Chapter 9 – Solar Radiation, Heat Balance and Temperature

What is solar radiation?
Solar radiation is energy emitted by the Sun in the form of electromagnetic waves. It includes visible light, ultraviolet, and infrared rays that reach Earth and drive climate and weather.

What is insolation?
Insolation is the incoming solar radiation received on Earth’s surface. It varies with latitude, season, time of day, and atmospheric conditions like cloud cover and dust.

What affects the amount of insolation?
Factors include latitude, angle of the Sun, day length, altitude, cloud cover, and Earth’s tilt and revolution.

Why is insolation higher at the equator?
The Sun’s rays strike the equator more directly, concentrating more energy over a smaller surface area compared to higher latitudes where the rays are slanted.

What is albedo?
Albedo is the percentage of incoming solar radiation reflected back by a surface. Snow and ice have high albedo, while dark soil or oceans have low albedo.

What is Earth’s average albedo?
Approximately 30%. This means 30% of incoming solar radiation is reflected by clouds, atmosphere, and Earth’s surface back into space.

What is the heat budget of Earth?
It refers to the balance between incoming solar radiation and outgoing terrestrial radiation. A balanced heat budget maintains Earth’s average temperature.

How is solar radiation distributed globally?
More energy is received at the equator and less at the poles. This uneven distribution creates atmospheric circulation and drives global wind and ocean current systems.

What is terrestrial radiation?
It is the longwave infrared radiation emitted by Earth’s surface after absorbing solar energy. It helps regulate planetary temperature and supports the greenhouse effect.

What is the greenhouse effect?
Greenhouse gases trap terrestrial radiation in the atmosphere, keeping Earth warm. Without this, the planet would be too cold to support life.

What are the major greenhouse gases?
Carbon dioxide, methane, nitrous oxide, water vapor, and ozone are key greenhouse gases that absorb heat and warm the atmosphere.

What is conduction?
The transfer of heat through direct contact between molecules. It is most effective in solids and plays a minor role in heating the atmosphere.

What is convection?
The transfer of heat through movement of fluids like air or water. Warm air rises and cool air sinks, creating convection currents in the atmosphere.

What is radiation (in heat transfer)?
Radiation is the transfer of energy via electromagnetic waves. The Sun’s energy reaches Earth through radiation, without needing a medium.

How does Earth’s atmosphere get heated?
Mostly through terrestrial radiation. The atmosphere absorbs little direct sunlight; instead, it is warmed from below by Earth’s surface through conduction, convection, and radiation.

What is temperature?
Temperature measures the degree of hotness or coldness of air. It’s influenced by insolation, altitude, latitude, ocean currents, and surface characteristics.

What is diurnal range of temperature?
The difference between maximum and minimum temperatures in a day. Deserts have high diurnal ranges due to clear skies and dry air.

What is annual range of temperature?
It’s the difference between the hottest and coldest months in a year. Continental interiors show higher annual ranges compared to coastal areas.

How does latitude affect temperature?
Lower latitudes (near equator) receive more direct sunlight, resulting in higher temperatures. Higher latitudes receive slanted rays and are cooler.

What is the effect of altitude on temperature?
Temperature decreases with height—approximately 6.5°C per 1,000 meters (called normal lapse rate). Hence, hill stations are cooler than plains.

What is the role of ocean currents in temperature?
Warm currents raise temperatures in coastal areas, while cold currents lower them. For example, the Gulf Stream warms Western Europe.

What is the role of clouds in temperature?
Clouds reflect sunlight, reducing daytime temperatures. At night, they trap outgoing terrestrial radiation, keeping temperatures warmer than cloudless nights.

What are isotherms?
Isotherms are lines drawn on a map connecting places of equal temperature. They help in analyzing global temperature patterns.

Why are isotherms curved and not straight?
Because temperature is affected by various factors like ocean currents, elevation, land-sea distribution, and wind patterns, which cause isotherms to bend.

What is temperature inversion?
It is a condition where temperature increases with altitude, contrary to the normal lapse rate. It can trap pollutants and affect weather conditions.

When does temperature inversion occur?
Typically during clear, calm nights when the ground cools rapidly, chilling the air above it and forming a cold layer near the surface.

What is the urban heat island effect?
Cities are warmer than surrounding rural areas due to concrete surfaces, pollution, and human activities, causing a dome of higher temperature over urban regions.

Why do coastal areas have moderate temperatures?
Due to the sea’s high heat capacity, coastal areas experience smaller temperature variations. Water heats and cools slowly compared to land.

What is specific heat?
It is the amount of heat required to raise the temperature of a substance. Water has high specific heat, influencing coastal climate.

Why are deserts hot during the day and cold at night?
Due to low humidity, cloudless skies, and lack of vegetation, deserts heat up quickly during the day and lose heat rapidly at night.