Atmosphere and Hydrosphere: Climate, Monsoon and Oceans
Atmosphere and Hydrosphere: Climate, Monsoon and Oceans
This topic decides 1 to 2 questions and the monsoon is its most reliable subject. Because the monsoon governs agriculture, and agriculture governs Bihar, the examiner treats it as more than weather. Learn the two branches and the retreating monsoon precisely.
Layers and Composition of the Atmosphere
Air is about 78 per cent nitrogen and 21 per cent oxygen, with carbon dioxide, argon and other gases making up the rest.
| Layer | Feature |
|---|---|
| Troposphere | All weather occurs here; lowest layer |
| Stratosphere | Contains the ozone layer; used by aircraft |
| Mesosphere | Meteors burn up here |
| Thermosphere | Radio waves reflect back from here |
| Exosphere | Outermost, merges into space |
Weather is the condition of the atmosphere at a place at a given moment; climate is the average of that condition over a long period. Mixing the two is a standard error.
The Indian Monsoon
The word monsoon comes from a term meaning season, and it refers to the seasonal reversal of winds.
| Season | Months | Character |
|---|---|---|
| Southwest monsoon | June to September | The rainy season; brings most of India's rain |
| Retreating monsoon | October to November | Winds withdraw; humid and hot |
| Northeast monsoon | October to December | Brings rain to Tamil Nadu coast |
| Winter | December to February | Dry and cool over most of India |
The southwest monsoon arrives in two branches, the Arabian Sea branch and the Bay of Bengal branch. The Bay of Bengal branch is the one that waters Bihar and the rest of the Ganga plain, moving up the valley from the east.
Mawsynram and Cherrapunji in Meghalaya receive the highest rainfall in the world. The monsoon's arrival date and strength decide the kharif harvest, which is why a delayed monsoon is a farm crisis rather than a weather story.
✗ Tamil Nadu gets most of its rain from the southwest monsoon | ✓ Tamil Nadu gets much of its rain from the retreating or northeast monsoon
The Hydrosphere
- About 71 per cent of the Earth's surface is water; only a small fraction is fresh water.
- There are five oceans; the Pacific is the largest and deepest, containing the Mariana Trench.
- Tides are caused mainly by the gravitational pull of the Moon.
- Ocean currents are warm or cold and strongly influence coastal climate.
दक्षिणी-पश्चिम मानसून ही भारत की अधिकांश वर्षा लाता है; बिहार में बंगाल की खाड़ी से।
TRE pointer: The Tamil Nadu rainfall question is the classic trap of this topic, because the intuitive answer is wrong. Learn the two branches by name, and remember that Bihar's rain comes from the Bay of Bengal branch travelling up the Ganga valley — that detail turns a general monsoon question into a state one. The weather-versus-climate definition is the second most repeated item here.
60-Second Recap
- Air is 78 per cent nitrogen and 21 per cent oxygen.
- Troposphere holds the weather; stratosphere holds the ozone layer.
- Weather is momentary; climate is the long-term average.
- Southwest monsoon runs June to September in two branches, Arabian Sea and Bay of Bengal.
- Bihar is watered by the Bay of Bengal branch; Tamil Nadu by the retreating monsoon.
- Pacific is the largest and deepest ocean; about 71 per cent of the surface is water.
Frequently Asked Questions
Which monsoon branch brings rain to Bihar?
The Bay of Bengal branch of the southwest monsoon, which enters from the east and travels up the Ganga valley. The Arabian Sea branch strikes the western coast first. Knowing which branch serves your own state converts a general geography fact into a state-paper answer.
Why does Tamil Nadu get rain in October and November?
Because of the retreating or northeast monsoon. As the winds withdraw, they pass over the Bay of Bengal, pick up moisture and strike the Tamil Nadu coast. This is why that state's rainfall pattern is the opposite of most of India's, and why the question is set so often.
What is the difference between weather and climate?
Weather describes the state of the atmosphere at a particular place and moment, such as a rainy afternoon. Climate is the average of weather conditions over a long period, usually decades, for the same place. One is momentary and the other is a long-run pattern.
Which layer of the atmosphere contains the ozone layer?
The stratosphere, the second layer from the ground. The ozone there absorbs harmful ultraviolet radiation. The troposphere below it is where all weather occurs. Candidates often place ozone in the troposphere, which is why this pair is worth learning together.