Solar Radiation, Heat Balance and Temperature

How the earth is heated by the sun, how the atmosphere is heated and cooled, the heat budget, the lapse rate and the spread of temperature.

Key ideas

• Insolation is incoming short-wave solar energy; it varies with the earth’s rotation, the angle of the sun’s rays, the length of the day, the clearness of the air and the aspect of the land.
• Slanting rays at high latitudes spread over a larger area and pass through more air, so each unit area gets less energy.
• The atmosphere is heated mostly from below: by conduction from the warm ground, convection upward, advection sideways and long-wave terrestrial radiation.
• The heat budget balances: the earth loses as much heat as it receives, so it neither warms nor cools over time.
• Between 40° N and 40° S there is a surplus of energy and towards the poles a deficit; winds and ocean currents carry heat poleward.
• Temperature depends on latitude, altitude, distance from the sea, air masses and ocean currents.
• An inversion (temperature rising with height) happens on long, clear, calm winter nights; cold air drains into valleys and fog forms.

Remember

Watch out

• Getting a smaller range with a negative month: 25 − (−10) = 35, not 15.
• Using 6.5 °C per 100 m instead of per 1,000 m.
• Mixing up advection (sideways, like the loo) and convection (upward).

Worked example