- What is a bomb cyclone? A bomb cyclone, also called explosive cyclogenesis or bombogenesis, is a mid-latitude cyclone that rapidly intensifies. A cyclone is a low-pressure weather system – where the atmospheric pressure at its center is lower than the surrounding areas – in which winds rotate inward. It rotates in an anti-clockwise direction in the Northern Hemisphere and in a clockwise direction in the Southern Hemisphere. The winds of a bomb cyclone can reach hurricane force – 74 miles (119 km) per hour – and more intense. These storms form during winter and can produce heavy amounts of rainfall. According to John Martin, professor of meteorology at the University of Wisconsin at Madison, they have a life span of about a week, during which they rise to peak intensity in about four to five days and then dissipate in the final two days.
- How is a bomb cyclone formed? Bomb cyclones form when conditions at the surface and at the jet stream level are ideal for the storm to intensify. The jet stream is a narrow band of fast winds in the upper atmosphere. A variety of atmospheric processes combine to produce these storms. Nearly all bomb cyclones involve a precursory disturbance in the winds in the central part of the troposphere — the lowest region of Earth’s atmosphere — about 3-5 miles (5-8 km) above the planet’s surface, Martin said. Another important feature of explosive cyclogenesis events that is common to many, but not all, is the warm ocean surface. Many of the most intense bomb cyclones form over oceans. Rainfall may be excessive. When water vapor turns into liquid and ice, as happens in these storms, a huge amount of energy – called latent heat energy – is released. Some of that energy makes the storm stronger. Because atmospheric pressure is so low, pressure differences during a hurricane can be very large, causing strong winds that can have devastating effects.
- When and where are they most likely to form? Explosive cyclogenesis occurs over most of the oceans and typically occurs during the cold season in both hemispheres – from approximately November to March in the Northern Hemisphere and from approximately May to August in the Southern Hemisphere, although these storms can occur earlier or later. . Particularly sensitive areas are located in the so-called hurricane track along the east coast of continents because this is where the warmest ocean currents exist, such as the Kuroshio off Japan and the Gulf Stream off North America, Martin said. According to John Knox, an atmospheric scientist and professor of geography at the University of Georgia, bomb cyclones can be very destructive and pose a particular threat to shipping interests, as many of them occur over oceans. Knox said, some bomb cyclones have occurred on the Great Lakes of North America and have caused ships to sink there too.
- What happens to atmospheric pressure? The average sea-level atmospheric pressure at mid-latitudes is about 1012 millibars or mb. In cyclones, it drops to 980 MB with regularity. With bomb cyclones, this can drop to 950 mb or less, and the rate at which they intensify is as little as 24 mb in 24 hours.
- Why can’t we call it a storm? While bomb cyclones can pack hurricane-force winds and sometimes exhibit hurricane characteristics, they are not hurricanes. They form by different physical processes and do not have the symmetry of hurricanes, which are also low-pressure systems. Knox said bomb cyclones sometimes develop “eyes” similar to the center of the storm. But a bomb cyclone originates in the mid-latitudes and is associated with weather fronts — the boundary between two air masses with different characteristics such as temperature — and a strong jet stream, Knox said. A hurricane originates in the tropics and is not associated with weather fluctuations or a strong jet stream, Knox said.
- Are bomb cyclones becoming more common? Global climate change, according to experts, is causing more frequent and more extreme weather events around the world. But are bomb cyclones becoming more common or more intense? Martin said it’s not clear what the issue is. The fact that the Earth is warming is having an impact on cyclone dynamics, which scientists are currently trying to understand, Martin said. A warmer planet means more water vapor in the air, Martin said, and that would strengthen at least the latent heat part of what powers these storms. However, the warming is not uniform, Martin said. Since observations suggest more warming at higher latitudes, Martin said, this could lead to bomb cyclones becoming weaker in general.
