- A sublayer of the troposphere
- In contact with the surface – experiences direct effect of friction at surface
- Dominated by turbulence and surface exchange processes: heat, moisture, momentum
- Exhibits large diurnal changes in many properties: depth, temperature,…
- Depth varies from a few 10s of metres (in very stable conditions), to ~2km over tropical oceans. A few 100 m to ~1 km is typical.
- Temperature decreases with altitude.
- Usually capped by a temperature inversion that inhibits mixing with the air in the free troposphere above.
N.B. A well defined boundary layer is not always present