A “bomb cyclone” suddenly appeared in southern Brazil. Why did this phenomenon suddenly occur?
From June 30 to July 3 this year, states in southern Brazil including Santa Catarina, Rio Grande do Sul, and Paraná were hit by bomb cyclones every hour. Winds of 100 kilometers to 120 kilometers per hour killed 12 people, forced more than 1,000 people to move to safe areas, and caused power outages for 1.9 million people. So why does this kind of weather appear? Bomb cyclone?
Actually, bomb cyclones are not weather anomalies. They are a frequent weather phenomenon with a frequency similar to that of general typhoons and hurricanes, but they do not often appear on land. Like typhoons and hurricanes caused by tropical depressions, they are also generated on the sea surface, and also because of low pressure. Low pressure occurs because temperatures rise in local areas. However, this kind of warming mostly occurs in temperate zones, mainly in temperate sea areas around 60 latitudes. If the central pressure drops by 24 mbar (hPa) or more within 24 hours, the air will flow to the middle, driven by the rotation of the earth. An explosive spin occurs. It mostly occurs in winter, but it can also occur in summer. Bomb cyclones are mainly distributed in four main areas: the northwest Pacific, which is the waters near Japan; the southwest Pacific, which is the waters of Australia and New Zealand; the North Atlantic and the South Atlantic. The southern states of Brazil are located in the western part of the South Atlantic Ocean, and June and July are also the winter months with a high incidence of bomb cyclones. Although the "cyclone bomb" is smaller in scope and shorter in duration than the storms caused by tropical depressions, it is still very destructive, mainly to housing, communications and other infrastructure, and will also cause large-scale precipitation in local areas. It can even lead to floods and snowstorms. Frequent human activities and greenhouse gas emissions have led to global warming and climate anomalies. This anomaly may also intensify the occurrence of various meteorological disasters, causing things to appear that should not have occurred.
The main reason why cyclone bombs are prone to causing disasters is actually because they rarely appear on land. This is different from storms caused by tropical depressions. For example, people were surprised by the storm that occurred in southern Brazil because they had never encountered such a storm before. Their knowledge of storms was limited to televised hurricanes in the Caribbean. Therefore, when a storm strikes, the local civil defense department and residents lack basic protective measures and response methods, and are often caught off guard. Many people's roofs are blown away by strong winds, and cities and villages are basically in a mess. This has brought new disasters to the local area that was already suffering due to the new crown epidemic.
After the incident, Brazilian President Jair Bolsonaro immediately reassured and said that power supply to the affected areas would be restored soon. At the same time, he himself also visited the affected areas for inspection afterwards.
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