition leads to a vortex-vortex interaction attractive at long distances and repulsive at short distances, which stabilizes unconventional stripe- and gossamer-like vortex patterns that we have visualized in this type-1.5 superconductor using Bitter decoration and also reproduced in numerical simulations.Comment: accepted in Phys. Rev. Let

Model independent approach to studies of the confining dual Abrikosov vortex in SU(2) lattice gauge theory

We address the problem of determining the type I, type II or borderline dual superconductor behavior in maximal Abelian gauge SU(2) through the study of the dual Abrikosov vortex. We find that significant electric currents in the simulation data call into question the use of the dual Ginzburg Landau Higgs model in interpreting the data. Further, two definitions of the penetration depth parameter take two different values. The splitting of this parameter into two is intricately connected to the existence of electric currents. It is important in our approach that we employ definitions of flux and electric and magnetic currents that respect Maxwell equations exactly for lattice averages independent of lattice spacings. Applied to specific Wilson loop sizes, our conclusions differ from those that use the dual GLH model.Comment: 18 pages, 14 figures, change title, new anaylysis with more figure

On expansion in the width for domain walls

The well-known idea to construct domain wall type solutions of field equations by means of an expansion in the width of the domain wall is reexamined. We observe that the problem involves singular perturbations. Hilbert-Chapman-Enskog method is used to construct a consistent perturbative expansion. We obtain the solutions to the second order in the width without introducing an effective action for the domain wall. We find that zeros of the scalar field in general do not lie on a Nambu-Goto trajectory. As examples we consider cylindrical and spherical domain walls. We find that the spherical domain wall, in contradistinction to the cylindrical one, shows an effective rigidity.Comment: 21 pages, LaTe