Atmosphere, Winds, Pressure, Cyclones and Climate Types
Atmosphere, Winds, Pressure, Cyclones and Climate Types
The atmosphere is layered by temperature, and differences in pressure drive the winds that shape climate. NTPC asks the layer holding the ozone, the planetary winds and pressure belts, local winds, the origin of western disturbances and tropical cyclone names.
1. Layers of the Atmosphere
| Layer | Height (about) | Key facts |
|---|---|---|
| Troposphere | Up to 8 km (poles) to 18 km (equator) | All weather occurs here; temperature falls with height |
| Stratosphere | Up to 50 km | Ozone layer; ideal for jet aircraft |
| Mesosphere | Up to 80-85 km | Coldest layer; meteors burn up here |
| Thermosphere (ionosphere) | Above 85 km | Reflects radio waves; auroras |
| Exosphere | Outermost | Very thin air |
Composition: nitrogen about 78%, oxygen about 21%, argon about 0.93%, carbon dioxide about 0.04%
2. Winds and Pressure
| Wind | Facts |
|---|---|
| Trade winds | Blow from the subtropical highs towards the equator (north-east and south-east trades) |
| Westerlies | From the subtropical highs towards the subpolar lows; "Roaring Forties" in the southern hemisphere |
| Polar easterlies | From the poles |
| Coriolis effect | Deflects winds to the right in the northern hemisphere and to the left in the southern |
| Local wind | Region |
|---|---|
| Loo | Hot, dry wind of north India in summer |
| Chinook | Warm wind, Rocky Mountains (USA and Canada) |
| Foehn | Warm wind, Alps |
| Sirocco | Hot wind from the Sahara towards Italy |
| Mistral | Cold wind, France |
Western disturbances: temperate cyclones from the Mediterranean region that bring winter rain to north-west India
3. Cyclones and Climate
| Item | Facts |
|---|---|
| Tropical cyclones | Called hurricanes (Atlantic), typhoons (western Pacific), cyclones (Indian Ocean), willy-willies (Australia) |
| Eye | Calm centre of a cyclone |
| Köppen classification | A tropical, B dry, C warm temperate, D cold, E polar |
✗ Ozone is concentrated in the troposphere | ✓ It is concentrated in the stratosphere
✗ Western disturbances come from the Bay of Bengal | ✓ They originate over the Mediterranean region
हिंदी नोट: ओज़ोन परत समताप मंडल (स्ट्रैटोस्फियर) में है; मौसम की घटनाएँ क्षोभमंडल में होती हैं। पश्चिमी विक्षोभ भूमध्य सागर क्षेत्र से आते हैं और उत्तर-पश्चिम भारत में सर्दियों में वर्षा लाते हैं। लू उत्तर भारत की गर्म हवा है।
Exam Pointer: Verified NTPC patterns: the layer with the most ozone (June 2022 CBT-2) and the origin of western disturbances (August 2025 UG CBT-1). Planetary-wind and local-wind questions are tagged syllabus-based.
Pariksha Pattern: Every Way NTPC Asks This Topic
Pattern 1: Layers of the atmosphere
[PYQ: NTPC CBT-2 16-Jun-2022 Shift-3]
EXAM LEVEL
Q. In which layer of the atmosphere is most ozone found?
The stratosphere.
Answer: Stratosphere
EXAMATLAS LEVEL
Q. In which layer does all weather occur, and in which do meteors burn up?
Weather occurs in the troposphere; meteors burn up in the mesosphere.
Answer: Troposphere; mesosphere
Pattern 2: Western disturbances and cyclones
[PYQ: NTPC UG CBT-1 13-Aug-2025 Shift-3]
EXAM LEVEL
Q. Where do the western disturbances that reach India originate?
Over the Mediterranean region.
Answer: Mediterranean region
EXAMATLAS LEVEL
Q. What are tropical cyclones called in the western Pacific and in the Atlantic, and what is the calm centre of a cyclone called?
Typhoons in the western Pacific and hurricanes in the Atlantic. The calm centre is the eye.
Answer: Typhoons; hurricanes; the eye
Pattern 3: Planetary winds and pressure belts
[Pattern: syllabus-based, PYQ-style]
EXAM LEVEL
Q. Which winds are called the "Roaring Forties"?
The westerlies of the southern hemisphere, around 40° S.
Answer: Southern hemisphere westerlies
EXAMATLAS LEVEL
Q. In which direction does the Coriolis effect deflect winds in the northern hemisphere, and from where do the trade winds blow?
To the right. Trade winds blow from the subtropical high-pressure belts towards the equator.
Answer: To the right; from the subtropical highs to the equator
Pattern 4: Local winds and climate types
[Pattern: syllabus-based, PYQ-style]
EXAM LEVEL
Q. What is the Loo?
A hot, dry summer wind of north India.
Answer: Hot dry wind of north India
EXAMATLAS LEVEL
Q. Match the local wind with its region: Chinook, Foehn, Sirocco.
Chinook: Rocky Mountains. Foehn: Alps. Sirocco: from the Sahara towards Italy.
Answer: Rockies, Alps, Sahara-Italy
60-Second Revision
- Troposphere (weather), stratosphere (ozone), mesosphere (meteors, coldest), thermosphere (radio).
- N2 78%, O2 21%.
- Trades, westerlies, polar easterlies; Coriolis right in the north.
- Western disturbances from the Mediterranean.
- Hurricane, typhoon, cyclone, willy-willy.