• The study of weather = METEROLOGYThe study of weather = METEROLOGY• Weather is the condition of the Weather is the condition of the

atmosphere at any given time or placeatmosphere at any given time or place• Much of weather forecasting and Much of weather forecasting and

prediction can be accomplished by direct prediction can be accomplished by direct observation – observation – LOOK OUT THE WINDOW!!LOOK OUT THE WINDOW!!

• To predict weather, you must make To predict weather, you must make observations of the clouds, wind, observations of the clouds, wind, temperature, humidity, air pressure and temperature, humidity, air pressure and precipitationprecipitation

Atmospheric Atmospheric CompositionComposition

• The Earth’s atmosphere is made up The Earth’s atmosphere is made up of many gases, but it is mostly of many gases, but it is mostly nitrogen and oxygennitrogen and oxygen (Reference (Reference Tables) Tables)

• It also contains water vapor, dust, It also contains water vapor, dust, and and ozoneozone – O – O33 (a form of oxygen (a form of oxygen which which absorbs UV raysabsorbs UV rays from the sun) from the sun)

• As you go higher in the atmosphere, As you go higher in the atmosphere, the amount of air and air pressure the amount of air and air pressure (weight of air) decreases(weight of air) decreases

Structure of the Structure of the AtmosphereAtmosphere

• made up of four layers, each with different made up of four layers, each with different characteristics (Reference Tables)characteristics (Reference Tables)

• Troposphere-Troposphere- lowest layer (we live in this lowest layer (we live in this layer). All of Earth’s weather occurs in the layer). All of Earth’s weather occurs in the troposphere. troposphere. Temperature decreasesTemperature decreases as you as you go higher.go higher.

• Stratosphere-Stratosphere- above the troposphere, has above the troposphere, has strong winds. strong winds. Temperature increasesTemperature increases as you as you go higher because of the absorption of UV go higher because of the absorption of UV rays by ozone.rays by ozone.

• Mesosphere-Mesosphere- above the stratosphere. above the stratosphere. Temperature decreasesTemperature decreases as you go higher. as you go higher.

• Thermosphere-Thermosphere- above the mesosphere. above the mesosphere. Temperature increasesTemperature increases as you go higher due as you go higher due to oxygen and nitrogen absorbing solar energyto oxygen and nitrogen absorbing solar energy

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ATMOSPHERIC ATMOSPHERIC VARIABLESVARIABLES

• things that can be measured and things that can be measured and change from moment to momentchange from moment to moment– Temperature Temperature – Air Pressure Air Pressure – Wind Speed and Direction Wind Speed and Direction – Water Content & Humidity Water Content & Humidity – Cloud Cover Cloud Cover – Precipitation Precipitation – Others (dust, transparency, pollen, Others (dust, transparency, pollen,

etc)etc)

TEMPERATURETEMPERATURE

• Measures the average kinetic energy Measures the average kinetic energy of molecules.of molecules.

• Heat enters the atmosphere from the Heat enters the atmosphere from the sun as solar radiation (Insolation)sun as solar radiation (Insolation)

• Average Kinetic Energy-Average Kinetic Energy- kinetic kinetic energy is the energy of motionenergy is the energy of motion

• The temperature of any material is an average of all of the kinetic energies- hence Average Kinetic Energy

3 ways to Measure 3 ways to Measure temperature:temperature:

• Fahrenheit– Water freezes at 32° – Water boils at 212°

• Celsius– AKA Centigrade (100 levels) – Water freezes at 0° – Water boils at 100° – Makes more sense and is easier to make a

thermometer

• Kelvin– Same scale as Celsius but 0 means zero energy – No degrees mark for Kelvin – 0K means that all atomic vibrations stop.

Air PressureAir Pressure

• the the weightweight of the air in a certain area of the air in a certain area• Sinking air pushes down more- cold air is Sinking air pushes down more- cold air is

usually high pressureusually high pressure• Rising air pushes down less- hot air is Rising air pushes down less- hot air is

usually low pressureusually low pressure • Air pressure is measured using an Air pressure is measured using an

instrument called a instrument called a barometerbarometer • It is measured in It is measured in inchesinches (height of the (height of the

mercury column in the barometer), or mercury column in the barometer), or with the metric units called with the metric units called millibarsmillibars

• Use your reference tables for Use your reference tables for converting inches to millibarsconverting inches to millibars

• Air pressure drops with Air pressure drops with increasing altitude (less air)increasing altitude (less air)

• Weather maps show Weather maps show sea levelsea level air pressureair pressure

• It ranges fromIt ranges from 960mb – 960mb – 1050mb1050mb

• IsoIsobars are lines on the bars are lines on the weather maps which connect weather maps which connect areas of equal air pressureareas of equal air pressure

Changes in Air PressureChanges in Air Pressure

• TemperatureTemperature-- warm air is lighter warm air is lighter than cold air!than cold air!

• HumidityHumidity-- humid (moist) air is humid (moist) air is lighter than dry air!! Water lighter than dry air!! Water vapor (Hvapor (H22O) weighs less than the O) weighs less than the N and O gases that it pushed outN and O gases that it pushed out

• Winds are caused by the Winds are caused by the unequal unequal heatingheating of the atmosphere of the atmosphere (remember that temperature (remember that temperature causes changes in air pressure)causes changes in air pressure)

Water Vapor in the AirWater Vapor in the Air • The amount of water vapor in the air The amount of water vapor in the air

depends on the air depends on the air temperaturetemperature• The warmer the air, the more water The warmer the air, the more water

vapor it can hold (think of those hot, vapor it can hold (think of those hot, humid summer days)humid summer days)

• The actual amount of water vapor in The actual amount of water vapor in the air is called the air is called specific humidityspecific humidity

Relative Humidity Relative Humidity • the amount of water vapor in the air, the amount of water vapor in the air,

comparedcompared to how much water vapor to how much water vapor it could hold at that temperatureit could hold at that temperature

• Relative humidity is a Relative humidity is a percentpercent measurementmeasurement

• Air with 100% humidity is said to be Air with 100% humidity is said to be saturatedsaturated– Precipitation will occurPrecipitation will occur

Finding Relative HumidityFinding Relative Humidity • use an instrument called a use an instrument called a hygrometerhygrometer• One particular type of hygrometer is called a One particular type of hygrometer is called a

sling psychrometersling psychrometer– This instrument is made of two thermometers This instrument is made of two thermometers

attached two a handleattached two a handle– One thermometer has a piece of gauze which is the One thermometer has a piece of gauze which is the

soaked with water - This is called the soaked with water - This is called the WET BULBWET BULB• The other thermometer is called the The other thermometer is called the DRY BULBDRY BULB

– These thermometers are swung in the air for a few These thermometers are swung in the air for a few minutes, and then the temperatures are recorded minutes, and then the temperatures are recorded (take the wet bulb temperature first)(take the wet bulb temperature first)

• The wet bulb thermometer should have a lower The wet bulb thermometer should have a lower temperature, since it temperature, since it removes heat from the removes heat from the thermometer as water evaporatesthermometer as water evaporates from it from it

• The two temperatures are then used to look up The two temperatures are then used to look up the relative humidity on a chart (Reference the relative humidity on a chart (Reference Tables)Tables)

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Condensation and DewCondensation and Dew • remember that remember that air’s ability to hold moisture air’s ability to hold moisture

decreases as the temperature decreasesdecreases as the temperature decreases• As the air cools, its relative humidity As the air cools, its relative humidity

increases increases • When the relative humidity reaches 100% When the relative humidity reaches 100%

(saturated), the water comes out of the air (saturated), the water comes out of the air as liquid dropletsas liquid droplets

• The temperature at which this will occur is The temperature at which this will occur is called thecalled the dew pointdew point

• **The dew point can be found using the **The dew point can be found using the same method for relative humidity, except same method for relative humidity, except use the dew point chart (Reference Tables)use the dew point chart (Reference Tables)

• Condensation can only occur if the water has Condensation can only occur if the water has something to condense onsomething to condense on

• Tiny particles in the air on which water Tiny particles in the air on which water condenses is called condenses is called condensation nucleicondensation nuclei

• This can be dust, salts, chemicals from burning This can be dust, salts, chemicals from burning fuel, etc.fuel, etc.

• * Water vapor that condenses on the ground is * Water vapor that condenses on the ground is called called dewdew (think of walking across wet grass in (think of walking across wet grass in the morning)the morning)

• If the dew freezes on the ground, it is called If the dew freezes on the ground, it is called frostfrost

• Water vapor condensing in the air forms cloudsWater vapor condensing in the air forms clouds• If the cloud forms close to the ground, it is If the cloud forms close to the ground, it is

called called fogfog

Condensation and DewCondensation and Dew

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Try These…Try These…

Dry Bulb Wet Bulb R Humidity

DPT

26°C 20 °C

6 °C 5 °C

12 °C 8 °C

18 °C 17 °C

14 °C 14 °C

0 °C -3 °C

57% 17 °C°C

86% 4 °C°C

57% 4 °C°C

91% 16 °C°C

100% 14 °C°C

45% -9 °C°C