Stratosphere has ideal conditions for flying aeroplanes. Choose the correct…

Concept

Earth's atmosphere is divided into layers based on how temperature changes with altitude. In the troposphere, temperature falls with height, and this instability drives the vertical mixing (convection) that produces clouds, storms and turbulence. The stratosphere above it has a temperature inversion — ozone absorbs solar UV radiation, so temperature rises with height — which suppresses vertical mixing and keeps the layer thermally stable.

Application

Applying this to flight conditions: because the stratosphere lacks the convective mixing found below, it stays largely clear of clouds, precipitation and the turbulence that convection generates, giving aircraft cruising there a smooth, stable and fuel-efficient path. This stability — not pressure or wind — is what makes the layer suited to flying.

Contrast

• High air pressure: pressure decreases roughly exponentially with altitude, so stratospheric pressure is a fraction of sea-level pressure — the opposite of "high."

• Low air pressure: the stratosphere's pressure is indeed low, but low pressure by itself reduces air density and aerodynamic lift; it does not explain why the layer favours flight.

• Free from clouds and related weather phenomena: the temperature inversion above the tropopause blocks the convective mixing that generates weather, leaving this layer largely free of clouds, storms and the turbulence they cause — the stability that actually makes it ideal for cruising aircraft.

• Windy conditions: strong sustained winds such as jet streams are concentrated near the tropopause/upper-troposphere boundary rather than being a defining property of the calmer stratosphere.

So the ideal flying conditions in the stratosphere arise because it is free from clouds and related weather phenomena.