The normal lapse rate of temperature of Earth’s atmosphere drops to 0 °C at the
- (a)upper part of ionosphere.
- (b)upper boundary of the tropopause.
- (c)lower part of mesosphere.
- (d)upper boundary of stratopause.
Correct — B, the upper boundary of the tropopause. Through the troposphere the temperature falls steadily with height — the normal (environmental) lapse rate, about 6.5 °C per kilometre. That fall stops at the tropopause: here the lapse rate drops to zero and the air becomes roughly isothermal, marking the top of the weather layer. So it is at the tropopause, the boundary above the troposphere, that the tropospheric lapse rate falls off to zero — not up in the mesosphere, at the stratopause, or in the ionosphere.
- (a)upper part of ionosphere. — Far out in the thermosphere/ionosphere temperature rises sharply with height; this is not the boundary at which the tropospheric fall in temperature ceases.
- (c)lower part of mesosphere. — In the mesosphere temperature falls again with height; the first isothermal boundary above the troposphere is the tropopause, well below the mesosphere.
- (d)upper boundary of stratopause. — The stratopause caps the stratosphere (~50 km), where temperature has risen to a maximum; it is not where the tropospheric lapse rate first drops to zero.
The atmosphere's temperature profile alternates by layer. In the troposphere temperature decreases with height at the normal lapse rate (~6.5 °C per km). At the tropopause the decrease halts — the lapse rate becomes zero and the layer is isothermal — marking the top of the troposphere. Above, in the stratosphere, temperature rises again because of ozone heating.
Read 'lapse rate drops to 0' as 'the temperature stops decreasing'. That happens at the tropopause, which is by definition the ceiling of the falling-temperature troposphere.
- In the troposphere temperature falls with height at the normal lapse rate (~6.5 °C per km).
- The tropopause is the boundary where this decrease stops — the lapse rate becomes zero (isothermal).
- Above the tropopause, in the stratosphere, temperature rises again (ozone heating).
- The troposphere is thickest over the equator (~16–18 km) and thinnest over the poles (~8 km).
The tropospheric lapse rate drops to zero at the tropopause, the top of the weather layer.
- Reading '0 °C' as an absolute temperature rather than the lapse rate falling to zero.
- Placing the boundary in the mesosphere or at the stratopause instead of the tropopause.
Where the tropospheric lapse rate falls to zero — the tropopause caps the falling-temperature layer.
The correct sequence of different layers of the atmosphere from the surface of the Earth upwards is
- (a) Troposphere, Stratosphere, Ionosphere, Mesosphere
- (b) Stratosphere, Troposphere, Ionosphere, Mesosphere
- (c) Troposphere, Stratosphere, Mesosphere, Ionosphere
- (d) Stratosphere, Troposphere, Mesosphere, Ionosphere
Answer(c) Troposphere, Stratosphere, Mesosphere, Ionosphere
Same concept — the vertical structure of the atmosphere. UPSC tests the order of the layers; this NDA item tests the tropopause, the boundary between the first two of them, where the lapse rate falls to zero.
Consider the following statements with reference to structure of the Earth's atmosphere: 1. Thickness of the troposphere is greatest at the equator 2. The air temperature of the tropopause is highest above the poles 3. The temperature in troposphere decreases at the rate of 1 °F for every 165 m of height Which of the statements given above is/are correct?
- (a) 1 only
- (b) 1 and 2 only
- (c) 2 and 3 only
- (d) 1, 2 and 3
Answer(b) 1 and 2 only
Same concept — the troposphere, the tropopause and the lapse rate. That NDA item probes the thickness and tropopause temperature; this one asks where the tropospheric lapse rate falls to zero.
- practice — not a real PYQ
The normal (environmental) lapse rate in the troposphere is approximately
- (a)1 °C per km
- (b)6.5 °C per km
- (c)10 °C per km
- (d)0 °C per km
Answer(b) 6.5 °C per km — temperature falls this much on average with height.
- practice — not a real PYQ
The boundary that separates the troposphere from the stratosphere is called the
- (a)stratopause
- (b)tropopause
- (c)mesopause
- (d)ionosphere
Answer(b) tropopause — where the temperature stops falling with height.