ATP-3-09-30 Observed Fires Download
Page 156 of 204
Chapter 6 6-26 ATP 3-09.30 28 September 2017 Figure 6-15. Maneuver-target line TERRAIN 6-107. Winds follow the contours of terrain. The type of terrain over which smoke travels has a tremendous effect on how the smoke will cover a specific area. Flat, unbroken terrain creates effective smoke further downwind. Trees and small buildings tend to break up smoke, which may then reform to cover a larger area and create effective smoke at the source. Steep hills or mountains create volatile winds, usually resulting in gaps and uneven smoke. Slopes and valleys create thermal slope winds at different times. Heating effects during the day cause up slope winds. Cooling effects at night cause down slope winds. 6-108. If the ground in the target area is rain soaked or snow covered, burning smoke rounds may not be effective. During very cold and dry conditions or in areas with snow cover, up to four times the number of smoke rounds may be needed to create an effective screen. 6-109. Shallow water can reduce the smoke produced by base ejecting rounds by as much as 50 percent. Bursting WP rounds are not affected as much by terrain in the target area; however, deep snow and cold temperatures can reduce the smoke cloud by 25 percent. 6-110. Table 6-18 summarizes atmospheric and terrain effects on smoke operations. Table 6-18. Conditions for smoke employment Factor Marginal Favorable Ideal Wind More than 10 knots 5 to 10 knots Less than 5 knots Atmospheric stability category Unstable or lapse Neutral Stable or inversion Humidity Low Moderate High Precipitation None Light rain Mist or fog Cloud cover None Scattered Overcast, low ceiling Terrain Even Gently rolling Complex topography Vegetation Sparse or none (desert) Sparse to medium dense Medium to heavily dense Time of day Late morning through late afternoon 1 to 2 hours before and after sunrise 1 hour before EENT to one hour before BMNT Legend. BMNT—before morning nautical twilight EENT—ending evening nautical twilight