Context: Recently, the bomb cyclone has caused record levels of snowfall, rainfall and winds all across the United States, right from the border with Canada up to the border with Mexico, an expanse of more than 3,000 kilometres. 

• The death toll due to weather-related incidents in the United States mounted to 34 and has left millions without power.

About Bomb Cyclone

• It is used by meteorologists to indicate a mid-latitude cyclone that intensifies rapidly. 

• It is a massive winter storm hammering the coast, bringing strong winds, flooding, ice and snow. 

• It is a combination of rapidly declining pressure and extreme cold. 

• This particular storm is the most explosive ever, observed on the east coast. 

• The change in pressure needed to classify a storm as bomb cyclone is latitude dependent. For example, at 60° latitude, bomb cyclone occurs if the central pressure decreases by 24 mbar (hPa) or more in 24 hours.

• It is called a bomb cyclone, a dramatic name for what happens when the storm explosively strengthens while the pressure plummets.

• Bomb cyclones put forecasters on high alert, because they can produce significant harmful impacts.

Characteristics of Bomb Cyclone

• Bomb cyclone is a predominantly maritime, winter event, but also occurs in continental settings, even in the summer.

• It can produce winds of 120 to 155 km/h, and yield heavy precipitation.

• It is characterized by cold winds, which are also expected to pick up, and temperatures could drop far below zero — enough to cause frostbite within minutes.

• This process is the extratropical equivalent of the tropical rapid intensification (It is a situation where a tropical cyclone intensifies dramatically in a short period of time).

Formation: The mechanism of formation of a bomb cyclone is similar to that of an extra-tropical cyclone. However, the rapid drop in pressure leads to bombogenesis.

• This can happen when a cold air mass collides with a warm air mass, such as air over warm ocean waters. The formation of this rapidly strengthening weather system is a process called bombogenesis.

• It occurs when a midlatitude cyclone rapidly intensifies, dropping at least 24 millibars over 24 hours.

• Note: A millibar measures atmospheric pressure.

Factors responsible for the rapid drop in pressure during bombogenesis

• Baroclinic instability and adiabatic processes are the principal factors.

• Other factors include the relative position of a 500-hPa trough, deep tropospheric frontogenetic processes, the influence of air–sea interaction, and latent heat release.

Most affected regions: The four most active regions where extratropical bomb cyclones occurs are:

• The Northwest Pacific,

• The North Atlantic,

• The Southwest Pacific, and

• The South Atlantic.

How does a Bomb Cyclone differ from a Hurricane?

• Hurricanes tend to form in tropical areas and are powered by warm seas. For this reason, they’re most common in summer or early fall, when seawater is warmest.

• Similarity with hurricanes: Though bomb cyclones share characteristics with hurricanes, they are not hurricanes:

• 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.