Spatial distribution of insolation
Topic: Solar Radiation, Heat Balance and Temperature · NCERT: Class 11, Ch 8 "Solar Radiation, Heat Balance and Temperature"
Meaning
This means how much sunlight reaches the Earth's surface in different places. It is about 320 W/sq m in the tropics and about 70 W/sq m at the poles. The most sunlight falls on subtropical deserts, because they have the fewest clouds. The equator is cloudier, so it gets less than the tropics. At the same latitude, continents get more than oceans. Middle and high latitudes get much less sunlight in winter.
Example
The Thar Desert of Rajasthan and the Sahara in North Africa are subtropical deserts with clear skies, so they receive more surface sunlight than the cloudy equatorial belt. In India, monsoon clouds cut insolation from June, so May is the hottest month.
Don't confuse with
- Insolation at the top of the atmosphere: this depends only on latitude and season. Surface insolation is also reduced by clouds and haze, which is why it peaks over deserts and not at the equator.