Water in the AtmosphereWater in the Atmosphere

The Water CycleThe Water Cycle

The Water CycleThe Water Cycle

The movement of water between the The movement of water between the atmosphere and Earth’s surface is called the atmosphere and Earth’s surface is called the water cyclewater cycle..

Three steps of the water cycle:Three steps of the water cycle:– EvaporationEvaporation– CondensationCondensation– PrecipitationPrecipitation

How Does the Water Cycle Work?How Does the Water Cycle Work?

DensityDensity makes the water cycle work. makes the water cycle work. Water is Water is moremore dense than air in its dense than air in its liquidliquid form so it collects form so it collects

together via gravity into bodies of water such as the oceans together via gravity into bodies of water such as the oceans and lakes etc. and lakes etc.

As it is heated by the As it is heated by the sunsun (driving energy source) and (driving energy source) and evaporatesevaporates, it becomes a gas and that gas is , it becomes a gas and that gas is lessless dense dense than air.than air.

As it rises to very high altitudes in the As it rises to very high altitudes in the tropospheretroposphere, it cools , it cools due to lower temperatures and becomes due to lower temperatures and becomes moremore dense than air dense than air again.again.

Once enough water vapor has Once enough water vapor has condensedcondensed into clouds and into clouds and the clouds move away from the source of water, the water the clouds move away from the source of water, the water vapor will eventually condense enough that the cloud is vapor will eventually condense enough that the cloud is moremore dense than the air.dense than the air.

PrecipitationPrecipitation will fall in the form of will fall in the form of rain, sleet, snow or hail.rain, sleet, snow or hail.

Density of Air in the AtmosphereDensity of Air in the Atmosphere

Phase Change Diagram ReviewPhase Change Diagram Review

EvaporationEvaporation

Evaporation Evaporation is the process by which water is the process by which water molecules in liquid water escape into the air molecules in liquid water escape into the air as water vapor.as water vapor.

Water molecules.Water molecules. Water molecules i a liquid state are Water molecules i a liquid state are moremore

dense than air. dense than air. When water is heated by the sun, the liquid When water is heated by the sun, the liquid

moves moves fasterfaster and becomes and becomes lessless dense dense causing it to rise into the atmosphere.causing it to rise into the atmosphere.

Examples of EvaporationExamples of Evaporation

HumidityHumidity-the measure of the amount of -the measure of the amount of water vapor in the airwater vapor in the air

Humidity depends upon Humidity depends upon temperature.temperature.

Examples of Evaporation Examples of Evaporation

Relative HumidityRelative Humidity-the percentage of water vapor -the percentage of water vapor that is actually in the air compared to the that is actually in the air compared to the maximum amount of water vapor the air can hold.maximum amount of water vapor the air can hold.

WarmWarm air is less dense and can “hold” more water air is less dense and can “hold” more water than cold air that is than cold air that is moremore dense. dense.

Warm air has more space to fit water vapor

Cold air has less space to fit water vapor

Measuring Relative HumidityMeasuring Relative Humidity

PsychrometerPsychrometer-Instrument used to measure -Instrument used to measure relative humidityrelative humidity

Made of 2 thermometersMade of 2 thermometers– Wet-bulbWet-bulb thermometer thermometer– Dry-bulb Dry-bulb thermometerthermometer

Measuring Relative HumidityMeasuring Relative Humidity

Wet-bulbWet-bulb thermometer-bulb has a cloth thermometer-bulb has a cloth covering that is moistened with watercovering that is moistened with water

PsychrometerPsychrometer is spun by the handle and air is spun by the handle and air blows over both thermometersblows over both thermometers

Wet-bulb thermometer is cooled by Wet-bulb thermometer is cooled by evaporationevaporation

Compare readings on the two thermometersCompare readings on the two thermometers

How to Determine Relative HumidityHow to Determine Relative Humidity

1.1. Measure the Measure the dry bulbdry bulb temperature. temperature.

2.2. Measure the Measure the wet bulbwet bulb temperature. temperature.

3.3. Calculate the Calculate the differencedifference between the dry bulb between the dry bulb and wet bulb temperatures. and wet bulb temperatures.

4.4. Find the Find the dry bulbdry bulb temperature on the table. temperature on the table.

5.5. Find the Find the differencedifference between the wet and dry bulb between the wet and dry bulb temperatures on the table. temperatures on the table.

6.6. The The relative humidityrelative humidity will be at the intersection of will be at the intersection of the row and column.the row and column.

Relative Humidity Table ExamplesRelative Humidity Table Examples

Example #1:Example #1: Suppose the relative humidity of the air is Suppose the relative humidity of the air is

51% and the reading of the dry-bulb 51% and the reading of the dry-bulb thermometer is 20thermometer is 2000C. What is the reading of C. What is the reading of the wet-bulb thermometer?the wet-bulb thermometer?

Answer: 14 Answer: 14 ooCC

Relative Humidity Table ExamplesRelative Humidity Table Examples

Example #2:Example #2: The readings on a sling psychrometer are The readings on a sling psychrometer are

14 14 00C for the dry-bulb thermometer and C for the dry-bulb thermometer and 12 12 00C for the wet-bulb thermometer. What is C for the wet-bulb thermometer. What is the relative humidity?the relative humidity?

Answer: 79%Answer: 79%

Example of EvaporationExample of Evaporation SweatSweat is your body’s natural way of is your body’s natural way of

cooling downcooling down. . When sweat reaches the surface of our When sweat reaches the surface of our

skin, it then skin, it then evaporatesevaporates, which cools us , which cools us down!down!

HeatHeat is transferred from your skin to the is transferred from your skin to the water which makes you feel cooler.water which makes you feel cooler.

Example of EvaporationExample of Evaporation

Outdoor dryingOutdoor drying: When you hang socks : When you hang socks outside to dry, you're using outside to dry, you're using energyenergy from the from the Sun and the wind to Sun and the wind to evaporateevaporate and disperse and disperse the water they contain. the water they contain.

CondensationCondensation

Condensation

CondensationCondensation

As As warmwarm, moist air rises in the , moist air rises in the atmosphere, its temperature begins to atmosphere, its temperature begins to decreasedecrease..

Molecules of water vapor in the air Molecules of water vapor in the air become liquid water in the process of become liquid water in the process of condensationcondensation..

How Clouds FormHow Clouds Form

Clouds form when water vapor in the air Clouds form when water vapor in the air condensescondenses to form liquid water or ice to form liquid water or ice crystalscrystals

Two conditions required for condensationTwo conditions required for condensation::– CoolingCooling of the air of the air– Presence of Presence of particlesparticles in the air in the air

The Role of CoolingThe Role of Cooling

Cold Cold air holds less water vapor than warm air holds less water vapor than warm airair

Dew PointDew Point-the temperature at which -the temperature at which condensation beginscondensation begins

Dew point Dew point aboveabove freezing=water vapor freezing=water vapor forms water dropletsforms water droplets

Dew point Dew point belowbelow freezing=water vapor may freezing=water vapor may change into ice crystalschange into ice crystals

Dew Point and HumidityDew Point and Humidity

The The higherhigher the dew point, the the dew point, the moremore moisture moisture in the airin the air– Example: Example: Key West, Florida has high dew Key West, Florida has high dew

points so it feels “sticky” or humidpoints so it feels “sticky” or humid

TheThe lower lower the dew point, the the dew point, the lessless moisture moisture in the airin the air– Example: Example: Death Valley, California has low dew Death Valley, California has low dew

points so it feels drypoints so it feels dry

The Role of ParticlesThe Role of Particles

For water vapor to For water vapor to condensecondense, tiny particles must , tiny particles must be present so the water has a surface on which to be present so the water has a surface on which to condensecondense

In In cloudcloud formation, most of these particles are salt formation, most of these particles are salt crystals, dust from soil, and smokecrystals, dust from soil, and smoke

Water vapor also condenses onto Water vapor also condenses onto solid surfacessolid surfaces, , such as such as blades of grassblades of grass or window panes or window panes

The Role of Particles continuedThe Role of Particles continued

Liquid water that condenses from the air Liquid water that condenses from the air onto a cooler surface is called onto a cooler surface is called dewdew

Ice that has been deposited on a surface Ice that has been deposited on a surface that is below freezing is called that is below freezing is called frostfrost

FogFog

CloudsClouds are classified by their shape and their altitude are classified by their shape and their altitude Different types of clouds are associated with different types Different types of clouds are associated with different types

of of weatherweather Clouds that form at or near the ground are calledClouds that form at or near the ground are called fog fog Fog often forms when the ground Fog often forms when the ground coolscools at night after a at night after a

warm, humid daywarm, humid day The ground cools the air just above the ground to the air’s The ground cools the air just above the ground to the air’s

dew pointdew point The next day the heat of the morning sun The next day the heat of the morning sun “burns”“burns” the fog the fog

off as its water droplets off as its water droplets evaporateevaporate

Cloud SeedingCloud Seeding

During drought conditions, a method called During drought conditions, a method called cloudcloud seedingseeding is used to produce is used to produce precipitation.precipitation.

Tiny crystals of Tiny crystals of silversilver iodideiodide and and drydry iceice are are sprinkled into clouds from airplanes.sprinkled into clouds from airplanes.

Water vapor can condense on the Water vapor can condense on the particlesparticles of silver iodide and dry ice of silver iodide and dry ice coolscools the water the water vapor from the air.vapor from the air.

As a result, As a result, cloudsclouds form. form.

PrecipitationPrecipitation

PrecipitationPrecipitation is any form of water that falls is any form of water that falls from clouds and reaches Earth’s surfacefrom clouds and reaches Earth’s surface

Not all clouds produce precipitationNot all clouds produce precipitation For precipitation to occur, cloud droplets or For precipitation to occur, cloud droplets or

ice crystals must grown ice crystals must grown densedense enough to fall enough to fall through the airthrough the air

Types of PrecipitationTypes of Precipitation

Common types of precipitation include:Common types of precipitation include:– RainRain– SleetSleet– Freezing rainFreezing rain– SnowSnow– HailHail

RainRain

Most Most commoncommon form of precipitation form of precipitation Drops of water Drops of water 0.5 mm0.5 mm in diameter in diameter Drizzle-drops of water less than 0.5 mmDrizzle-drops of water less than 0.5 mm Mist- drops of water smaller than drizzleMist- drops of water smaller than drizzle

SleetSleet

Raindrops fall through a layer of air that is Raindrops fall through a layer of air that is below below 00ooCC

Ice particles smaller than Ice particles smaller than 5 mm5 mm in diameter in diameter

Freezing RainFreezing Rain

Raindrops falling through cold air near the Raindrops falling through cold air near the ground do not freeze in the air, instead they ground do not freeze in the air, instead they freeze on a freeze on a cold surfacecold surface

SnowSnow

Water vapor in a cloud that is converted Water vapor in a cloud that is converted directly to ice crystals is called a directly to ice crystals is called a snowflakesnowflake

HailHail

Round pellets of ice larger than Round pellets of ice larger than 5 mm5 mm in in diameterdiameter

Form during Form during thunderstormsthunderstorms Difference between sleet and hail is the Difference between sleet and hail is the sizesize

of the ice pellets and where the ice pellets of the ice pellets and where the ice pellets formedformed

Measuring PrecipitationMeasuring Precipitation

Rain gauges-Rain gauges- open-ended can or tube that open-ended can or tube that collects rainfallcollects rainfall– The amount of rainfall is measured by dipping a The amount of rainfall is measured by dipping a

ruler into the water or by reading a marked ruler into the water or by reading a marked scalescale

Measuring sticksMeasuring sticks