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!

June–July ITCZ

Figure 6.11

Rossby Waves

Figure 6.16

Location of Polar Front and Sub-Polar Low Pressure

Blizzard of 1993

http://www.accuweather.com/en/weather-news/blizzard-of-93-the-storm-of-th/62671

Jet Streams

Figure 6.17

Mountain-Valley Breezes

Figure 6.19

Monsoonal Winds

Figure 6.20

Major Ocean Currents

Figure 6.21

© 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

Relative Humidity

Figure 7.8

© 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

Saturation Vapor Pressure

Figure 7.12

Maximum Specific Humidity

Figure 7.13

Humidity Patterns

Figure 7.11

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

Adiabatic Processes

Figure 7.17

Adiabatic Cooling

Figure 7.17

Adiabatic Heating

Figure 7.17

Precipitation TypesWhat are the major types of precipitation and how do they form?

Moisture Droplets

Figure 7.20

Raindrop and Snowflake Formation

Figure 7.21

Saturation Vapor Pressure

Figure 7.12

What is Rime Ice?

Rime IceA coating of tiny, white, ice particles caused by the rapid freezing of supercooled water droplets on impact with an object.

Rime Ice on Mt. Mitchell

Rime Ice on Beech Mountain

Heavy Rime

Icing on

Mt. Washington

Rime Icing on

Grandfather

Mountain

Snow Particle Photomicroscopy

Graupel

Snow Particle Photomicroscopy

Cloud Types and Identification  

Figure 7.22

Atmospheric Lifting Mechanisms 

Figure 8.6

Orographic Precipitation

Figure 8.9

Orographic Patterns

Figure 8.10

Average Annual Precipitation