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Modeling Tropical Cyclones in a Changing Climate  

Enrico Scoccimarro

Tropical cyclones (TCs) in their most intense expression (hurricanes or typhoons) are the main natural hazards known to humankind. The impressive socioeconomic consequences for countries dealing with TCs make our ability to model these organized convective structures a key issue to better understanding their nature and their interaction with the climate system. The destructive effects of TCs are mainly caused by three factors: strong wind, storm surge, and extreme precipitation. These TC-induced effects contribute to the annual worldwide damage of the order of billions of dollars and a death toll of thousands of people. Together with the development of tools able to simulate TCs, an accurate estimate of the impact of global warming on TC activity is thus not only of academic interest but also has important implications from a societal and economic point of view. The aim of this article is to provide a description of the TC modeling implementations available to investigate present and future climate scenarios. The two main approaches to dynamically model TCs under a climate perspective are through hurricane models and climate models. Both classes of models evaluate the numerical equations governing the climate system. A hurricane model is an objective tool, designed to simulate the behavior of a tropical cyclone representing the detailed time evolution of the vortex. Considering the global scale, a climate model can be an atmosphere (or ocean)-only general circulation model (GCM) or a fully coupled general circulation model (CGCM). To improve the ability of a climate model in representing small-scale features, instead of a general circulation model, a regional model (RM) can be used: this approach makes it possible to increase the spatial resolution, reducing the extension of the domain considered. In order to be able to represent the tropical cyclone structure, a climate model needs a sufficiently high horizontal resolution (of the order of tens of kilometers) leading to the usage of a great deal of computational power. Both tools can be used to evaluate TC behavior under different climate conditions. The added value of a climate model is its ability to represent the interplay of TCs with the climate system, namely two-way relationships with both atmosphere and ocean dynamics and thermodynamics. In particular, CGCMs are able to take into account the well-known feedback between atmosphere and ocean components induced by TC activity and also the TC–related remote impacts on large-scale atmospheric circulation. The science surrounding TCs has developed in parallel with the increasing complexity of the mentioned tools, both in terms of progress in explaining the physical processes involved and the increased availability of computational power. Many climate research groups around the world, dealing with such numerical models, continuously provide data sets to the scientific community, feeding this branch of climate change science.

Article

The History and Science of Hurricanes in the Greater Caribbean  

Sherry Johnson

The Caribbean’s most emblematic weather symbol is the hurricane, a large rotating storm that can bring destructive winds, coastal and inland flooding, and torrential rain. A hurricane begins as a tropical depression, an area of low atmospheric pressure that produces clouds and thunderstorms. Hurricane season in the Caribbean runs from June 1 through November 30, although there have been infrequent storms that formed outside these dates. Hurricanes are classified according to their maximum wind speed, and when a tropical system reaches the wind speed of a tropical storm (35 mph), it is given a name. Lists of names, which are rotated periodically, are specific to certain regions. If a named storm is responsible for causing a significant number of deaths or property damage, the name is retired and replaced with another. Most deaths in a storm came from drowning, from storm surge along the coast or from flooding or mudslides in the interior. Storm-related deaths also occur when structures collapse or when victims are struck by flying debris. One important and underestimated cause of death after the passage of a storm is disease. Even if the destruction is not immediate, the passage of a hurricane can leave significant ecological damage along the coast and in the interior. Hurricanes can have a devastating effect on a community that takes a direct hit. Repeated hurricane strikes can leave a sense of helplessness and hopelessness, “hurricane fatigue.” Conversely, survivors of a disaster are often left with a feeling of confidence that, since they have endured the effects of at least one deadly hurricane, they can do so again. Until the last half of the 18th century, meteorology remained primitive, but the Age of Enlightenment brought scientific and ideological advances. Major beneficiaries were royal navies whose navigation manuals and nautical charts became increasingly more accurate. In 1821, William C. Redfield established the circular nature of storms and their counterclockwise rotation, while other scientists showed how wind currents within the storms moved upward. Once the coiled structure of hurricanes were established by mid-century, the term “cyclone” was applied, based upon the Greek word for the coils of a snake. After the mid-19th century, scientists moved from information gathering to attempts to predict hurricane strikes. Technology, in the form of the telegraph, was a key component in creating a forecasting system aided by organizations such as the Colegio de Belén, in Havana, Cuba. Later in the century, governments worldwide created official observation networks in which weather reports were radiotelegraphed from ships at sea to stations on land. The 20th century experienced advances, such as the use of kites and balloons, and the introduction of weather reconnaissance aircraft during World War II. In April 1960, the first satellite was launched to observe weather patterns, and by the early 1980s, ocean buoys and sophisticated radar systems made forecasts increasingly more accurate.

Article

History of Typhoon Science  

Aitor Anduaga

A typhoon is a highly organized storm system that develops from initial cyclone eddies and matures by sucking up from the warm tropical oceans large quantities of water vapor that condense at higher altitudes. This latent heat of condensation is the prime source of energy supply that strengthens the typhoon as it progresses across the Pacific Ocean. A typhoon differs from other tropical cyclones only on the basis of location. While hurricanes form in the Atlantic Ocean and eastern North Pacific Ocean, typhoons develop in the western North Pacific around the Philippines, Japan, and China. Because of their violent histories with strong winds and torrential rains and their impact on society, the countries that ring the North Pacific basin—China, Japan, Korea, the Philippines, and Taiwan—all often felt the need for producing typhoon forecasts and establishing storm warning services. Typhoon accounts in the pre-instrumental era were normally limited to descriptions of damage and incidences, and subsequent studies were hampered by the impossibility of solving the equations governing the weather, as they are distinctly nonlinear. The world’s first typhoon forecast was made in 1879 by Fr. Federico Faura, who was a Jesuit scientist from the Manila Observatory. His brethren from the Zikawei Jesuit Observatory, Fr. Marc Dechevrens, first reconstructed the trajectory of a typhoon in 1879, a study that marked the beginning of an era. The Jesuits and other Europeans like William Doberck studied typhoons as a research topic, and their achievements are regarded as products of colonial meteorology. Between the First and Second World Wars, there were important contributions to typhoon science by meteorologists in the Philippines (Ch. Deppermann, M. Selga, and J. Coronas), China (E. Gherzi), and Japan (T. Okada, and Y. Horiguti). The polar front theory developed by the Bergen School in Norway played an important role in creating the large-scale setting for tropical cyclones. Deppermann became the greatest exponent of the polar front theory and air-masses analysis in the Far East and Southeast Asia. From the end of WWII, it became evident that more effective typhoon forecasts were needed to meet military demands. In Hawaii, a joint Navy and Air Force center for typhoon analysis and forecasting was established in 1959—the Joint Typhoon Warning Center (JTWC). Its goals were to publish annual typhoon summaries and conduct research into tropical cyclone forecasting and detection. Other centers had previously specialized in issuing typhoon warnings and analysis. Thus, research and operational forecasting went hand in hand not only in the American JTWC but also in China (the Hong Kong Observatory, the Macao Meteorological and Geophysical Bureau), Japan (the Regional Specialized Meteorological Center), and the Philippines (Atmospheric, Geophysical and Astronomical Service Administration [PAGASA]). These efforts produced more precise scientific knowledge about the formation, structure, and movement of typhoons. In the 1970s and the 1980s, three new tools for research—three-dimensional numerical cloud models, Doppler radar, and geosynchronous satellite imagery—provided a new observational and dynamical perspective on tropical cyclones. The development of modern computing systems has offered the possibility of making numerical weather forecast models and simulations of tropical cyclones. However, typhoons are not mechanical artifacts, and forecasting their track and intensity remains an uncertain science.

Article

Constructing Records of Storminess  

Frauke Feser

Storms are characterized by high wind speeds; often large precipitation amounts in the form of rain, freezing rain, or snow; and thunder and lightning (for thunderstorms). Many different types exist, ranging from tropical cyclones and large storms of the midlatitudes to small polar lows, Medicanes, thunderstorms, or tornadoes. They can lead to extreme weather events like storm surges, flooding, high snow quantities, or bush fires. Storms often pose a threat to human lives and property, agriculture, forestry, wildlife, ships, and offshore and onshore industries. Thus, it is vital to gain knowledge about changes in storm frequency and intensity. Future storm predictions are important, and they depend to a great extent on the evaluation of changes in wind statistics of the past. To obtain reliable statistics, long and homogeneous time series over at least some decades are needed. However, wind measurements are frequently influenced by changes in the synoptic station, its location or surroundings, instruments, and measurement practices. These factors deteriorate the homogeneity of wind records. Storm indexes derived from measurements of sea-level pressure are less prone to such changes, as pressure does not show very much spatial variability as wind speed does. Long-term historical pressure measurements exist that enable us to deduce changes in storminess for more than the last 140 years. But storm records are not just compiled from measurement data; they also may be inferred from climate model data. The first numerical weather forecasts were performed in the 1950s. These served as a basis for the development of atmospheric circulation models, which were the first generation of climate models or general-circulation models. Soon afterward, model data was analyzed for storm events and cyclone-tracking algorithms were programmed. Climate models nowadays have reached high resolution and reliability and can be run not just for the past, but also for future emission scenarios which return possible future storm activity.

Article

Hurricanes and Health  

Caleb Dresser, Satchit Balsari, and Jennifer Leaning

Hurricanes, also referred to as tropical cyclones or typhoons, are powerful storms that originate over warm ocean waters. Throughout history, these storms have had lasting impacts on societies around the world. High winds, rain, storm surges, and floods affect lives, land, and livelihoods and have a variety of effects on human health. The direct health impacts of hurricanes include drowning due to flooding and trauma resulting from storm surges, blown debris, and structural collapse. Systems for detection, forecasting, early warning, and communications can give populations time to make preparations before hurricane landfall. Evacuation, shelter use, and other preparedness efforts have reduced mortality from hurricanes in many parts of Asia and the Americas. Engineered defenses such as sea walls, flood barriers, and raised structures provide added protection in some settings. While effective in the medium term, such approaches are costly and require dedicated resources, and therefore they have not been implemented in many at-risk sites around the world. Indirect health impacts of hurricanes arise from damage to housing, electricity, water, and transportation infrastructure, and from effects on social supports, economies, and healthcare systems. Indirect health impacts can include infectious diseases, carbon monoxide poisoning, trauma sustained during cleanup, mental health effects, exacerbations of chronic disease, and increases in all-cause mortality. Indirect and long-term health consequences are poorly understood because dedicated study of specific impacts has occurred in only a handful of settings, and, given the diverse array of societies and geographies affected by hurricanes, it is unclear how generalizable the results of these studies may be. Policy makers face three interlinked challenges in protecting human health from hurricanes. First, climate change is leading to increased hazards in many locations by altering hurricane dynamics and contributing to sea-level rise. Second, patterns of intensifying coastal settlement and development are expected to increase population exposure. Third, unequal patterns of exposure and impact on specific populations will continue to raise issues of climate and environmental injustice. Situationally appropriate strategies to protect health from future storms will vary widely, as they must both address the locally relevant manifestations of hurricane hazards and adapt to the cultural and economic context of the affected population. In some areas, inexorable ocean encroachment may lead to consideration of managed retreat from high-risk coastlines; in others, the presence of very large coastal urban populations that cannot feasibly evacuate may lead to design and use of vertical shelters for temporary protection during storms. New ideas and programs are urgently needed in many settings to address hazards associated with extreme rainfall, rising seas on floodplains and low-lying islands, landslide risk in areas undergoing rapid deforestation, and structurally unsound housing in some urban settings. Policies to reduce greenhouse gas emissions will help reduce long-term risk from hurricanes and sea-level rise. Without concrete actions to address both hurricane hazards and population vulnerabiliy, the 21st century may be marked by increasingly dangerous hurricanes affecting growing coastal populations that will be left with few viable options for seeking safety.

Article

The Global Climatology of Tropical Cyclones  

Hamish Ramsay

Tropical cyclones, also known as hurricanes or typhoons, are one of the most violent weather phenomena on the planet, posing significant threats to those living near or along coastlines where tropical cyclone–related impacts are most pronounced. About 80 tropical cyclones form annually, a rate that has been remarkably steady over the period of reliable historical record. Roughly two thirds of these storms form in the Northern Hemisphere from about June to November, while the remaining third form in the Southern Hemisphere typically during the months of November to May. Our understanding of the global and regional spatial patterns, the year-to-year variability, and temporal trends of these storms has improved considerably since the advent of meteorological satellites in the 1960s because of advances in both remote-sensing technology and operational analysis procedures. The well-recognized spatial patterns of tropical cyclone formation and tracks were laid out in a series of seminal papers in the late 1960s and 1970s and remain an accurate sketch even to this day. Concerning the year-to-year variability of tropical cyclone frequency, the El Niño Southern Oscillation (ENSO) has by far the most dominant influence across multiple ocean basins, so much so that it is typically used as the main predictor for statistical forecasts of seasonal tropical cyclone activity. ENSO has a modulating influence on atmospheric circulation patterns, even in regions remote to the tropical Pacific, which, in turn, can act to enhance or inhibit tropical cyclone formation. While the meteorological and climate community has come a long way in our understanding of the global and regional climatological features of tropical cyclones, as well as some aspects of the broader relationship between tropical cyclones and climate, we are still hindered by temporal inconsistencies within the historical record of storm data, particularly pertaining to tropical cyclone intensity. Despite recent efforts to homogenize the historical record using satellite-derived intensity data back to the early 1980s, the relatively short period makes it difficult to discern secular trends due to anthropogenic climate change from natural trends occurring on decadal to multidecadal time scales.