A bomb cyclone sounds like something out of an action movie, but it’s a very real and powerful meteorological event.
- A bomb cyclone is a mid-latitude cyclone that experiences rapid intensification due to a sudden pressure drop.
- The pressure drop is at least 24 millibar in 24 hours.
- A bomb cyclone can occur anytime, but is more common in fall or winter.
- While a bomb cyclone results from a different process than a tropical cyclone, it can produce winds as strong as a hurricane (74 to 95 mph or 120-155 km/hr). But, even weaker bomb cyclones often cause significant damage.
What Is a Bomb Cyclone?
A bomb cyclone is a rapidly intensifying extratropical low-pressure system. The term “bomb” refers to the process of “bombogenesis,” which is when a mid-latitude cyclone rapidly intensifies, dropping pressure at least 24 millibars over 24 hours. The “cyclone” part of the name refers to the rotation of the storm system, much like a tropical cyclone.
History and Origin of the Name
The term “bomb cyclone” originated from meteorological literature in the 1980s. It comes from the term “bombogenesis,” which combines “cyclogenesis” (the formation of a cyclone) with the dramatic nature of an explosive bomb. Fred Sanders and John Gyakum coined the term based on the 1950s work by Tor Bergeron. Essentially, the term underlines the rapid and explosive development of the storm.
While “bomb cyclone” is perhaps the most dramatic term, other names for the phenomenon are:
- Weather bomb
- Explosive cyclogenesis
- Explosive development
The Process of Bombogenesis
Bombogenesis occurs when cold polar air meets warm tropical air. This collision of air masses can create a powerful low-pressure system. Factors that can contribute to bombogenesis include:
- Ocean Currents: Warm ocean currents, like the Gulf Stream, provide the necessary heat and moisture.
- Jet Streams: Dips or troughs in the jet stream encourage the formation and deepening of low-pressure systems.
- Air Mass Collision: The stark contrast between cold and warm air masses leads to rapid destabilization and intensification.
Can a Tropical Cyclone Become a Bomb Cyclone?
Sometimes a tropical cyclone transitions into an extratropical system that undergoes bombogenesis, thus becoming a bomb cyclone. Here’s how it happens:
- Tropical to Extratropical Transition: Tropical cyclones derive their energy from warm ocean waters and have a warm core. As they move poleward or over cooler waters, they may undergo a transition to become extratropical. In this phase, they start deriving their energy from the temperature contrasts in the atmosphere and they develop a cold core.
- Bombogenesis in the Transitioned System: Once the cyclone moves into the mid-latitude, it can still intensify if conditions are right. If the system’s central pressure drops by at least 24 millibars within 24 hours, it undergoes bombogenesis and becomes a “bomb cyclone.”
It’s worth noting that while both tropical cyclones and bomb cyclones can be very intense, the mechanisms driving their intensification are different. A tropical cyclone intensifies mainly due to warm ocean waters, while a bomb cyclone’s rapid intensification results from the dynamic interaction between air masses.
In some historic storm events, tropical cyclones have transitioned to powerful extratropical systems that underwent bombogenesis. When these events occur, they can bring a combination of impacts from both tropical systems (like heavy rainfall) and extratropical bomb cyclones (like strong winds and winter weather, if conditions permit).
When and Where Do Bomb Cyclones Happen?
Bomb cyclones can occur anytime of the year, but they are more common in fall and winter when temperature contrasts between polar and tropical air masses are more pronounced. While they form more often over water, some bomb cyclones form over land.
- North America: Particularly along the east coast, from the U.S. Eastern Seaboard up to Atlantic Canada. Bombogenesis also occurs around the Great Lakes.
- Europe: Northwestern parts, especially near the North Atlantic, including areas around the United Kingdom and Iceland.
- Asia: Less frequent but happen in regions like Japan.
- Australia: Along the Australian east coast above the East Australian Current.
Bomb cyclones in the Northern Hemisphere move toward the pole, while those in the Southern Hemisphere move toward the equator. The storms display less seasonality in the Southern Hemisphere.
Effects of a Bomb Cyclone
Bomb cyclones have a range of impacts:
- Strong Winds: Hurricane-force gusts occur in extreme cases, leading to power outages and downed trees.
- Heavy Precipitation: This includes heavy rain, snow, or a mix, leading to flooding or blizzard conditions.
- Coastal Effects: Storm surges, coastal flooding, and beach erosion can occur.
- Drop in Temperatures: Rapid drops in temperature can accompany a bomb cyclone, leading to flash freezing.
Preparing for a Bomb Cyclone
While bomb cyclones develop quickly, meteorologists watch for conditions that form them and usually give some advance warning.
- Stay Informed: Monitor local weather reports and alerts.
- Stock Up: Have enough food, water, and essential supplies for at least 72 hours.
- Secure Property: Ensure loose objects outside are tied down or brought indoors.
- Emergency Kit: Have an emergency kit ready with flashlights, batteries, first aid supplies, and important documents.
- Avoid Travel: Stay off roads to avoid accidents, especially in snowy or icy conditions.
- Stay Warm: Ensure you have a way to keep warm, especially if power outages occur.
Interesting Bomb Cyclone Facts
- Name Origin: The term “bomb” in “bomb cyclone” originates from “bombogenesis,” which is a fusion of “cyclogenesis” and the idea of an explosive development.
- Rapid Intensification: A storm undergoes bombogenesis if its central pressure drops at least 24 millibars in 24 hours.
- Temperature Contrasts: Bomb cyclones often form at latitudes where warm tropical air meets cold polar air, leading to significant atmospheric instability.
- Not Exclusive to Winter: While bomb cyclones are more common in the colder months, they occur any time of the year.
- Widespread Impacts: Bomb cyclones lead to a variety of weather conditions, including heavy snowfall, torrential rain, hurricane-force winds, and tornadoes.
- North Atlantic Oscillation (NAO): A positive phase of the NAO, which involves a strong Icelandic low and a strong Azores high, favors the formation of bomb cyclones in the North Atlantic.
- Historical Impact: The “Perfect Storm” of 1991, popularized by the book and film, was a hurricane merging with a non-tropical system that then underwent bombogenesis.
- Global Occurrences: While the North Atlantic is a prime location for bomb cyclones, they also occur in the North Pacific and around regions in Europe, particularly near the North Sea.
- Historical Records: Some of the most intense bomb cyclones have seen pressure drops of more than 50 millibars in 24 hours, though such extreme cases are rare.
- Safety Concerns: Due to their rapid intensification, bomb cyclones sometimes catch communities off-guard, emphasizing the importance of timely meteorological predictions and warnings.
- Oceanic Influences: Warm ocean currents, such as the Gulf Stream, play a vital role in the formation of bomb cyclones by providing the necessary heat and moisture for their development.
- Effects on Sea: Apart from the atmospheric impacts, bomb cyclones churn the ocean, leading to significant wave heights. Mariners avoid waters where a bomb cyclone is predicted.
- Economic Impacts: The intense weather associated with bomb cyclones leads to significant economic damages, from infrastructure damage to disruptions in travel and commerce.
- Research Value: Bomb cyclones interest meteorologists and climatologists, leading to extensive research on their prediction and effects.
- Lim, Eun-Pa; Simmonds, Ian (2002). “Explosive Cyclone Development in the Southern Hemisphere and a Comparison with Northern Hemisphere Events”. Monthly Weather Review. 130 (9): 2188–2209. doi:10.1175/1520-0493(2002)130<2188:ECDITS>2.0.CO;2
- MacDonald, Bruce C; Reiter, Elmar R (1988). “Explosive Cyclogenesis over the Eastern United States”. Monthly Weather Review. 116 (8): 1568–86. doi:10.1175/1520-0493(1988)116<1568:ECOTEU>2.0.CO;2
- Sanders, Frederick; Gyakum, John R (1980). “Synoptic-Dynamic Climatology of the ‘Bomb'”. Monthly Weather Review. 108 (10): 1589–606. doi:10.1175/1520-0493(1980)108<1589:SDCOT>2.0.CO;2
- Weng, H. Y.; Barcilon, A. (1987). “Favorable environments for explosive cyclogenesis in a modified two-layer Eady model”. Tellus A. 39A (3): 202–214. doi:10.1111/j.1600-0870.1987.tb00301.x