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[en] While extensive research consideration has been given to the Northern Hemispheric polar (PJ) and subtropical jet (STJ) streams, there have been fewer climatological studies relating these two jet types to tornado outbreaks. This study examines tornado outbreaks in two regions with substantial tornado risk, Plains Tornado Alley (PTA) and Southeast Tornado Alley (STA), and classifies the jet streak types associated with the outbreaks. Utilizing the Storm Prediction Center (SPC) tornado database and an objective jet identification scheme created from NCEP/NCAR Reanalysis 1 data, jet streaks were identified as STJ, PJ, merged (identified as STJ and PJ), superposed, or unidentified for a 30-year period between 1984 and 2013. Tornado outbreaks were categorized into different types based on these jet streak types. Results revealed STJ and PJ tornado outbreaks compose the majority of tornado outbreaks, as well as the most intense outbreaks, in both PTA and STA. STJ tornado outbreaks were found to be more common in PTA than in STA, while PJ outbreaks were more common in STA than in PTA. The study concludes by considering how a coupled jet structure may be important for tornado outbreaks.
[en] In the United States, a tornado design requirement was imposed on nuclear power plants in 1967. This requirement precipitated considerable study on the probability of toronado strikes and the consequent damage. As a data base, records of thousands of tornadoes which occurred in the U.S. in the last 50 years were available. Unfortunately, no such data base exists for tornadoes and other extreme atmospheric events in Canada. A theoretical study employing a Monte Carlo technique was used to simulate the tornado environment for a hypothetical site. This exercise concluded that a site the size of a large nuclear park such as Bruce can be traversed by a tornado every 500 years. The results are very preliminary since very little Canadian data or meteorological considerations have been involved. The results do, however, show that the frequency of a tornado strike is in the order of 10-3 events/annum and is therefore of concern in the safety assessment of nuclear facilities. (auth)
[en] The description is given of a cooling tower protected against projectiles carried by storms, which can be used, inter alia, for the cooling facilities of nuclear power stations. It is characterized by its being composed of several closed cooling cells arranged around the periphery of a central opening. Each cell has a cold air intake on the outside, several blowers located inside and a hot air outlet along the inside
[fr]On decrit une tour de refrigeration protegee contre les projectiles entraines par les tempetes qui peut etre utilisee, notamment pour les installations de refroidissement des centrales nucleaires. Elle est caracterisee par sa constitution en plusieurs cellules de refrigeration fermees disposees autour de la peripherie d'une ouverture centrale. Chacune de ces cellules comporte une entree d'air froid sur son cote exterieur, plusieurs ventilateurs situes a l'interieur et une sortie d'air chaud le long de son cote interieur
[en] This paper focuses on our proposal for the different roles that data and expert opinion play in uncertainty analysis. Parameters for which reliable data exist are estimated by classical statistical techniques. Their uncertainty bounds are statistical confidence limits. Uncertainty about data-free parameters is expressed as a range, or set, of plausible values, with no probabilistic connotations. For parameters with both data and opinion sources, conditional confidence limits can be used to assess both total uncertainty, and the separate contributions of data-based and data-free uncertainties
[en] The effects of tornadoes on buildings are examined to determine the wind forces on structures. The American National Standards Institute (ANSI) has developed guidelines for building code requirements for the minimum wind loads a building must be designed to withstand. The conservatism or nonconservatism on the ANSI approach is evaluated by simulating tornado-structure interaction numerically with a two-dimensional fluid dynamics computer code and a vortex model. Only external pressures are considered. The computer calculations yield the following percentages of the ANSI design pressures: rigid frame, 50 to 90%; individual wall panels, 75 to 200%; and wall corners, 50 to 75%
[en] The objective of this report is to document the results of an analytical study for determining the effects of tornadic wind pressures and missiles on critical structures and equipment at 100-N reactor. These particular structures and equipment are essential for maintaining the reactor in a safe, shutdown condition. The analyses show that structures, systems and components required for safe reactor shutdown and operations of the Emergency Core Cooling System (ECCS) would not be damaged by a 175 mph tornado, nor associated missiles, to the extent that the ECCS would not be able to function adequately
[en] Presented in this paper are Doppler spectra of a very large tornado that occurred on 22 May 1981 near Binger, Oklahoma. Tracking of the tornado was accomplished with the help of a novel ''polar spectra display.'' Bimodal tornado spectral signatures (TSS) were observed in about 40 scans. Direct measurements of maximum velocities from spectral skirts yielded a maximum tangential speed of 80 m s-1 (90 m s-1 relative to ground). A diameter of 1 km at 200 m above ground was deduced from a simplified model. Radial centrifuging of radar targets was estimated to be about 20 m s-1. With simple assumptions for radar target sizes and summation of forces, a beamwidth average convergence value of abou 2.5 x 10-2 s-1 was calculated for the tornado boundary layer
[en] Using rain gauge and satellite-based rainfall climatologies and the NOAA Storm Prediction Center tornado database (1952-2007), this study found a statistically significant tendency for fall-winter drought conditions to be correlated with below-normal tornado days the following spring in north Georgia (i.e. 93% of the years) and other regions of the Southeast. Non-drought years had nearly twice as many tornado days in the study area as drought years and were also five to six times more likely to have multiple tornado days. Individual tornadic events are largely a function of the convective-mesoscale thermodynamic and dynamic environments, thus the study does not attempt to overstate predictability. Yet, the results may provide seasonal guidance in an analogous manner to the well known Sahelian rainfall and Cape Verde hurricane activity relationships.