Question

Which one of the following is the main reason why tropical cyclones rarely form over the Bay of Bengal during the summer monsoon season?

• A. Strong vertical wind shear.
• B. Weak low-level relative vorticity.
• C. Dry mid-troposphere.
• D. Stable atmosphere.

Hint:

Cyclones need vertically aligned convection. Monsoon seasons create strong vertical wind shear, which tilts convection and suppresses cyclone development.

Answer 1

The Correct Option is A

Step 1: Conditions needed for tropical cyclone formation.
Tropical cyclones require: - Warm sea surface temperature (\(> 26.5^\circ C\)) for latent heat release.
- Sufficient Coriolis force (away from equator).
- High low-level relative vorticity (for cyclonic spin).
- A moist mid-troposphere.
- Weak vertical wind shear (so convection stays vertically aligned).


Step 2: Monsoon background over Bay of Bengal.
During the summer monsoon, the Bay of Bengal has high sea surface temperatures and abundant moisture. However, the monsoon circulation features very strong vertical wind shear (large difference between low-level monsoon westerlies and upper-level easterlies).

Step 3: Impact of strong shear.
Strong vertical wind shear tilts and disrupts the vertical alignment of convection, preventing the development of a warm-core cyclone structure. Hence, despite warm seas and moisture, cyclogenesis is suppressed.


Step 4: Eliminate other options.
- (B) Vorticity is actually high in the monsoon trough.
- (C) Mid-troposphere is moist, not dry.
- (D) The atmosphere is unstable, not stable.
Final Answer:
\[ \boxed{\text{Strong vertical wind shear}} \]