Atmospheric Moisture How does the moisture get in

Atmospheric Moisture

How does the moisture get in the atmosphere? ? • EVAPORATION – liquid to a gas • TRANSPIRATION – process of water being taken in and evaporating from plants

Factors that affect evaporation rates (adding water vapor to the atmosphere) 1. Temperature – warmer the temperature, evaporation increases 2. Surface Area – As surface area increase, the rate of evaporation increases 3. Relative Humidity – as relative humidity increases, the rate of evaporation decreases

Which will evaporate faster? Surface area – more surface area of water available, the more evaporation

ABSOLUTE HUMIDITY • Amount of Water Vapor in the atmosphere • Air that is full of water vapor is said to be saturated • The higher the temperature, the greater the capacity of the air can “hold” water • SO, • As the air temperature increases, the air can hold (less or more) water

Relative Humidity (RH) Percentage of air that is saturated at a given temperature 50% RH = air has ½ the water vapor needed to saturate the air RH = 100% means Air is saturated, it cannot add any more water vapor or condensation will occur

Dew Point Temperature at which condensation occurs It’s a direct measure of the moisture content in the air. Therefore, as the dew point temp increases the amount of moisture in the air increases Air Temp = Dew Point, then RH= 100%, which equals and occurs

• When the dew point ______ equals the air temperature, the air is _____, clouds saturated and precipitation is _____ likely 100% • Relative Humidity (RH) = _______

• The drier the air, the farther the dew point will be from the actual temperature

Circle on the graph where the probability of clouds and precipitation would be greatest

Relationships A. If the moisture content remains the same: As temperature increases, RH decreases Indirect relationship As temperature decreases, RH increases Indirect relationship

Measuring Dew Point Instrument: Sling Psychrometer has 2 thermometers, - dry bulb – Air temperature - Wet Bulb – a piece of moist cloth wrapped around the bulb - will be cooler due to evaporation

Psychrometer • The psychrometer is swung around, the wet bulb temperature drops because of the cooling effect when being evaporated • Wet bulb depression - difference between the dry and wet bulbs ESRT Page 12

• • To Find Dew Point (see ESRT p. 12) Find the wet bulb depression along the top of the chart Find the air temperature along the left side of the chart Where the two meet is the dew point (You may have to estimate) • Ex: • Dry bulb = 20°C Wet bulb = 17°C • Difference between Wet bulb and Dry Bulb = 3°C • • Dew point =

Dew Point = 15 o. C

• Dry Bulb = 11 o. C • Wet Bulb = 4 o. C • Difference between wet bulb and dry bulb = ______ 7 o. C • Dew Point = _____ -7 o. C

To Find the Relative Humidity • ESRT Page 12 • Same procedure as finding the dew point

• Dry Bulb = 20 o. C Wet Bulb = 17 o. C • Difference between wet and dry bulbs 3 • = ____ o. C

RH = 74%

• Dry Bulb = 11 o. C Wet Bulb = 4 o. C • Difference between wet and dry bulbs 7 • = ____ o. C 26% • RH = _______