Relative Humidity
Associated with that latent heat energy and water vapor in the atmosphere is the concept of humidity.
There are four measures we use to express humidity:
(1) Specific Humidity: the mass of water vapor in a parcel of air. Typically measured in grams per kilogram.
(2) Maximum Humidity: the maximum amount of water vapor that can be held in air of a given temperature. Expressed in grams per kilogram. Air at room temperature (20C) can hold three times as much water than air at 0C.
(3) Relative Humidity: The ratio of specific humidity to maximum humidity times 100. When the specific humidity equals the maximum humidity, the relative humidity equals 100% and the air is considered saturated.
(4) Dew point temperature: Temperature at which air with a given amount of moisture reaches saturation.
There are four measures we use to express humidity:
(1) Specific Humidity: the mass of water vapor in a parcel of air. Typically measured in grams per kilogram.
(2) Maximum Humidity: the maximum amount of water vapor that can be held in air of a given temperature. Expressed in grams per kilogram. Air at room temperature (20C) can hold three times as much water than air at 0C.
(3) Relative Humidity: The ratio of specific humidity to maximum humidity times 100. When the specific humidity equals the maximum humidity, the relative humidity equals 100% and the air is considered saturated.
(4) Dew point temperature: Temperature at which air with a given amount of moisture reaches saturation.
Relative humidity typically changes throughout the day even while specific humidity and dew point temperature remain constant. Consider that you wake up in the morning to see dew forming on the grass. The appearance of condensation implies that the air temperature cooled overnight to reach the dewpoint temperature, or equivalently specific humidity equalled maximum humidity. As morning turns into mid-morning, the increase in air temperature results in an increase in maximum humidity and the amount of water vapor that can be held in the air. By around 3PM when the daily high temperature is set, the air is substantially warmer and the amount of water vapor in the air is far less than the amount that could be held. Hence, relative humidity during the afternoon hours is typically the lowest
Now that you understand how to calculate relative humidity, you can practice this calculation while learning about the relationship between temperature and RH. Log into BBLearn and complete "Assignment 4.3: Relative Humidity."