Brazilian extreme wind climate

Uma característica importante da otimização dos processos de projeto em engenharia civil é a demanda pelo aperfeiçoamento da precisão das estimativas das cargas de projeto. As cargas de projeto devidas ao vento são baseadas em análises de registros de dados climatológicos para as quais modelos estatísticos são desenvolvidos. Tais modelos propõem níveis de carga com certas probabilidades de ocorrência durante um determinado período de retorno, ou intervalo médio de recorrência. Desde 1988, a NBR 6123: Forças devidas ao vento em edificações, a norma brasileira de cargas de vento, tem equilibrado a competição das necessidades de segurança e de conforto do usuário contra os custos de construção da cada vez mais alta silhueta urbana da nação. O mapa de isopletas do parâmetro de velocidade básica regional é o ponto inicial para todos os cálculos de cargas de projeto devidas ao vento na maior nação da América do Sul, com velocidades de vento regionais derivadas da distribuição de Fréchet, utilizando as máximas velocidades de rajada anuais equivalentes de 1950 a 1975 observadas, em aeródromos brasileiros. Além do potencial de utilizar mais de 40 anos de novos dados, incluindo dados da rede de observação automatizada do INMET, avanços nas comunidades científicas de engenharia do vento, meteorologia e estatística permitem o desenvolvimento de modelos climáticos mais detalhados e robustos. Há, também, uma crescente necessidade de separar os eventos de tempestades de vento em eventos não- sinóticos e sinóticos, devido às suas diferentes características. O estudo produz modelos climáticos regionais de ventos extremos atualizados em todo o Brasil, para serem usados tanto em casos de estados limite último e de serviço do projeto. Dados meteorológicos das duas maiores redes meteorológicas brasileiras, adquiridos de diversas fontes, foram utilizados, mas apenas após um exame completo da qualidade de cada fonte. Investigações foram feitas com relação a metadados históricos e atuais (altura, localização, tipo de anemômetro) de cada estação, com resultados variados. Correções de velocidades do vento foram feitas para terreno e altura, onde necessário. Algoritmos robustos para a separação de velocidades de vento pico não-sinóticas, sinóticas e duvidosas foram desenvolvidos e aplicados a uma série histórica de dados de 692 estações meteorológicas de superfície para gerar conjuntos de valores extremos para uma análise de valor extremo com Método de Tempestades Independentes modificado. Constatou-se que os ventos não-sinóticos são dominantes na maioria do Brasil para todos os períodos de retorno. Parâmetros meteorológicos relacionados a ventos extremos não-sinóticos e sinóticos foram mapeados por todo o país. Um mapa de isopletas de velocidades básicas do vento foi proposto para uma versão atualizada da NBR 6123, acompanhado dos fatores probabilísticos atualizados para uma DGVE Tipo I – Distribuição de Gumbel. Recomendações chave incluem a necessidade de maiores investigações sobre as características de ventos não-sinóticos no Brasil e o melhoramento dos registros de metadados por parte das organizações meteorológicas.A critical feature of the continual optimisation of civil engineering design processes is the demand to improve accuracy of design load estimations. Design wind loads are based on analyses of recorded historical meteorological data for which statistical models are developed. Such models propose load levels of certain probabilities of occurrence over a particular return period, or mean recurrence interval. Since 1988, NBR 6123: Forças devidas ao vento em edificações, Brazil’s wind loading code, has balanced the competing needs of public safety and tenant comfort against construction costs of the nation’s ever-growing skyline. The isopleth map of the regional basic velocity parameter is the basis for all wind design load calculations in South America’s largest nation, with regional wind speeds derived from the Fréchet distribution of annual maxima equivalent gust speeds from 1950 to 1975 observed at Brazilian aerodromes. Besides the potential to utilise more than 40 years of new data, including data from INMET’s automated observing network, advances across the scientific communities of wind engineering, meteorology and statistics allow for the development of more detailed and robust climatic models. There is also a growing need to separate wind storm events into non-synoptic and synoptic events due to their different characteristics. The study produces updated regional extreme wind climate models across Brazil to be used for both serviceability and ultimate design load cases. Meteorological data from the two Brazilian meteorological networks acquired from several sources were utilised, but only after thorough examination of the quality of each source. Investigations were made regarding historical and current metadata (height, location, anemometer type) of each station with mixed success. Corrections to wind speeds were made for terrain and height where necessary. Robust algorithms for the separation of non-synoptic, synoptic and suspicious peak wind speeds were developed and applied to time-series data from 692 surface weather stations to generate sets of extreme values for a modified Method of Independent Storms extreme value analysis. Non-synoptic winds were found to dominant the majority of Brazil for all return periods. Meteorological parameters relating to non-synoptic and synoptic extreme winds were mapped across the country. An isopleth map of basic wind speeds was proposed for an updated version of NBR 6123, with accompanying updated probabilistic factors for a GEVD Type I – Gumbel distribution. Key recommendations include the need for further investigations into non-synoptic wind characteristics in Brazil and the improvement of metadata records by meteorological organisations

Extreme wind climate of Uruguay

Uruguay belongs to the second most prone region of the world to the occurrence of severe convective storms, and to the region of South America that presents the highest frequency of occurrence of intense cyclogenesis events. Both meteorological processes produce high winds in the country, which represent a risk for the physical integrity and lives of the population, produce losses and damage to their properties and to critical infrastructure; impact the agronomic, energy, insurance and construction sectors. In particular, wind loading is the dominant environmental loading for buildings and structures in Uruguay. Extra-tropical cyclones can produce extensive wind damage and sustain high winds speeds in large parts of the country over several hours; however, research carried out for specific sectors of the country showed that intense convective activity had been responsible for most of the wind damage and incidences reported in their cases. The analysis of 4 years of meteorological data from 25 automatic weather stations distributed across the country also showed the significance of intense convective activity in the extreme wind climate of Uruguay: the highest wind gusts, as well as the highest 10min mean wind speeds, presented distinctive non-synoptic and transient characteristics, and usually occurred under intense convection. On the other hand, the geographic behaviour of high winds found differed from the geographic distribution presented in the official national extreme wind map, established by the national code UNIT 50-84 Wind actions on structures: the highest wind gusts would not occur along the South Atlantic and Río de la Plata coastlines and along the border with Argentina. Instead, more high wind events with higher wind speeds would be registered toward the northwest of the country. In this area, wind gusts of 40m/s were measured several times at 10m height at fixed locations in open terrain in just 4 years. In addition, a clear seasonal trend was found in wind gust speeds as well as in 10min mean wind speeds, with the highest wind speeds mainly occurring from October to March, and especially in November and February, in accordance with the behaviour of severe convective activity in the region. It could also be verified that intense convective activity as well as synoptic high wind events generate their highest wind speeds mainly from the southwest quadrant. A similar seasonal trend was found in the 10min mean wind speeds annual maxima measured along 35 years at the official meteorological station at Carrasco airport in Montevideo, capital city of Uruguay, implying that convective activity, apart from producing the highest wind gusts across all the country, would also dominate the maxima 10min mean wind speeds measured at 10m height for longer return periods. In addition, it could be observed that the extreme value distribution of 10min mean wind speeds annual maxima for Montevideo may be adequately modelled by a Gumbel distribution, while the UNIT 50-84 wind code proposes a Frechet distribution for wind gust speeds extreme statistics. The characteristics of non-synoptic high wind events, generally related to the occurrence of intense convective activity, should be considered in national and regional wind codes. In particular, extreme wind maps should be directly based in measurements of wind gust speeds, as there is not a direct relation between mean and wind gust speeds during severe convection. For these studies, the wind gust averaging period, the time response of the wind measuring system, as well as the quality of the wind data should be considered and carefully analysed. In order to recommend adequate models for the flow structure of strong convective outflows for national and regional wind codes, calculations, and physical and numerical simulations, additional research and full-scale measurements would be needed. Besides the international recognition of the necessity of more full-scale measurements, these models may need to consider regional characteristics. Other aspects of the Uruguayan wind code for actions on structures are also discussed, and the necessity of their review and update is emphasised.Uruguay se encuentra en la segunda región del mundo de mayor ocurrencia de tormentas convectivas severas, y en la región de América del Sur con mayor frecuencia de formación de ciclones extratropicales intensos. Ambos procesos meteorológicos producen vientos intensos en el país, los cuales representan un riesgo para la integridad física de la población, producen pérdidas y daños materiales a sus propiedades y a infraestructuras críticas, e impactan sectores como el agronómico, de la energía, seguros y construcción del país. En particular, la acción del viento es la carga ambiental que domina el diseño estructural en Uruguay. Los ciclones extratropicales pueden generar importantes daños por viento y velocidades elevadas en una amplia zona del país durante varias horas. Sin embargo, estudios realizados para sectores específicos nacionales mostraron que la actividad convectiva intensa había sido responsable de la mayor parte de los daños e incidencias por viento informadas en esos casos. El análisis de 4 años de datos meteorológicos de 25 estaciones automáticas distribuidas en el país también indica que las tormentas convectivas intensas dominan su clima de vientos extremos: las ráfagas de viento más intensas y las mayores velocidades promediadas en 10min corresponden a eventos no sinópticos, con marcadas características transitorias, y generalmente ocurren durante actividad convectiva intensa. Por otra parte, se encontró que el comportamiento geográfico de los vientos fuertes difiere del indicado en el mapa nacional de vientos extremos dado por la norma de viento UNIT 50-84: las ráfagas de viento más intensas no ocurrirían cerca de la franja costera del país o de la frontera con Argentina, sino que se registrarían velocidades más intensas más frecuentemente hacia el noroeste del país. En varios puntos de esa zona se midieron varias veces ráfagas de viento de 40m/s a 10m de altura en 4 años.También se identificó una clara tendencia estacional tanto en las mayores velocidades de ráfaga como en las mayores velocidades medias en 10min, con valores más altos entre octubre y marzo, y sobre todo en noviembre y febrero, coincidiendo con el comportamiento de la actividad convectiva severa en la región. Así mismo, se verificó que tanto las tormentas convectivas intensas como los eventos de viento intenso de escala sinóptica producen sus vientos más fuertes del cuadrante suroeste. Se encontró una tendencia estacional similar en los máximos anuales en 10min medidos durante 35 años en la estación de Carrasco, Montevideo, implicando que la actividad convectiva también dominaría las máximas velocidades medias en 10min a 10m de altura, para periodos de retorno mayores. Adicionalmente, se pudo observar que la estadística de vientos extremos promediados en 10min para Montevideo puede ser modelada adecuadamente por una distribución Gumbel, mientras que la norma UNIT 50-84 propone una distribución Frechet para las ráfagas de viento. Las características de los vientos no sinópticos, generalmente relacionados a la ocurrencia de actividad convectiva intensa, y con marcadas características transitorias, deberían considerarse en las normas de acción del viento nacionales y regionales. Al no existir una relación directa entre la velocidad media y de ráfaga durante los mismos, los mapas de vientos extremos deberían basarse en medidas de velocidades de ráfagas. Para ello, los tiempos de promediación de las ráfagas, el tiempo de respuesta de los sistemas de medición y la calidad de los datos de viento utilizados deben ser tenidos en cuenta y analizados cuidadosamente. Para recomendar modelos de la estructura del flujo durante eventos convectivos intensos para normas de viento nacionales y regionales, cálculos y simulaciones físicas y numéricas, se necesitaría realizar investigaciones y medidas de velocidad adicionales.Internacionalmente se reconoce la necesidad de contar con más medidas de campo, y por otra parte, estos modelos pueden necesitar considerar características particulares de la región. Se discute también otros aspectos de la norma UNIT 50-84 y se enfatiza su necesidad de revisión y actualización

Wind Climate of the Whitehorse Area

Measurements from Whitehorse upper-air and nearby mountaintop stations were analyzed with a focus on wind energy development in the region. Fifty years of measurements indicate the region has become warmer and windier. Measurements at the upper-air station have shown increases of 2.7°C for surface temperature and 1 m s-1 for mid-valley winds over the past 50 years (1956– 2005). The winters have warmed more dramatically than the summers. Winter temperature inversions have become shallower, and a mid-valley winter jet has become a predominant feature. Wind data for 2001–05 indicate that a minimum annual mean wind speed of 6 m s-1 begins at about 150 m above the Whitehorse valley floor, or 850 m above sea level. At this elevation and higher, wind speeds reach a maximum in December and a minimum in July. The predominant wind direction above the mountaintops was from the southwest, while stations within the Whitehorse Valley recorded winds from the south-southeast. Stations that were more exposed to the southwest reported more predominant winds from this direction. An analysis of the relationship between geostrophic and valley winds concluded that, relative to winds aloft, valley winds were as strong in parallel valleys as they were in perpendicular valleys. The pressure gradients associated with the winds aloft were the dominant forcing mechanism for winds in a perpendicular valley. Geostrophic winds that were parallel to the valley forced the valley winds along the same direction through a downward momentum transport. Wintertime inversions suppress the downward momentum transport, but pressure-driven winds are only indirectly modulated by stratification (because of turbulent friction, which is likely to be suppressed by stable stratification) and so are less sensitive to that factor. Further investigation of wind energy potential is recommended for hills within the valleys, particularly in areas well exposed to southwest winds.Des mesures prises dans la haute atmosphère de Whitehorse et dans les stations de sommets de montagnes environnantes ont été analysées en portant une attention particulière à la formation de l’énergie éolienne dans la région. D’après des mesures prélevées sur une période de 50 ans, la région est maintenant plus chaude et plus venteuse qu’elle ne l’était auparavant. Les mesures de la station de la haute atmosphère attestent d’augmentations de 2,7° C pour la température de surface et de 1 m s-1 pour les vents en milieu de vallée au cours des 50 dernières années (1956-2005). Les hivers se sont réchauffés de façon plus spectaculaire que les étés. Les inversions de températures d’hiver sont devenues plus minces, tandis qu’un jet d’hiver en milieu de vallée est maintenant une caractéristique prédominante. Les données relatives au vent pendant les années 2001 à 2005 indiquent une vitesse du vent moyenne annuelle minimale de 6 m s-1 commençant à environ 150 m au-dessus du plancher de la vallée de Whitehorse, soit à 850 m au-dessus du niveau de la mer. À cette altitude et au-dessus de celle-ci, les vitesses du vent atteignent leur maximum en décembre et leur minimum en juillet. La direction prédominante du vent au-dessus des sommets de montagnes provenait du sud-ouest, tandis qu’aux stations de la vallée de Whitehorse, les vents venaient du sud et du sud-est. Les stations les plus exposées au sud-ouest ont signalé plus de vents prédominants provenant de cette direction. L’analyse de la relation entre les vents géostrophiques et les vents de la vallée a permis de conclure que relativement aux vents d’en haut, les vents de la vallée étaient aussi forts dans les vallées parallèles que dans les vallées perpendiculaires. Les gradients de pression associés aux vents d’en haut constituaient le mécanisme de la force dominante pour les vents d’une vallée perpendiculaire. Les vents géostrophiques qui étaient parallèles à la vallée forçaient les vents de la vallée à adopter la même direction en raison d’un transport au mouvement descendant. Les inversions d’hiver supprimaient le transport au mouvement descendant, mais les vents obéissant à la pression ne sont qu’indirectement modulés par la stratification (en raison du frottement turbulent, ce qui est susceptible d’être supprimé par la stratification stable) et par conséquent, ils sont moins sensibles à ce facteur. Nous recommandons qu’une enquête plus poussée soit réalisée sur l’énergie éolienne naturelle des collines des vallées, particulièrement dans les endroits bien exposés aux vents du sud-ouest

Seasonal variability of wind climate in Hungary

One of the most important effects of climate variability and climate change may come from changes in the intensity and frequency of climatic extremes. Responding to the need of new climatologic analyses, complex wind field research was carried out to study and provide reliable information about the state and variability of wind climate in Hungary. First of all, special attention was paid on creation of a high quality, homogeneous data series. The research is based on 36-yearlong (1975-2010) wind data series of 36 Hungarian synoptic meteorological stations. The means and extremes of near-surface wind conditions assist in estimating the regional effects of climate change, therefore a complex wind climate analysis was carried out. Spatial and temporal distribution of mean and extreme wind characteristics were estimated; wind extremes and trends were interpolated and mapped over the country. Furthermore, measured and ERA Interim reanalysis data were compared in order to estimate the effects of regional climate change

The importance of decadal-scale climate variability to wind-driven modulation of hypoxia in Chesapeake Bay

Millions of dollars are spent annually to reduce nutrient loading to Chesapeake Bay, with a fundamental goal of reducing the extent and severity of low dissolved oxygen (hypoxia) during the summertime months^1^. Yet despite recent reductions in nutrient loading, large volumes of the Bay continue to be impacted by hypoxia and anoxia during the summer months^2-3^. One obstacle to assessing efforts to improve water quality in the Bay and other estuarine systems is a complete understanding of the physical processes that modulate dissolved oxygen and the long-term variability of these processes. Here I analyze a 58-year data set of estimated hypoxic volume in the Bay^2^ and demonstrate the importance that wind direction plays in controlling the extent and severity of summertime hypoxia. This analysis indicates that wind direction explains a greater percentage of the observed inter-annual variation in hypoxic volume than estimates of nutrient loading. The implication is that physical processes play a dominant role in modulating hypoxia and that much of the increased hypoxia observed since the early 1980s can be attributed to changes in wind forcing that are the result of decadal-scale climate variability. These findings emphasize the importance of understanding the physical processes that modulate dissolved oxygen in coastal and estuarine systems and highlight the potential impact that climate change may have on water quality in Chesapeake Bay and other estuarine systems

An Ill Wind? Climate Change, Migration, and Health

Background: Climate change is projected to cause substantial increases in population movement in coming decades. Previous research has considered the likely causal influences and magnitude of such movements and the risks to national and international security. There has been little research on the consequences of climate-related migration and the health of people who move