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CONTENTS
Volume 15, Number 2, March 2012
 

Abstract
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Key Words
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Address
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Abstract
A substantial part of South Africa is subject to more than one strong wind source. The effect of that on extreme winds is that higher quantiles are usually estimated with a mixed strong wind climate estimation method, compared to the traditional Gumbel approach based on a single population. The differences in the estimated quantiles between the two methods depend on the values of the Gumbel distribution parameters for the different strong wind mechanisms involved. Cluster analysis of the distribution parameters provides a characterization of the effect of the relative differences in their values, and therefore the dominance of the different strong wind mechanisms. For gusts, cold fronts tend to dominate over the coastal and high-lying areas, while other mechanisms, especially thunderstorms, are dominant over the lower-lying areas in the interior. For the hourly mean wind speeds cold fronts are dominant in the south-west, south and east of the country. On the West Coast the ridging of the Atlantic Ocean high-pressure system dominate in the south, while the presence of a deep trough or coastal low pressure system is the main strong wind mechanism in the north. In the central interior cold fronts tend to share their influence almost equally with other synoptic-scale mechanisms.

Key Words
cluster analysis; mixed strong wind climate; extreme winds; South Africa.

Address
A.C. Kruger and S.S. Sekele : Climate Service Division, South African Weather Service, Private Bag X097, Pretoria 0001, South Africa
A.M. Goliger : Division of Built Environment, CSIR, P. O. Box 395, Pretoria 0001, South Africa
J.V. Retief : Department of Civil Engineering, Universitof Stellenbosch, Private Bag X1, Matieland 7602, South Africa

Abstract
Codes for structural design usually assume that the incident mean wind velocity is parallel to the ground, which constitutes a valid simplification for frequent winds caused by sypnoptic events. Wind effects due to other phenomena, such as thunderstorm downbursts, are simply neglected. In this paper, results of recent and ongoing research on this topic in Brazil are presented. The model of the threedimensional wind velocity field originated from a downburst in a thunderstorm (TS), proposed by Ponte and Riera for engineering applications, is first described. This model allows the generation of a spatially and temporally variable velocity field, which also includes a fluctuating component of the velocity. All parameters are related to meteorological variables, which are susceptible of statistical assessment. An application of the model in the simulation of the wind climate in a region sujected to both EPS and TS winds is discussed next. It is shown that, once the relevant meteorological variables are known, the simulation of the wind excitation for purposes of design of transmission lines, long-span crossings and similar structures is feasible. Complementing the theoretical studies, wind velocity records during a recent TS event in southern Brazil are presented and preliminary conclusions on the validity of the proposed models discussed.

Key Words
thunderstorms; winds; downdraft; downburst; vertical profile; fluctuating velocities; mixed climate; extreme values; registered velocities.

Address
Jorge D. Riera : PPGEC, EE, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brasil Av. Osvaldo Aranha
99, 3o. Andar, 90035-970, Porto Alegre, RS, Brazil
Jacinto Ponte Jr. : UNISINOS, Universidade do Vale do Rio dos Sinos, Sao Leopoldo, RS, Brazil

Abstract
Severe wind is one of the major natural hazards in Australia. The component contributors to economic loss in Australia with regards to severe wind are tropical cyclones, thunderstorms and subtropical (synoptic) storms. Geoscience Australia\'s Risk and Impact Analysis Group (RIAG) is developing mathematical models to study a number of natural hazards including wind hazard. This paper discusses wind hazard under current and future climate conditions using RIAG\'s synoptic wind hazard model. This model can be used in non-cyclonic regions of Australia (Region A in the Australian-New Zealand Wind Loading Standard; AS/NZS 1170.2:2011) where the wind hazard is dominated by synoptic and thunderstorm gust winds.

Key Words
Australia; natural hazard; climate simulation; synoptic wind; wind hazard.

Address
L.A. Sanabria and Cechet, R.P. : Risk and Impact Analysis Group, Geoscience Australia, Canberra, Australia

Abstract
Argentina is a large country with several areas dominated by different climate mechanisms. Since 2008, damage to civil structures caused by strong winds has been surveyed in Chaco and the neighbouring areas. Chaco is a province of NEA, the north-east region of the Argentina, which also includes the provinces of Formosa, Corrientes and Misiones. The strong wind events in NEA are related to severe convective storms. In this work, we present findings about wind-induced damage in NEA and the prevailing meteorological conditions. We emphasise seven particular cases for which the conditions of the atmosphere were reconstructed through reanalysis.

Key Words
wind; damage; civil structures; infrastructure.

Address
Bruno Natalini : CONICET-Facultad de Ingenieria, Universidad Nacional del Nordeste, Resistencia, Argentina
Jorge L. Lassig and Claudia Palese : Facultad de Ingenieria, Universidad Nacional del Comahue, Neuquen, Argentina
Mario B. Natalini : Facultad de Ingenieria, Universidad Nacional del Nordeste, Resistencia, Argentina

Abstract
Damaging winds, associated with a variety of weather phenomena, are frequently experienced in New Zealand. Observations and modelling of two recent extreme wind events; the Taranaki tornado outbreak of July 2007, and the Greymouth down-slope easterly wind storm of July 2008 are described in detail here. Post-event engineering damage surveys, rare for New Zealand, were done for these storms and the results are summarized here. Finally, the issue of sampling extreme wind events is raised and the need to include detailed numerical modelling analysis to understand wind gust climatologies at observing sites and extending these to wider regions is discussed.

Key Words
extreme winds; New Zealand; tornado; down-slope winds, lee-slope winds; wind damage; damage surveys.

Address
R. Turner, M. Revell, S. Reese, S. Moore and S. Reid : NIWA, Wellington, New Zealand

Abstract
The meteorological events that cause most strong winds in Brazil are extra-tropical cyclones, downbursts and tornadoes. However, one hurricane formed off the coastline of southern Brazil in 2005, a tropical storm formed in 2010 and there are predictions that others may form again. Events such as those described in the paper and which have occurred before 1987, generate data for the wind map presented in the Brazilian wind loading code NBR-6123. This wind map presents the reference wind speeds based on 3-second gust wind speed at 10 m height in open terrain, with 50-year return period, varying from 30 m/s (north half of country) to 50 m/s (extreme south). There is not a separation of the type of climatological event which generated each registered velocity. Therefore, a thunderstorm (TS), an extra-tropical pressure system (EPS) or even a tropical cyclone (TC) are treated the same and its resulting velocities absorbed without differentiation. Since the flow fields generated by each type of meteorological event may be distinct, the indiscriminate combination of the highest wind velocities with aerodynamic coefficients from boundary layer wind tunnels may lead to erroneous loading in buildings.

Key Words
extreme winds; tornadoes; downbursts; tropical cyclones; wind codes.

Address
Acir M. Loredo-Souza : Laboratorio de Aerodinamica das Construcoes, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil


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