Chapter 4: Insolation and Temperature

Chapter 4: Insolation and Temperature – p. 1 of 14

Chapter 4: Insolation and Temperature

1. The Impact of Temperature on the Landscape

1. all organisms have certain temperature tolerances
2. most inorganic components of landscape are affected by long-run temperature conditions

1. temperature is a basic factor in soil development
2. repeated temperature fluctuations are prominent cause in breakdown of exposed bedrock

1. Energy, Heat and Temperature

1. Energy

1. energy: ability to do work
2. anything that changes the state or condition of matter
3. kinetic energy: the energy of movement
4. constant movement of molecules in all substances
5. associated with how hot or cold something is
6. increased kinetic energy results in a substance warming up

1. Temperature and Heat

1. temperature

1. description of the average kinetic energy of the molecules in a substance
2. degree of hotness or coldness of a substance
3. more vigorous the jiggling of the molecules, the higher the temperature of a substance

1. heat/thermal energy

1. energy that transfers from one object or substance to another because of a difference in temperature
2. energy transferred from object with higher temperature to object with lower temperature

1. Measuring Temperature

1. Fahrenheit Scale

a.sea level freezing point of water = 32oF

b.sea level boiling point of water = 212oF

1. Celsius Scale

1. component of International System of measurement (SI)
2. sea level freezing point of water = 0oC
3. sea level boiling point of water = 100oC
4. conversions:

1)oF = (oC x 1.8) + 32o

2)oC = (oF – 32o)/1.8

1. Kelvin Scale

1. measures absolute temperature

1)scale begins at absolute zero, the lowest possible temperature

2)absolute zero: temperature at which molecules have their minimum kinetic energy

3)100o range between the freezing and boiling points of water

4)there are no negative values

1. conversions

1)oC = oK – 273o

2)oK = oC + 273o

1. Solar Energy

1. Intro

1. the sun supplies essentially all the energy that drives most of the atmospheric processes on Earth
2. unequal heating of the Earth by the sun puts the atmosphere in motion and is responsible for the most fundamental patterns of weather and climate
3. the sun produces energy by nuclear fusion

1. Electromagnetic Radiation

1.form of sun’s radiant energy

2.does not require a medium for transmission

3.speed of light = 186,000 mi/sec; energy travel time sun to Earth = 8 mins

4.wavelength: distance from the crest of one wave to the crest of the next

5.electromagnetic spectrum: electromagnetic radiation of all wavelengths (Fig 4-5)

6.3 areas of spectrum of particular interest to physical geographer

1. visible light

1)fairly narrow band with wavelength: 0.4 – 0.7 µm (micrometers)

2)comprises 47% of energy from sun to Earth (Fig 4-5)

1. ultraviolet waves

1)wavelength: 0.01 – 0.4 µm

2)just shorter than human eye can sense

3)comprises 8% of total energy coming from the sun to Earth

4)much absorbed by ozone layer of the atmosphere

1. infrared waves

1)wavelength: 0.7 – 1,000 µm (1mm)

2)just longer than human eye can sense

3)range:

a)from short/near infrared

b)to thermal infrared

4)comprises 45% of total energy from sun to Earth

7.shortwave radiation

1. solar radiation is almost completely in the form of visible light, ultraviolet and short infrared radiation
2. virtuallyall solar radiation is shortwave radiation

8.longwave radiation

1. all terrestrial radiation (radiation emitted by earth) is longwave radiation(4µ is wavelength boundary between shortwave and longwave radiation)
2. entirely in the thermal infrared portion of spectrum

1. Insolation
2. incoming solar radiation
3. solar constant: the fairly constant amount of solar insolation (averaged over a year) received at the top of the atmosphere

1. 1372 watts per square meter (W/m2) = 1 calorie/cm2

1)1 watt = 1 joule/sec

2)1 joule = 0.239 calories

3)calorie: amount of heat required to raise temperature of 1 gram of water (at 15oC) by 1oC

1. Solar Power
2. solar energy

1. during a 24 hour day, an average of 164 watts of solar energy strikes each square meter of Earth’s surface – enough energy to meet the electrical generation needs of the entire planet
2. overall solar power provides only 0.1% of the global energy
3. photovoltaic cells

1. advantages:

1. low capital cost
2. requires little maintenance
3. no energy source other than sun is required to create electricity
4. potential for decentralized energy electrical generation

1. disadvantages:

1. only 15-12% efficient: capture a limited portion of the solar spectrum; a sizable amount of captured photon energy is lost as heat
2. solar dependent: limited electrical generation capacity when cloudy/hazy, none when it’s dark

1. Basic Heating and Cooling Processes in the Atmosphere

1. Radiation

1. radiation: process by which electromagnetic radiation is emitted from an object
2. hotter objects, such as our sun, emit more energy at shorter wavelengths
3. cooler bodies, such as Earth, radiate mostly long waves
4. black body: a body that emits the maximum amount of radiation possible at every wavelength

1. perfect radiators; radiate with almost 100% efficiency
2. the sun and Earth function essentially as black bodies
3. the atmosphere is not as efficient a radiator as the sun or Earth’s surface

1. Absorption

1. absorption: the ability of an object to assimilate energy from electromagnetic waves that strike it
2. the temperature of on object increases when energy is absorbed
3. good radiators tend to be good absorbers; poor radiators tend to be poor absorbers
4. good absorbers: sun, Earth, mineral matter (rock, soil); darker colors; water vapor and CO2
5. poor absorbers: snow, ice, lighter colors, nitrogen

1. Reflection

1. reflection: ability of an object to repel electromagnetic waves without altering either the object or the waves
2. good absorbers are poor reflectors, and vice versa (explains unmelted snow on a sunny day)

1. Scattering

1. scattering: deflection of electromagnetic waves that involves a change in direction but no change in wavelength
2. amount of scattering depends on wavelength as well as size, shape, and composition of the molecule or particulate
3. shorter waves are more readily scattered than longer ones by atmospheric gases

1. Rayleigh scattering: scattering of shortest wavelengths of visible light, violet and blue
2. violets and blues more likely to be scattered in the visible part of spectrumblue skies
3. more atmosphere to traverse at sunrise/sunset  orange/red skies
4. Mie scattering: scattering of almost all wavelengths of visible light by larger particles that results in sky appearing gray

1. Transmission

1. transmission: process whereby electromagnetic waves pass completely through a medium
2. transmission variability

1. poor transmitter: Earth materials
2. good transmitter: water

1. greenhouse effect

1. transmission generally depends on wavelength of radiation
2. glass

1)readily transmits shortwave radiation but not longwave radiation

2)that’s why heat builds up in a closed automobile

1. greenhouse effect: the trapping of heat in the lower troposphere because of differential transmissivity for short and long waves

1.greenhouse gases readily transmit incoming shortwave radiation from the sun but do not easily transmit outgoing longwave terrestrial radiation

2.most important greenhouse gases: water vapor and CO2

3.terrestrial radiation is absorbed by greenhouse gases and reradiated back toward the surface, delaying the energy loss to space

4.one of the most important heating processes in the troposphere

a.w/o greenhouse effect, Earth’s average temperature would be 5oF(rather than current average = 59oF)

b.global warming: increase in CO2 atmosphere resulting in an increase in the average global temperature

1. Conduction

1. conduction: movement of heat energy from one molecule to another without changes in the relative position of the molecules

1. enables heat to be transferred from one part of a stationary body to another or from one object to a second object when the 2 are in contact
2. results from molecular collision
3. when 2 molecules of unequal temperature are in contact with one another, heat passes from the warmer to the cooler until they attain the same temperature

1. variation in ability to conduct

1. good conductors: metals
2. poor conductors: earth materials, air

2)only air layer touching the ground is heated much

3)dry air is a lessefficient conductor than moist air

1. Convection

1. convection: heat is transferred from one point to another by the predominantly vertical circulation of a fluid(including air)

1. heated molecules move from one place to another
2. convectioncauses warm air to rise
3. convection cell: updraft of warm air and a downdraft of air after it has cooled

1. Advection: when the dominant direction of heat transfer in a moving fluid is horizontal
2. Adiabatic Cooling and Warming

1. whenever air ascends or descends its temperature changes due to a variation in pressure
2. Expansion: Adiabatic Cooling: cooling by expansion in rising air

1. increased altitude  decreased air pressure  expansion  reduced collisions  temperature drop
2. adiabatic: without the gain or loss of heat
3. in the atmosphere any time air rises it cools adiabatically

1. Compression: Adiabatic Warming: warming by compression in descending air

1. decreased altitude  increased air pressure  compression  increased collisions  temperature rise
2. in the atmosphere any time air descends it warms adiabatically
3. adiabatic cooling of rising air: one of the most important processes in cloud development and precipitation

1. Latent Heat

1. latent heat: energy stored or released when a substance changes state
2. evaporation: liquid water is converted to gaseous water vapor

1. energy is stored
2. cooling process

1. condensation: gaseous water vapor condenses to liquid water

1. energy is released
2. warming process

1. The Heating of the Atmosphere

1. there is an annual balance between incoming and outgoing radiation

1. incoming shortwave radiation and outgoing longwave radiation are in a long-term balance (total amount of insolation received by Earth and its atmosphere equals the total amount of terrestrial radiation returned to space)
2. global energy budget: annual balance between incoming and outgoing radiation for the entire globe

1. Earth’s energy budget (using 100 units to represent total insolation at top of atmosphere) (Fig 4-17)

1. incoming shortwave solar radiation = 100

1. albedo= 31

1)albedo: reflectivity of an object

2)Earth’s albedo:the fraction of total solar radiation that is reflected back, unchanged, into space

3)almost 1/3 of the incoming solar radiation is reflected back into space without being absorbed or altered

1. absorbed by Earth’s atmosphere = 24

1)absorbed by the ozone layer = 3

2)absorbed by the rest of the atmosphere = 21

3)this energy heats the Earth’s atmosphere directly

1. absorbed by Earth’s surface = 45

1)almost half the incoming solar radiation passes through the Earth’s atmosphere and is absorbed by Earth’s surface

2)this energy heats the Earth’s surface

1. outgoing radiation lost to space = 100

1. albedo = 31
2. longwave radiation emitted to space by the atmosphere = 61

1)incoming radiation that heats atmosphere directly = 24

a)radiation absorbed by ozone in the atmosphere and reemitted as longwave radiation= 3

b)radiation absorbed directly by atmosphere and reemitted as longwave radiation= 21

2)energy transferred from Earth’s surface to the atmosphere by conduction and convection = 4

3)heat transferred from Earth’s surface to the atmosphere through latent heat in water vapor = 19

4)net atmospheric gain of energy through absorption of terrestrial radiation (longwave) by greenhouse gases = 14

a)radiation from Earth’s surface to the atmosphere = 110

b)radiation from the atmosphere to Earth’s surface = 96

1. longwave radiation emitted from Earth’s surface transmitted directly through atmosphere (atmospheric window) without being absorbed = 8

1. atmosphere heated mostly from below rather than from above

1. sun is original source of energy
2. atmosphere mostly heated from longwave radiation emitted from surface of Earth
3.  troposphere in which cold air overlies warm air constant convective activity and vertical mixing

1. Focus: Monitoring Earth’s Radiation Budget
2. AVHRR (Advanced Very High Resolution Radiometer) sensors aboard permanent orbiting satellites monitor Earth’s radiation budget
3. available solar energy (Fig 4-C)

1. total incoming shortwave radiation measured at top of the atmosphere measured in watts per square meter (W/m2)
2. influenced only by angle of sun and number of hours of daylight
3. highestaverage daily insolation in June occurs over the Arctic: low solar angle of incidence but 24 hours of daylight
4. absorbed solar energy (Fig 4-D)

1. total amount of shortwave energy absorbed by the atmosphere and surface
2. difference between the total shortwave energy at the top of the atmosphere and the total shortwave radiation reflected back to space
3. high absorption in subtropical latitudes
4. outgoing longwave radiation (Fig 4-E)

1. nighttime emission of longwave radiation
2. very high in subtropical and Midlatitude desert regions in southwestern US, northern Africa and east-central Eurasia: because of clear nighttime skies and low water vapor content of air

1. Variations in Heating by Latitude and Season

1. Intro

1. latitudinal and vertical imbalances in the energy budget are among fundamental causes of weather and climate variations
2. radiation differences  temperature differences  air density differences  pressure differences  wind differences  moisture differences
3. world weather and climate differences caused by unequal heating of Earth and its atmosphere that is the result of latitudinal and seasonal variation in how much energy is received by Earth

1. Latitudinal and Seasonal Differences

1. Angle of Incidence

1. angle of incidence: angle at which rays from the sun strike the Earth
2. primary determinant of intensity of solar radiation at any spot on Earth
3. the closer to 90o the angle of incidence, the smaller the surface area heated by a given amount of insolation and the more effective the heating
4. insolation received by high latitude regions is much less intense than that received by tropical areas during the year as a whole

1. Atmospheric Obstruction

1. sunlight received at Earth’s surface is half as strong as at the top of Earth’s atmosphere on average
2. factors influencing:

1)path length (amount of atmosphere radiation has to pass through – determined by angle of incidence)

2)transparency of the atmosphere

1. depletes solar radiation more in high latitudes than low latitudes

1. Day Length

1. longer days allow more insolation to be received and thus more heat absorbed
2. in mid and high latitudes there are pronounced seasonal differences

1. Latitudinal Radiation Balance (Figs 4-21 and 4-22)

1.energy surplus in low latitudes, from 28oN to 33oS, where there is consistently high angle of incidence

2.energy deficit in latitudes poleward of 28oN and 33oS is associated with low angles of incidence

3.world radiation variations largely latitudinal with interruptions based on presence or absence of frequent cloud cover

4.incoming and outgoing radiation for Earth-atmosphere complex as a whole balances

5.net radiation balance for Earth = 0

1. Land and Water Contrasts
2. Heating

1.a land surface heats up more rapidly and reaches a higher temperature than a comparable water surface subject to the same insolation

2.reasons

1. Specific Heat

1)specific heat of water is 5 times as great as that of land

a)specific heat: amount of energy required to raise temperature of 1 gram of a substance 1oC

b)water can absorb more solar energy without its temperature increasing

1. Transmission

1)water is a better transmitterof radiation than land

a)sun rays penetrate water more deeply

b)heat diffused over a larger volume of water

1. Mobility

1)in water turbulent mixing and ocean currents (convection) disperse heat more broadly and deeply

2)heat in land is dispersed only by conduction, and land is a very poor conductor

1. Evaporative Cooling

1)evaporation much more prevalent over water

2)the requisite latent heat for evaporation is drawn from the water, dropping the temperature

1. Cooling

1. a land surface cools more rapidly and to a lower temperature than a water surface when both are overlain by air at the same temperature
2. Implications

1. both the hottest and the coldest places on Earth are found in the interiors of continents
2. a continental climate experiences greater seasonal extremes of temperatures than a maritime climate

1)summers are hotter; winters are colder

2)compare San Diego and Dallas, Fig 4-24

a)same latitude

b)annual average temperatures are almost the same

c)monthly average temperatures vary significantly

1. oceans act as great reservoirs of heat, moderating temperature extremes
2. greater latitudinal temperature ranges in the Northern Hemisphere than in the Southern Hemisphere because more land surface in the Northern Hemisphere (39% v. 19%)

1. Mechanisms of Heat Transfer

1. Intro

1. atmospheric and ocean circulation  persistent shifting of warmth from the low latitudes toward the high latitudes

1. moderates the buildup of heat in equatorial regions
2. moderates the loss of heat in the polar regions

1. Atmospheric Circulation

1. 75-80% of all horizontal heat transfer is accomplished by atmospheric circulation
2. discussed Chapter 5

1. Oceanic Circulation

1. Intro

1. currents: oceanic water movements
2. relationship between general circulation patterns of the atmosphere and oceans

1)air blowing over the surface of the water, wind, is the principal force driving the major surface ocean currents

2)ocean currents reflect average wind conditions over a period of several years

1. The Basic Pattern (Fig 4-25)

1. subtropical gyres: enormous, elliptical ocean current systems centered on the oceanic subtropical high-pressure cells

1)centered in each ocean ~ 30oN and S, except Indian Ocean (where it’s closer to equator)

2)flows clockwise in northern hemisphere; counterclockwise in southern hemisphere

1. equatorial current

1)on equatorward side of each subtropical gyre at ~ 5o – 10o N and S

2)flows westward

3)equatorial countercurrent

a)in between the equatorial currents, along the equator

b)flows eastward

1. general circulation:

1)equatorial current flows poleward along western margins of oceanbasins

2)currents flow eastward at the poleward margins of the ocean basins

3)currents then flow equatorward along eastern margins of the ocean basins

1. forces driving currents:

1)impelled by wind

2)influenced by Coriolis effect, deflective force of Earth’s rotation

a)to right in northern hemisphere

b)to left in southern hemisphere

1. Northern and Southern Variations

1. little poleward flow in northern hemisphere makes it to the Arctic Ocean due to proximity of continents
2. in North Atlantic a portion flows northward between Greenland and Europe
3. west wind drift

1)one continuous flow in the southern hemisphere because of lack of land masses

2)westward flow around globe at ~ 60oS

1. Current Temperatures

1. temperatures of the currents impact latitudinal heat transfer
2. current temperatures:

1)low latitude currents = warm water