Bomb Cyclone

Source: India Today

Context:

An unprecedented Bomb Cyclone is wreaking havoc across the United States and Canada.

About:

1. 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.
2. It becomes a bomb when its central pressure decreases very quickly—by at least 24 millibars in 24 hours.
3. In simple terms, bombogenesis is a storm (low pressure area) that undergoes rapid strengthening.
4. This can happen when a cold air mass collides with a warm air mass, such as air over warm ocean waters.
5. The vast majority of such storms occur over the ocean. The storm can be tropical or non-tropical in nature.

Key Features:

Bomb cyclones have cold air and fronts:

Cold air rapidly weakens hurricanes, while it is an essential ingredient for bomb cyclones.

Bomb cyclones form during winter:

Hurricanes form from late spring to early fall, while bomb cyclones form from late fall to early spring.

Bomb cyclones form at higher latitudes:

Hurricanes form in tropical waters, while bomb cyclones form over the northwestern Atlantic, northwestern Pacific and sometimes the Mediterranean Sea.Many of the infamous storms that have battered the East Coast and sank ships in the northwestern Atlantic Ocean throughout history were bomb cyclones. 

Favourable conditions for Bomb cyclones to form

1. Baroclinic instability is one of the principal mechanisms for the development of most explosively deepening cyclones. Deep tropospheric frontogenetic processes.
2. Influence of air–sea interaction, and latent heat release
3. Upper-level winds, also known as ―jet streams:

When a strong jet stream 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 leading to Bombogenesis.

Areas prone to Bomb Cyclones:

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. In the Northern Hemisphere the maximum frequency of explosively deepening cyclones is found within or to the north of the Atlantic Gulf Stream and Kuroshio Current in the western Pacific.

In the Southern Hemisphere it is found with Australian east coast lows above the East Australian Current, which shows the importance of air-sea interaction in initiating and rapidly developing extratropical cyclones.

Impact of Bomb Cyclones:

Bomb Cyclones can produce heavy flooding, blizzard conditions and wind speeds comparable to a Category 1 hurricane.

The fast strengthening is usually a sign of a very powerful storm system and so much of the danger lies in the fact that bomb cyclones can lead to damages before giving time to prepare.