Can we use satellite-based soil-moisture products at high resolution to investigate land-use differences and land-atmosphere interactions? a case study in the savanna

The use of soil moisture (SM) measurements from satellites has grown in recent years, fostering the development of new products at high resolution. This opens the possibility of using them for certain applications that were normally carried out using in situ data. We investigated this hypothesis through two main analyses using two high-resolution satellite-based soil moisture (SBSM) products that combined microwave with thermal and optical data: (1) The Disaggregation based on Physical And Theoretical scale Change (DISPATCH) and, (2) The Soil Moisture Ocean Salinity-Barcelona Expert Center (SMOS-BEC Level 4). We used these products to analyse the SM differences among pixels with contrasting vegetation. This was done through the comparison of the SM measurements from satellites and the measurements simulated with a simple antecedent precipitation index (API) model, which did not account for the surface characteristics. Subsequently, the deviation of the SM from satellite with respect to the API model (bias) was analysed and compared for contrasting land use categories. We hypothesised that the differences in the biases of the varied categories could provide information regarding the water retention capacity associated with each type of vegetation. From the satellite measurements, we determined how the SM depended on the tree cover, i.e., the denser the tree cover, the higher the SM. However, in winter periods with light rain events, the tree canopy could dampen the moistening of the soil through interception and conducted higher SM in the open areas. This evolution of the SM differences that depended on the characteristics of each season was observed both from satellite and from in situ measurements taken beneath a tree and in grass on the savanna landscape. The agreement between both types of measurements highlighted the potential of the SBSM products to investigate the SM of each type of vegetation. We found that the results were clearer for DISPATCH, whose data was not smoothed spatially as it was in SMOS-BEC. We also tested whether the relationships between SM and evapotranspiration could be investigated using satellite data. The answer to this question was also positive but required removing the unrealistic high-frequency SM oscillations from the satellite data using a low pass filter. This improved the performance scores of the products and the agreement with the results from the in situ data. These results demonstrated the possibility of using SM data from satellites to substitute ground measurements for the study of land–atmosphere interactions, which encourages efforts to improve the quality and resolution of these measurements

The Climate of Medieval Madrid as Deduced From Documents and the “Libro de la Montería” (14th-16th Centuries)

El presente trabajo pretende analizar cuáles eran las características climáticas que se sucedían en Madrid y su Tierra a lo largo del año, fundamentalmente entre los siglos XIV y XVI. Se intentará comprobar, dentro de las limitaciones que impone la documentación de la época, si en aquel tiempo se daba también un clima mediterráneo, o no, y si este ha variado mucho desde entonces. Igualmente se podrá comprobar algo que tal vez podría, aunque no debería, sorprendernos: el hombre medieval tenía muy claros muchos conceptos meteorológicos y climatológicos, aunque siempre aprehendidos con una finalidad práctica, para aplicarlos en su vida cotidiana tan cercana y dependiente de la naturaleza.This paper analyses climatic characteristics in Madrid and surroundings throughout the year between the 14th and 16th centuries. Within the constraints imposed by the contemporary documentation available, the aim is to determine whether or not a Mediterranean climate existed in the Middle Ages, and if the characteristics of this climate have changed. In addition, I shall demonstrate that medieval people had a clear understanding of meteorological and climatic concepts, although these were applied for practical purposes in a daily life closely associated with nature and the environment

Application of a GOY model to atmospheric boundary layer data

This article analyzes the possibility of applying a GOY theoretical model to atmospheric boundary layer data. Bearing this in mind, relative scaling exponents of velocity structure functions are used to compare the model with the data under study. In the model, these exponents are set based on two parameters (q and δ), which are appropriate to define the model that better features a certain atmospheric state.This research has been funded by the Spanish Ministry of Science and Innovation (projects CGL 2006-12474- C03-03 and CGL2009-12797-C03-03). GR58/08 program (supported by BSCH and UCM) has also partially financed this work through the Research Group “Micrometeorology and Climate Variability” (no 910437)

Usable boundary for visibility-based surveillance-evasion games

We consider a surveillance-evasion game in an environment with obstacles. In such an environment, a mobile pursuer seeks to maintain the visibility with a mobile evader, who tries to get occluded from the pursuer in the shortest time possible. In this two-player zero-sum game setting, we study the discontinuities of the value of the game near the boundary of the target set (the non-visibility region). In particular, we describe the transition between the usable part of the boundary of the target (where the value vanishes) and the non-usable part (where the value is positive). We show that the value enjoys a different behaviour depending on the regularity of the obstacles involved in the game. Namely, we prove that the boundary profile is continuous for the case of smooth obstacles, and that it exhibits a jump discontinuity when the obstacle contains corners. Moreover, we prove that, in the latter case, there is a semi-permeable barrier emanating from the interface between the usable and the non-usable part of the boundary of the target set.Comment: 33 pages, 8 figure

Sparse approximation in learning via neural ODEs

We consider the neural ODE and optimal control perspective of supervised learning with $L^1(0,T;\mathbb{R}^{d_u})$ control penalties, where rather than only minimizing a final cost for the state, we integrate this cost over the entire time horizon. Under natural homogeneity assumptions on the nonlinear dynamics, we prove that any optimal control (for this cost) is sparse, in the sense that it vanishes beyond some positive stopping time. We also provide a polynomial stability estimate for the running cost of the state with respect to the time horizon. This can be seen as a \emph{turnpike property} result, for nonsmooth functionals and dynamics, and without any smallness assumptions on the data, both of which are new in the literature. In practical terms, the temporal sparsity and stability results could then be used to discard unnecessary layers in the corresponding residual neural network (ResNet), without removing relevant information.Comment: 24 pages, 5 figure

Reachable set for Hamilton–Jacobi equations with non-smooth Hamiltonian and scalar conservation laws

We give a full characterization of the range of the operator which associates, to any initial condition, the viscosity solution at time T of a Hamilton–Jacobi equation with convex Hamiltonian. Our main motivation is to be able to treat the case of convex Hamiltonians with no further regularity assumptions. We give special attention to the case H(p)=|p|, for which we provide a rather geometrical description of the range of the viscosity operator by means of an interior ball condition on the sublevel sets. From our characterization of the reachable set, we are able to deduce further results concerning, for instance, sharp regularity estimates for the reachable functions, as well as structural properties of the reachable set. The results are finally adapted to the case of scalar conservation laws in dimension oneThis project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement NO: 694126-DyCon), the Alexander von Humboldt-Professorship program, the European Unions Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 765579-ConFlex, the Transregio 154 Project “Mathematical Modelling, Simulation and Optimization Using the Example of Gas Networks”, project C08, of the German DFG, the Grant MTM2017-92996-C2-1-R COSNET of MINECO (Spain) and the Elkartek grant KK-2020/00091 CONVADP of the Basque governmen

Propagation and effects of a mesoscale gravity wave over a weakly-stratified nocturnal boundary layer during the SABLES2006 Field Campaign

This research has been funded by the Spanish Ministry of Education and Science (projects CGL2004-03109 and CGL2006-12474-C03-03). IV PRICIT program (supported by CM and UCM) has also partially financed this work through the Research Group ”Micrometeorology and Climate Variability” (n◦ 910437)

Similarity scales in the stable boundary layer: a test against data

Póster elaborado para la European Geosciences Union General Assembly celebrada los días 22-27 de abril de 2012 en Viena.The research was partially supported by European Union 7th Framework Programme (FP7/2007-2013) under grant agreement no. 212095 (CityZen) in the frame of the BOLCHEM model development activity. This research has also been partly funded by the Spanish Ministry of Education and Science (project CGL2009-12797- C03-03). The GR35/10 program (supported by Banco Santander and UCM) has also partially financed this work through the Research Group “Micrometeorology and Climate Variability” (nº 910437)

TAMAÑO DE TRANSACCIONES, INTRODUCCIÓN DE ÓRDENES Y PREFERENCIAS POR PRECIOS EN LOS SPLITS DE ACCIONES

In this study we analyse the effect of stock splits on stocks¿ trading activity using intraday data from a sample of 46 stock splits from the Spanish stock market. In particular, we study changes to trading activity, trading composition, the information asymmetry of stocks, the distribution of the order flow, in order to test two versions of the liquidity hypotheses: the optimal relative tick size and the price preferences hypotheses. The results obtained suggest that stock splits do not uniformly improve liquidity of shares. Following stock splits there is a drop in trading volume and depth and a significant increase in the relative bid-ask spread. We detect a change in trading composition, with a statistically significant increase in the smallest transactions, fundamentally on the buyer side of the lowest priced shares. The level of information asymmetry does not diminish, given that the adverse selection component of the effective spread reduces only insignificantly for the full sample, although it falls significantly in small transactions. Finally there are significant changes in the percentage of orders that provide liquidity to the market. As a whole, the findings are consistent with the idea that splits, despite higher transaction costs, encourage the entry of new individual investors attracted by the lower stock prices. En este trabajo se analiza el efecto de los splits en la negociación de las acciones, utilizando datos intradiarios de una muestra de 46 activos del mercado de capitales español. Los resultados obtenidos sugieren que los splits no mejoran la liquidez, dado que se reduce el volumen de negociación y la profundidad, y se incrementa paralelamente el spread relativo. Se detecta un cambio en la composición de la negociación, con un incremento estadísticamente significativo de las transacciones pequeñas, fundamentalmente del lado comprador, en las acciones de precio relativamente más bajo. La asimetría informativa no disminuye, dado que el componente de selección adversa del spread efectivo se reduce de forma insignificante para el conjunto de la muestra, aunque cae significativamente en las transacciones pequeñas. Finalmente, no cambia significativamente el porcentaje de órdenes que suponen provisión de liquidez. En conjunto, la evidencia obtenida resulta consistente con la idea de que los splits, pese a los mayores costes de transacción, fomentan la entrada de nuevos inversores individuales atraídos por los menores precios de los títulos.Splits. Actividad negociadora. Liquidez. Microestructura. Splits. Trading activity. Liquidity. Microstructure.

Analysis of gravity waves generated at the top of a drainage flow

Drainage or katabatic flows are common mesoscale circulations established as a result of differential radiative cooling of near-surface air masses in sloping terrain. The initial irruption of these flows, with sudden shifts in wind speed and direction, may result in vertical displacements of air parcels from their equilibrium position, which prove to be a common source of internal gravity waves. This paper illustrates this mechanism and describes the main features of the oscillations following the study of observational data gathered throughout one night during the Stable Atmospheric Boundary Layer Experiment in Spain 2006 (SABLES2006) field campaign.This research has been funded by the Spanish Ministry of Science and Innovation (Projects CGL2004-03109, CGL 2006-12474- C03-03, and CGL2009-12797-C03-03). The GR58/08 program (supported by BSCH and UCM) has also partially financed this work through the Research Group ‘‘Micrometeorology and Climate Variability’’ (910437)