Water in the Atmosphere

Water exists in the atmosphere as: Gas  water vapor Solid  ice crystals Liquid  water droplets

Changing States Solid to liquid: Melting Liquid to solid: Freezing Ice absorbs heat and turns to liquid Liquid to solid: Freezing Water loses heat, and turns to ice

Liquid to Gas: Evaporation Gas to liquid: Condensation Heat is released into surroundings Liquid to Gas: Evaporation Heat is absorbed from surrounding

Gas to solid: Deposition Solid to gas: Sublimation Heat absorbed Gas to solid: Deposition Heat released

Humidity The amount of water vapor in the atmosphere is called humidity. Air that has reached its water vapor capacity is said to be saturated Humidity depends on temperature since different temperatures have different saturation points

Relative Humidity Relative Humidity is the amount of water in the atmosphere compared to how much water the air can hold Indicates how near the air is to saturation Actual Moisture X 100 = Relative Humidity Maximum Moisture

Hot Air vs. Cold Air The warmer the air the more water vapor it can hold By changing the temperature of the air you can increase or decrease the relative humidity Constant water vapor and higher temp = lower RH Constant water vapor and lower temp = higher RH

Warm, saturated air contains more water vapor than cold saturated air

Specific Humidity Number of grams of water vapor in 1 kg of air (g/kg) Actual amount of water vapor in air Hot, summer day in NC--> 20 g/kg Cold, winter day in NC--> 5 g/kg

Measuring Humidity Measured with hygrometer One type of hygrometer is called a psychrometer Made of two thermometers- 1 dry, 1 wet Dry thermometer = air temperature Wet thermometer = as water evaporates it removes energy from thermometer, lowering the temperature Compare both thermometers in table to find RH Ex. In cloud no evaporation because air already saturated.

Sling Psychrometer and RH Table Smaller differences between wet and dry = higher RH Larger differences between wet and dry = lower RH

Hair Hygrometer Instrument that records the changing length of hairs when humidity changes Human hair stretches when humidity increases

Heat Index Determines what the air temperature ‘feels’ like. High air temp + low RH = air temp feels lower than it really is High air temp + high RH = air temp feels higher than it really is

Dew Point Dew point – temperature to which air must be cooled to reach saturation If the temperature drops to the dew point then the moisture in the air will begin to condense and form dew (> 0 C) or frost (< 0 C) If humidity is high, a small temperature drop will reach dew point. If humidity is low, a large temperature drop will reach dew point.