An approach for modelling snowcover ablation and snowmelt runoff in cold region environments

Reliable hydrological model simulations are the result of numerous complex interactions among hydrological inputs, landscape properties, and initial conditions. Determination of the effects of these factors is one of the main challenges in hydrological modelling. This situation becomes even more difficult in cold regions due to the ungauged nature of subarctic and arctic environments. This research work is an attempt to apply a new approach for modelling snowcover ablation and snowmelt runoff in complex subarctic environments with limited data while retaining integrity in the process representations. The modelling strategy is based on the incorporation of both detailed process understanding and inputs along with information gained from observations of basin-wide streamflow phenomenon; essentially a combination of deductive and inductive approaches. The study was conducted in the Wolf Creek Research Basin, Yukon Territory, using three models, a small-scale physically based hydrological model, a land surface scheme, and a land surface hydrological model. The spatial representation was based on previous research studies and observations, and was accomplished by incorporating landscape units, defined according to topography and vegetation, as the spatial model elements. Comparisons between distributed and aggregated modelling approaches showed that simulations incorporating distributed initial snowcover and corrected solar radiation were able to properly simulate snowcover ablation and snowmelt runoff whereas the aggregated modelling approaches were unable to represent the differential snowmelt rates and complex snowmelt runoff dynamics. Similarly, the inclusion of spatially distributed information in a land surface scheme clearly improved simulations of snowcover ablation. Application of the same modelling approach at a larger scale using the same landscape based parameterisation showed satisfactory results in simulating snowcover ablation and snowmelt runoff with minimal calibration. Verification of this approach in an arctic basin illustrated that landscape based parameters are a feasible regionalisation framework for distributed and physically based models. In summary, the proposed modelling philosophy, based on the combination of an inductive and deductive reasoning, is a suitable strategy for reliable predictions of snowcover ablation and snowmelt runoff in cold regions and complex environments

Structural and Magnetic Dynamics in the Magnetic Shape Memory Alloy Ni2_2MnGa

Magnetic shape memory Heusler alloys are multiferroics stabilized by the correlations between electronic, magnetic and structural order. To study these correlations we use time resolved x-ray diffraction and magneto-optical Kerr effect experiments to measure the laser induced dynamics in a Heusler alloy Ni$_2$MnGa film and reveal a set of timescales intrinsic to the system. We observe a coherent phonon which we identify as the amplitudon of the modulated structure and an ultrafast phase transition leading to a quenching of the incommensurate modulation within 300~fs with a recovery time of a few ps. The thermally driven martensitic transition to the high temperature cubic phase proceeds via nucleation within a few ps and domain growth limited by the speed of sound. The demagnetization time is 320~fs, which is comparable to the quenching of the structural modulation.Comment: 5 pages, 3 figures. Supplementary materials 5 pages, 5 figure

Coherent Acoustic Perturbation of Second-Harmonic-Generation in NiO

We investigate the structural and magnetic origins of the unusual ultrafast second-harmonicgeneration (SHG) response of femtosecond-laser-excited nickel oxide (NiO) previously attributed to oscillatory reorientation dynamics of the magnetic structure induced by d-d excitations. Using time-resolved x-ray diffraction from the (3/2 3/2 3/2) magnetic planes, we show that changes in the magnitude of the magnetic structure factor following ultrafast optical excitation are limited to $\Delta/$ = 1.5% in the first 30 ps. An extended investigation of the ultrafast SHG response reveals a strong dependence on wavelength as well as characteristic echoes, both of which give evidence for an acoustic origin of the dynamics. We therefore propose an alternative mechanism for the SHG response based on perturbations of the nonlinear susceptibility via optically induced strain in a spatially confined medium. In this model, the two observed oscillation periods can be understood as the times required for an acoustic strain wave to traverse one coherence length of the SHG process in either the collinear or anti-collinear geometries.Comment: 26 pages, 7 figure

Dynamic pathway of the photoinduced phase transition of TbMnO3_3

We investigate the demagnetization dynamics of the cycloidal and sinusoidal phases of multiferroic TbMnO$_3$ by means of time-resolved resonant soft x-ray diffraction following excitation by an optical pump. Using orthogonal linear x-ray polarizations, we suceeded in disentangling the response of the multiferroic cycloidal spin order from the sinusoidal antiferromagnetic order in the time domain. This enables us to identify the transient magnetic phase created by intense photoexcitation of the electrons and subsequent heating of the spin system on a picosecond timescale. The transient phase is shown to be a spin density wave, as in the adiabatic case, which nevertheless retains the wave vector of the cycloidal long range order. Two different pump photon energies, 1.55 eV and 3.1 eV, lead to population of the conduction band predominantly via intersite $d$-$d$ transitions or intrasite $p$-$d$ transitions, respectively. We find that the nature of the optical excitation does not play an important role in determining the dynamics of magnetic order melting. Further, we observe that the orbital reconstruction, which is induced by the spin ordering, disappears on a timescale comparable to that of the cycloidal order, attesting to a direct coupling between magnetic and orbital orders. Our observations are discussed in the context of recent theoretical models of demagnetization dynamics in strongly correlated systems, revealing the potential of this type of measurement as a benchmark for such complex theoretical studies

Dynamics of the photoinduced insulator-to-metal transition in a nickelate film

The control of materials properties with light is a promising approach towards the realization of faster and smaller electronic devices. With phases that can be controlled via strain, pressure, chemical composition or dimensionality, nickelates are good candidates for the development of a new generation of high performance and low consumption devices. Here we analyze the photoinduced dynamics in a single crystalline NdNiO$_3$ film upon excitation across the electronic gap. Using time-resolved reflectivity and resonant x-ray diffraction, we show that the pump pulse induces an insulator-to-metal transition, accompanied by the melting of the charge order. Finally we compare our results to similar studies in manganites and show that the same model can be used to describe the dynamics in nickelates, hinting towards a unified description of these photoinduced phase transitions.Comment: 17 pages, 6 figure

Gestión del agua subterránea en el centro-este de La Pampa : Una propuesta de actuación ante factores de incertidumbre hidrológica

El presente trabajo pretende introducir una discusión de una compleja situación hidrológica de la región Centro-Este de La Pampa, donde las peculiares características hidrológicas del ámbito subhúmedo-seco siempre han trasladado una situación al campo social y económico que hay que solucionar. Ante esta situación, las aguas subterráneas juegan un papel sumamente importante en estas condiciones de incertidumbre y se establecen como un recurso importante moderador en la planificación en un área de extrema fragilidad hidrológica. Por eso se pretende que, a partir del conocimiento hidrogeológico se pueda comprender y corregir la actividad socio económico de la región. Como resultado se demuestra que es posible obtener elementos de gestión en un área de extrema variabilidad hidrológica, con un factor importante de incertidumbre, a partir del conocimiento y trasladar los mismos a la actividad socio económico de la región y a su vez que sirvan como soporte para la toma de decisiones.This paper aims to introduce an analysis of a complex hydrological situation of the Central-East of La Pampa, where the peculiar hydrological characteristics of field-dry subsumed always been perceived as a serious problem that is transferred to the social and economic fields to be solve. In this situation, groundwater plays a major role in these conditions of uncertainty and constitutes a regulatory element of planning in an area of extreme fragility hydrological from knowledge, and moves them to the socio economic development of the region. As a result it is shown that it is possible to obtain management elements in an area of extreme hydrological variability, with a factor of uncertainty based on knowledge and move them to the socio economic development of the region and in turn serve as support for decision.Universidad Nacional de La Plat

A coupled hydrology-biogeochemistry model to simulate dissolved organic carbon exports from a permafrost influenced catchment

Funded by Natural Environment Research Council. Grant Number: NE/K000268/1 Natural Sciences and Engineering Research Council of CanadaPeer reviewedPublisher PD

Identificación y caracterización hidrológica de lagunas del noreste de la provincia de La Pampa

Fil: Dornes, Pablo F.. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Comas, Rocío N.. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Cardín, Daniel. Dirección General Catastro de La Pampa. Casa de Gobierno; ArgentinaFil: Pochetti, Roberto. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Ianni, Juan. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Kruse, Eduardo Emilio. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentin