News: The intense storm that hit Delhi recently appeared in an unusual shape in the India Meteorological Department’s (IMD’s) weather radar imagery. The storm looked like a crescent or an archer’s bow. In technical terms, such presentations of storms are called “bow echoes”.
About Bow Echo
- A bow echo is essentially a line of storms, also called a squall line, on the radar that looks like a bow.
- This squall line can sometimes be embedded in a larger squall line.
- Bow echoes are often associated with severe weather, including damaging straight-line winds.
- Naming: The term was coined in the 1970s by Ted Fujita, a Japanese American meteorologist known for developing the scale to classify tornadoes.
- Range: A bow echo can extend from 20 km to 100 km.
- Timeframe: It can last between three and six hours.
- Formation
- When rain-cooled air comes down to the ground, and spreads out horizontally, a boundary called the gust front is created between the rain-cooled air and warm-moist air on the surface.
- This front pushes up the warm-moist air into the atmosphere, which forms new thunderstorms.
- These new thunderstorms produce more rain, thereby creating more rain-cooled air, which helps the gust front to maintain its strength.
- As this process keeps repeating itself, there comes a point when there is an inflow of air on the trailing side of the line of storms and bends it like an archer’s bow.
- The cycle lasts as long as new thunderstorms keep forming at the front, helping the system grow and move forward with strong winds.
- Derecho: If the bow echo (or series of bow echoes) progresses more than 400 kilometers with widespread wind gusts 93 km/h or greater, then the bow echo is classified as a derecho.
