Humidity

Water Vapor Can make up as little as 1/10 th of 1% to 4% of the atmosphere. Scientists agree that it is the most important atmospheric gas when it comes to looking at our weather processes.

Humidity Humidity is our general term for water vapor in the air. Meteorologists use three methods to express humidity, or water-vapor content: mixing ratio, relative humidity, and dew- point temperature.

Vapor Pressure This is the pressure of vapor resulting from the evaporation of the liquid. As more and more molecules escape from the water’s surface, the more some of these molecules return to the liquid through condensation.

Saturation When the number of water vapor molecules leaving the surface equals the number of molecules returning, the air is described as saturated.

Mixing Ratio The comparison of water vapor in the air to dry air. Water vapor for saturation depends on the temperature. The higher the temp, the more water vapor needed for saturation.

Mixing Ratio Activity Pause

Relative Humidity Most common measurement used to describe the amount of water vapor in the air. It tells you how close it is to being saturated.

Find Relative Humidity Equation: Relative humidity (%) = water vapor content x 100 saturation mixing ratio Relative humidity (%) = 5 g/kg x 100 = 25% 20 g/kg

Relative Humidity Activity Pause

Dew-point Temperature The temperature at which saturation occurs Put another way, the dew point is the temperature at which relative humidity of the air is 100%

Dew-point Example Before we determined that 1 kilogram of air at 25 degrees C that contains 5 grams of water vapor has a relative humidity of 25%. If we lowered the temp to 5 degrees C, the relative humidity would increase to 100%, and the air would be saturated. Therefore, 5 degrees C is the dew-point temperature.