Chapter 3
Atmospheric Energy and
Global Temperatures
Energy Pathways & Principles
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Some insolation (incoming solar radiation) is
absorbed by earth, the rest is reflected
Absorbed energy is reradiated as longwave
energy out from Earth. Longwave radiation
absorbed by greenhouse gasses keeps the
Earth warm. Without greenhouse gasses, Earth
would be much cooler (15 C or 27 F)!
Going back in time, periods of low atmospheric
greenhouse gas concentrations tended to be
cooler, and times of high greenhouse gas
concentrations were warmer.
Insolation
Figure 3.2
Energy Pathways
Figure 3.1
Energy Pathways
Radiation balance is composed of inputs, transfers, &
outputs.
Transfers include convection, conduction, and latent heat of
vaporization (explained later).
Net radiation: the balance between all incoming radiation
(positive quantity) and all outgoing radiation (negative
quantity) carried by both shortwave radiation and longwave
radiation
Transmission: the passage of shortwave and longwave
energy through space, the atmosphere, or water
Scattering: the deflection and redirection of insolation by
gasses, dust, water vapor, and ice
Energy Pathways (con’t.)
 Albedo: the % reflectivity of a substance
Typical albedos of some surfaces (%)
clouds:
15-90
concrete:
17-27
asphalt:
5-15
green crops: 5-25
wet soil:
15-30
fresh snow: 80-90
water:
5-60 (5-10% when solar altitude >30°)
Refraction
Figure 3.4
Albedo and Reflection
Figure 3.5
Clouds and Albedo
Figure 3.6
Heat Transfer
Figure 3.7
The “Greenhouse Effect” & Atmospheric
Warming
The lower atmosphere absorbs heat energy
primarily in the form of terrestrial infrared radiation
(IR).
A real greenhouse traps heat inside by utilizing
glass or plastic walls and the roof.
The atmosphere delays transfer of heat from Earth
into space by absorbing IR radiation, and then
reradiating some of it back to Earth.
Clouds and Earth’s “Greenhouse”
Figure 3.8
Outgoing Shortwave Energy (reflected)
Figure 3.9
Outgoing Longwave Energy
Figure 3.9
Earth–Atmosphere Radiation Budget
Figure 3.10
Diurnal (24 hr.) Radiation and Temperature Change
Daily temperature change is a function of the
balance between incoming shortwave and
outgoing longwave radiation.
When incoming energy exceeds outgoing energy,
temperature rises. Thus, daily highs are
generally reached sometime after solar noon.
When outgoing energy exceeds incoming energy,
temperature drops. Thus, the lowest
temperatures are usually recorded just after
sunrise.
Radiation Balance & Seasonal Temperature Change
In mid latitudes, warmest time of yr lags after the summer
solstice, just as daily highs are after solar noon. (July in OR)
In mid latitudes, coldest time of yr lags after the winter solstice,
just as daily lows are after sunrise. (Jan in OR)
In most tropical areas, the warmest month is determined by the
interaction between insolation and cloud cover. In areas of
seasonally abundant precipitation, the warmest month can be
just before the big rains begin. (next slide) In drier tropical
areas, the warmest month may lag the time of solar maximum
by a month or two.
Everything else equal, coastal areas have longer lags between
solar maxima and temperature maxima than interior areas. (San
Francisco)
Mexico City and Bangalore
http://media.diercke.net/omeda/800/112397E_Klimadia_Mexico_City.jpg
http://www.bangalore.climatemps.com/
Simplified Surface Energy Balance:
NET Radiation = + SW (insolation) – SW (reflection) + LW (IR) – LW(IR)
Figure 3.13