Welcome to this deck on weather hazards. We'll explore how the Earth's atmosphere works on a global scale, creating distinct climate zones and powerful weather systems. You'll learn about the three-cell model of atmospheric circulation, how this system leads to the formation of tropical storms, and we'll finish by looking at examples of extreme weather right here in the UK.

The engine that drives all weather on Earth is the sun. Because the Earth is a sphere, the sun's energy is most concentrated at the equator, making it hottest there, and least concentrated at the poles, making them coldest. This difference in heating creates a global system of air circulation, as the atmosphere tries to move heat from the equator towards the poles to balance things out.

This global circulation system can be simplified into a model with three large loops of moving air in each hemisphere. These are called circulation cells. The three cells are the Hadley cell, the Ferrel cell, and the Polar cell. Together, they explain why we have rainforests at the equator, deserts at 30 degrees latitude, and unsettled weather in the UK.

Let's start with the Hadley cell. At the equator, the intense solar heating warms the air, causing it to rise. As it rises, it cools and condenses, forming huge clouds and leading to heavy rainfall. This is why tropical rainforests are found along the equator. This rising air creates a zone of low pressure.