Lesson
Content
Most of this weeks background information is available in Chapters
1-3. Here is some additional information on the standard atmosphere,
and
some
brief
notes.
You
should already know some basic definitions, such as Latitude,
Longitude, Altitude and Gravity.
Below is a brief summary of some of these topics.
Temperature,
Density, Pressure
DENSITY tells us how much matter is in a given space. Density decreases
with altitude.
PRESSURE - Even though we can't feel the constant bombardment of
air, the push of tiny molecules, we can detect rapid changes. Ears
popping - air collisions outside the ear drum lessen. Ear popping,
occurs as the molecules on the inside and outside equalize.
Pressure is force per unit area. The pressure at any level in the
atmosphere may be measured in terms of the total weight of the air
above any point - atmospheric pressure. Pressure always decreases
with altitude.
Blow up a balloon - the number of molecules, and the speed, colliding
against the sides determines the air pressure inside. You have to
do work to blow up the balloon. Which brings us to the definition
of
ENERGY, which is the ability or capacity to do work on some
form of matter. Work is done on matter when matter is either pushed,
pulled or lifted over some distance. Energy must be conserved, but
it can
be converted between different forms.
KINETIC ENERGY - energy associated
with motion.
TEMPERATURE is a measure of the average speed of molecules. Vertical
distribution of temperature
Kinetic energy and the movement of molecules. Pressure,
density and temperature are related via the ideal gas law.
At the surface a parcel has the same temperature as air around it.
When we raise the parcel the air pressure is lower; molecules push
on "sides" to expand parcel - this is work; less energy
(kinetic energy) cooler temperature. Rising parcels of air always
cool due to expansion. Sinking or subsiding air always warms by compression.
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Energy
Energy is everywhere. Energy is the ability or capacity to do work on some form
of matter. By doing work on something we give it energy, which it can in turn
use to do work on other things. Energy exists in many forms, it cannot be created
or destroyed, it merely changes form.
Kinetic energy - also depends on its mass.
Potential energy, represents the potential to do work. In atmospheric
science, gravitational potential energy.
Another example is radiant energy - the energy we get from the sun.
Heat is energy in the process of being transferred from one object to
another because of the temperature difference between them. After heat
is transferred it is stored as "internal energy" which is the
total energy stored in the molecules.
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Energy
Transfer
How is energy transferred in the atmosphere? Before we do this lets discuss
the concept of sensible heat, specific heat and latent heat.
Sensible heat - heat we feel and measure with a thermometer
Specific Heat - The amount of heat needed to raise the temperature of
one gram of a substance 1C. Water has a much higher capacity for storing
energy than other substances -e.g. sand or air. Water is therefore very
important in determining a regions climate/weather.
CONDUCTION - transfer of heat from molecule to molecule. warmer colder.
The greater the temperature difference the faster the transfer. Some materials
are better conductors of heat than others, metals are good conductors,
air is poor.
CONVECTION - transfer of heat by the mass movement of a fluid such
as air.
ADVECTION. - Meteorologists think of convection as vertically moving
air, horizontal winds can also move heat energy.
RADIANT ENERGY - travels in the form of waves that release energy when
they are absorbed by an object. These waves have electric and magnetic properties
- electromagnetic waves. Electromagnetic waves do not need molecules to propagate
them - speed of light 186,000 mi/sec. Wave characteristics - horizontal distance
between two successive crests is the wavelength.
LATENT HEAT - heat energy required to change a substance from one state
to another. We will discuss this method more later in the course. Evaporation
cools the environment. As molecules leave, faster ones leave first, average
speed decreases and so the temperature of the object cools. Latent heat
is responsible for keeping a cold drink with ice colder than one without
ice.
As ice melts its temperature doesn't change, added heat breaks down the
rigid crystal pattern. When ice melts, heat is taken in; when it freezes
heat is
liberated. Phase changing is important for transferring energy in the atmosphere.
For example, Evaporation over tropical waters, the water vapor can move
poleward and condense.
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