Avielevate / DGCA CPL papers / Aviation Meteorology / Humidity and Stability
Humidity and Stability — DGCA CPL Aviation Meteorology
Chapter 03 of the Aviation Meteorology paper. 53 practice questions in the Avielevate bank, every one with its answer key, filterable into a timed set on this chapter alone.
What this chapter covers
The learning objectives we file Humidity and Stability questions under, and how many sit behind each. These come straight out of the bank and are regenerated whenever it changes — they are what is there today, not a claim.
| Learning objective | In the bank |
|---|
| 0306 Humidity & Moisture | 25 questions |
| 0307 Atmospheric Stability | 28 questions |
Sample Humidity and Stability questions, answered and explained
Real questions from this chapter, with the answer marked and the reasoning written out — the same explanations you get inside the app.
030040 · Humidity and Stability
Which instrument is used to measure the humidity of the air?
- Ahydrometer
- Bhygrometer
- Cwet bulb thermometer
- Dhygroscope
Why that is the answer
A hygrometer is the general term for an instrument designed specifically to measure atmospheric humidity - this includes types such as the hair hygrometer (using the expansion/contraction of human hair with moisture content), electronic capacitance sensors, and the wet-and-dry bulb (psychrometer) arrangement, all of which fall under the broad category of hygrometers used to determine humidity. Option a, a hydrometer, is a completely different instrument used to measure the density or specific gravity of liquids (e.g., battery acid, aircraft fuel) and has nothing to do with air humidity. Option c, a wet bulb thermometer, is only one component of a psychrometer (used alongside a dry bulb thermometer to derive humidity via the difference in readings) - it is a temperature-measuring device on its own, not a complete humidity-measuring instrument by itself. Option d, 'hygroscope', is not the standard recognised instrument name for measuring humidity (hygroscopic refers to a substance's tendency to absorb moisture). The correct, standard term for the humidity-measuring instrument is hygrometer, option b.
- Hygrometer = general instrument category for measuring humidity (hair, capacitance, psychrometer-based).
- Hydrometer measures liquid density, unrelated to air humidity.
- Wet bulb thermometer is only one part of a psychrometer, not a full humidity instrument.
- Correct instrument name is hygrometer - option b.
030338 · Humidity and Stability
When warm air is advected into the upper part of a layer:
- AThe layer becomes more stable
- BThe layer becomes less stable
- CIn the Northern Hemisphere, wind speed will always decrease with height
- DIn the Northern Hemisphere, the wind will back with increasing height
Why that is the answer
Advection means the horizontal transport of an air mass property (like temperature) into a region by wind flow. If warm air is advected into the UPPER part of a layer while the lower part of the layer remains as it was, the temperature at the top of the layer increases relative to the temperature at the bottom. This makes the vertical temperature difference across the layer smaller — the Environmental Lapse Rate (ELR) within that layer DECREASES (the air becomes less cold with height than before, or the temperature gradient flattens/weakens). A smaller/reduced ELR, being further below the DALR, corresponds to an atmosphere that is MORE resistant to a parcel continuing to rise (a lifted parcel becomes even colder relative to its surroundings), meaning stability within the layer INCREASES. This is the classic mechanism behind warm air advection aloft creating a stable layer or even a temperature inversion (as also happens with subsidence/anticyclonic warming aloft). Options (c) and (d) describe wind behaviour with height (backing/veering, speed shear) related to the thermal wind concept, which is a separate topic from the direct stability effect asked about here, and are not the direct consequence being tested. Since warming the upper part of the layer directly increases stability, the correct answer is (a).
- Warm air advected into the top of a layer raises temperature aloft relative to the base
- This reduces the vertical temperature gradient (ELR decreases) within the layer
- A reduced ELR (further below DALR) means increased resistance to lifting: stability increases
- Correct answer: a
030502 · Humidity and Stability
The wet bulb temperature is usually lower than the dry bulb temperature because:
- Acondensation releases latent heat
- Bevaporation produces a cooling effect
- Cthe bulb thermometer absorbs latent heat
- Dcondensation forms on the muslin wick covering the bulb
Why that is the answer
The wet bulb thermometer's bulb is wrapped in a wet muslin wick and exposed to ventilated air. Whenever the surrounding air is not fully saturated, water evaporates from the wick into the air. Evaporation is an endothermic process — it requires latent heat of vaporisation, which is drawn from the water and the thermometer bulb, cooling them below the ambient (dry bulb) air temperature. This cooling effect is why the wet bulb reading is normally lower than the dry bulb reading, and the size of this 'wet bulb depression' is directly related to how dry the air is (drier air causes more evaporation and hence more cooling). Option (a) is the correct underlying mechanism: evaporation causes cooling. Option (c) incorrectly reverses the direction — latent heat is released from the wick, not absorbed by it (the water loses heat as it evaporates, cooling the thermometer). Option (d) is meteorologically backwards, since condensation would only occur on the wick in already-saturated air and would release heat, warming rather than cooling it, and does not explain the normal depression seen. Option (a) here refers to condensation releasing heat, which is not what causes the wet bulb's lower reading. The correct explanation is evaporative cooling. Therefore, the correct answer is (b).
- Wet bulb wick loses water to evaporation when air is unsaturated
- Evaporation requires latent heat, drawn from the water/thermometer, causing cooling
- This evaporative cooling is why wet bulb reads lower than dry bulb
- Correct answer: b
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Frequently asked
How many Humidity and Stability questions are there for the DGCA CPL Aviation Meteorology paper?
Avielevate's bank carries 53 published Humidity and Stability questions for Aviation Meteorology, mapped across 2 learning objectives. Every one has its answer key, and explanations are being written across the whole bank.
How much of the Aviation Meteorology paper is Humidity and Stability?
The DGCA does not publish a per-chapter breakdown of its papers, so nobody can honestly tell you — and we will not guess. What we can tell you is what students who have just sat a paper reported meeting, which is measured rather than rumoured: that is the exam recall report inside the app.
What is the best way to revise Humidity and Stability?
Sit a short timed set on this chapter alone, tag how sure you were of each answer, then drill the two that actually leak marks: the ones you got right while guessing, and the ones you got wrong while confident. Avielevate does that tagging for you and puts anything you got wrong back in front of you on a spaced schedule.
The rest of the Aviation Meteorology paper
One account covers every chapter of every paper.
← All Aviation Meteorology chapters · All six DGCA CPL papers