BOW ECHO from Vajirao & Reddy Institute

BOW ECHO

Context: The intense storm that hit Delhi recently appeared in an unusual crescent or archer’s bow shape on the India Meteorological Department’s (IMD’s) weather radar imagery, technically termed a "bow echo." WHAT IS BOW ECHO?

• A bow echo is essentially a line of storms, also called a squall line, that appears in a distinctive archer's bow or crescent shape on weather radar imagery.
• Scale and Duration: A bow echo can extend from 20 km to 100 km in length and typically lasts between 3 and 6 hours.
• Significance for Meteorologists: Meteorologists specifically track bow echoes because they are often a precursor to more destructive windstorms.
• They are associated with severe straight-line winds.
• Origin of Term: The term "bow echo" was coined in the 1970s by Ted Fujita, a Japanese American meteorologist renowned for developing the Fujita scale for classifying tornadoes.

HOW DOES A BOW ECHO FORM? The formation of a bow echo involves a self-sustaining cycle of atmospheric processes:

• Rain-Cooled Air Descent: When precipitation from thunderstorms falls, it cools the air.
  • This rain-cooled air descends to the ground due to its higher density.
• Horizontal Spread and Gust Front: As this cool air reaches the surface, it spreads out horizontally.
  • This creates a leading edge or boundary known as a gust front, which separates the rain-cooled air from the surrounding warm, moist air at the surface.
• Lift and New Thunderstorms: The gust front acts like a mini cold front, pushing up the warm, moist air into the atmosphere.
  • This forced ascent of warm, moist air leads to the formation of new thunderstorms along the gust front.
• Reinforcing Cycle: These new thunderstorms produce more rain, which in turn creates more rain-cooled air.
  • This continuous production of rain-cooled air helps the gust front to maintain and even intensify its strength.
• Bow Formation: As this process repeats and intensifies, a point is reached where there is a strong inflow of air on the trailing side of the line of storms.
  • This inflow, combined with the strong winds at the leading edge, causes the entire squall line to bend outwards, forming the characteristic archer’s bow shape.
• Sustained Strong Winds: The cycle continues as long as new thunderstorms keep forming at the front, helping the system to grow and move forward, generating and sustaining strong, damaging straight-line winds.

BOW ECHOES IN INDIA

• Not a New Phenomenon: Bow echoes are not a new phenomenon in India.
• Previous Occurrences:
  • On May 31, 2022, a bow echo formed over Delhi and Noida. Although short-lived (lasting about an hour), it produced winds of up to 100 kmph.
  • Such squall lines have also been observed during thunderstorm activity in Odisha in recent times.
• Common Occurrence: According to senior IMD scientists, these phenomena have appeared often in India during intense thunderstorms.
• Delhi Storm Example: The recent Delhi storm (May 2025), with winds reaching up to 100 kmph, was a clear example of a bow echo's destructive potential.

  Note: Connect with Vajirao & Reddy Institute to keep yourself updated with latest UPSC Current Affairs in English. Note: We upload Current Affairs Except Sunday.