Bomb Cyclone

Bomb Cyclone

Subject – Geography

Context – ‘Bomb cyclone’ hits eastern U.S., triggers transport chaos, outages

Concept –

• A bomb cyclone is a large, intense midlatitude storm that has low pressure at its center, weather fronts and an array of associated weather, from blizzards to severe thunderstorms to heavy precipitation.
• It becomes a bomb when its central pressure decreases very quickly—by at least 24 millibars in 24 hours.
• When a cyclone “bombs,” or undergoes bombogenesis, this tells us that it has access to the optimal ingredients for strengthening, such as high amounts of heat, moisture and rising air. Most cyclones don’t intensify rapidly in this way.
• Bomb cyclones put forecasters on high alert, because they can produce significant harmful impacts.
• The U.S. Eastern Seaboard is one of the regions where bombogenesis is most common. That’s because storms in the midlatitudes—a temperate zone north of the tropics that includes the entire continental U.S.—draw their energy from large temperature contrasts.
  • Along the U.S. East Coast during winter, there’s a naturally potent thermal contrast between the cool land and the warm Gulf Stream current.
• Over the warmer ocean, heat and moisture are abundant. But as cool continental air moves overhead and creates a large difference in temperature, the lower atmosphere becomes unstable and buoyant. Air rises, cools and condenses, forming clouds and precipitation.
• Intense cyclones also require favorable conditions above the surface. Particularly strong upper-level winds, also known as “jet streaks,” and high-amplitude waves embedded within storm tracks can help force air to rise.
• When a strong jet streak overlies a developing low-pressure system, it creates a feedback pattern that makes warm air rise at an increasing rate. This allows the pressure to drop rapidly at the center of the system. As the pressure drops, winds strengthen around the storm. Essentially, the atmosphere is trying to even out pressure differences between the center of the system and the area around it.