ATMOSPHERIC ENERGY and GLOBAL TEMPERATURES Physical Geography (Geog. 300) Prof. Hugh Howard American River College
RADIATION FROM the SUN
SOLAR RADIATION Primarily shortwave (UV-SIR) Insolation Incoming Solar Radiation Controlled by circle of illumination, length of day, latitude, etc. Can be transmitted through Atmosphere Water
Sun Emits Primarily Shorter Wavelengths
SCATTERING and REFRACTION Scattering (Diffuse Radiation) Reflection of radiation in all directions Caused by interference with atmospheric molecules or Earth s surface Refraction Bending of radiation, altering its wavelength Like bending light through a prism
Scattering of Sunlight (diffuse radiation)
Refraction of Sunlight
SOLAR CONSTANT The top of the atmosphere receives 1,400 watts/m 2 of solar radiation Radiation is unevenly distributed Insolation at Ground Level
SOLAR CONSTANT What happens to this radiation? Reflection: Albedo Albedo is the proportion of reflected radiation Higher for light objects, lower for darker objects Absorption Assimilation and conversion of radiation Raises the temperature of the absorbing body
Reflection and Absorption
Reflection: Albedo
The ENERGY BALANCE A conceptual model that describes what happens to solar radiation as it enters the Earth system Insolation Incoming solar radiation Net radiation Insolation minus outgoing radiation
The Energy Balance
REFLECTED RADIATION Reflected by clouds: 21% Scattered by atmosphere: 7% Reflected by ground: 3% Total Albedo: 31% This shortwave radiation leaves Earth, and is not converted to longwave (heat) radiation
ABSORBED RADIATION Absorbed by ground: 45% 25% direct, 20% diffuse Absorbed by gases and dust: 18% Absorbed by clouds: 3% Absorbed by stratospheric ozone: 3% Total Absorbed Radiation: 69% This shortwave radiation is converted to longwave (heat), and leaves Earth
HEAT and TEMPERATURE
Transfer of energy HEAT From warmer objects to cooler objects Different types Sensible Heat Heat that we can sense Measured with a thermometer Latent Heat Heat exchanged with a phase change of water
Radiation HEAT TRANSMISSION EMR given off by hot objects Convection Vertical transfer of heat through the movement of air or water; mixing Conduction Transfer of heat from molecule to molecule; contact
Transmission of Heat
TEMPERATURE A measure of the kinetic energy of molecules (average) How fast they vibrate Measure of sensible heat
TEMPERATURE SCALES Fahrenheit U.S. is the only major country to use it Water freezes at 32 and boils at 212 (at sea level; lower w/ increased elevation) Celsius Metric Water freezes at 0 and boils at 100
Kelvin TEMPERATURE SCALES International System of Units (SI) The absolute scale Water freezes at 273 and boils at 373 Absolute zero (0 K) Temperature at which all molecular movement stops (no sensible heat)
Temperature Scales
FACTORS that CONROL AIR TEMPERATURE
SEASON and TIME of DAY Season Surplus of insolation during summer Deficit during winter Time of day Surplus of insolation during the day Deficit at night
LATITUDE Equatorial regions receive the most insolation, year round Polar regions receive large amounts but only during summer Surplus Between 40 N&S Deficit Above 40 N&S
Insolation and Latitude
Temperature and Latitude
ELEVATION Higher elevations are generally cooler The Environmental Lapse Rate (ELR) Describes how temperatures change in relation to altitude in stationary air The average ELR in the troposphere 3.5 F/1,000 ft (6.4 C/1,000m) (the Normal Lapse Rate)
CLOUD COVER Approximately 50-75% of Earth is covered with clouds at any given time Can lower temperatures by reflecting incoming shortwave radiation Can raise temperatures by trapping longwave radiation from Earth (greenhouse effect)
LAND-WATER CONTRASTS Maritime Effect Land near large bodies of water lack extremes temperature cycles; temperatures are more consistent Continental Effect Land isolated from large bodies of water has extreme hot and cold temperature cycles
Land-Water Temperature Contrasts
Continental and Maritime Effects
GROUND COVER Wetter ground = cooler Evaporation removes latent heat Lighter ground = cooler Light surfaces absorb less radiation Urban hotter than rural Urban Heat Island Heat generation, limited vegetation, etc. Urban Dust Dome
The Urban Heat Island
ADVECTION The horizontal transfer of heat through the movement of air or water Areas can be warmed or cooled as advectional winds come and go
DAILY and ANNUAL TEMPERATURE CYCLES
DAILY TEMPERATURE CYCLE Pattern of temperature change during a 24 hour period The Diurnal Cycle Maximum temperatures Usually occur in mid-afternoon Surface takes time to respond to maximum insolation (at solar noon)
DAILY TEMPERATURE CYCLE Temperatures drop after mid-afternoon Less insolation Natural air conditioning High ground temperatures cause warm air to rise; the warm air is replaced by cooler, descending air Minimum temperatures Occur shortly after sunrise
Daily Temperature Cycle
ANNUAL TEMPERATURE CYCLE Pattern of temperature change during a year Maximum temperatures Usually occur about a month after maximum insolation (summer solstice) Minimum temperatures Usually occur shortly after minimum insolation (winter solstice)
ANNUAL TEMPERATURE CYCLE Seasonal temperature extremes are greater toward the poles Poles influenced more by Earth s tilted axis Poles tilt away from the sun dramatically during winter, and toward during summer Six months of light and six of dark at the poles Equatorial temperatures are fairly constant
Annual Temperature Cycles
LAPSE RATES and TEMPERATURE INVERSIONS
LAPSE RATES The Environmental Lapse Rate (ELR) Describes how temperatures change in relation to altitude in stationary air The average ELR in the troposphere 3.5 F/1,000 ft (6.4 C/1,000m) Adiabatic Lapse Rate Will be covered later
Environmental Lapse Rate (ELR)
TEMPERATURE INVERSION An inverted, or backward lapse rate Temperatures increase with increasing altitude
TEMPERATURE INVERSION In the troposphere, inversions can result from the following Cooling of Earth s surface at night, creating a layer of cool air that rests below relatively warmer air Cold air rushing down into valleys from upslope
FOG Inversions can cause low-lying fog Air that comes into contact with cold ground can be cooled to the point of condensation Radiation Fog, or Tule Fog Common in the Central Valley
Smoke + Fog SMOG Under inversion conditions, pollutants get trapped in the low-lying layer of cool air
The GREENHOUSE EFFECT
GREENHOUSE EFFECT Natural process that raises average temperatures on Earth by 63 F Makes possible life as we know it Works on the same principles that Make greenhouses warm enough to grow certain plants Make the interior of a car far hotter than the outside temperature on a sunny day
GREENHOUSE EFFECT As Earth absorbs shortwave radiation from the sun, Earth gets heated This heat gets radiated from Earth in the form of longwave radiation (heat) Greenhouse gases in the atmosphere absorb the longwave radiation and send it back to Earth Counter Radiation
The Greenhouse Effect Counter Radiation
ENHANCED GREENHOUSE EFFECT Is not natural Caused by the addition of large volumes of CO 2 and other greenhouse gases to the atmosphere Burning of fossil fuels, removal of forests Causing Climate Change Increased temperatures, flooding (melting of icecaps), and extreme weather
CLIMATE CHANGE CONSENSUS 97% of climate scientists agree that Climate change happening Is very likely the result of human activities Increased addition of greenhouse gases to the atmosphere Most leading scientific organizations have issued statements supporting this position
Climate Change Consensus
Climate Change Consensus
Climate Change Consensus
Climate Change Consensus
Climate Change Consensus
WORLD PATTERNS of AIR TEMPERATURE
TEMPERATURE MAPS Represent temperatures and temperature differences Symbolized with Isotherms Lines of constant temperature Any point along a given isotherm represents the same temperature Data derived from weather stations and by interpolation
TEMPERATURE MAPS Temperature Gradients Differences in temperatures from one place to the next Identified by spacing of isotherms Isotherms closer together Means a dramatic change Isotherms further apart Means a gradual change
Temperature Map: Isotherms
AVERAGE TEMPERATURES Warmer toward the equator, colder toward the poles Insolation decreases with distance from equator Coldest/warmest on land, not water Continental Effect Maritime Effect
Average January Temperatures
AVERAGE TEMPERATURES Equatorial temperatures are more constant than in higher latitudes Insolation is more consistent Higher elevations are colder than lower elevations Andes, Himalayas, etc. Environmental Lapse Rate
Annual Average Temperature July Temperatures Cycles
Average January Temperatures
Average July Temperatures
TEMPERATURE RANGES Differences between average January and July temperatures Greatest in northern continental interiors Increased seasonality of polar regions The Continental Effect Southern hemisphere is more stable The Maritime Effect
Annual Temperature Ranges
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ATMOSPHERIC ENERGY and GLOBAL TEMPERATURES Physical Geography (Geog. 300) Prof. Hugh Howard American River College