Humidity Flashcards
What is humidity?
The amount of water vapour in the air is humidity
Relative humidity (7)
The ratio of water vapour actually in the air (content) to the maximum water vapour possible in air (capacity) at that temperature; expressed as a percentage. (Compare Vapour pressure, Specific humidity.)
The most common measure of humidity in weather reports is relative humidity, a ratio (expressed as a percentage) of the amount of water vapour that is actually in the air compared to the maximum water vapour possible in the air at a given temperature.
(actual water vapor/maximum water vapor in the air at that temperature) * 100
What is saturation equlibrium?
Because there is a maximum amount of water vapour that can exist in a volume of air at a given temperature, the rates of evaporation and condensation can reach equilibrium at some point; the air is then saturated, and the balance is saturation equilibrium.
What is Saturation?
State of air that is holding all the water vapour that it can hold at a given temperature, known as the dew-point temperature.
At saturation, or 100% relative humidity, any further addition of water vapour or any decrease in temperature that reduces the evaporation rate results in active condensation
What is Dew-Point temperature?
The temperature at which a given mass of air becomes saturated, holding all the water it can hold. Any further cooling or addition of water vapour results in active condensation.
When is relative humidity the lowest during the day?
Relative humidity is lowest in the late afternoon, when higher temperatures increase the rate of evaporation.
What is Vapour pressure ?
That portion of total air pressure that results from water vapour molecules, expressed in millibars (mb). At a given dew-point temperature, the maximum capacity of the air is termed its saturation vapour pressure.
What is Specific humidity
The mass of water vapour (in grams) per unit mass of air (in kilograms) at any specified temperature. The maximum mass of water vapour that a kilogram of air can hold at any specified temperature is termed its maximum specific humidity. (Compare Vapour pressure, Relative humidity.)
What is a hair hygrometer?
Hair hygrometer (7) An instrument for measuring relative humidity; based on the principle that human hair will change as much as 4% in length between 0% and 100% relative humidity
The instrument connects a standardized bundle of human hair through a mechanism to a gauge. As the hair absorbs or loses water in the air, it changes length, indicating relative humidity
What is a Sling psychrometer?
A weather instrument that measures relative humidity using two thermometers—a dry bulb and a wet bulb—mounted side by side.
One is the dry-bulb thermometer; it simply records the ambient (surrounding) air temperature. The other thermometer is the wet-bulb thermometer; it is set lower in the holder, and the bulb is covered by a moistened cloth wick. The psychrometer is then spun, or “slung,” by its handle or placed where a fan forces air over the wet-bulb wick. After several minutes of spinning, the temperatures on each bulb are compared with a relative humidity (psychrometric) chart to find the relative humidity.
