The lowest layer of atmosphere extending from the surface to the Tropopause, approximately 11 km above sea level.
The Troposphere contains 75% of the mass of the Atmosphere and almost all of the water vapour. There is considerable movement and mixing of air within the Troposphere and it is within this layer of the Atmosphere that most of the Weather occurs.
Within the Troposphere, temperature and pressure decrease uniformly with height until the Tropopause.
The lowest level of the Troposphere, where the airflow is affected by friction with the ground, is sometimes referred to as the Planetary Boundary Layer.
Close to the tropopause, where air masses create a temperature gradient, strong bands of winds called Jet Streams develop.