Transcript Microclimatology 1 FALL 2008.ppt
GEOGRAPHY 3015A
Atmospheric Scales The Boundary Layer
Vary in
SPACE
and
TIME
The portion of the atmosphere influenced by the Earth’s surface over a time period of
one day MICRO
10 -2 to 10
Small-scale turbulence
3 m Height: <100m to 2km
LOCAL
10 2 to 5x10 4 m
Small to large cumulus cloud
MESO MACRO
10 5 to 10
Hurricanes, cyclones,
8
jet stream
10 4 to 2x10 5
Thunderstorms/Local winds
m
See Fig 1.1, p. 4
m
Characteristics:
Turbulence
(i) frictional drag over surface (ii) convection
Variable height
(i) diurnal heating (ii) large scale weather systems affect stability
Troposphere
Extends to limit of surface influence (~10km)
Atmospheric/Planetary Boundary Layer
<100 m to 2km height (See previous page)
Turbulent Surface Layer
Intense small-scale turbulence from convection and friction ~ 50m by day, a few metres at night
Roughness Layer
Extends to 1-3 + times the height of surface elements Highly irregular flow
Laminar Boundary Layer
Non-turbulent, ~ 0.1-5 mm layer adhering to surface
See p. 5
Vertical Extent
• •
Noctilucent clouds
poorly understood near edge of atmosphere
troposphere
We won’t concern ourselves with this scale in this course
The Earth-Atmosphere System First Law of Thermodynamics
Energy can neither be created, nor destroyed
Energy Input = Energy Output + Energy Storage Change
The energy output is
not
necessarily in the same form as the energy input
Modes of Energy Exchange in the Earth-Atmosphere System
1.
2.
3.
Conduction Convection Radiation
What happens to solar energy ?
1.
2.
3.
Absorption
(absorptivity= )
Results in conduction, convection and long-wave emission
Transmission
(transmissivity= )
Reflection
(reflectivity= )
+
+
= 1 The response varies with the surface type: Snow reflects
40 to 95% of solar energy and requires a phase change to increase above 0 °C
Forests
and
oceans absorb
more than
dry lands
why dry lands still “heat up” more during the day) (later we’ll see
Water transmits
solar energy and has a high
heat capacity
Characteristics of Radiation
Energy due to rapid oscillations of electromagnetic fields, transferred by photons
The energy of a photon is equal to Planck’s constant, multiplied by the speed of light, divided by the wavelength
E = hv
All bodies above 0 K emit radiation
Black body
unit area.
emits maximum possible radiation per
Emissivity,
= 1.0
All bodies have an emissivity between 0 and 1
Electromagnetic Radiation
Consists of
electrical field
(E) and
magnetic field
(M) Travels at speed of light (C) The shorter the
wavelength
, the higher the
frequency
This is important for understanding information obtained in remote sensing
Temperature determines E,
emitted
Higher frequencies
(shorter wavelengths) are emitted from bodies
at a higher temperature
Max Planck determined a characteristic emission curve whose shape is retained for radiation at 6000 K (Sun) and 288 K (Earth)
Energy emitted =
(T 0 ) 4 Radiant flux
or
flux density
refers to the rate of flow of radiation per unit area (eg., W m -2 )
Irradiance
=
Emittance
= incident radiant flux density emitted radiant flux density
Wien’s Displacement Law
As the temperature of a body increases, so does the total energy and the proportion of shorter wavelengths
max = (2.88 x 10 -3 )/(T 0
) *wavelength in metres
Sun
max = 0.48
m
Ultraviolet to infrared - 99%
short-wave
(0.15 to 3.0 m)
Earth
max = 10
m
Infrared - 99%
longwave
(3.0 to 100 m)
Transmission through the Atmosphere Some wavelengths of E-M energy are absorbed and scattered more efficiently than others H 2 O, CO 2 , and ozone have the strongest absorption spectra Transmission Light moves through a surface (eg. on a natural surface) Wavelength dependent (eg. leaves) Radiation emitted from Earth is of a much longer wavelength and is of much lesser energy
Terrestrial radiation Solar radiation
Microwaves are longest wavelengths used in remote sensing We are blind to everything except this narrow band UV are shortest wavelengths practical for remote sensing
Spectral Signatures
Characteristic spectral responses of different surface types. Bands are those of the SPOT remote sensing satellite.
Atmospheric Windows
window absorption
Diffuse (D) and Direct (S) Solar Radiation
Clouds, water vapour, dust particles, salt crystals absorb and reflect some of the incoming solar radiation (K ).
Most is transmitted through clear skies (S) but some is scattered, resulting in a diffuse component (D) Clouds are very effective at scattering, resulting in D.
The proportion of extraterrestrial radiation, K ext reflected, absorbed and transmitted define atmospheric reflectivity, a , absorptivity, a , and transmissivity, a
Diffuse Radiation
Measured using a shade disk Radiation from entire sky except from within 3 of Sun
S
is weaker when the
zenith angle
is large
S = S i cos Z
Why ? The beam is simply spread out over a larger area (Figure 1.7, p. 15) The total short-wave radiation received at the surface (K ) is defined as:
K
= S + D
A proportion is reflected:
K
=
K
Net short-wave radiation
,
K*
, is defined as follows:
K* = K
OR
K* = K
- K (1-
)
Field Research
Spatiotemporal patterns of plant ecophysiological stress in grassland, alpine krumholtz and riparian environments of southern Alberta
Measurements: Microclimate stations (16) Photosynthesis processes (LI-COR 6400XTR, TPS-1) Fluorescence (FMS2, LI-COR 6400XTR) Reflectance (Unispec-SC) Sites: Lakeview Ridge, Waterton Lakes National Park (PI=Letts) Lethbridge Coulee Microclimate Station (PI=Letts) Pearce Corners Cottonwood Grove (PI=Rood) Helen Schuler Coulee Centre, Lori’s Island (PI=Letts) Lethbridge Flux Station (PI=Flanagan) Research Assistants: Kevin Nakonechny, Deborah Ball, Clint Goodman, Leslee Shenton, Davin Johnson