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Moisture, Clouds, and PrecipitationCurrent Weather
Finish Atmospheric Circulation
Humidity
Clouds
Precipitation
For Next Class: Read Chapter 7 (pp. 205-214)
Reminder: Exam 1 on September 11!
© AMS 12
Water Vapor in the Atmosphere
Humidity: any one of many ways of describing the amount of water vapor in the air Varies with the season, from one day to the
next, within a single day, and from one place to another
13© AMS
Water Vapor in the Atmosphere
Relative Humidity Compares the actual amount of water vapor
in the air with the amount of water vapor that would be present if that same air were saturated• Expressed as a percentage• When air is saturated, relative humidity is 100%• Varies inversely with temperature
© AMS 15
Water Vapor in the Atmosphere
Vapor Pressure Pressure produced by the gas molecules
composing air depends on • mass of the molecules• kinetic molecular activity
Air pressure at a given location can be thought of as the weight per unit area of the column of air above that location
Water vapor’s contribution to the total air pressure is known as vapor pressure
© AMS 16
Water Vapor in the Atmosphere
Saturated Air Raising the air temperature
increases saturation vapor pressure
Lowering the air temperature reduces saturation vapor pressure
20© AMS
Water Vapor in the AtmospherePrecipitable Water
Depth of water that would be produced if all the water vapor in a vertical column of air were condensed into liquid water
Average depth decreases with latitude in response to the poleward decline in mean air temperature
Varies with the seasons
Not always indicative of the amount of precipitation that might fall at a particular location
Rime IceA coating of tiny, white, ice particles caused by the rapid freezing of supercooled water droplets on impact with an object.