Water Vapor and Water Vapor and the Atmospherethe Atmosphere

Water in the Water in the AtmosphereAtmosphere

� PrecipitationPrecipitation is any is any form of water that form of water that falls from a cloud.falls from a cloud.

� When it comes to When it comes to understanding understanding atmospheric processes, atmospheric processes, water vapor is the water vapor is the most important gas in most important gas in the atmospherethe atmosphere

Water Changes StateWater Changes StateThe three states of matter solid, liquid, and gas The three states of matter solid, liquid, and gas

(plasma is the fourth)(plasma is the fourth)

HumidityHumidityamount of amount of water vapor in water vapor in air.air.

Relative Relative HumidityHumidity

� Ratio of the air’s Ratio of the air’s actual water-vapor actual water-vapor content compared with content compared with the amount of water the amount of water vapor air can hold at vapor air can hold at that temperature and that temperature and pressure.pressure.

� Lowering air Lowering air temperature causes an temperature causes an increase in relative increase in relative humidityhumidity

� Raising air Raising air temperature causes a temperature causes a decrease in relative decrease in relative humidityhumidity

Dew PointDew PointDew point Dew point is the is the temperature to temperature to which a parcel of which a parcel of air would need to air would need to be cooled to be cooled to reach saturation.reach saturation.

How do I measure How do I measure humidity?humidity?

Instrument: Instrument: HygrometerHygrometer Psychrometer : a type of Psychrometer : a type of

hygrometer consisting of hygrometer consisting of two identical two identical thermometers mounted thermometers mounted side by sideside by side

Dry bulb: give the present Dry bulb: give the present air temperatureair temperature

Wet bulb: has thin wet Wet bulb: has thin wet wick tied around the endwick tied around the end

Cloud FormationCloud Formation

Clouds form Clouds form when air is when air is cooled to its cooled to its dew pointdew point

CloudsCloudsClouds are Clouds are classified on classified on the basis of the basis of their form their form and height.and height.

Three Types of CloudsThree Types of CloudsCirrus Cirrus ((cirruscirrus = curl of hair) = curl of hair)

high, white, and thinhigh, white, and thinCumulus Cumulus ((cumuluscumulus = a pile) = a pile)

rounded individual cloud rounded individual cloud masses that have a flat base masses that have a flat base and the appearance of rising and the appearance of rising domes or towersdomes or towers

Stratus Stratus ((stratusstratus = a layer) = a layer) best described as sheets or best described as sheets or layers that cover much or all layers that cover much or all of the skyof the sky

Classification of Classification of Clouds by HeightClouds by HeightHigh CloudsHigh Clouds Have bases above 6000 Have bases above 6000

metersmeters Cirrus: high, white and thinCirrus: high, white and thin Cirrostratus: flat layersCirrostratus: flat layers Cirrocumulus: fluffy massesCirrocumulus: fluffy masses

Middle Clouds (Alto)Middle Clouds (Alto) Have bases between 2000 and Have bases between 2000 and

6000 meters6000 meters Altocumulus: rounded masses Altocumulus: rounded masses

that are larger and denser that are larger and denser than cirrocumulus cloudsthan cirrocumulus clouds

Altostratus: uniform white to Altostratus: uniform white to grayish sheet covering the sky grayish sheet covering the sky with the sun or moon visible as with the sun or moon visible as a bright spot a bright spot

Low CloudsLow Clouds Have bases below 2000 Have bases below 2000

metersmeters Stratus: uniform layer of Stratus: uniform layer of

clouds that covers much of the clouds that covers much of the skysky

Stratocumulus: scalloped Stratocumulus: scalloped bottom that appears as long bottom that appears as long parallel rolls or broken rounded parallel rolls or broken rounded patchespatches

Nimbostratus: grayish clouds Nimbostratus: grayish clouds covering most of the sky often covering most of the sky often producing precipitationproducing precipitation

Cumulonimbus: cloud covering all Cumulonimbus: cloud covering all three height producing three height producing thunderstormsthunderstorms

FogFog A cloud with A cloud with

its base at or its base at or very near the very near the ground.ground.

How Does Precipitation Form?How Does Precipitation Form?

For precipitation For precipitation to form, cloud to form, cloud droplets must droplets must grow in volume grow in volume by roughly one by roughly one million times.million times.

Forms of PrecipitationForms of Precipitation� The type of precipitation The type of precipitation

that reaches Earth’s that reaches Earth’s surface depends on the surface depends on the temperature profile in the temperature profile in the lower few km of the lower few km of the atmosphereatmosphere

RainRain: : drops of water that drops of water that fall from a cloud and have a fall from a cloud and have a diameter of at least 0.5 mmdiameter of at least 0.5 mm

SnowSnow: : light, fluffy,light, fluffy, six-six-sided ice crystalssided ice crystals

Forms of Forms of PrecipitationPrecipitation

� SleetSleet: fall of small particles of : fall of small particles of clear to translucent iceclear to translucent ice

� GlazeGlaze: when raindrops become : when raindrops become supercooled as they fall through supercooled as they fall through subfreezing air and turns to ice subfreezing air and turns to ice when they impact objectswhen they impact objects

HailHail: form of solid precipitation : form of solid precipitation which consists of balls of which consists of balls of irregular lumps of ice produced irregular lumps of ice produced in cumulonimbus cloudsin cumulonimbus clouds