Hurricane Katrina (August 29, 2005)
Lethbridge, Alberta
Current weather conditions
17h00
January 10,
2006
Mainly clear
Temp.:
5°C
Pressure:
Visibility:
99.7
kPa 
32km
Humidity:
55%
DewPoint:
-3°C
Wind:
SW 24
km/h
Weather
Climate
Current state of
the atmosphere
Statistical analysis
or characterization
of what is normal or
expected
air temperature
atmospheric pressure
humidity
clouds
precipitation
visibility
wind
Long term averages
*Means*
*Extremes*
*Variability*
78% N2
21% O2
H2O
CO2
CH4
CFCs
N2O
O3
Aerosols
NO2
CO
SO2
Hydrocarbons
Gravity pulls gases
toward earth's
surface
101.325 kPa
UNSTABLE
STABLE
What happens to solar energy ?
1.
Absorption (absorptivity=)
Results in conduction, convection
and long-wave emission
2.
Transmission (transmissivity=)
3.
Reflection (reflectivity=)
 +   +  = 1
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
Then why do dry lands still “heat up” more?
Oceans transmit solar energy and have 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 emits maximum possible radiation per unit area.
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
Stefan-Boltzmann Law
As the temperature of an object increases, more
radiation is emitted each second
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 300 K (Earth)
Energy emitted = (T0)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)/(T0)
*wavelength in metres
Sun’s max = 0.48 m
Ultraviolet to infrared - 99% short-wave (0.15 to 3.0 m)
Earth’s max = 10 m
Infrared - 99% longwave (3.0 to 100 m)
Terrestrial
radiation
Microwaves are longest
wavelengths used in
remote sensing
Solar
radiation
We are blind to
everything except
this narrow band
UV are shortest
wavelengths practical
for remote sensing
Transmission through the Atmosphere
Some wavelengths of
E-M energy are
absorbed and scattered
more efficiently than
others
H2 O, CO 2, and ozone
have the strongest
absorption spectra
Transmission
Light moves through a
surface (eg. on a natural
surface)
8-11 m window
Wavelength dependent
(eg. leaves)
Radiation emitted from Earth is of
a much longer wavelength and is of
much lesser energy
ALBEDO: April, 2002
white and red
are high albedo,
green and yellow
are low albedo
http://profhorn.aos.wisc.edu/wxwise/AckermanKnox/Earth's Albedochap2/Albedo.html
Characteristic spectral responses of different surface types. Bands are those
of the SPOT remote sensing satellite.
•white snow
•old snow
•vegetation
•light colour soil
•dark colour soil
•clouds
•calm water surface
0.80-0.95
0.40-0.60
0.15-0.30
0.25-0.40
0.10
0.50-0.90
0.10 (midday)
NET ALL_WAVE RADIATION
DAYTIME:
Q* = K - K + L - L
Q* = K* + L*
NIGHT:
Q* = L*
Radiation Balance Components
L
Source: NOAA
Conduction
The transfer of heat from
molecule to molecule
within a substance
Convection and Thermals
Convection
The transfer of heat by
the mass movement of a
substance (eg. air)
Rising air expands and cools
Sinking air is
compressed and
warms
•Heat capacity
The ratio of the amount of heat energy absorbed
by a substance to its temperature rise
•Specific heat
The amount of heat energy required to raise the
temperature of 1g of a substance by 1°C
•Latent heat
The heat energy required to change a substance
from one state to another
•Sensible heat
Heat energy that we can feel and sense with a
thermometer
Radiation Sensors
(PAR and K)
Thermometer
and radiation
shield
SENSIBLE
HEAT
Photo:
My Tausa, Cundinamarca,
Colombia weather station
(3243 m asl)
Raingauge
Datalogger
Check this out:
http://www.jgiesen.de/sunshine/index.htm
N
Temperature (C)
20
15
10
5
0
-5
-10
-15
-20
-25
-30
-35
-40
Dec 15, 2004
Jan 19, 2005
10 cm Air Temp (south-facing)
10 cm Air Temp (north facing)
15
Dec 15, 2004
Temperature (C)
10
5
Jan 19, 2005
0
-5
-10
-15
10 cm Soil Temp (south facing)
10 cm Soil Temp (north-facing)
10
Dec 15, 2004
Jan 19, 2005
5
0
-5
-10
-15
-20
-25
-30
-35
-40
-45
10 cm Dewpoint (south facing)
10 cm Dewpoint (north facing)
10 – 100 m
0.0001 – 0.001 m
Mie scattering
0.01 to 1.0 m
LONG PATH LENGTH OF LIGHT THROUGH
THE EARTH’S ATMOSPHERE
MOST OF THE THE VIOLET, BLUE AND
GREEN LIGHT IS SCATTERED
(from Pacific)
(Prairie cold)
•OUTGASSING
•TORRENTIAL RAINS PRODUCED
LAKES AND OCEANS
•DISSOLVED AND UNDISSOLVED
ELEMENTS
•PRESENT VOLUME 1,360,000,000 km3
•VOLUME IS STABLE
Water
Reservoir
Percent
Oceans
Ice caps, glaciers
97.24%
2.14%
Ground water
Fresh-water lakes
Inland seas
0.61%
0.009%
0.008%
Soil moisture
Atmosphere
Rivers
0.005%
<0.001%
<0.0001%
Source: U.S. Geological Survey
Some fast-moving
molecules escape
from the liquid
In cool air, H2O molecules
are more likely to join
nuclei
CHANGES
DOES NOT
CHANGE
MASS/VOLUME
g H2O / m3 air
Specific humidity:
the mass of water vapour (g) per mass
of air (kg)
Maximum specific humidity is the
maximum mass of water vapour that can
be held by 1kg of air at a given
temperature
MASS OF WATER VAPOUR
TOTAL MASS OF DRY AIR
g H2O / kg air
A ratio that compares the amount of
water vapour in the air to the
maximum water vapour capacity at
that temperature
The relative humidity of saturated
air is 100%
RH = [H20 vapour content/H20 capacity] x 100
The portion of atmospheric pressure that is
made up of water vapour molecules
(mb or kPa)
SATURATION VAPOUR PRESSURE:
The pressure that water vapour molecules
would exert if the air were saturated
(at a given temperature)
RELATIVE
HUMIDITY
SPECIFIC
HUMIDITY
Sling psychrometer
http://www.csgnetwork.com/canhumidexcalc.html
Why do surfaces facing
the wind have more frost?
BLACK FROST
•A surface is required for condensation
•Condensation nuclei >0.1 m best
•About 10-1000 large nuclei per cm3
(more in lower troposphere and over land)
•Hygroscopic or hydrophobic
Source: Dust, volcanoes, factory smoke,
forest fires, ocean spray salt, sulphate
particles from phytoplankton
Fog forms
if Td is reached
Cold water advection fog
WHY DOES FOG
FORM HERE?
Warm water advection fog
CAN ADVECTION
FOG FORM OVER
LAND MASSES?
YES
Pages 142-155
Laboratory Notes
Absolute stability
Environmental lapse rate <
moist adiabatic lapse rate
Environmental lapse rate >
Dry adiabatic lapse rate
Solar heating of Earth’s surface
Warm air advection at surface
Air moving over a warm surface
Cold advection
Radiational cooling of clouds
LIFTING
OF ENTIRE
AIRMASS
Rainshadow