Download Chapter 1 - U.S. Coast Guard Auxiliary

NOTICE:
The information contained within this document is
copyright © U.S. Coast Guard Auxiliary Association
No attempts to add, modify or delete information
contained within this document shall be made. If
errors are discovered, please contact the U.S. Coast
Guard Auxiliary’s National Training Directorate.
Reviewed, DIR-T USCGAUX
Chapter 1 – What Drives the Weather?
Reviewed, DIR-T USCGAUX
Overview
 Overview of the AUXWEA course.
 Solar radiation, heat and temperature:
 The relationship between solar energy and weather.
 Energy balance in the atmosphere.
 Temperature and temperature scales.
 Specific Heat—its definition and importance.
 Types of energy transfer within and between objects.
 Global winds and the Coriolis Effect.
 Global wind and pressure patterns.
 The impact of Earth’s rotation on the nature of global winds.
Reviewed, DIR-T USCGAUX
3
Reviewed, DIR-T USCGAUX
4
Purpose of the Course
 This course is designed to give an Auxiliarist, whether pilot,
coxswain, or crew, a basic understanding of meteorology and
weather phenomena so they can be safer and more effective
in their roles.
 By necessity, it includes some very simple physical principles,
but nothing above high school level.
 It will not make observers or forecasters of you, but will teach
you how to make use of the vast stores of information about
current and forecast conditions.
 The focus at the end of the course is on education about
weather dangers and how to avoid or overcome them.
Reviewed, DIR-T USCGAUX
5
Course Outline
 Part I—The Science of Meteorology.
 Chap 1—What Causes the Weather?
 Chap 2—Pressure and Winds.
 Chap 3—Moisture, Latent Heat and Stability.
 Part II—The Wide Variety of Weather Phenomena.
 Chap 4—Air Masses, Fronts and Cyclones.
 Chap 5—Clouds, Precipitation and Optical Phenomena.
 Chap 6—Severe Weather.
 Part III—How do I Apply This Information?
 Chap 7—Observation and Forecast Data Sources.
 Chap 8—Preparing for and Executing a Mission.
Reviewed, DIR-T USCGAUX
6
How to Approach Your Study
 First, be sure to read the text and answer the study questions
PRIOR to class. This PPT presentation is simply an opportunity
to generate discussion, answer questions, and provide a
review of the material. You should read the study guide prior
to coming to class.
 If you are unsure about something in the material, ask the
instructor and/or discuss it with your fellow students.
 Appendices A and B in the Student Study Guide have more
information that can take your knowledge to the next level.
You are not responsible for this content.
 Finally, approach the course with a sense of adventure and
have fun!
Reviewed, DIR-T USCGAUX
7
Some Basic Definitions
 Meteorology is the science of the atmosphere, its physical
characteristics and principles, including weather in all its
forms.
 Weather is the current state of the atmosphere or its
forecast state, at a given time or for a given time span, and
for a given place or a defined area.
 Climate is the long-term average of the weather at a given
location or over a defined area. Typical time spans are 30
years or more.
Reviewed, DIR-T USCGAUX
8
Reviewed, DIR-T USCGAUX
9
Overview
 The importance of solar energy.
 Spectrum.
 Variation with latitude and season.
 Distribution within the atmosphere.
 The nature of energy and heat.
 Temperature.
 Types of energy.
 Heat as the manifestation of energy.
 The common temperature scales.
 The nature and importance of Specific Heat.
 The transfer of energy.
Reviewed, DIR-T USCGAUX
10
Solar Radiation
 The Sun is a large thermonuclear furnace that derives its
energy from the fusion of hydrogen.
 It radiates energy at all wavelengths, with the peak in the
visible (green) part of the spectrum.
 It also emits large amounts of energy in the infrared and
ultraviolet portions of the spectrum.
 Besides the visible, the ultraviolet energy is important in the
energy balance of the upper atmosphere (more in Chap 3).
 The very small portion of the total solar output that arrives
at the Earth has a profound effect on the weather.
Reviewed, DIR-T USCGAUX
11
The Solar Spectrum
 The sun radiates as though it
had an average temperature of
5,250 °C (black line)
 The yellow shows the spectrum
at the top of the atmosphere.
 The red spectrum is at sea
level, after the atmosphere has
absorbed and reflected part of
the energy.
 A nm is one billionth of a meter.
Reviewed, DIR-T USCGAUX
12
Distribution of Solar Energy
 Radiation that impinges
straight down on a surface
deposits more energy per
unit area than one that
impinges at an angle.
 The solar energy at the
equator is therefore more
concentrated than at the
poles.
©1997, USA Today. Reprinted with permission
Reviewed, DIR-T USCGAUX
13
The Effect of Seasons
©1997, USA Today. Reprinted with permission
 The Earth’s axis tilts by 23.5°. As it revolves around the
Sun, its axis points in various directions relative to the
Sun, but always to Polaris.
 The northern and southern hemispheres receive more
energy at certain times of the year.
 Northern in June and southern in December.
 Same amounts in March and September.
Reviewed, DIR-T USCGAUX
14
Energy Balance in the Atmosphere
Reflected Solar Energy
©1997, USA Today. Reprinted with permission
 Not all Solar energy is absorbed at the surface.
 Clouds and dust scatter visible light.
 Bright surfaces reflect more than dark surfaces.
Reviewed, DIR-T USCGAUX
15
Energy Balance (continued)
Courtesy of Intergovernmental Panel on Climate Change
 Once absorbed, energy is re-radiated and re-absorbed many
times over, in the infrared portion of the spectrum. It balances
at the surface and the top of the atmosphere.
Reviewed, DIR-T USCGAUX
16
Temperature and Heat
 Temperature is a measure of the average kinetic energy of
molecules in an object.
 Thermal energy (e.g. calories) is the total kinetic energy of
molecules in an object.
 Heat is the thermal energy being transferred from one
object to another.
 Heat always flows from the hotter object to the colder one.
Reviewed, DIR-T USCGAUX
17
What is Temperature?
COLD
Less kinetic
energy
Molecules
move slower
In cold air
Mercury
doesn’t
rise
WARM
More kinetic
energy
Molecules
move rapidly
in warm air
causing
mercury
to rise
©1997, USA Today. Reprinted with permission
A measure of kinetic energy—molecular motion.
Reviewed, DIR-T USCGAUX
18
The Two Primary Temperature Scales
212°
100°
32°
0°
Fahrenheit
Water boils (at
1 atmosphere)
Ice melts
Celsius
©1997, USA Today. Reprinted with permission
Reviewed, DIR-T USCGAUX
19
Converting Fahrenheit and Celsius
Temperature Conversion:
F = [C x 9/5] + 32
[C x 2, minus 10%]
C = ( F - 32 ) x 5/9
Approx. {(F-32) plus 10%} / 2
Reviewed, DIR-T USCGAUX
20
Specific Heat
 Specific Heat is defined as the energy it takes to raise a
fixed amount of substance by a fixed number of degrees.
 The units normally used in Meteorology are calories per
gram per degree Celsius.
 This calorie is the gram-calorie (cal).
 For measuring food energy the Kilogram-calorie (Kcal) is used.
It is a thousand times as large as the calorie.
 The calorie is defined by the Specific Heat of water—the
amount of energy it takes to raise one gram of water one °C.
 The specific heats of soil, vegetation, etc. are lower than
water, so they heat and cool faster (more in Chap 3).
Reviewed, DIR-T USCGAUX
21
How Energy is Transferred
 There are three common methods to transfer heat energy
from one object to another, or from one part of an object to
another:
 Conduction—molecular motion transferred from one molecule
to another. Occurs in solids and liquids, but very little in gases.
 Convection—the physical movement of parts of the substance,
usually vertically, as in heated water. Also occurs in gases.

In meteorology, horizontal movement is called advection.
 Radiation—the remote transfer of energy by electromagnetic
radiation. It does not require a medium for transfer, it is actually
more efficient in a vacuum.
 Examples of each of these are on the next slide.
Reviewed, DIR-T USCGAUX
22
Methods of Energy Transfer
Conduction
Convection
Radiation
Reviewed, DIR-T USCGAUX
23
Station Model--Temperature
 Weather measurements are
plotted on surface charts in
a specific way.
 Shown here is the station,
represented by the circle,
and the temperature in °F.
 We will add other data as
the class continues.
Reviewed, DIR-T USCGAUX
24
Reviewed, DIR-T USCGAUX
25
Overview
 The Coriolis Effect.
 What it is and what it is not.
 How it affects winds.
 Global Circulation.
 Without Coriolis.
 With Coriolis.
 Pressure bands.
 Prevailing winds.
 Effect of oceans and continents.
Reviewed, DIR-T USCGAUX
26
What is the Coriolis Effect?
 A term added to equations of motion when converted from
a fixed (inertial) to a rotating reference frame (the Earth).
 The Coriolis Effect has several properties:
 It causes winds to curve to the right in the northern




hemisphere.
It causes winds to curve to the left in the southern
hemisphere.
It increases with increasing Latitude (zero at the equator).
It increases with increasing wind speed.
It is effective only over long distances {NOT in sinks!}.
 Although it is not a true force, it behaves like one.
 A simplified picture of why it exists is on the next slide.
Reviewed, DIR-T USCGAUX
27
Why is There a Coriolis Effect?
 The disk is rotating like the
©1997, USA Today. Reprinted with permission
Earth viewed from above
the north pole.
 The man draws what
appears to him to be a
straight line (like a ball
thrown in space).
 An observer on the disk
(Earth) will observe the line
curving.
Reviewed, DIR-T USCGAUX
28
Global Circulation on a Nonrotating Earth
 Heat causes air at the equator
to rise. It sinks when it
reaches the poles.
 Winds at the surface blow
from the poles.
 This circulation is called a
Hadley cell.
 The Coriolis Effect changes
this model.
Reviewed, DIR-T USCGAUX
Courtesy of NOAA
29
Global Circulation on a Rotating
Earth
 With the Coriolis Effect, a
single Hadley cell is not
stable and breaks into three
cells.
 Where air rises, the surface
pressure is low.
 Where air falls, the surface
pressure is high.
 Coriolis also affects the
direction of the winds.
Polar Cell
Ferrel Cell
Hadley
Cell
Reviewed, DIR-T USCGAUX
Courtesy of NOAA
30
Cross-section, with Jet Streams
Courtesy of NOAA
Reviewed, DIR-T USCGAUX
31
Pressure Bands
©2008, US Power Squadrons. Reprinted with permission
Reviewed, DIR-T USCGAUX
32
Prevailing Winds
 The three cells and the
resulting pressure bands
cause surface winds.
 The Coriolis Effect bends the
winds.
 The prevailing winds are:
 The Trade Winds.
 The Prevailing Westerlies.
 The Polar Easterlies.
©2008, US Power Squadrons. Reprinted with permission
Reviewed, DIR-T USCGAUX
33
Global Circulation Summary
Courtesy of University of Connecticut
Reviewed, DIR-T USCGAUX
34
Summary of Global Circulation
 From the equator to the poles, the pressure bands are:
 Equatorial low, called the Doldrums (light winds).
 Mid-latitude highs, called the Horse Latitudes (also
light winds).
 The sub-polar lows.
 The polar highs.
 The winds are:
 Northeast and southeast trade winds.
 Prevailing westerlies.
 Polar easterlies.
 This simple picture is complicated by the continents.
Reviewed, DIR-T USCGAUX
35
Effects of Continents and Oceans
©1997, USA Today. Reprinted with permission
Reviewed, DIR-T USCGAUX
36
Summary (1 of 3)
 Meteorology is the scientific study of the atmosphere.
 Weather is the current or forecast state of the atmosphere.
 Climate is the average of the weather over a long period.
 The Sun is the source of all energy driving the weather.
 More solar energy falls on the equator than on the poles.
 Axial tilt and the Earth’s orbit drive seasonal changes.
 The energy balance of the Earth is complex and ever
changing.
 The Sun’s energy is strongest in the visible portion of the
spectrum, the Earth’s is strongest in the Infrared.
Reviewed, DIR-T USCGAUX
37
Summary (2 of 3)
 Temperature is due to the average kinetic energy of atoms
 The main temperature scales are Fahrenheit and Celsius.
 Pure ice melts at 32 °Fahrenheit or 0 °Celsius.
 At standard pressure, pure water boils at 212 °F or 100 °C
 Specific heat is the energy required to raise the
temperature of one gram of a substance by 1° C.
 A calorie is defined as the specific heat of pure water.
 Heat energy is transported by conduction, convection and
radiation.
 In meteorology, horizontal transport is an analog of
convection, called advection.
Reviewed, DIR-T USCGAUX
38
Summary (3 of 3)
 Global circulation is driven by unequal heating between the equator
and the poles and is modified by the Coriolis effect.
 The Coriolis effect is due to the Earth’s rotation and acts like a force,
but is not one.
 It increases with increasing wind speed and increasing latitude and
operates only over long distances.
 From the equator to the poles, the pressure belts are:
 The doldrums (low), horse latitudes (high), sub-polar lows, and polar
highs.
 Land and oceans break these into semi-permanent highs and lows.
 The wind belts are:
 The trade winds (easterly), the prevailing westerlies, and the polar
easterlies.
Reviewed, DIR-T USCGAUX
39
Chapter 1 Questions
QUESTION
ANSWER
How does the amount of energy per unit
area that arrives at the top of the
atmosphere change with latitude?
The largest temperature swings are:
With the seasons.
With the same heat input, do the oceans
or land heat faster?
The Specific Heat of a substance is:
Temperature is defined as:
Decreases with increasing latitude.
The land.
The rate of temperature increase for a
given energy input.
A measure of the average kinetic
energy of molecules.
Reviewed, DIR-T USCGAUX
40
Chapter 1 Questions
QUESTION
ANSWER
A temperature of 0° Celsius is:
The melting point of pure water ice.
The transfer of heat by the horizontal
movement of air is:
Advection.
The transfer of heat between bodies that
are not in contact is:
Radiation.
The vertical movement of air is called:
Winds near the equator are called:
Convection.
Trade Winds.
Reviewed, DIR-T USCGAUX
41
Chapter 1 Questions
QUESTION
ANSWER
The region of low pressure near the
equator is called:
The doldrums.
The Intertropical Convergence Zone (ITCZ)
is located:
Near the equator.
Heat is transported north and south from
the equator by:
Winds and ocean currents.
The region of relatively high pressure near
30° latitude is known as the:
Horse Latitudes.
How does the Coriolis Effect vary with
latitude?
Increases with increasing latitude.
Reviewed, DIR-T USCGAUX
42
End of Chapter 1
 Do you have any
questions?
 Chapter 2 covers
Pressure and Winds
Reviewed, DIR-T USCGAUX