TemperatureTemperature

What is temperature?What is temperature?

Heat – form of energy that flows from one system or object to another b/c they have different temperatures

Temperature – a measure of the average kinetic energy of individual molecules We feel the effect of temperature as sensible heat transfer from warmer to

cooler objects

Temperature and Heat are related b/c changes in temperature occur by Temperature and Heat are related b/c changes in temperature occur by absorption or emission (gain/loss) of heat energyabsorption or emission (gain/loss) of heat energy

Surface TemperatureSurface Temperature

During the day, SW inputs usually exceeds LW outputs and heating of During the day, SW inputs usually exceeds LW outputs and heating of the surface occursthe surface occurs

Latent and sensible heat are also important in determining surface Latent and sensible heat are also important in determining surface temperature (e.g. desert vs. oasis)temperature (e.g. desert vs. oasis)

Temperature ScalesTemperature Scales

Kelvin (K)Kelvin (K) = absolute temperature scale, -273.15 degrees = absolute temperature scale, -273.15 degrees Celsius or 0 degree KCelsius or 0 degree K

Celsius (C)Celsius (C) = international standard = international standard

Fahrenheit (F)Fahrenheit (F) = used in the US = used in the US

Measuring TemperatureMeasuring Temperature

Thermometer Thermometer – an instrument used to measure temperature– an instrument used to measure temperature Alcohol thermometerAlcohol thermometer: alcohol has a freezing point -112 C so it is : alcohol has a freezing point -112 C so it is

used for cold weather measurementsused for cold weather measurements Mercury thermometerMercury thermometer – mercury has a freezing point of -39 C so it – mercury has a freezing point of -39 C so it

is better suited for less extreme environmentsis better suited for less extreme environments

Thermometers measure temp based on the thermal Thermometers measure temp based on the thermal properties of the liquids above:properties of the liquids above:- Fluids Fluids expandexpand when heated, when heated, contractcontract when cooled when cooled- The rise and fall of the fluid is measured using calibrations marked The rise and fall of the fluid is measured using calibrations marked

on the tubeon the tube

Measuring TemperatureMeasuring Temperature

Standard Temperature Standard Temperature Measurement:Measurement:

- Taken outdoorsTaken outdoors- Thermometer is placed within a Thermometer is placed within a

thermometer shelterthermometer shelter- A white (for albedo) box with A white (for albedo) box with

vents (for air flow) that shades vents (for air flow) that shades the thermometer from direct the thermometer from direct sunlightsunlight

- Temperatures taken at a Temperatures taken at a standard height of 1.2m above standard height of 1.2m above the groundthe ground

Different Temperature Measurements:Different Temperature Measurements:

Max temperatureMax temperature – highest temp reading – highest temp reading Min temperatureMin temperature – lowest temp reading – lowest temp reading Daily mean temperatureDaily mean temperature – average of the max and min daily temp – average of the max and min daily temp

Monthly mean temperatureMonthly mean temperature – average of daily mean temps – average of daily mean temps Annual temperature rangeAnnual temperature range – difference between the lowest and highest – difference between the lowest and highest

monthly mean temperatures for a yearmonthly mean temperatures for a year

Air vs Surface TemperatureAir vs Surface Temperature

Air temperature is measured a short distance (usually 1.2m or 4ft) Air temperature is measured a short distance (usually 1.2m or 4ft) above the surfaceabove the surface

Air temperature can be quite different than surface temperatureAir temperature can be quite different than surface temperature

However, air temperature tends to mirror surface temperatureHowever, air temperature tends to mirror surface temperature

Earth’s temperature patterns influenced by four physical Earth’s temperature patterns influenced by four physical properties:properties:

1)1) Latitude Latitude 2)2) ElevationElevation3)3) Cloud CoverCloud Cover4)4) Land vs. oceanLand vs. ocean

What factors control temperature?What factors control temperature?

1) Latitude1) Latitude

LatitudeLatitude

Latitude controls:Latitude controls:1)1) DaylengthDaylength2)2) Angle of incidenceAngle of incidence

Insolation is the single most important influence on temperature variationsInsolation is the single most important influence on temperature variations

Why don’t world temperature patterns follow latitudinal bands?Why don’t world temperature patterns follow latitudinal bands?

Latitude and air temperatureLatitude and air temperature Seasonal range in air temperature is strongly dependent on latitude – Seasonal range in air temperature is strongly dependent on latitude –

increases as you get closer to the polesincreases as you get closer to the poles More direct rays of sunlight during summerMore direct rays of sunlight during summer Longer daylength in summer; shorter in winterLonger daylength in summer; shorter in winter

Equatorial locations may actually be warmer during an equinox than Equatorial locations may actually be warmer during an equinox than during a solstice!during a solstice!

Generally, air temperature lags behind solar radiation by one month over Generally, air temperature lags behind solar radiation by one month over land and by two months over waterland and by two months over water

2) Altitude/Elevation2) Altitude/Elevation

What is the impact of elevation on What is the impact of elevation on temperature?temperature?

Elevation: Elevation: temperature decreases with increasing elevation temperature decreases with increasing elevation within the tropospherewithin the troposphere

At similar latitudes, mountainous areas experience lower air At similar latitudes, mountainous areas experience lower air temperatures than locations near sea leveltemperatures than locations near sea level

Remember that density also decreases with increasing altitude:Remember that density also decreases with increasing altitude: As the atmos thins, the no. of air molecules decreaseAs the atmos thins, the no. of air molecules decrease Fewer molecules in the air means less energy absorptionFewer molecules in the air means less energy absorption Less SW radiation is reflected and scattered into spaceLess SW radiation is reflected and scattered into space Surface gains and looses energy more rapidly under lower atmospheric Surface gains and looses energy more rapidly under lower atmospheric

pressurepressure

3) Cloud Cover3) Cloud Cover

Cloud Cover- Cloud Cover- clouds are the most variable factor influencing clouds are the most variable factor influencing the Earth’s EBthe Earth’s EB

Cover approximately 50% of the earth and their effect on temperature Cover approximately 50% of the earth and their effect on temperature depends on their type, height and densitydepends on their type, height and density

Moderate temperature Moderate temperature → decreasing daytime temps and increasing → decreasing daytime temps and increasing nighttime tempsnighttime temps

Clouds absorb and reflect SW energy during the day → cooling effectClouds absorb and reflect SW energy during the day → cooling effect Clouds absorb and reradiate LW energy at night → warming effectClouds absorb and reradiate LW energy at night → warming effect

4) Land vs. Ocean4) Land vs. Ocean

Land and Water ContrastsLand and Water Contrasts

- Land has different thermal properties than water resulting in Land has different thermal properties than water resulting in differences in temperaturedifferences in temperature

- Land and water absorb and store energy differently b/c of the physical Land and water absorb and store energy differently b/c of the physical nature of land and waternature of land and water

Four main differences:Four main differences:5)5) EvaporationEvaporation6)6) TransparencyTransparency7)7) Specific HeatSpecific Heat8)8) MovementMovement

Land-Water ContrastsLand-Water Contrasts

1) 1) evaporationevaporation:: More energy at the ocean surface goes into evaporation than on landMore energy at the ocean surface goes into evaporation than on land 84% of all evaporation on earth occurs over the ocean84% of all evaporation on earth occurs over the ocean Evaporation is a cooling processEvaporation is a cooling process Results in lower temperatures over oceans than on landResults in lower temperatures over oceans than on land

2) 2) transparencytransparency:: Light can be transmitted through water but not through landLight can be transmitted through water but not through land Light striking land does not penetrate but is absorbed Light striking land does not penetrate but is absorbed → heat surface→ heat surface Energy transmits through water to a depth of approx. 60mEnergy transmits through water to a depth of approx. 60m Energy has a greater distribution within water than on landEnergy has a greater distribution within water than on land

Land-Water ContrastsLand-Water Contrasts

3) 3) Specific heatSpecific heat:: Heat capacity of a substanceHeat capacity of a substance When equal volumes of land and water are compared, water requires When equal volumes of land and water are compared, water requires

more energy to increase its temperature than landmore energy to increase its temperature than land Water can hold more heat than soil (specific heat is x4)Water can hold more heat than soil (specific heat is x4) Land heats and cools quick, water heats and cools slowLand heats and cools quick, water heats and cools slow

4) 4) movementmovement:: Land is solid and does not move whereas water is fluid and capable of Land is solid and does not move whereas water is fluid and capable of

movementmovement Mixing between warm and cold layers is possible within water and not Mixing between warm and cold layers is possible within water and not

possible within landpossible within land Mixing spreads available energy over and even greater volumeMixing spreads available energy over and even greater volume

What is the impact on daily temperatures?What is the impact on daily temperatures?

LESS DIURNAL TEMPERATURE CHANGE!LESS DIURNAL TEMPERATURE CHANGE!

Marine locations have cooler days and warmer nights than comparable Marine locations have cooler days and warmer nights than comparable inland locationsinland locations

Marine effect (maritime) Marine effect (maritime) – locations that exhibit the moderating influences – locations that exhibit the moderating influences of the ocean. Smaller range between max and min daily and annual of the ocean. Smaller range between max and min daily and annual temps.temps.

Continental Effect (continentality) Continental Effect (continentality) – areas that are less affected by the – areas that are less affected by the sea. Greater range between max and min daily and annual temp.sea. Greater range between max and min daily and annual temp.

Diurnal (Daily) Cycle of Air TemperatureDiurnal (Daily) Cycle of Air Temperature

Generally follows the sun; however, it lags due to the delay in Generally follows the sun; however, it lags due to the delay in heating the atmosphereheating the atmosphere

Coldest air temperature usually occurs just after sunrise – no Coldest air temperature usually occurs just after sunrise – no solar radiation during nightsolar radiation during night

Warmest air temperature occurs about 3pm when turbulent Warmest air temperature occurs about 3pm when turbulent mixing begins (warm bubbles of air rise and are replaced by mixing begins (warm bubbles of air rise and are replaced by colder air from aloft)colder air from aloft)

End of material contained in the End of material contained in the Midterm!Midterm!

Diurnal (Daily) Cycle of Air TemperatureDiurnal (Daily) Cycle of Air Temperature

An inversion may occur in the morning hours since the earth’s surface An inversion may occur in the morning hours since the earth’s surface cools rapidly when the sun setscools rapidly when the sun sets

Global temperature patternsGlobal temperature patterns

Temperature patterns result from:Temperature patterns result from:- LatitudeLatitude- Elevation above sea levelElevation above sea level- Cloud coverCloud cover- Land-ocean heating differencesLand-ocean heating differences

Maximum monthly mean temperature occurs in July (N. Hem)Maximum monthly mean temperature occurs in July (N. Hem) Lag after summer solstice b/c inputs are still larger than outputs shortly Lag after summer solstice b/c inputs are still larger than outputs shortly

after max insolationafter max insolation Similar to lag in daily air temperatureSimilar to lag in daily air temperature

Minimum monthly mean temperature occurs in January (N. Hem)Minimum monthly mean temperature occurs in January (N. Hem) Lag after winter solstice b/c inputs are still smaller than outputs shortly after Lag after winter solstice b/c inputs are still smaller than outputs shortly after

min insolationmin insolation Similar to lag in daily air temperatureSimilar to lag in daily air temperature

Horizontal Temperature Pattern:Horizontal Temperature Pattern:

Isotherms Isotherms – lines of equal temperature– lines of equal temperature Trend east and westTrend east and west Deviate from trends due to mountains and land-ocean contrastsDeviate from trends due to mountains and land-ocean contrasts

Thermal EquatorThermal Equator – isotherm connecting points of highest – isotherm connecting points of highest temperaturetemperature Hovers around latitudinal equatorHovers around latitudinal equator Shifts north in summer (according to location of max insolation)Shifts north in summer (according to location of max insolation) Shifts south in winterShifts south in winter

January temperature patterns:January temperature patterns: Temp decreases north and south of the thermal equatorTemp decreases north and south of the thermal equator Isotherms bend south over land Isotherms bend south over land

Cooler temps are found south over land than over waterCooler temps are found south over land than over water Land looses heat more quickly than waterLand looses heat more quickly than water

Lowest temp over Siberia (continental location)Lowest temp over Siberia (continental location) Isotherms move further south over mountainous regions (elevation Isotherms move further south over mountainous regions (elevation

effect)effect)

July temperature patterns:July temperature patterns: Temperature still decreases north and south of thermal equatorTemperature still decreases north and south of thermal equator Lower temperature is S. Hem than at equivalent latitudes in N. HemLower temperature is S. Hem than at equivalent latitudes in N. Hem

Max insolation in N. HemMax insolation in N. Hem Shift is not as dramatic in S. Hem b/c S. Hem has more oceans and Shift is not as dramatic in S. Hem b/c S. Hem has more oceans and

less land arealess land area Milder winter temps due to surrounding oceans (moderating effect)Milder winter temps due to surrounding oceans (moderating effect)

Isotherms bend north over land and mountainsIsotherms bend north over land and mountains

Annual temperature range:Annual temperature range: Identifies areas of moderate or extreme annual temp variationsIdentifies areas of moderate or extreme annual temp variations Most extreme variation over SiberiaMost extreme variation over Siberia

Continental locationContinental location Extreme north latitudeExtreme north latitude

Moderate along the equatorModerate along the equator Little variation in insolation during the yearLittle variation in insolation during the year Little temperature variations annuallyLittle temperature variations annually

Moderate over the S. HemModerate over the S. Hem Moderating effect of large oceans and little landModerating effect of large oceans and little land Most extremes occur over desert areas (low cloud cover)Most extremes occur over desert areas (low cloud cover)

Problem Set #3Problem Set #3

Wind Chill and Heat IndexWind Chill and Heat Index

Air temperature and the Human Body:Air temperature and the Human Body:

The human body responds not only to the air temperature but also to wind The human body responds not only to the air temperature but also to wind speed and humidity (amount of water vapour in the air).speed and humidity (amount of water vapour in the air).

- Body tries to maintain temperature of 36.8 CBody tries to maintain temperature of 36.8 C- Wind and humidity can exacerbate the effect of air temperature on the Wind and humidity can exacerbate the effect of air temperature on the

human bodyhuman body

→→Wind Chill FactorWind Chill Factor

Wind Chill Factor:Wind Chill Factor:

Cold weather is greatest cause of weather related death in Cold weather is greatest cause of weather related death in US.US. Wind enhances the rate at which the body loses heat to the Wind enhances the rate at which the body loses heat to the

atmosphereatmosphere Makes it feel colder than the air temperature actually isMakes it feel colder than the air temperature actually is The “The “wind chill indexwind chill index” was developed to describe the relative ” was developed to describe the relative

discomfort/danger resulting from the combination of wind and tempdiscomfort/danger resulting from the combination of wind and temp

Wind Chill Index:Wind Chill Index:

Since 2000, WCI calculated using the wind speed at average height (5 Since 2000, WCI calculated using the wind speed at average height (5 feet) of the human body’s facefeet) of the human body’s face

Incorporate modern heat transfer theoryIncorporate modern heat transfer theory Use a consistent standard for skin tissue resistanceUse a consistent standard for skin tissue resistance Assumes the worst case scenario for solar radiation (clear night sky)Assumes the worst case scenario for solar radiation (clear night sky) Adjustments for solar radiation (i.e. the impact of sun) for a variety of Adjustments for solar radiation (i.e. the impact of sun) for a variety of

sky conditions (sunny, partly sunny and cloudy)sky conditions (sunny, partly sunny and cloudy)

To calculate wind chill:To calculate wind chill:

WC (F) = 35.74 + 0.6215 * T – 35.75 * (VWC (F) = 35.74 + 0.6215 * T – 35.75 * (V0.160.16) + 0.4275 * T * (V) + 0.4275 * T * (V0.160.16))

Example:Example:Newark Newark → Wednesday January 17→ Wednesday January 17thth 2007 2007High Temperature 35 FHigh Temperature 35 F Wind speed = 13 mphWind speed = 13 mph

WC (F) = 35.74 + 0.6215 * WC (F) = 35.74 + 0.6215 * 35 35 – 35.75 * (– 35.75 * (13130.160.16) + 0.4275 *) + 0.4275 *3535* (* (13130.160.16))

WC = 18.55 FWC = 18.55 F

Wind chill warning Wind chill warning → → wind chill temperature is forecast to be wind chill temperature is forecast to be minus 25 degrees F or lowerminus 25 degrees F or lower

Wind chill advisory Wind chill advisory → → wind chill temperature is forecast to be wind chill temperature is forecast to be between minus 10 to minus 24 degrees Fbetween minus 10 to minus 24 degrees F

Wind chill does not affect your car’s antifreeze protection or freezing Wind chill does not affect your car’s antifreeze protection or freezing pipes. It’s an indicator of how to dress properly for winter weather:pipes. It’s an indicator of how to dress properly for winter weather: Entrapped insulating air warmed by body heatEntrapped insulating air warmed by body heat Loose-fitting, lightweight, warm clothing in several layersLoose-fitting, lightweight, warm clothing in several layers Tightly-woven, water-repellant, hooded outer garments with mittensTightly-woven, water-repellant, hooded outer garments with mittens

Only cold winter temperatures take a greater weather-related death toll Only cold winter temperatures take a greater weather-related death toll than the summer’s heat and humidity.than the summer’s heat and humidity.

Heat Index:Heat Index: Is an accurate measure of how hot is really feels when the affect of Is an accurate measure of how hot is really feels when the affect of

humidity are added to high temperaturehumidity are added to high temperature Human body contains several mechanisms to maintain its internal Human body contains several mechanisms to maintain its internal

operating temperature 98.6 Foperating temperature 98.6 F When threatened with above “normal” temperatures, the body will When threatened with above “normal” temperatures, the body will

try to dissipate excess heat:try to dissipate excess heat: Varying circulation of bloodVarying circulation of blood Losing water through the skin and sweat glandsLosing water through the skin and sweat glands pantingpanting

Heat Index:Heat Index: Higher humidity reduces the body’s ability to evaporate perspirationHigher humidity reduces the body’s ability to evaporate perspiration This lessens the body’s ability to regulate temperature by coolingThis lessens the body’s ability to regulate temperature by cooling

Conditions can exceed the body’s ability to cope; sunstroke, heat Conditions can exceed the body’s ability to cope; sunstroke, heat cramps, heat exhaustioncramps, heat exhaustion

The The HIHI chart shows actual air temperature and relative chart shows actual air temperature and relative humidityhumidity This chart is based on shady, light wind conditionsThis chart is based on shady, light wind conditions Exposure to direct sunlight can increase the HI by up to 15 FExposure to direct sunlight can increase the HI by up to 15 F

Example:Example:At 90% relative humidity and 90 F At 90% relative humidity and 90 F HI = 120 F (cat 2 risk) HI = 120 F (cat 2 risk)

To actually calculate the HI:To actually calculate the HI:

HI HI =16.923+((1.85212*10^-1)*T)+(5.37941*RH)-((1.00254*10^-1)*T*RH)=16.923+((1.85212*10^-1)*T)+(5.37941*RH)-((1.00254*10^-1)*T*RH)+((9.41695*10^-3)*T^2)+((7.28898*10^-3)*RH^2)+((3.45372*10^-+((9.41695*10^-3)*T^2)+((7.28898*10^-3)*RH^2)+((3.45372*10^-4)*T^2*RH)-((8.14971*10^-4)*T*RH^2)+((1.02102*10^-5)*T^2*RH^2)-4)*T^2*RH)-((8.14971*10^-4)*T*RH^2)+((1.02102*10^-5)*T^2*RH^2)-((3.8646*10^-5)*T^3)+((2.91583*10^-5)*RH^3)+((1.42721*10^-((3.8646*10^-5)*T^3)+((2.91583*10^-5)*RH^3)+((1.42721*10^-6)*T^3*RH)+((1.97483*10^-7)*T*RH^3)-((2.18429*10^-8)*T^3*RH^2)6)*T^3*RH)+((1.97483*10^-7)*T*RH^3)-((2.18429*10^-8)*T^3*RH^2)+((8.43296*10^-10)*T^2*RH^3)-((4.81975*10^-11)*T^3*RH^3) +((8.43296*10^-10)*T^2*RH^3)-((4.81975*10^-11)*T^3*RH^3)