A gaseous envelope gravitationally bound to a celestial body; in the case of the Earth, with an average composition, by volume, of 79% nitrogen, 20% oxygen, 0.03% carbon dioxide, and traces of rare gases. This surprisingly uniform composition is achieved by convection in the turbosphere and by diffusion above it, especially above 100 km, where diffusion is rapid in the thin atmosphere, and stirring is weak. Also present are atmospheric moisture, ammonia, ozone, and salts and solid particles. The atmosphere is commonly divided into the troposphere, the stratosphere, and the ionosphere. Since the troposphere contains the majority of the atmospheric mass, and virtually all of the atmospheric water vapour, most weather events occur within it. The atmospheric energy balance is the balance between incoming short-wave energy from the Sun and outgoing long-wave energy from the Earth. Outgoing energy loss is greater than incoming energy gain; this is equivalent to a cooling of 1°C or 2°C per day. However, this heat loss is mostly compensated for by the latent heat released by the condensation of atmospheric water vapour into precipitation.

Typical annual global values for the energy balance of the atmosphere are:

• • net radiative loss = −99.4 W m⁻²

• • sensible heat gain = 20.4 W m⁻²

• • latent heat gain = 79.0 W m⁻²

Annual global precipitation is therefore linked closely to the atmospheric energy balance and can change only if there are associated changes in the global energy balance (see Lockwood in J. Holden 2012).