Water in he Air空气中的水.pptVIP

Water in the Air Most important fact – The air contains water vapor. Only a certain amount of water vapor can be circulated in air at a given temperature, since temperature is a measure of energy. Clouds, fog, dew and frost all form when the temperature drops below the temperature required for the current amount of water vapor in the air to remain in the air, and the “extra” water vapor condenses to liquid water in the form of clouds(in air), fog(near ground cloud), dew(on ground) or frost(on ground when temperature 0 Celsius.) Sling psychrometer or hygrometer Water’s Changes of State Humidity definitions Relative Humidity is the % of water vapor in the air compared to the air’s carrying capacity at that temperature (demo later) Dew point is the temperature that air is cooled to when it reaches its saturation point. At its dew point the relative humidity is 100% and water vapor condenses to water Humidity is the amount of water vapor in the air. This may be expressed as grams of water per cubic meter of air. It is sometimes called specific humidity. Absolute humidity is how much water vapor can be carried in air at a certain temperature, in units like grams/cubic meter Specific Humidity Graph Relative Humidity Adiabatic Temperature Changes Atmospheric Stability Absolute Stability: Air which is cooler than the air around it tends to sink, due to higher density. Air that resists rising is called stable air. Notice the air here would always be colder than the surrounding air. So, it wouldn’t rise unless it was forced to. Dry Wet Adiabatic Rates and Latent Heat Psychrometer activity/calculations Latent heat To review – what is latent heat and how does it make air unstable? Condensation is exothermic. There is potential energy contained in the water vapor which is energy stored there during the evaporation process. When the water vapor condenses back to water, this heat is released into the air, causing the air to get warmer. Example: when you take a shower, the air in