Why in the News?

New Delhi recently faced a severe thunderstorm with winds up to 100 kmph, forming a bow echo — a crescent-shaped pattern seen on weather radar.

About Bow Echo:

What is it: A bow echo is a storm pattern on radar that looks like a curved bow, similar to an archer’s bow.
Storm Type: It forms inside a mesoscale convective system (MCS) — a large group of organised thunderstorms.
Origin of Term: The term was first used by Ted Fujita, who also created the Fujita scale for tornadoes.
How It Forms:
- Heavy rain causes cool air to sink and spread out near the ground.
- This cool air forms a gust front, which pushes warm, moist air upward, creating new storms.
- A rear inflow jet — strong mid-level winds — pushes the storm forward, bending it into a bow shape.
- Bookend vortices may form at both ends of the bow, and the northern end can sometimes generate tornadoes.

Size and Duration: Bow echoes usually span 20 to 200 km and last 3 to 6 hours.
Wind Strength: They often produce straight-line winds over 100 km/h, like those seen in Delhi’s recent storm.
Derechos: In severe cases, bow echoes can grow into derechos, which are long-lasting and widespread windstorms.
Impacts:
- Damaging Winds: Knock down trees, power lines, and damage buildings.
- Brief Tornadoes: May form at the storm’s edges, especially at the northern end.
- Microbursts and Downbursts: Intense short-lived wind blasts within the storm that cause local destruction.

[UPSC 2013] During a thunderstorm, the thunder in the skies is produced by the-

1. Meeting of cumulonimbus clouds in the sky 2. Lightning that separates the nimbus clouds 3. Violent upward movement of air and water particles.

Select the correct answer using the codes given below.

Options: (a) 1 only (b) 2 and 3 (c) 1 and 3 (d) None of the above produces the thunder*