A stochastic model of throughfall for extreme events

International audienceAlthough it is well known that forest canopies reduce the amount and intensity of precipitation at the ground surface, little is known about how canopy interception modifies extreme events. The effects of forest cover on intensity-duration-frequency relationships were investigated, using a stochastic model to extrapolate measured rainfall and throughfall to throughfall expected during extreme events. The model coupled a stochastic model of rainfall with stochastic representations of evaporation and precipitation transfer through canopies. Stochastic evaporation was governed by probability distributions sensitive to storm size, and transfer through canopies was governed by a black-box linear system. The modelled reduction of extreme-event intensities by canopies was 5?30%, depending on duration and return interval. The reduction was 15?20% in low return interval events (2 y) at all durations. In contrast, intensities of high return interval events (90 y) were proportionally more reduced at short durations (~30% reduced) than at long durations (~5% reduced). The model suggested that evaporative losses reduced intensity in the frequent events (2 y return interval), but water transfer through the canopy was more important for the reduction in intensity in the rarest extreme events. High return intervals of long duration were least affected by canopies because evaporative losses were the least proportion of rainfall. Extreme events larger than 10- or 20-y return interval probability threshold occurred only 31?69% as often in throughfall as in rainfall. Keywords: canopy interception, throughfall, stochastic rainfall modelling, rainfall intensity, linear systems, landslide

Time scale and intensity dependency in multiplicative cascades for temporal rainfall disaggregation

[1] Multiplicative random cascades (MRCs) can parsimoniously generate highly intermittent patterns similar to those in rainfall. The elemental MRC model parameter is the cascade weight, which determines how rainfall at one scale is partitioned at the next smallest scale in the cascade. While it is known that the probability density of these weights may vary with both time scale and rainfall intensity, nearly all previous studies have considered either time scale or intensity separately. We examined the simultaneous dependency of the weights on both factors and assessed the impacts of explicitly including these dependencies in the MRC model. On the basis of the observed relationships between cascade weights and time scale and intensity, four progressively more “dependent” models were constructed to disaggregate a long time series of daily rainfall to hourly intervals. We found that inclusion of the intensity dependency on the model parameters that generate dry intervals greatly improved performance. For the relatively small range of time scales over which the rainfall was disaggregated, varying model parameters with time scale resulted in minor improvement

Versatile Ion-polarized Techniques On-line (VITO) experiment at ISOLDE-CERN

The VITO (Versatile Ion-polarized Techniques Online) project is a new experimental setup at the ISOLDE facility at CERN. VITO is a dedicated beam line for producing laser-induced spin-polarized beams of both, atoms and ions, and it has been commissioned in response to the continuously growing demand for the use of spin-polarized beams. The new VITO beam line is a modification of the formerly existing ultra-high vacuum beam line, connecting ASPIC (Apparatus for Surface Physics and Interfaces at CERN), and it has been under construction since the beginning of 2014. Once fully commissioned, VITO will open up numerous possibilities for carrying out multidisciplinary experiments in the areas of nuclear and solid state physics, fundamental interaction physics and biophysics. In its final stage the VITO beam line will provide three fully independent experimental stations: UHV chamber for material science applications, a P-asymmetry station where highly-polarized ions will be available, and a central open-end station suitable for travelling experiments. The VITO beam line will operate in two different modes providing either beams of spin-polarized atoms or ions, or non-polarized ion beams to all three end stations operating from 10(-10) mbar to 50 mbar. Recent experimental campaigns with stable and radioactive beams have allowed for testing VITO's constituent parts and have demonstrated 96% of ion beam transmission to the collection chamber installed on the central station. The first experimental results obtained with on-line Perturbed Angular Correlation (PAC) spectroscopy using Cu-68m ion-beams will be briefly discussed. (C) 2016 Elsevier B.V. All rights reserved

Transition, the Evolution of Stock Market Efficiency and Entry into EU: The Case of Romania

In this paper we demonstrate that the measurement of stock market efficiency is an important activity in establishing whether eastern European countries satisfy the Copenhagen Criteria for EU membership. Specifically, we argue that developing an efficient stock market should be an important policy focus for countries with aspirations to join the EU as it helps to demonstrate the existence of a functioning market economy. We illustrate this issue by examining the evolution of stock market efficiency in the Bucharest Stock Exchange from mid-1997 to September 2002. We use a GARCH model on daily price data and model the disturbances using the Student-t distribution to allow for ‘fat-tails’. We find strong evidence of inefficiency in the Bucharest Stock Exchange in that the lagged stock price index is a significant predictor of the current price index. This result is robust to the inclusion of variables controlling for calendar effects of the sort that have been observed in more developed stock markets. The level of inefficiency appears to diminish over time and we find evidence consistent with stock market efficiency in Romania after January 2000. Copyright Springer 2005stock market efficiency, transition, G14, P34,

The cross-section of equity returns and assets’ fundamental cash-flow risk

Return decomposition, Cash-flow news, Discount-rate news, Consumption growth, E21, G11, G12,