Dual polarization radar Lagrangian parameters: a statistics-based probabilistic nowcasting model     

Bruno Lisbôa Medina  Luiz A. T. Machado 《Natural Hazards》2017,89(2):705-721

The aim of this study is to present a statistics-based Lagrangian nowcasting model to predict intense rainfall convective events based on dual polarization radar parameters. The data employed in this study are from X-band radar collected during the CHUVA-Vale campaign from November 2011 to March 2012 in southeast Brazil. The model was designed to catch the important physical characteristics of storms, such as the presence of supercooled water above 0 °C isotherm, vertical ice crystals in high levels, graupel development in the mixed-phase layer and storm vertical growth, using polarimetric radar in the mixed-phase layer. These parameters are based on different polarimetric radar quantities in the mixed phase, such as negative differential reflectivity (Z _DR) and specific differential phase (K _DP), low correlation coefficient (ρ _hv) and high reflectivity Z _h values. Storms were tracked to allow the Lagrangian temporal derivation. The model is based on the estimation of the proportion of radar echo volume in the mixed phase that is likely to be associated with intense storm hydrometeors. Thirteen parameters are used in this probabilistic nowcasting model, which is able to predict the potential for future storm development. The model distinguishes two different categories of storms, intense and non-intense rain cell events by determining how many parameters reach the “intense” storm threshold.  相似文献   

Vertical acceleration demands on column lines of steel moment‐resisting frames          下载免费PDF全文

Lukas Moschen  Ricardo A. Medina  Christoph Adam 《地震工程与结构动力学》2016,45(12):2039-2060

In this paper, vertical peak floor acceleration (PFA_v) demands on elastic multistory buildings are statistically evaluated using recorded ground motions. These demands are applicable to the assessment of nonstructural components that are rigid in the vertical direction and located at column lines or next to columns. Hence, PFA_v demands of the floor system away from column lines and their effects on nonstructural components are not addressed. This study is motivated by the questionable general assumption that typical buildings are considered to be relatively flexible in the horizontal (lateral) direction but relatively rigid in the vertical (longitudinal) direction. Consequently, only few papers address the evaluation of vertical component acceleration demands throughout a building, and there is no consensus on the relevance of vertical accelerations in buildings. The results presented in this study show that the vertical ground acceleration demands are amplified throughout the column line of a steel frame structure. This amplification is in many cases significant, depending on the vertical stiffness of the load‐bearing system, damping ratio, and the location of the nonstructural component in the building. From these outcomes it can be concluded that the perception of a rigid‐body response of the column lines in the vertical direction is highly questionable, and further research on this topic is required. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Shoreline relaxation at pocket beaches     

Imen?TurkiEmail author  Raul?Medina  Nabil?Kakeh  Mauricio?González 《Ocean Dynamics》2015,65(9-10):1221-1234

A new physical concept of relaxation time is introduced in this research as the time required for the beach to dissipate its initial perturbation. This concept is investigated using a simple beach-evolution model of shoreline rotation at pocket beaches, based on the assumption that the instantaneous change of the shoreline plan-view shape depends on the long-term equilibrium plan-view shape. The expression of relaxation time is developed function of the energy conditions and the physical characteristics of the beach; it increases at longer beaches having coarse sediments and experiencing low-energy conditions. The relaxation time, calculated by the developed model, is validated by the shoreline observations extracted from video images at two artificially embayed beaches of Barcelona (NW Mediterranean) suffering from perturbations of sand movement and a nourishment project. This finding is promising to estimate the shoreline response and useful to improve our understanding of the dynamic of pocket beaches and their stability.  相似文献   

The 1992 Tafilalt seismic crisis (Anti-Atlas, Morocco)     

Ihsane Bensaid  Taj-Eddine Cherkaoui  Fida Medina  Bento Caldeira  Elisa Buforn  Anas Emran  Youssef Hahou 《Journal of Seismology》2012,16(1):35-53

The Tafilalt region, located at the eastern end of the Anti-Atlas chain in Morocco, was shaken on 23 and 30 October 1992 by two moderate earthquakes of magnitude mb ∼ 5 and intensity ∼ VI MSK64, which caused two deaths and great damage in the area between Erfoud and Rissani. The review of data available on the seismic crisis allowed us to improve the knowledge on the macroseismic, instrumental and source parameters of the earthquakes. The main results of the present study are: (1) location of the epicentres with the help of data from a close portable network allowed us to propose new epicentral coordinates at 31.361° N, 4.182° W (23 October) and 31.286° N, 4.347° W (30 October); both events have focal depths of 2 km; (2) the shock of 30 October was followed by a series of 305 aftershocks, most of which were located west of Rissani; the 61 best-constrained events had focal depths of 5 to 19 km and magnitudes 0.7 to 3; (3) the largest damage was located in an area between the two epicentres within the Tafilalt valley and was probably amplified by site effects due to the proximity of the water table within the Quaternary sediments; (4) focal mechanisms of the main events correspond to strike-slip faulting with fault planes oriented N–S (left lateral) and E–W (right lateral); the only mechanism available for the aftershocks also corresponds to strike-slip faulting; (5) spectral analysis shows that the scalar seismic moment (Mo) of the first event is slightly larger than the second; the corresponding values of Mw are 5.1 and 5.0, respectively; (6) the dimensions of the faults for a circular fault model are 7.7 ± 1.4 and 7.4 ± 1.2 km, respectively; the average displacement is 4 cm for the first event and 3.7 cm for the second; the stress drop is 0.4 and 0.3 MPa, respectively, in agreement with standard values; (7) the Coulomb Stress test performed for both earthquakes suggests a relationship between both events only when the used location is at the limit of the horizontal uncertainty; (8) finally, the occurrence of these shocks suggests that the Anti-Atlas is undergoing tectonic deformation in addition to thermal uplift as suggested by recent publications.  相似文献