GEOG 140
Intro Physical Geography
Lecture Notes
Atmosphere and Surface Energy Balances
Energy Essentials
Energy Pathways and Principles
-transmission
-passage of shortwave and longwave energy through the
atmosphere and water
-scattering (three types)
- rayleigh-scattering by nitrogen and oxygen molecules causes
blue skies
- mie-dust, smoke, pollen, water vapor- causes red sunsets
- nonselective-water droplets –white clouds
- scattering results in diffuse radiation (versus direct radiation)
-refraction
-bending of light rays due to change in density of media (air to
water, space to atmosphere) which changes the speed of
insolation
-rainbow, prism. mirage, additional daylight
-albedo and reflection
-reflection – energy “bounces back into space without being
absorbed
-albedo – the reflective quality (brightness) of a surface expressed
as a percent
- absorption (heating) and reflection (no heating)
- reflection - color, composition, and slope
- reflection + absorption = 100%
-Earth albedo 31% average over the year
-21% -clouds
-7% -reflected and scattered by atmosphere
-3% -surface (combined land and water)
-clouds, aerosols, and the atmosphere’s albedo
-cloud-albedo forcing
-increase in albedo caused by clouds
-cloud-greenhouse forcing
-increase in greenhouse warming caused by clouds
-absorption
-energy that is not part of the 31% direct and diffuse energy
reflected by the Earth/Atmosphere is absorbed (69%)
-45%-land and water surfaces
-24%-atmosheric gases, dust, clouds and ozone
-conduction, convection, and advection (heat transfer in a system)
-conduction
-molecule to molecule transfer of heat energy
-convection
-mixing of liquids and gases through strong vertical motion
-advection
-mixing of liquids and gases through horizontal motion
Energy Balance in the Troposphere
-greenhouse effect and atmospheric warming
-blanket effect of the atmosphere-the greenhouse effect
-shortwave energy penetrates window of greenhouse (or car)
-longwave energy resulting from absorbed shortwave energy
blocked by glass
-heating occurs
-some longwave energy from the Earth’s surface is absorbed by
various gases and reradiated back towards Earth
-carbon dioxide, water vapor, nitrous oxide, methane,
CFC’s
-delays loss of longwave energy to space-warms Earth
-selective absorption
-clouds and the Earth’s greenhouse
-cloud type, height, thickness and percent cover important to
heating of the lower atmosphere
-high altitude –ice crystals-50%
-low altitude- thick-90%
-Earth-Atmosphere radiation balance
-surplus in earth energy budget
-deficit in atmosphere
-together-balanced but still regional and seasonal differences
between tropics and he poles
-incoming solar (shortwave ) energy
-Earth albedo 31%
-surface 3%
-clouds 21%
-diffuse reflection and scattering (atmosphere) 7%
-atmospheric absorption 24% (heating-21%)
-atmospheric gases and dust 18%
-clouds 3%
-ozone 3% (no heating)
-Earth absorption 45%
-direct sunlight 25%
-diffuse sunlight 20%
-energy balance maintained by energy transfers from the surface
-non-radiative
-conduction
-convection
-latent heat of evaporation
-radiative
-infrared radiation between surface, atmosphere,
and space
-longwave thermal energy (to space ) 69%
-atmospheric heating 21%
-surface heating 45%
-radiated by ozone 3%
Energy Balance at Earth’s Surface
-simplified surface energy balance
insolation –reflection+ incoming longwave-outgoing longwave
=net radiation
-net radiation
-similar amounts of shortwave and longwave energy reach Earth’s
surface
-majority of outgoing radiation is longwave
-difference between the two=net radiation
-about one quarter of the radiation originally arriving at the
top of the atmosphere
-greatest at low latitudes
-smallest (or negative) at high latitudes (over ice)
-differences between land (lower) and ocean (higher)
-most important factor affecting Earth’s climates
-vaporization of water-vegetation distribution
-vital in shaping the heat energy balance of the Earth
-energy expended from non-vegetated surfaces by three pathways
-latent heat-evaporation /precipitation
-sensible heat flow (two-way)
-convection (vertical heat transfer process)
-ground surface colder than the overlying air
-downward radiative transfer
-ground heat flow(conduction)
-smallest of the components
-global distribution
-latent heat loss (70% of net radiation)
-over land
-greatest either side on the equator
-decline in subtropics
-increase in mid latitudes
-decrease towards the poles
-over water –greatest in the subtropics
-less cloud cover
sensible heat loss (30% of net radiation)
-over land
-greatest in the subtropics
-decreasing at the equator and the poles
-over oceans
-increase with latitude
Examples
-El Mirage, CA
-Pitt Meadow BC
Closing thoughts
atmosphere heated by longwave radiation absorbed mainly in the lower portions
-atmosphere heated from below not by direct rays from the sun
atmosphere emits longwave radiation
counter-radiation reaches earth
temp would be –4F rather than 59F