Table of Contents
Context: At least 17 people died, millions are without power and travel disrupted as record-breaking cold gripped the USA due to bomb cyclone.
What is a Bomb Cyclone?
- Explosive cyclogenesis (also referred to as a weather bomb, bomb cyclone or bombogenesis) is the rapid deepening of an extratropical cyclonic low-pressure area.
- 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.
About Cyclones
- Cyclones are rapid inward air circulation around a low-pressure area whereas anti-cyclones are circulation of winds around a high-pressure area.
| Pressure system | Pressure condition at the centre | Pattern of wind direction | ||
| Northern Hemisphere | Southern Hemisphere | |||
| Cyclone | Low | Anticlockwise | Clockwise | |
| Anti-cyclone | High | Clockwise | Anticlockwise | |
- Types: There are two types of cyclones.
- Tropical cyclones (also called typhoon or hurricane, an intense circular storm that originates over warm tropical oceans).
- Extra Tropical cyclones (also called temperate cyclones or middle latitude cyclones or Frontal cyclones or Wave Cyclones).
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.
- 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.
- 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.
Tropical Cyclones
- A tropical cyclone is a warm-core, low pressure system without any “front” attached, that develops over the tropical or subtropical waters, and has an organized circulation.
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