aim : what is relative humidity? do now : in your notes, describe what the term “humid” means
DESCRIPTION
Aim : What is relative humidity? Do Now : In your notes, describe what the term “humid” means. Humidity – is a measure of how much water vapor is in the air. WHY? - Because it expands!. - Warmer air can hold more water vapor than cooler air. Warm air. Cold air. - PowerPoint PPT PresentationTRANSCRIPT
II. Relative Humidity (RH) describes “how full” the air is with water vapor, expressed as a percent (%).- compare the size of the air to the amount of water.
- Saturation occurs when the air contains the maximum amount of water vapor that it can hold at any given temp. and pressure.
**When saturated, warm air contains more water vapor than cold saturated air.
Cold air
Warm air
Both parcels are at 100% RH
III. Changing the Relative Humidity
a. Water vapor enters or leaves the air. (evaporation or
condensation)
b. The temperature changes. (changes the size of the air)
How can you change the Relative Humidity? (Think what is the definition of RH)
IV. Dew Point Temperature - the temp. at which the air will be
saturated with water vapor (RH = 100%)
=
- The closer the air temp. is to the dew point temperature:
– the air is more saturated, RH is closer to 100% and there is better chance for condensation. 1) At what time
is the RH the highest?
2) At what time is RH the lowest?
3) When is the greatest chance of rain?
V. Measuring Dew Point and RH
- using a Sling Psychrometer, you can measure the temperature of the air by “slinging” the thermometers in the air.
- There is a dry bulb temperature and wet bulb temperature.
- The wet bulb temperature is always lower.
Example:
A student measure the temperature of the air using a sling psychrometer and found that the Dry Bulb Temp. = 240C and the Wet Bulb Temp. = 200C. What is the wet bulb depression temperature?
- calculate difference between dry and wet bulb temps. This is called the wet bulb depression.