Question

What is the normal rate of decrease of temperature in troposphere with increase in height?

• A. $4^\circ\mathrm{C}/1000\ \mathrm{m}$
• B. $5^\circ\mathrm{C}/1000\ \mathrm{m}$
• C. $6.5^\circ\mathrm{C}/1000\ \mathrm{m}$
• D. $10^\circ\mathrm{C}/1000\ \mathrm{m}$

Hint:

Remember the important lapse rates: \[ \boxed{ \begin{aligned} \text{Normal Environmental Lapse Rate} &\rightarrow 6.5^\circ\mathrm{C}/1000\ \mathrm{m}, \text{Dry Adiabatic Lapse Rate} &\rightarrow 10^\circ\mathrm{C}/1000\ \mathrm{m}, \text{Saturated Adiabatic Lapse Rate} &\rightarrow \approx 5\text{--}6^\circ\mathrm{C}/1000\ \mathrm{m}. \end{aligned} } \] Mnemonic: “Normal = 6.5, Dry = 10.”

Answer 1

The Correct Option is C

Concept: The average rate at which air temperature decreases with altitude in the troposphere under normal atmospheric conditions is called the Normal (Environmental) Lapse Rate.

Step 1: Recall the standard lapse rate. The normal environmental lapse rate is \[ \boxed{6.5^\circ\mathrm{C}\ \text{per}\ 1000\ \mathrm{m}} \]

Step 2: Eliminate the incorrect options. \[ \begin{aligned} A. &\ 4^\circ\mathrm{C}/1000\ \mathrm{m}\rightarrow \text{Incorrect.} B. &\ 5^\circ\mathrm{C}/1000\ \mathrm{m}\rightarrow \text{Incorrect.} C. &\ 6.5^\circ\mathrm{C}/1000\ \mathrm{m}\rightarrow \text{Correct normal lapse rate.}\checkmark D. &\ 10^\circ\mathrm{C}/1000\ \mathrm{m}\rightarrow \text{Dry adiabatic lapse rate, not the normal environmental lapse rate.} \end{aligned} \] Hence, \[ \boxed{\text{(C)}} \]