| [Home] [Index] [News] |
| [Previous] [Next] | Click to view: [General content] ...then... [Operational content] ...then... [Expert content] | ||||||
|
|
Operational Awareness for Advanced Firefighters & Fire Behaviour Analysts | ||||||
|
The air above the ground, in general terms gets cooler as you get higher. Below the cloud base the dry adiabatic lapse rate applies, while above it the saturated adiabatic lapse rate applies. This is the case right through the troposphere (the lowest layer of the atmosphere), except for the very lowest part, adjacent to the ground. At night radiative heat loss to space makes the ground surface cool, also cooling the air that comes into contact with it. Thus, except for during the heat of the afternoon, the air gets warmer above the ground. This is the mixing layer, and is a form of inversion. It develops overnight and breaks down during the late morning. That breakdown is due the ground warming up and also turbulent mixing caused by air flowing above the inversion. This turbulence is the cause of wind gustiness in the morning. If this inversion is in place it will limit the dispersion of smoke from fuel reduction burns. The depth of the inversion and the wind speed under it are the key controlling factors in dispersion. . |