What is earths atmosphere

1
Lecture 2
What is earths atmosphere?
2
Earth's atmosphere is a layer of gases
surrounding the planet earth and retained by the
Earth's gravity
It contains roughly 78 nitrogen and 21 oxygen,
trace amounts of other gases, and water vapor.
This mixture of gases is commonly known as air.
3
(No Transcript)
4
The Troposphere is the lowermost portion of
Earth's atmosphere. It is the densest layer of
the atmosphere and contains approximately 75 of
the mass of the atmosphere and almost all the
water vapor and aerosol.
aerosols or fine particles, are tiny particles of
solid (a smoke) or liquid (an aerosol) suspended
in a gas. They range in size from less than 10
nanometers to more than 100 micrometers in
diameter.
Some aerosols occur naturally, originating from
volcanoes, dust storms, forest and grassland
fires, living vegetation, and sea spray. Human
activities, such as the burning of fossil fuels
also generate aerosols.
The troposphere extends from the Earth's surface
up to the tropopause where the stratosphere
begins. The depth of the troposphere is greatest
in the tropics (about 16km) and smallest at the
poles (about 8km).
The troposphere is the most turbulent part of
the atmosphere and is the part of the atmosphere
in which most weather phenomena are seen.
Generally, jet aircraft fly just above the
troposphere to avoid turbulence.
5
The stratosphere is a layer of Earth's atmosphere
that is stratified in temperature, with warmer
layers higher up and cooler layers farther down.
This is in contrast to the troposphere near the
Earth's surface, which is cooler higher up and
warmer farther down. The stratosphere is situated
between about 10 km and 50 km altitude above the
surface at moderate latitudes, while at the poles
it starts at about 8 km altitude. The
stratosphere sits directly above the troposphere
and directly below the mesosphere. The
stratosphere is layered in temperature because it
is heated from above by absorption of ultraviolet
radiation from the Sun. Within this layer,
temperature increases as altitude increases the
top of the stratosphere has a temperature of
about 270 K, about the same as the ground level
temperature. This top is called the stratopause,
above which temperature again decreases with
height. The vertical stratification, with warmer
layers above and cooler layers below, makes the
stratosphere dynamically stable there is no
regular convection and associated turbulence in
this part of the atmosphere. The heating is
caused by an ozone layer that absorbs solar
ultraviolet radiation, heating the upper layers
of the stratosphere.
6
The mesosphere is the layer of the earths
atmosphere that is directly above the
stratosphere and directly below the thermosphere.
The mesosphere is located about 50-80/85km above
Earth's surface. Within this layer, temperature
decreases with increasing altitude. The main
dynamical features in this region are the
atmospheric tides which are driven by momentum
propagating upwards from the lower atmosphere and
extending into the lower thermosphere. Atmosphere
diagram showing the mesosphere and other layers.
The layers are not to scale from Earth's surface
to the top of the stratosphere (50km) is just
under 1 of Earth's radius. this region of the
atmosphere is only directly accessible through
the use of sounding rockets. As a result the
region is one of the most poorly understood in
the atmosphere
7
The stratosphere and mesosphere are referred to
as the middle atmosphere. The mesopause, at an
altitude of about 80 km, separates the mesosphere
from the thermospherethe second-outermost layer
of the Earth's atmosphere.
The thermosphere is the layer of the Earth's
atmosphere directly above the mesosphere and
directly below the exosphere. Within this layer,
ultraviolet radiation causes ionization
Thermospheric temperatures increase with altitude
due to absorption of highly energetic solar
radiation by the small amount of residual oxygen
still present. Temperatures are highly dependent
on solar activity
8
The climate
is commonly considered to be the weather
averaged over a long period of time.
Weather
is the variation in the atmosphere over short
periods of time.
9
1- Solar variations are the fluctuations of the
amount of energy emitted by the sun
2-Orbital variations Variations in the
Earth's orbit around the sun it has
significant impact on the atmospheric heat
distribution around the globe. it caused
variations in the intensity of radiation emitted
by the sun.
3- Volcanism emissions 4- Gas emissions (man
made)
10
Sunspots are dark areas on the surface of the
Sun and are thus cooler than its average
surface.
Sunspot helps provide an explanation for the
continuous up and down jiggling of the earths
Temperature.
11
The nature of Radiative Energy
12
Example An object with a temperature of 20 C has
surface properties approximating those of a black
body. Calculate the black body Heat flux from
this object and calculate the total heat flow
rate if the surface area is 0.2 m2.
13
For any given temperature, the black body
emissive power Peaks at some particular
wavelength, the location of the peak Emissive
power can be predicted by
14
Example Assume that the sun radiates with an
effective black body Temperature of 5,800 K,
whereas the earth radiates with a black Body
temperature of 288 K. for each body, find the
wavelength of Maximum emissive power.
15
Global temperature model
Zero-dimensional energy balance model
incoming energy from the Sun outgoing energy
from the Earth
Albedo is the fraction of solar energy (shortwave
radiation) reflected from the Earth back into
space.
16
Energy absorbed by earth (1 - a)SpR2
a is the fraction of incoming solar radiation
that is reflected albedo, approximately
0.1 to 1
Energy radiated back to space by earth d 4 p
R2Te4
d 4 p R2Te4
(1 - a)SpR2
17

• S is the solar constant - the incoming solar
  
• radiation per unit area - about 1370
  Wm-2
• R is Earth's radius
• approximately 6.371106m
• ? is well known, approximately 3.14159
• d is the stefan-Boltzmann constant
• approximately 5.6710-8 w/m2-k4
• T earths blackbody temperature Kelvins

(1 - a)S 4 d T4
18
254 K -19 C
C K-273 254- 273
Magnitude of greenhouse effect Ts (actual
surface temp.)-Te (effective temp.)
However, average global surface T is 14 C then,
natural greenhouse effect warms the surface by
33 C
19
A glacier is a large, long-lasting river of ice
that is formed on land glaciers grow and
collapse
20
2) Ocean variability
changes within the ocean/atmosphere systems
Darker lines represent deep-water currents,
lighter lines represent those running on the
surface
circulation plays an important role in supplying
heat to the polar regions
21
(No Transcript)
22
Muir Glacier, 2003(Courtesy USGS
Muir Glacier, 1899(Courtesy USGS)
Alaskan glaciers
23
Effects of Global Warming on Environment There
are many environmental problems coming from the
increase concentration of greenhouse gases in
Earth's atmosphere. As Jeff Rubin of ABC NEWS
reported, ?Several signs indicate that we've
begun changing Earth's climate increased water
vapor in the atmosphere, glaciers and polar ice
caps appear to be melting, floods and droughts
are becoming more severe, and sea levels have
risen, on average, between 4 and 10 inches since
1990.? (www.abc.com/sections/us/global106.html)
Experts concur, ?We are already beginning to see
this (global warming) taking place - a lot more
flooding, a lot more droughts,?
                                              
                                                  
                                          Flooding
form global warming may be already happening.