The correct option is It is lower over the equator than over the poles..
Explanation
The Tropopause is the transitional boundary separating the Troposphere from the Stratosphere. Within the Troposphere, temperature decreases with an increase in altitude, a phenomenon governed by the Normal Lapse Rate (approximately 6.5°C per km).
Detailed Analysis:
- Height Variation: The thickness of the Troposphere is not uniform across the globe. It extends to a height of approximately 18 km at the Equator due to strong convection currents and intense surface heating. In contrast, it extends only up to about 8 km at the Poles.
- Temperature Differential: Because the air at the Equator rises to a much greater height (18 km), it undergoes cooling for a longer vertical distance compared to the air at the Poles (8 km).
- Result: Consequently, the temperature at the equatorial tropopause drops to approximately -80°C, whereas the temperature at the polar tropopause is relatively higher, around -45°C.
Conclusion on Options:
- It is constant everywhere. is incorrect because the temperature varies significantly with latitude.
- It is lower over the equator than over the poles. is correct as the temperature is significantly lower (-80°C) over the Equator compared to the Poles (-45°C).
- It is higher over the equator than over the poles. is incorrect based on the lapse rate principle described above.
- It is 0°C everywhere. is incorrect as the temperatures are far below freezing point.
Key Takeaway:
While surface temperatures are highest at the Equator, the temperature at the Tropopause is lowest at the Equator due to the greater vertical extent of the Troposphere allowing for prolonged adiabatic cooling.