Water Vapor and Water Vapor and the Atmospherethe Atmosphere

Water in Water in the the

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

When it comes to When it comes to understanding understanding atmospheric atmospheric processes, water vapor processes, water vapor is the most important is the most important gas in the atmospheregas in the 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 actual Ratio of the air’s actual water-vapor content water-vapor content compared with the compared with the amount of water vapor amount of water vapor air can hold at that air can hold at that temperature and temperature and pressure.pressure.

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

Raising air temperature Raising air temperature causes a decrease in causes a decrease in relative humidityrelative humidity

Dew PointDew PointDew point Dew point is is the temperature the temperature to which a to which a parcel of air parcel of air would need to would need to be cooled to be cooled to reach reach saturation.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 masses that have a flat base and the appearance base and the appearance of rising domes or towersof rising domes or towers

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

Classification of Classification of Clouds by Clouds by

HeightHeightHigh 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 Have bases between 2000

and 6000 metersand 6000 meters Altocumulus: rounded Altocumulus: rounded

masses that are larger and masses that are larger and denser than cirrocumulus denser than cirrocumulus cloudsclouds

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

Low CloudsLow Clouds Have bases below 2000 metersHave bases below 2000 meters Stratus: uniform layer of Stratus: uniform layer of clouds that clouds that

covers much of the skycovers much of the sky Stratocumulus: scalloped bottom that Stratocumulus: scalloped bottom that

appears as long parallel rolls or broken appears as long parallel rolls or broken rounded patchesrounded patches

Nimbostratus: grayish clouds covering Nimbostratus: grayish clouds covering most of the sky often producing most of the sky often producing precipitationprecipitation

Cumulonimbus: cloud covering all three Cumulonimbus: cloud covering all three height producing thunderstormsheight producing thunderstorms

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 How Does Precipitation Form?Form?

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

Forms of Forms of PrecipitationPrecipitation 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 temperature profile in the lower few km of the 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