Why does the height of a mercury column in a barometer decrease during a storm?
The barometer measures atmospheric pressure ( P_a = rho g h ). During a storm, atmospheric pressure drops, reducing the force supporting the mercury column, causing its height to decrease, as noted in the chapter.
Ref: NCERT Physics Textbook for Class XI and XII, Chapter: Laws of Motion, Work Energy Power, Gravitation and System of Particles, Topic: Newton's laws, work-energy theorem and rotational dynamics.