.png)
Temperature – UPSC Geography Notes
Overview: Temperature is one of the most important elements of weather and climate. It refers to the degree of hotness or coldness of a place measured in terms of heat energy. Understanding temperature patterns helps explain climatic zones, winds, and rainfall distribution — key areas for UPSC Geography preparation.
Table of Contents
- 1. What is Temperature?
- 2. Factors Affecting Temperature
- 3. Distribution of Temperature
- 4. Isotherms and Their Importance
- 5. Temperature Inversion
- 6. Daily and Annual Range of Temperature
- 7. Global Temperature Patterns
- 8. UPSC Quick Revision Notes
- 9. Previous Year Question
1. What is Temperature?
Temperature is the measure of heat energy present in the atmosphere. It is expressed in degrees Celsius (°C) or Fahrenheit (°F). The Sun is the main source of heat and energy on Earth, and temperature varies from place to place depending on several natural factors.
2. Factors Affecting Temperature
- (a) Latitude: Temperature decreases from the equator to the poles because the Sun’s rays become more slanted and spread over a larger area.
- (b) Altitude: Temperature decreases with height at an average rate of 6.5°C per 1000 m. This is known as the lapse rate.
- (c) Distance from the Sea: Coastal areas have moderate temperatures (maritime climate) while interiors have extremes (continental climate).
- (d) Ocean Currents: Warm currents raise temperatures along coasts, while cold currents lower them.
- (e) Cloud Cover: Clouds reduce day temperatures by blocking sunlight and increase night temperatures by trapping heat.
- (f) Slope and Aspect: South-facing slopes in the Northern Hemisphere receive more sunlight and are warmer.
- (g) Land and Water Contrast: Land heats and cools faster than water, leading to temperature variations.
3. Distribution of Temperature
The temperature across the globe is uneven due to differences in solar radiation and the factors above.
- Equatorial region: Highest temperature throughout the year.
- Polar region: Lowest temperatures, extreme cold.
- Mid-latitudes: Moderate temperature, with distinct seasons.
4. Isotherms and Their Importance
Isotherms are lines drawn on a map joining places having the same temperature. They help in visualizing the spatial distribution of temperature.
- Isotherms generally run parallel to the latitudes.
- They bend towards poles or equator due to ocean currents and land-water contrasts.
- Example: In January, isotherms bend southward in the Northern Hemisphere over land due to cold conditions.
5. Temperature Inversion
Under normal conditions, temperature decreases with height. But sometimes, this pattern reverses — the temperature increases with height instead. This phenomenon is called Temperature Inversion.
Causes of Temperature Inversion:
- Clear and calm nights with strong radiation cooling of the ground.
- Cold air settles near the ground while warm air lies above it.
- Common in valleys and mountain basins.
Types of Temperature Inversion:
- Radiation Inversion: Occurs during clear nights when ground loses heat rapidly.
- Advection Inversion: When warm air moves over a cold surface.
- Topographic Inversion: Found in valleys where cold air sinks below warm air layers.
Effects: Fog formation, air pollution trapping, frost, and reduced air visibility.
6. Daily and Annual Range of Temperature
- Daily Range: Difference between maximum and minimum temperature in a day.
- Annual Range: Difference between mean temperature of the hottest and coldest months of the year.
Coastal regions have a small range of temperature, while continental interiors show a high range.
7. Global Temperature Patterns
- Equatorial regions remain warm year-round due to vertical Sun rays.
- Subtropical deserts (like Sahara) experience very high temperatures.
- Polar areas remain below freezing for most of the year.
- Southern Hemisphere is relatively cooler than the Northern Hemisphere due to larger oceanic area.
8. UPSC Quick Revision Notes
Main factors: Latitude, Altitude, Ocean currents, Cloud cover.
Lapse rate = 6.5°C per 1000 m.
Temperature inversion → temperature increases with height.
Daily range = Max - Min temp (day).
Annual range = Max month - Min month (year).
Isotherms = Lines of equal temperature.
Equator → highest temp, Poles → lowest temp.
9. Previous Year Question
Q. Why does temperature generally decrease with increasing altitude in the troposphere?
(a) Air pressure increases with height
(b) Air becomes thinner and absorbs less heat from the Earth’s surface
(c) Solar radiation decreases with altitude
(d) None of the above
Answer: (b) Air becomes thinner and absorbs less heat from the Earth’s surface
Related Keywords
Temperature UPSC Notes, Factors Affecting Temperature, Temperature Inversion, Isotherms, Range of Temperature, Geography Notes for UPSC, Physical Geography NCERT, Climatology UPSC.
Sources: NCERT Class XI – Fundamentals of Physical Geography, Goh Cheng Leong (Certificate Physical and Human Geography), IMD & NASA Climate Studies (simplified for UPSC learning).
Next Topic → Pressure and Winds (UPSC Geography Notes)
