Transcript Introduction

Warming the Earth and Atmosphere
Dr. Craig Clements
San José State University
MET 10: Chapter 2
Temperature
Is the measure of the average speed or
thermal energy of the particles in a substance.
(How fast the atoms/molecules are moving)
Three temperature
scales:
•Kelvin
•Celsius °K= °C+273
•Fahrenheit
•What does 0° K mean?
Absolute zero,
molecules would
posses minimum
amount of energy and
no thermal motion.
Heat
is energy in the process of being transferred from
one object to another because of the temperature
difference between them.
Latent Heat (Hidden Warmth)
Water vapor is an invisible gas that becomes visible
when it changes into larger liquid or solid particles
(such as ice).
This process of transformation is known as a
change of state or phase change. The heat energy
required to change a substance such as water from
one state to another is called latent heat.
Latent Heat (Hidden Warmth)
Example: cooling produced by evaporating water
Examine a small drop of water. At drop’s surface
water molecules are constantly escaping
(evaporating).
Because the more energetic, fast-moving
molecules escape most easily, the average motion
of all the molecules left behind decreases.
Since temperature is a measure of the average
molecular motion, the slower motion suggests a
lower water temperature.
Evaporation is a cooling process
Latent Heat (Hidden Warmth)
Evaporation is a cooling process because the
energy needed to evaporate the water– to
change its phase from liquid to a gas– comes
from the water.
The energy lost during evaporation can be
thought of as carried away by the water vapor
molecule. The energy is thus “stored” or “hidden”
and we call this latent heat.
Condensation
Opposite of evaporation is condensation.
Condensation is a process where a gas changes
into a liquid.
Is condensation a cooling process or warming
process?
Warming.
Phase changes
Latent Heat
Latent heat is an important source of atmospheric
energy.
Once the vapor molecules become separated from the
earth’s surface, they are transported by the wind.
Rising to high altitudes where the air is cold, the vapor
changes into liquid and ice cloud particles.
During these processes, a tremendous amount of heat
energy is released into the environment.
Energy transmission
There are three modes of energy transmission
in the atmosphere.
 Conduction: the transfer of energy in a substance by
means of molecular excitation without any net external
motion.
 Convection: the transfer of energy by mass motions
within a fluid or gas, resulting in actual transport of
energy.
 Radiation: the propagation of electromagnetic waves
through space.
Conduction
Convection
In meteorology, the vertical exchange of
heat is called convection
During the process of convection,
bubbles of air form at the surface and
rise. These vertical currents are known
as thermals.
The horizontal motion of air (wind)
carries properties of the air (temperature,
moisture, etc.) with it. This is called
advection.
The sport of paragliding is dependent on thermals
Photographer unknown
The Rising and Sinking Air Game
Take an invisible “blob” called an air parcel. This air parcel is
wrapped with imaginary elastic, plastic like a balloon.
The parcel can expand and contract freely.
But…neither external air nor heat is able to mix with the air
inside.
Also, as the air parcel moves, it does not break apart, but
remains as a single unit.
At the earth’s surface the parcel has the same temperature
and pressure as the surrounding air.
The Rising and Sinking Air Game
Suppose we lift the parcel. Remember air pressure always
decreases as we move up into the atmosphere.
As the parcel rises, it enters a region where the surrounding
air pressure is lower.
To equalize the pressure, the parcel molecules inside push
the parcel walls outward, expanding it. The molecules use
some of their own energy to expand the parcel. This energy
loss shows up as slower molecular speeds = lower parcel
temperature.
Air that rises always expands and cools!
The Rising and Sinking Air Game
The Rising and Sinking Air Game
If the parcel is lowered, it returns to a region where the air
pressure is higher.
The higher outside pressure squeezes (compresses) the
parcel back to its original (smaller) size.
Because the air molecules have a faster rebound velocity
after striking the sides of the a collapsing parcel, the average
speed of the molecules goes up.
This increase in molecular speed represents a warmer parcel
temperature. Therefore,
Air that sinks always warms by compression!
Electromagnetic radiation

 Radiation is the transfer of energy by rapid oscillations
of electromagnetic fields.
 The most important general characteristic is its
Defined as the crest-to-crest distance
wavelength (), ______________________________.
 Radiation travels through space at the speed of light
(3 x 108 m s-1) or 670,616,630 MPH.
Radiation
 What emits radiation?
– All objects with a temperature greater than
0°K emit some type of radiation (energy)
 Examples:
 Radiation laws:
– Warmer objects emit more intensely than cold
objects. (Stefan-Boltzmann Law)
– Warmer objects emit a higher proportion of
their energy at short wavelengths than cold
objects. (Wien’s Law)
Wien’s Law:
λ=w/T
λ = maximum wavelength (μm)
w = constant = 0.2897 (μm K)
T= temperature of the object (K)
Stefan-Boltzmann Law:
E = σT4
E = radiation emitted (W m-2)
σ = Stefan-Boltzmann constant= 5.67 x 10-8 (W m-2 K-4)
T= temperature of the object (K)
Review questions
 Considering the previous discussion
– Which object would emit more (intensity) radiation:
Earth or Sun?
Sun
– If you were examining the radiation emitted by both
the Sun and Earth, which would have a longer
wavelength?
Earth
– What wavelength radiation are you emitting right
now?
infrared
Solar Radiation (Sunlight)
 Sunlight is primarily made up of the
following:
– Visible Light (44%)
– Infrared Radiation (48%)
– Ultraviolet Radiation (7%)
Unit: 1 m =
0.000001 m
Terrestrial or Longwave Radiation
 Planets mainly emit
infrared radiation
 Radiation emitted by
planets occurs
mainly at
longer
wavelengths _____
than those
contained in solar
radiation
Solar Radiation
(“Shortwave”)
Terrestrial
Radiation
(“Longwave”)
Solar vs. Terrestrial Radiation
 The sun is much
hotter than planets;
therefore, sunlight
consists of shorter
wavelengths than
planetary radiation;
 Thus …
Energy from the Sun
 Obviously, the Sun provides the Earth with it’s energy.
The question is, how much of the Sun’s energy does
the Earth get?
 Sun’s energy is either
– Scattered (reflected away) or
– Absorbed
 Scattering happens by bouncing off
– Particles in the atmosphere
– Earth’s surface
 Absorption happens when certain gases absorb the
energy
– The reality is the only certain gases absorb certain
wavelengths.
Absorption of radiation
 Absorption of shortwave radiation by atmospheric
gas molecules is fairly weak;
– most absorption of shortwave radiation occurs
at the Earth’s surface.
 Most gases do not interact strongly with longwave
radiation, however
– Greenhouse gas molecules absorb certain
wavelengths of longwave radiation.
Absorption of
Radiation in the
Earth’s
Atmosphere
Absorption of
Radiation in the
Earth’s
Atmosphere
Fig 2.11
Incoming solar radiation
 Each ‘beam’ of incoming sunlight can be either:
– Reflected back to space: Albedo
 Clouds
 Atmosphere
 Surface
– Or absorbed; either by atmosphere (e.g.
clouds or ozone) or Earth’s surface.
Recap
or solar radiation comes from the sun
Shortwave
______________
and is composed of both ultraviolet and visible
radiation
Longwave, terrestrial or infrared
 __________________ radiation comes from
the Earth and is composed of infrared radiation
 Recall that everything (above a temperature of
0K) emits some type of radiation (energy) with
a particular wavelength.
Review - sensors that measure radiation
Pyranometer
 A _________________
measures solar
radiation.
Pyrgeometer
 A__________________
measures infrared
radiation (terrestrial) that comes from the Earth.