© 1999 Lockheed Martin Energy Research Corporation CA79 EFFECTS OF WEATHER AND TERRAIN.

© 1999 Lockheed Martin Energy Research Corporation CA79

EFFECTS OF WEATHER AND TERRAIN


© 1999 Lockheed Martin Energy Research Corporation

OBJECTIVES

CA80

• Describe the effects of weather on the movement of agent vapor following an accidental release

• Describe how terrain factors influence movement of agent vapor following an accidental release



CA81

• Weather elements and chemical properties determine– how far a chemical warfare agent vapor plume will travel

– how concentrated the chemical warfare agent will be within the plume


WINDSPEED

• One of the most important factors determining how far vapor plume will go is windspeed

• Higher windspeed: vapor plume disperses quickly and shorter downwind hazard distance

• Lower windspeed: vapor plume more likely remains intact, lengthening downwind hazard distance


WIND DIRECTION

• Since vapor plume will ride wind current, wind direction is always important

• Vapor plumes do not drift upwind• Mechanical turbulence, brought

about by wind blowing over and around objects, tends to mix agent vapor with surrounding air, making concentration less, thereby reducing hazard

Weather vane symbolizing wind direction


VERTICAL TEMPERATURE

GRADIENT• The difference between temperature of air at ground

level and at higher levels• Perhaps most important element in determining

vertical dispersion and travel of vapor plume• During day solar radiation heats ground more than

surrounding air– air next to ground is warm and rises

– cooler air from above sinks to ground surface

– mixing called thermal turbulence


• Disperses chemical warfare agent vapors, thereby reducing likelihood of dangerous concentrations of chemical agent vapors in the plume

• Occurs during daylight hours and is more pronounced on sunny, summer days

THERMAL TURBULENCE

CA85


INVERSION

• At times, ground cooler than air overhead; creates a condition known as an inversion

• Thermal mixing does not occur during inversions

• Occurs mainly at night

Thermal mixing does not occur during inversions Low-level Inversion

No Inversion


• Thermal mixing moderate• Occur when temperature of air overhead is somewhat

cooler than air at ground level but temperature gradient not enough to produce strong vertical mixing

• Tend to occur at sunrise, sunset, and during cloudy, overcast days

CA87

NEUTRAL CONDITIONS

Neutral conditions common at sunrise and sunset and on overcast days


STABILITY CLASSES

Stabilityclass Windspeed Solar heating Mixing

A Slow Sunshine –strong heating

Good

B Slow Sunshine –strong heating

Good

C Variable Sunshine – heating ReducedD Variable Sunshine – heating ReducedE Slow Night – cooling NegligibleF Slow Night – cooling Negligible

CA88


• Removes agent from atmosphere• Water runoff containing chemical warfare agent

collects in low places• Agent is not neutralized

– some chemical changes may take place

• Snow may cover agent– agent still toxic even at

freezing temperatures

• When snow melts, chemical warfare agent contamination problem may remain

CA89

PRECIPITATION

Precipitation has complex effects on dispersion of agent


TERRAIN

• In hilly terrain– air near ground warms and moves uphill in daytime

– air near ground cools and flows downhill at night

• On open ground– ground warms rapidly on sunny days increasing temperature

gradient

– ground cools at night and temperature gradient decreases or reverses

– temperature gradient is more pronounced in desert areas


VEGETATION

• Reduces spread of contamination• Reduces windspeed

– absorption - penetration of chemical warfare agent into vegetation

– adsorption - build-up of chemical warfare agent on the surface of vegetation

• May give off agent vapors after absorption and adsorption

• Heavy forests tend to reduce amount of thermal turbulence under their canopies creating neutral conditions


BODIES OF WATER

• Large bodies of water also affect temperature gradients because water retains heat better than soil

Inlet of the Chesapeake Bay from Aberdeen Proving Ground


DETERMINING THE HAZARD

• Hazard from a chemical release would depend on– how much agent is released into the air

– the amount of agent involved

– the chemical properties of agent

– the temperature gradient

• Windspeed and direction would determine how soon an agent plume arrives at a given point


COMPUTER MODELING

• The Army uses computer simulation models to estimate how far vapor chemical release will travel and the concentration of agent at various distances from the source of the release

• This information is used in the models to estimate extent of hazard

• Based upon model results, decisions such as if and where to evacuate, how soon to begin evacuation, and when to shelter, would be made

© 1999 Lockheed Martin Energy Research Corporation CA79 EFFECTS OF WEATHER AND TERRAIN.

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Transcript of © 1999 Lockheed Martin Energy Research Corporation CA79 EFFECTS OF WEATHER AND TERRAIN.