Physical Science 22 Water and Wind

Objectives

• Describe the three phases of the water cycle• Explain how temperature and humidity are

related• Identify various cloud types by their appearance

and the altitudes at which they typically occur• Use the concept of pressure gradients to explain

how winds are created, and explain how Earth’s rotation affects their direction

The Water Cycle

• Water cycle- the continuous movement of water from the ocean to the atmosphere to the land and back to the ocean

• Components:

evaporation

transpiration

condensation

precipitation

Evaporated water vapor condenses to form precipitation

• Transpiration- the process by which plants release water vapor into the air through stomata

• Precipitation- any form of water that falls to Earth’s surface from the clouds

Air contains varying quantities of water vapor

• Humidity- the amount of water vapor in the air

• Relative humidity- the actual quantity of water vapor present in the air compared with the maximum quantity of water vapor that can be present at that particular temperature

• Air that has a relative humidity of 100% is said to be saturated

Warmer temperatures evaporate more water

• At warm temperatures molecules move very quickly and are farther apart

• Water is more likely to exist as a gas

• Warm air can hold more water vapor than cold air can

Water vapor becomes liquid at dew point

• Dew point- the temperature at which air or a gas begins to condense to a liquid

• The higher the humidity the higher the dew point

Clouds form as warm, moist air rises

• Fog- a low-lying cloud

• Clouds are formed when warm air rises and water vapor condenses into tiny droplets of liquid as it cools

• In the troposphere

• Clouds are comprised of tiny water droplets and small ice crystals (at higher altitudes)

Clouds are classified by their form and the altitude at which they occur• It is all in the name derived from three root

words:

cirrus- thin and wispy

(6km-11km above surface)

stratus- sheetlike an layered

(low altitudes < 6km)

cumulus – white and fluffy with flat bottoms (500m-12km above surface)

Cloud names reflect combined characteristics

Turn to page 752 in your textbook

To the best of your ability sketch figure 13 in your notes. Be sure to label the cloud type and altitude

Read the section on page 753 describing the cloud types

What type of clouds produce precipitation?

(constant precipitation vs. thunderstorms)

Air Pressure

• Barometric pressure- the pressure due to the weight of the atmosphere; also called air pressure or atmospheric pressure

• Air pressure- the pressure that results from the weight of a column of air extending from the top of the thermosphere to the point of measurement

• At sea level barometric pressure of air at 0°C is around 760mm of mercury.

• 1 atmosphere (atm)

• SI unit is ? = 1N/m2

Wind

• Differences in pressure create wind

• When air pressure varies from place to place a pressure gradient exists

• The air in a pressure gradient move from areas of high pressure to areas of low pressure

• Wind- this movement of air from a high-pressure area to a low pressure area

Earth’s rotation affects the direction of winds

• Coriolis effect- the curving of the path of a moving object from an otherwise straight path due to the Earth’s rotation

Predictable air circulation forms wind patterns

• Winds in the Northern hemisphere cure clockwise

• Winds in the Southern Hemisphere curve counterclockwise

• Turn to page 755 in your textbook read through both sections

• In your notebook sketch figure 17 be sure to designate latitude, wind belts, direction

Global wind patterns form circulation cells