Month Day Topic
Aug.
26
Introduction
28
The ecosystem concept
Sept.
2
Climate/soils
4
Soils II
9
Energy and water
balance
11
Vegetation/climate
16
Carbon
18
GPP/NPP
23
NEP
C,M&M
1
2
3
4
4
5
6
6
Spatial scale of climate
processes
Macroclimate
Global
Mesoclimate
Regional
Microclimate
Local
Nanoclimate
Organismal
Picture of sun
Radiation
• Shortwave (K): UV and visible
• Longwave (L): Infra-red, heat
Energy in =
Energy out
343 Watts/m2
Incoming radiation
is mostly short
wave (vis, NIR, UV)
31% reflected by
clouds or surface
Energy in =
Energy out
343 Watts/m2
Incoming radiation
is mostly short
wave (vis, NIR, UV)
31% reflected by
clouds or surface
20% absorbed by
clouds and
atmosphere
49% absorbed by
earth surface
Radiation absorption
=
increased T
Longwave re-radiation
Energy emitted =   T4
 = emissivity (0-1; black body-perfect radiator-equals 1)
 = Stefan-Boltzman constant (5.67x10-8 watts m-2 k-4)
T = Absolute temp of emitting object (K)
The “greenhouse” effect
Energy Losses
from the earth’s
surface
23% lost as latent
heat flux
water vapor
7% lost as sensible
heat flux
conduction,
convection
Remainder lost as
outgoing longwave
At the ecosystem “surface”…
Net radiation
• Energy input to ecosystem (absorption)
• Balance between
– Input (long- and short-wave radiation)
– Output (long- and short-wave radiation)
Sunshine
Reflectance
Clouds, gas
Earth’s surface
Rnet = (Kin – Kout) + (Lin – Lout)
How warm is the sky
relative to the land?
= (1 – albedo)Kin +  (sky Tsky4- sur Tsur4)
http://geography.uoregon.edu/envchange/clim_animations/#Global%20Energy%20Balance
Ecosystem characteristics that
affect Rnet
• Albedo
• Surface temperature (diff. between sky
and surface T)
– Factors that modify surface T
• Roughness: canopy structure cause mixing and
cooling
• Water
Net radiometer
kin
kout
Radiation budget of a douglas fir forest
Season
Disturbance
Canopy roughness
Energy partitioning
Rnet = H + LE + G + S
Rnet = net radiation
H = sensible heat flux
LE = evapotranspiration
G = ground heat flux
S = change in storage
S
• Converted to chemical energy via Ps
• Change in temperature of vegetation and soil
• < 10% of Rnet in most ecosystems
• Often ignored in studies of microclimate
G = Ground
• Conductive heat loss from surface
• Depends on:
– Thermal conductivity of substance
– Thermal gradient
• Negligible in tropical and temperate systems,
big at high latitudes and altitudes
LE = latent heat
• Convective heat loss from surface
• Evapotranspiration
• Depends on vapor pressure gradient between
ecosystem and atmosphere
• Transfers water from ecosystem to
atmosphere
H = sensible heat
• Conductive and convective heat loss from the
surface
• Depends on:
– T difference between surface and overlying air
– Turbulence
• Convective turbulence = eddies
Energy available for turbulent
exchange (momentum)
• Available energy = Rnet – (G + S)
= H + LE
• Bowen ratio: H/LE
– inversely related to proportion of Rnet that
drives water loss
– Driven by water availability
Characterizing functional
differences among ecosystems…
• Albdeo
• Bowen ratio
Lecture ended here