Chapter 14: Climate
This chapter moves from daily weather to the global patterns of temperature, pressure, and winds. It explains why some places are hot and wet while others are cold and dry.
1. Factors Affecting Climate
Climate isn’t random; it is controlled by several “Master Factors”:
- Latitude: The closer to the Equator, the hotter it is (direct rays). The closer to the Poles, the colder it is (slanting rays).
- Altitude: For every 165 meters you climb, the temperature drops by 1°C. This is why mountains have snow even in the tropics.
- Distance from Sea: The sea heats and cools slower than land.
- Maritime Climate: Coastal areas (mild summers, cool winters).
- Continental Climate: Inland areas (very hot summers, freezing winters).
- Ocean Currents: Warm currents warm the coast; cold currents cool and dry the coast.
2. Global Pressure Belts
The Earth is divided into “stripes” of high and low pressure:
- Equatorial Low Pressure (Doldrums): Hot air rises, creating a zone of calm and rain.
- Sub-Tropical High Pressure (Horse Latitudes): Air sinks, creating dry, calm conditions (where most deserts are).
- Sub-Polar Low Pressure: Where warm and cold air meet.
- Polar High Pressure: Very cold, heavy air sinking at the poles.
3. Planetary Winds
Winds always blow from High Pressure to Low Pressure.
- Trade Winds: Blow toward the Equator. They are very steady.
- Westerlies: Blow from the Sub-tropical High toward the Poles (affecting Europe/USA).
- Polar Easterlies: Cold winds blowing away from the Poles.
4. Types of Rainfall
- Convectional: Heat causes air to rise, cool, and dump rain (common in the Tropics).
- Orographic (Relief): Air is forced over a mountain. The Windward side gets rain; the Leeward side is a “Rain Shadow.”
- Cyclonic (Frontal): Warm air meets cold air and is forced to rise over it.
10 Revision Questions with Mnemonics
Q1: What is the “Rain Shadow” area?
- Answer: The dry side of a mountain (Leeward side).
- Mnemonic: “Windward is Wet; Leeward is Lacking rain.”
Q2: What are the “Doldrums”?
- Answer: The calm, low-pressure zone at the Equator.
- Mnemonic: “Doldrums are Dull and Damp.”
Q3: How does altitude affect temperature?
- Answer: Temperature decreases as altitude increases.
- Mnemonic: “High up is Heavenly cool.”
Q4: What is the “Maritime Effect”?
- Answer: The sea keeps coastal temperatures moderate (mild).
- Mnemonic: “Maritime is Mellow.”
Q5: Why are most hot deserts found on the western sides of continents at 30° Latitude?
- Answer: Due to the Sub-tropical High Pressure (sinking air) and Off-shore Trade Winds.
- Mnemonic: “Sinking air is Sunny and dry.”
Q6: What is a “Front” in meteorology?
- Answer: The boundary where a warm air mass meets a cold air mass.
- Mnemonic: “Front is a Fight between temperatures.”
Q7: Which way do Trade Winds blow in the Northern Hemisphere?
- Answer: From the North-East to the South-West.
- Mnemonic: “N.E.T.” (North-East Trades).
Q8: What is Convectional Rainfall?
- Answer: Rainfall caused by intense heating of the ground.
- Mnemonic: “Convection is like a Cooking pot” (Heat rises, then spills over).
Q9: What happens to air as it rises?
- Answer: It expands, cools, and condenses into clouds.
- Mnemonic: “E.C.C.” (Expand, Cool, Condense).
Q10: What is the Coriolis Force?
- Answer: The force that deflects winds to the right in the North and left in the South.
- Mnemonic: “N.R.S.L.” (North Right, South Left).
Quick Summary Table: Global Wind Systems
| Wind Type | Direction | Character | Mnemonic |
|---|---|---|---|
| Trade Winds | Toward Equator | Constant & Tropical | “Trades are Trustworthy” |
| Westerlies | Toward Poles | Variable & Stormy | “Westerlies are Wild” |
| Monsoons | Seasonal | Changes with Season | “Monsoon Moves” |
