Transcript Slajd 1 - lodz.pl

Processes forcing the climatic conditions
Heat transport
Water cycle
Atmospheric circulation
Radiation
There are four main processes of energy transport in the
atmosphere:
radiation,
molecular conduction
turbulent conduction
latent heat
sensible heat
Thermal Energy
 All matter is composed of atoms or molecules, which are
in constant motion
 Molecular or atomic motion = “thermal energy”
 Heating atoms causes them to move faster, which
represents an increase in thermal energy.
 Temperature is a measure of thermal energy.
Radiation is the way of energy transport by electromagnetic wave
moving with the speed of light. It does not demand any medium.
Energy is transmitted in portions called kwantums.
wavelength
crest
through
wavelength × frequency = speed of light
Energy of a wave
Energy is proportional to frequency,
and inversely proportional to wavelength
E=h
= h (c/ )
where h = Planck’s constant
In other words, waves with shorter wavelengths
(or higher frequency) have higher energy
Each body with temperature higher than 0K (-273,13ºC) emits
radiation to space, ie. emits an electromagnetic wave moving with
the speed of light differing in wavelength, frequency and
amplitude.
All bodies, with temperature greater than absolute 0, emit
radiation.
The rate at which something radiates and absorbs energy
depends strongly on its surface characteristics, such as
color, texture, moisture and temperature.
There is a group of bodies called black bodies. The rate at
which they radiate energy depends only on their
temperature. They are perfect absorber of radiation
(absorb all radiation that strikes them) and a perfect
emitter (emit the maximum radiation possible at their
temperature).
Blackbody Radiation
Law of Planck
Blackbody radiation—radiation emitted by a body that at all
wavelengths emits (or absorbs) energy in the amount described by law
of Planck.
Basic Laws of Radiation
1) All objects emit radiant energy.
Basic Laws of Radiation
1) All objects emit radiant energy.
2) Hotter objects emit more energy than colder objects.
Basic Laws of Radiation
1) All objects emit radiant energy.
2) Hotter objects emit more energy than colder objects. The
amount of energy radiated is proportional to the
temperature of the object raised to the fourth power.
Basic Laws of Radiation
1) All objects emit radiant energy.
2) Hotter objects emit more energy than colder objects. The
amount of energy radiated is proportional to the
temperature of the object raised to the fourth power.
 This is the Stefan Boltzmann Law
E =  T4
E = flux of energy (W/m2)
T = temperature (K)
 = 5.67 x 10-8 W/m2K4 (a constant)
Basic Laws of Radiation
1) All objects emit radiant energy.
2) Hotter objects emit more energy than colder objects (per
unit area). The amount of energy radiated is proportional
to the temperature of the object.
3) The hotter the object, the shorter the wavelength () of
emitted energy.
Basic Laws of Radiation
1) All objects emit radiant energy.
2) Hotter objects emit more energy than colder objects (per
unit area). The amount of energy radiated is proportional
to the temperature of the object.
3) The hotter the object, the shorter the wavelength () of
emitted energy.
This is Wien’s Law
max  3000 m
T(K)
 Stefan-Boltzmann law
E =  T4
E = flux of energy (W/m2)
T = temperature (K)
 = 5.67 x 10-8 W/m2K4
(a constant)
 Wien’s law
max  3000 m
T(K)
The amount of energy emitted by the black body at
wavelength  is depends only on the object temperature and
is described by Planck's law:
E 
c – speed of light (3,0·108m/s),
h - Planck's constant (h=6,63·10-34J·s),
2 c h
2

5
1
e
hc / kT
1
k Bolzmann's constant (k=1,38·10-23J/K)
T temperature in Kelvin scale
solar spectrum
Earth's spectrum
We can use these equations to calculate properties of energy
radiating from the Sun and the Earth.
6,000 K
300 K
T
(K)
Sun
6000
Earth
300
max
(m)
Part of
spectrum
E
(W/m2)
T
(K)
max
(m)
Sun
6000
0.5
Earth
300
10
Wien’s law:
Part of
spectrum
max  3000 m
T(K)
E
(W/m2)
Sun
T
(K)
max
(m)
6000
0.5
Part of
spectrum
Visible
(yellow?)
Earth
300
10
infrared
E
(W/m2)
Sun
T
(K)
max
(m)
6000
0.5
Part of
spectrum
E
(W/m2)
Visible 7 x 107
(green)
Earth
300
Stefan-Boltzmann law:
10
infrared
E =  T4
460
energy
Hotter objects emit
more energy than colder
objects
E=σT4
Sun
Earth
0.01
0.1
1
10
100
1000
wavelength
Hotter objects emit at
shorter wavelengths.
energy
max = 3000/T
Sun
Earth
0.01
0.1
1
10
100
1000
wavelength
Outgoing Longwave Radiation (OLR)
Anomalies
Drier-than-average conditions
(orange/red shading)
Wetter-than-average conditions
(blue shading)
From October – December 2011,
variability in OLR anomalies (focused
mostly over the Indian Ocean and
Maritime Continent) was associated
with the MJO.
Time
Since April 2010, negative OLR
anomalies have been observed near the
Maritime Continent and positive OLR
anomalies have prevailed over the
western and central Pacific.
Recently, eastward propagation of
negative OLR anomalies is evident in
association with the MJO.
Longitude
Climate Prediction
Center / NCEP
visible light
UV
infrared radiation
wavelength
Intensity of solar radiation at the upper boundary of the atmosphere
is called solar constant and amounts on average 1353 W/m2.
Solar constant is not perfectly constant. The elliptical path of the
Earth around the Sun brings the Earth closer to the Sun in January
(147 mln km in aphelium) than in July (152 mln km in perihelium).
From this reason the changes in solar constant during the year are
about 3.5%.
Since 1978 the remote sensing has been measured. It appears that the
solar constant is also changing with solar activity. These changes did
not exceed the level of 0.08% during the 30 years of measurements.
In very long time scale (thousands of years) the orbital parameters of
the Earth path around the Sun cause some changes in solar constant.
The intensity of solar radiation is also changing in the long history of
the Earth. 3.5 billions of years ago the Sun emitted only 70 % of
radiation it is emitting today.
Solar radiation is emitted in each direction equally. Because
the distance from the Sun to the Earth is really huge than the
radiation reaching the surface is parallel. The amount of
energy reaching the earth surface in the time unit is called
intensity of direct solar radiation.
Radiation that strikes a surface at an angle is spread over a
larger area than the radiation that strikes the surface
directly.
I '  I  sinh
1. All objects with temperature above absolute zero emit radiation.
2. The higher the object temperature, the greater the amount of
radiation emitted per unit surface area and the shorter the
wavelength of maximum emission.
3. The Earth absorbs solar radiation only during the daylight
hours; however, it emits infrared radiation continuously, both
during day and at night.
4. The Earth’s surface behaves as a black body, making it a much
better absorber and emitter of radiation than is the atmosphere
reflection
absorption and
emission
scattering
In the atmosphere the radiation can be:
scattered,
absorbed
reflected.
When sunlight strikes a very small objects such as air molecules and
dust particles the light itself is deflected in all directions – forward,
sideward and backward. It is called scattering.
Scattering on a tiny particles was firstly described by English scientist
lord Rayleigh (1842-1919) and is called a Rayleigh scattering.
i
I

k

4
iλ - intensity of scatttered radiation of
wavelenght λ,
Iλ - intensity of direct radiation of
wavelenght λ,
k – coefficient of scattering.
Absorption
During the absorption process, the infrared radiation is converted
into internal energy.
Gases in our atmosphere are selective absorbers. Ozone, for example,
absorbs UV radiation, especially at wavelengths between 0.2 and 0.3
μm, and an infrared radiation at 9.6 V μm.
Molecular oxygen absorb UV radiation below 0.2 μm.
Water vapor and carbon dioxide absorb energy in the infrared
wavelengths.
ABSORPTION in the ATMOSPHERE
During the absorption process, the absorbed radiation is converted
into internal energy.
Gases in our atmosphere are selective absorbers. Ozone, for example,
absorbs UV radiation, especially at wavelengths between 0.2 and 0.3
μm, and an infrared radiation at 9.6 V μm.
Molecular oxygen absorb UV radiation below 0.2 μm.
Water vapor and carbon dioxide absorb energy in the infrared
wavelengths.
visible
infrared
Absorption of radiation by gases in the atmosphere
gas
absorption wavelenghts
oxygen O2
0,01-0,2 m
ozone O3
0,2-0,3 m, 9,6 m
water vapor H2O
0,81 m, 0,93 m, 1,13 m,
1,37-2,66 m, 6,26m, 9-34
m
carbon dioxide CO2
2,3-3,0 m,
12,5-16,5 m
4,2-4,4
m,
White or shiny objects reflect sunlight from their surface.An object that
reflects a great deal of radiation of sunlights absorbs (and emits) very
little.
The percent of radiation returning from the surface compared to the
amount of radiation stiking it is called the albedo of the surface.
surface or object
albedo
surface or object
albedo
fresh snow
75-95%
grassy field
10-30%
cloud (thick)
60-90% dry, plowed field
5-20%
cloud (thin)
30-50%
10%
ice
30-40% forest
sand
15-45%
water
3-10%
Earth surface radiation balance
R  ( I  sinh i)  (1  A)  Eef
income
direct radiation
Eef  Ez  Ezw
scattered radiation
direct radiation falling on flat surface
total radisation
radiationfalling
emitted
onby
flat
the
surface
Earth
solar radiation
absorbed
by the
Earth surface
radiation
transmitted
downward
efective radiation of the Earth
outcome
Daily course of
temperature and
balance of
radiation
The Earth annual radiation balance and
temperature course
Influence of ground cover type on heat
balance
Q  H  LE  G
net radiation input
latent heat
used for evapotranspiration
sensible heat
used for warming of the air
exchange with the ground
Types of heat balance
Differences in heating of land and water surfaces
transparency
type of conductivity (turbulent or no)
transpiration losses
specific heat
comparison of maritime and continentals climates
the temperature range
the shift of maximum temperature
Questions and problems:
1. Describe some of the transformations energy goes through as water
evaporates from the ocean.
2. How does the temperature of the object influence the radiation that
it emits?
3. If the Earth's surface continually radiates energy, why it does not
became colder and colder?
4. In the northern latitudes the oceans are warmer in summer than
they are in winter. In which season do the oceans lose heat most
rapidly to the atmosphere by conduction? Explain.
5. If all of the greenhouse gases were removed from the Earth's
atmosphere, how would this influence the Earth's average
temperature? Explain
How to explain glaciations?
Tjeerd van Andel
Nowe spojrzenie na starą planetę, PWN, 1997
Chapter 5
8th November 2012