Temperature Gradients Temperature alone does not affect smoke, except as it relates to temperature gradients. Temperature gradients are determined by comparing the air temperature at .5 meter above the ground with the air temperature at 4 meters. Figure G-2 depicts temperature gradients and smoke behavior. Unstable conditions exist when air temperature decreases with an increase in altitude, causing vertical air currents and turbulence. Smoke tends to rise, breaking up and becoming diffused.
Unstable conditions are best for producing smoke curtains.
Neutral conditions exist when there is little or no change with an increase in altitude, or when wind speeds are less than 9 kilometers per hour. Vertical movement of air is limited during neutral conditions. Neutral conditions are favorable for producing smoke blankets and smoke hazes. Stable conditions exist when there is an increase in air temperature as altitude increases, greatly limiting vertical air movement and allowing smoke clouds to remain low to the ground. This is the most favorable temperature gradient for smoke, providing that there is enough wind to carry the smoke over the target area.