Surface air temperature

Review of last lectureReview of last lecture• Earth’s energy balance at the top of the atmosphere Earth’s energy balance at the top of the atmosphere

and at the surface. What percentage of solar energy is and at the surface. What percentage of solar energy is absorbed by the surface?absorbed by the surface?

• Atmospheric influences on radiation (3 ways)Atmospheric influences on radiation (3 ways)

• The three types of atmospheric scattering. What causes The three types of atmospheric scattering. What causes the blue sky? Why causes the reddish-orange sunsets? the blue sky? Why causes the reddish-orange sunsets?

• What cause the greenhouse effect? What are the major What cause the greenhouse effect? What are the major greenhouse gases? Why is methane important? greenhouse gases? Why is methane important?

• Sensible heat flux (dry flux from warm to cold regions) Sensible heat flux (dry flux from warm to cold regions) and latent heat flux (wet flux from wet to dry regions)and latent heat flux (wet flux from wet to dry regions)

Temperature BasicsTemperature Basics • TemperatureTemperature – measure of average kinetic energy – measure of average kinetic energy

(motion) of individual molecules in matter(motion) of individual molecules in matter

• IsothermsIsotherms – maps, connect lines of equal temperature – maps, connect lines of equal temperature

Different temperature scales Different temperature scales (units)(units)

• All scales are relativeAll scales are relative

• degrees F =degrees F = 99⁄⁄55 degrees C + 32degrees C + 32

• degrees K = degrees C + 273.15degrees K = degrees C + 273.15

Measurement of TemperatureMeasurement of TemperatureMeasurement of Temperature

• Thermometers are used to measure temperature with either mercury or alcohol.

• A maximum thermometer is used to record daily temperature maximums while a minimum thermometer records minimums.

Instrument Shelters• Weather instruments require

shelters that protect them from solar radiation.

• They are painted white to create a high albedo.

• Must be 5 ft from the ground /surface to reduce laminar layer bias.

Air Temperature and the Human Air Temperature and the Human BodyBody

• Human comfort not only affected by temperatureHuman comfort not only affected by temperature• Two important considerations Two important considerations wind and humidity wind and humidity• Wind Chill IndexWind Chill Index

– relates temperature and wind speedrelates temperature and wind speed• Heat IndexHeat Index

– relates temperature and humidityrelates temperature and humidityWind Chill Index

Heat Index

Video: Video: The 1995 The 1995 Chicago heat Chicago heat wavewave

Seasonal variation of surface air Seasonal variation of surface air temperaturetemperature

Principal Controls on Temperature   Principal Controls on Temperature   

1.1. Latitudinal variations in net radiationLatitudinal variations in net radiation

2.2. Land-Water ContrastsLand-Water Contrasts

3.3. Atmospheric CirculationAtmospheric Circulation

4.4. Ocean CurrentsOcean Currents

5.5. AltitudeAltitude

6.6. Local EffectsLocal Effects

• tropic-to-tropic – energy surplus• poles – energy deficits• ~ 38o N/S – balance

• imbalance of net radiation at surface Equator/Tropics vs. high latitudes

• drives global circulation• agents: wind, ocean currents, weather systems

Controls on temperature 1. Latitudinal Variations in Net Radiation

Daily/Seasonal Radiation Patterns

• insolation peak vs. temperatureinsolation peak vs. temperature• daily lagdaily lag• seasonal lagseasonal lag• Lag is function of type of surface, wetness, wind, etcLag is function of type of surface, wetness, wind, etc

• T decreases poleward• larger T gradient in winter• isotherms shift seasonally• T over land > water in summer• NH steeper T gradient

Seasonal Seasonal Temp Temp DistributioDistributio

nsns

Controls on temperature 2. Land-water contrasts

• Surface influences heating • Heat Capacity – water > land… (water takes longer heat/cool)• Mixing – fluids can be physically mixed• Transparency – greater penetration (distributed over greater volume)• Evaporation – consumes large amount of energy – big over water

Temperature Ranges (Summer minus Winter)Large over land, small over ocean

• large scale circulation patterns resulted from pressure differences (gradients)• generates winds move warm/cold air around affects temperature• influences cloud cover

Controls on temperature 3. Atmospheric circulation

Controls on temperature 4. Ocean currents

Infrared Satellite image of the Gulf Stream

Red/orange = 25-29oC

Yellow/green = 17-24oC

Blue = 10-16oC

Purple = 2-9oC

• Temperature decreases with increasing altitude ground acts as heat source

Controls on temperature Controls on temperature 5. Altitude5. Altitude

• slope orientation: North v. South-facing slopes temperature/moisture regimes vegetation

Controls on temperature Controls on temperature 6. Local effects6. Local effects

forested v. open fields

SummarySummary

• Temperature, 3 unitsTemperature, 3 units

• 6 factors controlling temperature6 factors controlling temperature