Academic Reading — Test 64

Reading passage

Tropical cyclones are among the most powerful weather systems on Earth, capable of producing destructive winds, torrential rain and dangerous storm surges. In the southern hemisphere, these intense low-pressure systems form over warm tropical oceans, typically where the sea-surface temperature exceeds about twenty-six degrees Celsius. Although the underlying physics is the same as in the northern hemisphere, southern-hemisphere cyclones rotate clockwise rather than anticlockwise, a difference caused by the direction of the Coriolis effect on either side of the equator. The season during which they are most likely to develop runs broadly from November to April, when ocean waters are at their warmest. The practice of giving cyclones names is comparatively recent and was introduced largely for practical reasons. Before names were used, forecasters identified storms by their latitude and longitude, a method that proved cumbersome and prone to confusion, especially when several systems were active at the same time. A short, memorable name reduces the risk of error when warnings are broadcast to the public and exchanged between meteorological agencies. It also helps coastal communities follow the progress of a particular storm without mistaking it for another. For these reasons, the naming of cyclones is now regarded as an essential part of the warning process rather than a mere convenience. Responsibility for naming is divided geographically. The world's tropical oceans are split into basins, and each basin is overseen by a designated meteorological centre that draws up its own list of names in advance. In the southern hemisphere, the Australian Bureau of Meteorology, along with services in nations such as Fiji, Indonesia, Papua New Guinea and several countries bordering the south-western Indian Ocean, maintains these lists. The names are typically arranged in alphabetical order and are used in sequence as new storms form. Many regions now alternate between names traditionally regarded as male and female, a change adopted after earlier lists used only female names, a convention that was eventually criticised as unbalanced. Once a particular cyclone has caused severe loss of life or extensive damage, its name is usually withdrawn permanently and replaced, so that the same name is never associated with two separate disasters. Tracking a cyclone is a separate and equally important task that relies on a combination of technologies. Satellites positioned high above the Earth provide the broadest view, allowing forecasters to observe the overall shape, size and movement of a system, including the formation of a clear central eye in the most intense storms. Closer to the surface, networks of weather radar measure rainfall and wind structure as a cyclone nears the coast, while automatic buoys moored in the ocean record pressure, temperature and wave height. In some basins, specially equipped aircraft fly directly into storms to gather measurements that cannot be obtained from a distance, although such flights are less common in the southern hemisphere than in parts of the north. The data from all these sources are fed into computer models that calculate the likely future path, or track, of the system. Forecasters express the uncertainty in their predictions through what is often called a track-forecast cone. Because the exact path of a cyclone can never be predicted with complete certainty, the cone widens as it extends further into the future, indicating the range of positions the centre of the storm might reasonably occupy. A common misunderstanding among the public is that the cone shows the size of the cyclone itself; in fact it represents only the probable error in the forecast position, and damaging winds and rain frequently extend well beyond its edges. Intensity is described using a category scale based chiefly on wind speed, and warnings are updated regularly as fresh observations arrive. The combined effort of naming and tracking allows authorities to issue clear, timely advice, giving residents the best possible chance to secure property and, where necessary, evacuate before the storm arrives. International cooperation underpins the whole system. Cyclones pay no attention to national boundaries, and a storm that threatens one country today may strike a neighbour tomorrow. To ensure that warnings remain consistent, the responsible centres share data freely and follow procedures coordinated through the World Meteorological Organization, a specialised agency of the United Nations. This collaboration means that a cyclone keeps the same name throughout its life, even as it crosses from one country's area of responsibility into another's. Such standardisation has done much to reduce confusion and to save lives across the vast and often sparsely monitored waters of the southern hemisphere.