Which of the following statements with reference to Surface inversion of temperature is/are correct? 1. It causes instability in the lower layers of the atmosphere. 2. This inversion commonly lasts for a few hours until the Sun comes up. Select the answer using the code given below:
- (a)1 only
- (b)2 only
- (c)Both 1 and 2
- (d)Neither 1 nor 2
Correct — B, 2 only. A surface inversion forms on a long, clear, still winter night: the ground radiates its heat away, cools faster than the air above it, and by early morning the air is warmer aloft than at the surface — the normal lapse rate turned upside down. Cold, dense air lying under warmer, lighter air is a stable arrangement, not an unstable one. Nothing wants to rise through it, which is exactly why smoke and dust collect under the inversion layer and spread sideways, and why dense morning fog is a winter commonplace. So statement 1 has the sign wrong: surface inversion promotes stability. Statement 2 is right — the inversion is short-lived, holding for a few hours only until the Sun rises and begins to warm the ground, which restores the normal decrease of temperature with height and breaks the layer up.
- (a)1 only — Inverts the truth twice over. Surface inversion promotes stability, and the short duration described in statement 2 is correct.
- (c)Both 1 and 2 — Statement 2 is correct but statement 1 is not. Warm air sitting on top of cold air suppresses vertical motion; instability requires the opposite arrangement.
- (d)Neither 1 nor 2 — Rejects the duration claim, which is the accurate half. A surface inversion typically lasts only a few hours and breaks after sunrise.
Temperature normally falls with height in the troposphere, at the normal lapse rate. When that reverses and temperature rises with height, the layer is called an inversion. A surface inversion is the commonest kind and is produced by radiational cooling of the ground on a long winter night with clear skies and still air. Over the polar regions, inversion is the normal state through the year. A second family of inversions is produced in hills and valleys by air drainage, cold dense air sliding downslope under gravity and pooling in valley bottoms with warmer air above it.
The item is really testing one idea: what the vertical arrangement of density does to vertical motion. Put the cold, heavy air at the bottom and the atmosphere is content to stay where it is — stable. Put warm, light air at the bottom, as happens on a hot afternoon, and it rises — unstable. Once that is clear, statement 1 falls immediately, and the two practical consequences follow: pollutants trapped near the ground on winter mornings in cities across the Indo-Gangetic plain, and the morning fog that goes with them. Statement 2 supplies the other half of the picture, that this is a matter of hours, not days.
- Inversion of temperature is a reversal of the normal lapse rate, so that temperature rises rather than falls with height.
- A long winter night with clear skies and still air is the ideal setting: the ground radiates away the day's heat and by early morning is cooler than the air above it.
- Surface inversion promotes stability in the lower layers, so smoke and dust collect beneath the inversion layer and spread horizontally.
- Dense fog on winter mornings is a common consequence, and the inversion usually lasts only a few hours until the Sun warms the ground again.
- Over polar areas temperature inversion is normal throughout the year; in hills and valleys, air drainage produces inversions that protect plants from frost damage.
Cold air underneath warm air is a stable stack — which is why statement 1, claiming instability, fails.
- Assuming any temperature anomaly must make the air turbulent; an inversion does the opposite and locks the lower air in place.
- Confusing surface inversion with the inversion at the tropopause or in the stratosphere, which is a permanent feature and a different phenomenon.
- Forgetting that the valley-bottom inversion produced by air drainage can persist far longer than the few morning hours of a radiation inversion.
As a two-statement item on the cause, duration or consequences of inversion, or as a cause-and-effect pairing linking winter fog and trapped pollution to a stable inversion layer.
Consider the following statements on 'Fog': 1. Fog is simply a cloud that forms close to the ground. 2. Radiation fog is associated with radiation cooling of the land at night. 3. Advection fog forms when moisture is blown over a cold surface and is chilled by contact. Which of the statements given above are correct?
- (a) 1 and 2 only
- (b) 2 and 3 only
- (c) 1 and 3 only
- (d) 1, 2 and 3
Answer(d) 1, 2 and 3
The same winter night, seen through its most visible product. Radiation cooling of the land after dark is what chills the surface air below the air above it, and the fog that item describes forms inside the stable layer this one is about.
- practice — not a real PYQ
Smoke and dust particles collecting beneath a layer and spreading horizontally near the ground on a winter morning is best explained by which one of the following?
- (a)Strong convection currents
- (b)Surface inversion of temperature
- (c)The passage of a jet stream
- (d)An increase in the normal lapse rate
Answer(b) Surface inversion of temperature — the stable layer suppresses vertical motion, so pollutants cannot disperse upward and spread sideways instead.
- practice — not a real PYQ
Which one among the following conditions is most favourable for the formation of a surface inversion of temperature?
- (a)A short summer night with a strong breeze
- (b)A cloudy night with high humidity
- (c)A long winter night with clear skies and still air
- (d)An afternoon of intense solar heating
Answer(c) A long winter night with clear skies and still air — clear skies let the ground radiate heat away freely, and calm air prevents mixing.