The Radiation and Surface Energy
Budgets
C. David Whiteman
Atmos 3200/Geog 3280
Mountain Weather and Climate
Snowpatch Spire, Bugaboos © CD Whiteman
Definitions
•
The surface radiation budget: The radiation budget at
the earth’s surface, considered in terms of the fluxes
through a plane at the earth-atmosphere interface.
The radiation budget includes both solar (shortwave)
and terrestrial (longwave) radiation fluxes.
•
The surface energy budget: The energy or heat budget
at the earth’s surface, considered in terms of the
fluxes through a plane at the earth-atmosphere
interface. The energy budget includes net all-wave
radiation, and sensible, latent and ground heat fluxes.
Surface radiation and energy budgets
Q* = R = net radiation
Kdn = incoming solar
Q*+ QG+QH+QE = 0
Kup = reflected solar
K* = net solar
Ldn = incoming longwave
Lup = outgoing longwave
L* = net longwave
Q*+ QG+QH+QE = 0
QG = G = ground heat flux
QH = H = sensible heat flux
Oke (1978)
QE = L = latent heat flux
Q* = K* + L* = Kdn + Kup + Ldn + Lup
Radiation Budget
Global energy balance
Radiation measurements, Hardheim forest
(Freiburg Met. Inst.)
UL and LL:
CM21
pyranometer
UR and LR:
CG1Schultze
pyrgeometer
All 4 have
upper and
lower domes
Whiteman photo
Surface radiation budget
Figure 4.8.
Typical diurnal evolution
of the four components
of net radiation at the
earth’s surface under
cloudless conditions on a
June day at a semiarid
site near the Columbia
River in eastern Oregon.
The extraterrestrial
shortwave radiation is the
theoretical radiation that
would be received outside
the earth’s atmosphere on
a plane that is parallel to
the earth’s surface below.
Whiteman (2000)
Albedo or reflectivity, α
Figure 4.11.
Whiteman (2000)
♦
The solar reflectivity or
albedo of most natural
materials at the earth’s
surface is between 0.05
and 0.30. Bright surfaces
like fresh snow or thick
clouds have relatively high
albedos. Clouds can
reflect sunlight back to
space before it reaches
the ground.
Absorbed solar radiation depends strongly on albedo: Kup = Kdn (α)
• Snow cover reflects solar radiation and diminishes absorbed solar radiation
• Annually, snow cover at high elevation later in season than in valleys tends to cause
absorbed solar radiation to diminish with elevation
Emissivities, ε
Figure 4.12.
Emissivities are between 0.85
and 1.00 for most natural
materials. High clouds, polished
aluminum, and silver have lower
emissivities.
Whiteman (2000)
♦
♦
♦
Stefan-Boltzmann Law Lup = εσT4
As elevation increases:
– Temperature decreases, longwave radiation decreases
– Optical thickness of atmosphere decreases (less greenhouse gases, including
water vapor), atmospheric transparency to outgoing radiation increases, more
longwave radiation escapes
Emissivity (ε) of snow and ice is high
Revolution of Earth around Sun
N Hem terminology
Ahrens (1994)
Sun path, summer and winter
Northern Hemisphere
Ahrens (1994)
Cosine law of illumination
Ahrens (1994)
Variations in slope and azimuth angles presented by topography
determine the radiant loading across the landscape.
Surface Energy Budget
SEB measurements - Bowen ratio stations
Whiteman photos
SEB measurements - Eddy correlation
Whiteman photo
Surface energy budget
Figure 4.9.
The surface energy
budget terms vary
diurnally. The data
shown are for a June day
at a semiarid site near
the Columbia River in
Eastern Oregon. The net
radiation curve in this
figure is repeated from
Fig. 4.8, but is plotted on
a different scale.
Whiteman (2000)
Surface energy budget
•
•
•
•
•
R = - (G + H + L ) (Watts/m2)
R = net solar and terrestrial radiation at the earth’s surface (+ into surface)
•
•
•
Absorbed solar radiation (incoming – reflected)
Incoming longwave radiation emitted by gases and clouds in the atmosphere
Outgoing longwave radiation emitted by the earth’s surface
G – storage of energy into the deep soil (- into soil)
H – heat flux into atmosphere(- into atmosphere)
L – Latent heat (evaporation) flux into atmosphere (- into atmosphere)
Typical day and night surface energy budgets
Figure 4.10.
Typical values of the surface
energy budget components at
midnight and noon. The
numerical values are from
Figure 4.9
Whiteman (2000)
Mountainous Terrain
Extraterrestrial solar radiation on slopes
Whiteman (2000)
Brush Valley, Colorado photo
Whiteman photo
Brush Creek Valley topography
Whiteman et al. (1989)
Brush Valley digital model calculations
Whiteman (1990)
Surface energy budget components
Whiteman et al. (1989)
Meteor Crater insolation and SHF (W/m2)
Microclimates
•
•
•
Small topographic irregularities
Differences in slope angle and aspect
Types (Turner 1980)
•
Sunny windward slope (high radiation;
high wind)
•
Sunny lee slope (high radiation; low
wind)
•
•
Shaded windward
Shaded lee