The correct option is 2 and 3 only.
Explanation
The Tropopause is the boundary zone separating the Troposphere from the Stratosphere. The physical characteristics of this layer, including height and temperature, vary significantly with latitude due to differences in surface heating and convection.
Statement-wise Analysis:
- Statement 1 is Incorrect: The troposphere extends to a height of approximately 18 km at the equator due to strong convection currents. As temperature decreases with altitude (Normal Lapse Rate), the air cools for a greater vertical distance, reaching a temperature of about minus 80°C over the equator.
- Statement 2 is Correct: At the poles, the troposphere extends only up to about 8 km. Since the vertical distance for cooling is shorter, the temperature at the polar tropopause is relatively warmer, standing at approximately minus 45°C.
- Statement 3 is Correct: Comparing the two values, the temperature at the tropopause is significantly lower over the equator (-80°C) than over the poles (-45°C). This is a counter-intuitive but fundamental characteristic of the atmospheric structure.
Key Takeaway:
The height of the tropopause is directly proportional to surface temperature (higher at the equator), but the temperature at the tropopause is inversely related to its height (colder at the equator, warmer at the poles).