The weather might seem like it creates weeks of dreary, grey drizzle. But it can also put on a truly sensational—and, often, deadly—show. But what explains these explosive events?
The Earth’s atmosphere is driven by heating from the Sun. Weather is the response of the atmosphere to the uneven pattern of heat energy that it receives. Visible and ultraviolet light warms the Earth during the day, more strongly at low latitudes, but the Earth emits an almost exactly equal total amount of infrared radiation in all directions.
On average, the Earth receives 340 W m-2 from the Sun. About one third of this energy is scattered straight back into space by clouds and ice on the surface. The remaining energy, roughly the equivalent of placing a small radiator every 2m in a lattice covering the Earth’s surface and running them continuously, is absorbed by the surface and atmosphere.
But the Sun’s power is focused on the day side and, in particular, near the Equator. On average, the atmosphere and surface absorb over 300 W m-2 in the Tropics but less than 100 W m-2 in Polar Regions. The Earth’s surface at the equator is face-on to the Sun’s light, but at a large angle to it near the poles where the same power falls over a larger surface area.
