Aerographer’s Mate Second Class, Volume 1

8/9/2019 Aerographers Mate Second Class, Volume 1

1/479

NAVEDTRA 10370Naval Education and August 1988 Training ManualTraining Command 0502-LP-213-5900 (TRAMAN)

Aerographers MateSecond Class,

Volume 1

DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.

The public may request copies of this document by followingthe purchasing instruction on the inside cover.


2/479

Although the words he, him, and hisare used sparingly in this manual to enhancecommunication, they are not intended to begender driven nor to affront or discriminateagainst anyone reading this material.

DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.

The public may request copies of this document by writing to Superintendent of Documents, Government PrintingOffice, Washington, DC 20402-0001 or to the Naval Inventory Control Point (NICP) - Cog I Material, AttentionCash Sales, 700 Robbins Avenue, Philadelphia PA 19111-5098.


3/479

AEROGRAPHERS MATESECOND CLASS,

VOLUME 1

NAVEDTRA 10370

1988 Edition Prepared by AGCM Patrick J. OBrien, AGCM Harry H. H ale, and AGCM Ingolf H. Su hm ann


4/479


5/479

PREFACE

This training manual (volume 1 of a 2 volume set) is one of a series of training manuals prepared for enlisted personnel of the Navy and NavalReserve who are studying for advancement in the Aerographer (AG) rating.As indicated by the t itle, this man ua l is based upon th e professiona l qualifica-tions for the rate of AG2 as set forth in the Manual of Qualifications for

Advancement, NAVPERS 18068 (Series).

The NRTC (Nonresident Training Course) is not included with thismanual. Information on course administration and ordering is available in

NAVEDTRA 10061.

This manua l was prepared by the Naval Education a nd Training ProgramManagement Support Activity, Pensacola, Florida, for the Chief of NavalEducation and Training.

Your suggestions and comments on this manual are invited. Address themto Commanding Officer, Code 3102, NETPMSA, Pensacola, FL 32509-5000.

1988 Ed ition

S t o c k O r d e r i n g N o .0502-LP -213-5900

Published by

NAVAL EDUCATION AND TRAININGPROGRAM MANAGEMENT SUPPORT ACTIVITY

UNITED STATESGOVERNMENT PRINTING OFFICE

WASHINGTON, D.C.: 1988

i


6/479

THE UNITED STATES NAVY

GUARDIAN OF OUR COUNTRYThe United States Navy is responsible for maintaining control of thesea and is a ready force on watch at home and overseas, capable of strong action to preserve the peace or of instant offensive action towin in war.

It is u pon the maint enan ce of this cont rol that our count rys gloriousfuture depends; the United States Navy exists to make it so.

WE SERVE WITH HONOR

Tradition, valor, an d victory are the Navys her itage from the past . Tothese may be added dedication, discipline, and vigilance as the

watchwords of the present and the future.

At home or on distant stations we serve with pride, confident in therespect of our country, our shipmates, and our families.

Our r esponsibilities sober u s; our adversities str engthen us.

Service to God and Country is our special privilege. We serve withhonor.

THE F UTURE OF TH E NAVY

The Navy will always employ new weapons, new techniques, andgreater power to protect and defend the United States on the sea,under th e sea, and in the air.

Now and in the future, control of the sea gives the United States hergreatest advantage for the maintenance of peace and for victory inw a r.

Mobility, surprise, dispersal, and offensive power are the keynotes of the new Navy. The roots of the Navy lie in a strong belief in thefuture, in continued dedication to our tasks, and in reflection on ourheritage from the past.

Never have our opportunities and our responsibilities been greater.

ii


7/479

C O N T E N T S

UNIT 1 FUNDAMENTALS OF METEOROLOGY

LESSON 1.

2.

3.

4.

5 .

System of measurement . . . . . . . . . . . . . . . . . . . .

Earth - Sun relationship . . . . . . . . . . . . . . . . . . . .

Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Moisture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

UNIT 2 ATMOSPHERIC PHYSICS

LESSON 1. Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2. Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3. Gas laws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4. Atmospheric energy . . . . . . . . . . . . . . . . . . . . . . . .

UNIT 3 ATMOSPHERIC CIRCULATION

LESS ON 1. Gener al circula tion . . . . . . . . . . . . . . . . . . . . . . . . .

2. Secondary circulation . . . . . . . . . . . . . . . . . . . . . .

3. Tertiary circulation . . . . . . . . . . . . . . . . . . . . . . . .

UNIT 4 AIR MASSES AND FRONTS

LESSON 1.

2 .

3 .

4.

5 .

6 .

7.

Air masses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fronts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The cold front . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The warm front . . . . . . . . . . . . . . . . . . . . . . . . . . .

The occluded fronts . . . . . . . . . . . . . . . . . . . . . . . .

The quasi-stationary front . . . . . . . . . . . . . . . . . .

Modifications of fronts . . . . . . . . . . . . . . . . . . . . .

ii i

1-1-1

1-2-1

1-3-1

1-4-1

1-5-1

2-1-1

2-2-1

2-3-1

2-4-1

3-1-1

3-2-1

3-3-1

4-1-1

4-2-1

4-3-1

4-4-1

4-5-1

4-6-1

4-7-1


8/479

UNIT 5 ATMOSPHERIC PHENOMENA

LES SON 1. Hydr omet eors . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2. Lithometeors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3. Photometeors . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4. Electrometeors . . . . . . . . . . . . . . . . . . . . . . . . . . . .

UNIT 6 CLIMATOLOGY AND WORLD WEATHER

LESSON 1.

2.

3.

4.

5.

6.

7.

Climate and climatology . . . . . . . . . . . . . . . . . . . .

Clima tic elem ent s . . . . . . . . . . . . . . . . . . . . . . . . . .

Expression of climatic elements . . . . . . . . . . . . . .

Classification of climate . . . . . . . . . . . . . . . . . . . .

Climatic controls . . . . . . . . . . . . . . . . . . . . . . . . . .

Climatological data . . . . . . . . . . . . . . . . . . . . . . . .

World weather . . . . . . . . . . . . . . . . . . . . . . . . . . . .

UNIT 7 SURFACE CHARTS AND THEIR ANALYSIS

LESSON 1.

2.

3.

4.

5.

Fundamentals of surface chart analysis . . . . . . .

Isobar ic an alysis . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fr onta l an alysis . . . . . . . . . . . . . . . . . . . . . . . . . . .

Finalizing the analysis . . . . . . . . . . . . . . . . . . . . . .

South ern Hem ispher e an alysis . . . . . . . . . . . . . . .

UNIT 8 UPPER-AIR CHARTS AND THEIR ANALYSIS

LESSON 1.

2.

3.

4.

5.

Upper-air analysis . . . . . . . . . . . . . . . . . . . . . . . . .

Use of constant-pressure charts . . . . . . . . . . . . . .

Circulation patterns on upper-air charts . . . . . .

Convergence and divergence . . . . . . . . . . . . . . . . .

Rotational motion as it affects the

atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

UNIT 9 TROPICAL METEOROLOGY AND ANALYSIS

LESS ON 1. Genera l aspects of tr opical an alysis . . . . . . . . . .

2. Tropical a na lysis . . . . . . . . . . . . . . . . . . . . . . . . . . .

3. Tropical phenomena . . . . . . . . . . . . . . . . . . . . . . .

i v

5-1-1

5-2-1

5-3-1

5-4-1

6-1-1

6-2-1

6-3-1

6-4-1

6-5-1

6-6-1

6-7-1

7-1-1

7-2-1

7-3-1

7-4-1

7-5-1

8-1-1

8-2-1

8-3-1

8-4-1

8-5-1

9-1-1

9-2-1

9-3-1


9/479

UNIT 10 SATELLITE, RADAR, AND LDATSIMAGERY INTERPRETATION

LESSON 1. Environm enta l satellite imagery an alysis . . . . . . 10-1-1

2. Cloud interpretation . . . . . . . . . . . . . . . . . . . . . . . 10-2-1

3. Interpreting subsynoptic- and synoptic-scalecloud features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-3-1

4. Radar and LDATS interpretation . . . . . . . . . . . . 10-4-1

A P P E N D I X

I. Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AI-1

II . Tropical cyclone intensity analysiste chn iqu e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AII-1

INDE X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I NDEX-1

v


10/479

SUMMARY OF AEROGRAPHERSMATE 2 TR AINI NG MANUALS

VOLUME 1

Aerographers Mate 2, Volume 1, NAVEDTRA 10370 is designed to servepersonnel in the AG rating. Subjects covered in this volume include:fundamentals of meteorology, atmospheric physics, atmospheric circulation,atmospheric phenomena, air masses, fronts, climatology, tropical meteorology,weather chart analysis, and imagery interpretation (satellite, radar, and LDATS(lightning detection and tracking system)).

VOLUME 2

Aerographer s Mate 2, Volume 2 , NAVEDTRA 10371 covers thefollowing areas: oceanography, oceanographic imalysis, fundamentals of hydroacoustics, meteorological and oceanographic products and theirin terpre ta t ion , spec ia l products and computa t ions , br ie f ing techniques ,administration, supply, and publications.

NONRESIDENT TRAINING COURSES

Two separate nonresident training courses are available for study andcompletion. Their titles and NAVEDTRA numbers are listed below:

Aerographers Mate 2, Volume 1, NAVEDTRA 80370 Aerographers Mate 2, Volume 2, NAVEDTRA 80371

v i


11/479

Just prior to this TRAMAN being printed, theWor ld Me teo ro log i ca l Organ iza t i on adop tedhectopasca ls (hPa) as i t s s tandard uni t of measurement for pressure. This TRAMAN usesthe old standard of millibars (mb). Because theunits of hectopascals and millibars are inter-changeable (1 hPa = 1 mb) hectopascals shouldbe substituted for millibars.

v ii


12/479


13/479

UNIT 1

F U N D A M E N TAL S O FM E T E O R O L O G Y

F O R E W O R D

Meteorology is the study of atmospheric phenomena. This study consistsof physics, chemistr y, and dyna mics of the at mosphere. It a lso includes m anyof th e direct effects the a tm osphere ha s upon E ar th s sur face, the oceans ,an d life in general. The goals often a scribed to meteorology are th e completeunderstanding and accurate prediction of atmospheric phenomena.

Meteorology may be subdivided into a large number of specialized sciences.These specialized sciences will be covered in depth in Unit 6.

The treatment of meteorology in this manual progresses from the overallfundam enta ls of meteorology to a th orough description of at mospheric physicsand circulation, air masses, fronts, and meteorological elements. Thisinformation supplies the necessary background for you to understand chartanalysis, tropical analysis, satellite analysis, and chart interpretation. Withthis knowledge you can become a confident, well-informed weather analyst,interpreter, and briefer.

This f irst unit covers the following lessons: Lesson 1, Systems of Measurement; Lesson 2, Earth-Sun Relationship; Lesson 3, Pressure; Lesson4, Temperature; and Lesson 5, Moisture.

1-0-1


14/479


15/479

UNIT 1LESSON 1

S YS T E M O F M E AS U R E M E N T

OVERVIEW OUTLINE

Recognize how the Metric System and the English Metric SystemSystem are used in meteorology.

English System

SYSTEM OF MEASUREMENT

To work in the field of meteorology, you musthave a basic understanding of the science of measurement (metrology). When you can measurewhat you are talking about and express i t innumerical values, you then have a knowledge of your subject. To measure how far something ismoved, or how heavy it is, or how fast it travels,you may use a specific measurement system. Thereare many such systems throughout the worldtoday. The Metric System (CGS, centimeter-grarn-second) has been recognized for use in science and

research. Therefore, that system is discussed inthe paragraphs that follow, with brief pointsof comparison to the English System (FPS,foot-pound-second).

Lea rn ing Ob jec t i ve : Recogn ize t he un i t sof measure used in the Metr ic Sys tem andthe En gl ish Sys tem and how th ese sys temsof measurement a re used in Meteoro logy.

The metric system is easy to learn as it isbased on decimals. Because metrics are widelyused in the field of meteorology, they are usedthroughout the manual . An in t roduct ion tometrics is presented in this unit. For a moredetailed discussion of metrics, you should referto OCC-ECC, The Metric System, NAVEDTRA475-01-00-79.

As you saw earlier, the metric system usescentimeter-gram-seconds (CGS) to describe physi-cal events. These units measure length, weight,and time, respectively. The derivation of thoseunits are described briefly.

LENGTH

To fam iliar ize you with t he convent iona l un itsof metric length, start with the meter.

The meter is slightly larger than the Englishyard (39.36 inches vs 36 inches). Prefixes are usedin conjunction with the meter to denote smaller

or larger units of the meter. Each larger unit isten t imes larger tha n t he next smaller unit . (Seetable 1-1-1. )

Table 1-1-1.Common p re f ixes used in th e Met r i c Sys t

1-1-1


16/479

Since th e C in CGS represent s centimeters (cm)you should see from ta ble 1-1-1 that the centimeteris one-hundredth of a meter, .01M, or 10 -2 M.Conversely, 1 M equals 100 cm.

To describe a gram , the G in th e CGS system,you must first have a familiarization with area andvolume.

AREA AND VOLUME

A square has four equal sides and it is aone -p l ane f i gu re - l i ke a shee t o f pape r. Todetermine how much surface area is enclosedwithin the square you multiply the length of oneside by the length of the other equal side. If thesides were 1 centim eter (cm) in length t he a rea of the square would be 1 cm x 1 cm = 1 square cm,or 1 cm 2.

Now, if squares having an area of 1 cm 2 werestacked on top of each other until the stack was1 cm tall, you would end up with a cube whosesides were each 1 cm in length . To determ ine th evolume of the cube you simply multiply th e lengthby the width and height. Because each side is 1cm you end up w i th a vo lume o f 1 cub i ccentimeter (cm 3) (1 cm x 1 cm x 1 cm = 1 cm 3).More simply sta ted, mu ltiply the ar ea of one sideof the cube by the height of the cube. Onceyou understand how the volume of a cube isdetermined, you are now ready to review the Gin the CGS system.

W E I G H T

The conventional unit of weight in the metricsystem is the gram (gm). You could use table 1-1-1and substi tute the word gram for meter and thesymbol (gm) for the symbol (M). You would thenhave a table for metric weight. The gram is theweight of 1 cm 3 of pure water at 4C. At thispoint it may be useful to compare the weightof an object to i ts mass. The weight of the1 cm 3 of water is 1 gm. Weight and mass are

proportional to each other. However, the weightof the 1 cm 3 of water changes as you move awayfrom the gravitational center of Earth. In spacethe 1 cm 3 of water is weightless, but it is still amass . Mass i s exp re s sed a s a func t ion o f inertia/acceleration, while weight is a function of gravitational force. When we express the move-ment of an object we use the terms mass and

acceleration.

TIME

Time is measured in hours, minutes, andseconds in both systems. Hence, the second neednot be explained in the CGS system. With aknowledge of how the CGS system can be usedto express physical entities, you n ow have all th ebackground t o express such things as densit y andforce.

DENSITY

With the previous explanation of grams andcentimeters, you should be able to understandhow physica l fac tors can be measured anddescribed. For example, density is the weightsomething has per unit of volume. The densityof water is given as 1 gram per cubic centimeteror 1 gm/cm 3. By comparison, the density of waterin the English system is 62.4 pounds per cubic footor 62.4 lb/ft 3 .

F O R C E

Force is measured in dynes. A dyne is the forcethat moves a mass of 1 gram, 1 centimeter persquare second. This is commonly written as gmcm per sec 2, gm cm/sec/sec or gm/cm/sec 2. Theforce necessary for a gram to be accelerated at980.665 cm/sec 2at45 latitude is 980.665 dynes.For more detailed conversion factors commonlyused in meteorology and oceanography, refer toSmithsonian Meteorology Tables.

1-1-2


17/479

UNIT 1LESSON 2

E ART H -S U N R e l a t i o n s h i p

OVERVIEW OUTLINE

Describe how the Earth-Sun relationship affects Su nradiation and incoming solar radiation. Ea r th

Radiation

Insolation

Radiation (Heat) Balance in the Atmosphere

EARTH-SUN RELATIONSHIP

The Sun is a great thermonuclear reactor about93 million miles from Earth. It is the originalsource of energy for the atmosphere and life itself.The Su ns en ergy is efficiently stored on E ar th insuch things as oil, coal, and wood. Each of thesewas pr oduced by some biological mea ns when th eSun acted upon living organisms. Our existence

depends on the Sun because without the Sun therewould be no warmth on Earth, no plants to feedanimal life, and no animal life to feed man.

The Sun is important in meteorology becauseall natural phenomena can be traced, directly orindirectly, to the energy received from the Sun.Al though the Sun radia tes i t s energy in a l ldirections, only a small port ion reaches ouratmosphere. This relatively small portion of theSun s total ener gy represents a lar ge port iono f t h e h e a t e n e rg y f o r o u r E a r t h . I t i s o f such impor tance in meteorology tha t everyAerographer s Mate sh ould have at least a basic

knowledge about the Sun and the effects it hason Eart hs weat her.

Lea rn ing Ob jec t i ve : Desc r ibe how rad i a -t i on a n d i n s ol a t io n a r e a f fe c t e d b y t h eE a r t h -S u n r e l a t i on s h i p .

SUN

The Sun may be regarded as the only sourceof heat energy th at is supplied to Eart hs sur faceand the atmosphere. All weather and motions inthe atmosphere are due to the energy radiatedfrom the Sun.

T h e S u n s co r e h a s a t e m p e r a t u r e o f 15,000,000K an d a s ur face temper at ur e of about6,000K (10,300F). The Sun radiates electro-magnetic energy in all directions. However, Earthintercepts only a small fraction of this energy.Most of the electromagnetic energy radiated byth e Sun is in th e form of light waves. Only a tinyfraction is in the form of heat waves. Even so,better t han 99.9 percent of Ear ths hea t is der ivedfrom the Sun in the form of radiant energy.

Solar Composi t ion

The Sun may be described as a globe of gasheated to incandescence by thermonuclear reac-tions from within the central core.

The main body of the Sun, although com-posed of gases, is opaque an d ha s several distin ctlayers. (See fig. 1-2-1. ) The first of these layersbeyond th e r adiat ive zone is th e convective zone.This zone exten ds very nea rly to the Sun s sur face.Here, heated gases ar e raised buoyant ly upwardswith some cooling occurring and subsequentconvective action similar to that which occurswithin E ar ths at mosphere: The next layer is a

1-2-1


18/479

Figu re 1-2-1.One-quar ter cross-sect ion depic t ing solar s t ructure .

well-defined visible surface layer referred to as thephotosphere. The bottom of the photosphere isthe solar surface. In this layer the temperature hascooled to a sur face tem perat ur e of 6,000K at th ebottom to 4,300K at t he t op of the layer. All thelight and heat of the Sun is radiated from thephotosphere. Above the photosphere is a moretransparent gaseous layer referred to as thechromosphere with a thickness of about 1,800miles (3,000 km). It is hotter than the photo-sphere. Above the chromosphere is the corona,a low density high temperature region. It isextended far out into interplanetary space by thesolar winda steady outward streaming of thecoronal materiai. Much of the electromagneticradiation emissions consisting of gamma raysthrough x- rays , u l t ravio le t , v is ib le and radiowaves, originate in the corona.

With in the so lar a tmosphere we see theoccurrence of transient phenomena (referred toas solar activity), just as cyclones, frontal systems,and thunderstorms occur within the atmosphere

of Earth. This solar activity may consist of thephenomena discussed in the following paragraphswhich collectively describe the features of the solardisk (the visual image of the outer surface of thesun as observed from outside regions). (See fig.1-2-2. )

So l a r P rominences /F i l amen t s

Solar prominences/fiiaments are injections of gases from the chromosphere into the corona.They appear as great clouds of gas, sometimesrestin g on th e Suns surface and at oth er timesfloating free with no visible connection. Whenviewed against t he solar disk, th ey appear a s longdark ribbons and are called filaments. Whenviewed against the solar limb (the dark outer edgeof the solar disk), they appear bright and arecalled prominences. (See fig. 1-2-2. ) They displaya variety of shapes, sizes, and activity that defygeneral description. They have a fibrous st ru ctu reand appear to resist solar gravity. They may

1-2-2


19/479

Figure 1-2-2 . F e a t u r e s o f t h e s o la r d i s k .

extend 18,500 to 125,000 miles (30,000 to 200,000 k m)above th e chromosphere. The m ore a ctive types h avetemperatures of 10,000K or more and appear hottertha n the sur rounding atmosphere.

S u n s p o t s

Sunspots ar e r egions of str ong localized ma gneticfields and indicate relatively cool areas in thephotosphere. They appear darker than theirsurroundings and may appear singly or in morecomplicated groups dominated by larger spots nearthe cent er. (See fig. 1-2-2. )

Sunspots begin as small dark areas known aspores. These pores develop into full-fledged spots in afew days, with maximum development occurring inabout 1 to 2 weeks. When sunspots decay the spotshrinks in size and its magnetic field also decreasesin size. This life cycle may consist of a few days forsmall spots to near 100 days for larger groups. The

larger spots normally measure about 94,500 miles(120,000 km) across. Sunspots appear to have cyclicvariations in intensity, varying through a period of about 8 to 17 years. Variation in number and sizeoccurs throughout the sunspot cycle. As a cyclecomm ences, a few spots a re observed at h igh lat itudesof both solar hemispheres, and the spots increase insize and number. They gradually drift equatorwardas t he cycle progresses, an d th e intens ity of the spotsreach a maximum in about 4 years. After this period,decay sets in an d near th e end of the cycle only a few

spots a re left in th e lower lat itu des (50 to 100).

P l a g e s

Plages are large irregular bright patches thatsurround sunspot groups. (See fig. 1-2-2. ) Theynormally appear in conjunction with solar promi-nences or filaments and may be systematicallyarr anged in radial or spiral patt erns. Plages

1-2-3


20/479

ar e feat ur es of th e lower chromosphere an d oftencompletely or partially obscure an underlyingsunspot.

F l a r e s

Solar flares are perhaps the most spectacularof the eruptive features associated with solaractivity. (See fig. 1-2-2. ) They look like flecks of light that suddenly appear near activity centersand come on instantaneously as though a switchwere thrown. They rise sharply to peak brightnessin a few minutes, then decline more gradually. Thenumber of flares may increase rapidly over an areaof activity. Small flarelike brightening are alwaysin progress dur ing the more ac t ive phase of activity centers. In some instances flares may takethe form of prominences, violently ejectingmaterial into the solar at mosphere and breakinginto smaller high-speed blobs or clots. Flareactivity appears to vary widely between solar

activity centers. The greatest flare productivityseems to be during the week or 10 days whensunspot activity is at its maximum.

Flares are classified according to size andbrightness. In general, the higher the importanceclassification, the stronger the geophysical effects.Some phenomena associated with solar flares haveimm ediat e effects; oth ers h ave delayed effects (15minutes to 72 hours after flare).

So l a r f l a r e ac t i v i t y p roduces s i gn i f i can td i s r u p t i on s a n d p h e n om e n a w i t h i n E a r t h satmosphere. During solar flare activity, solarparticle streams (solar winds) are emitted andoften intercept Earth. These solar particles arecomposed of electromagnetic radiation whichintera cts with Ea rt hs ionosphere. This results inseveral reactions such as: increased ionization(electrically charging neutral particles), photochemical changes (absorption of radiation),atm ospheric heating, electrically cha rged pa rticlemotions, and an influx of radiation in a variety

Figu re 1-2-3.Rotat ion of Ear th about i t s axis (dur ing equinoxes) .

1-2-4


21/479

of wavelengths and frequencies which includeradio and radar frequencies.

Some of the resulting phenomena include thedisruption of radio communications and radardetection. This is due to ionization, incomingra dio waves, and th e motion of cha rged par ticles.Satellite orbits can be affected by the atmospheric

heating and satellite transmissions may be affectedby all of the reactions previously mentioned.Geomagnetic disturbances like the aurora borealisand aurora austral is result primarily from themotion of electr ically cha rged pa rt icles within th eionosphere.

E A RT H

Of th e nine planets in our solar system , Eart his the third nearest to (or from) the Sun. Earthvaries in distance from the Sun during the year.The Sun is 94 million miles (150,400,000 km) insummer and 91 million miles (145,600,000 km)

in winter.M o t i o n s

Ea r th i s sub j ec t t o fou r mo t ions i n i t smovement through space: rotation about its axis,

revolution around the Sun, precessional motion(a slow conical movement or wobble) of the axis,an d th e solar motion (the m ovement of th e wholesolar system with space). Of the four motionsaffecting Earth, only two are of any importanceto meteorology.

The first motion is rotation. Earth rotates on

its a xis once every 24 hour s. One-ha lf of Ea rt hssurface is therefore facing the Sun at all times.Rota tion about Ea rt hs axis tak es place in aneastward direction. Thus, the Su n a ppears to r isein the east and set in the west . (See fig. 1-2-3. )

The second motion of Earth is its revolutionaround the Sun. The revolution around the Sunand the tilt of Earth on its axis are responsiblefor our seasons . Ear th makes one comple terevolu t ion around the Sun in approximate ly365 1/4 days. Ea rt hs axis is at a n a ngle of 23 1/2to its plane of rotation and points in a nearly fixeddirection in space toward the North Star (Polaris).

So ls t i c e s and E qu inoxes

When Earth is in its summer solstice, as shownfor June in figure 1-2-4, the Northern Hemisphere

Figure 1-2-4.Revo lu t ion o f Ea r th a round the Sun .

1-2-5


22/479

is inclined 23 1/2 TOWARD the Sun. Thisinclina tion resu lts in more of th e Suns ra ysreaching the Nor thern Hemisphere than theSouthern Hemisphere. On or about June 21,direct sunlight covers the area from the NorthPole down to latitude 66 1/2N (the ARCTICCIRCLE). The area between the Arctic Circle andth e North Pole is receiving th e Sun s ra ys for 24hours each day. Dur ing th is t ime the mostperpendicular rays of the Sun are received at23 1/2N latitude (the TROPIC OF CANCER).Because the Southern Hemisphere is tilted AWAYfrom t he Sun at t his time, the indirect rays of theS u n r e a c h o n l y t o 6 6 1 / 2 S l a t i t u d e ( t h eANTARCTIC CIRCLE). Therefore, the areabetween the Antarctic Circle and the South Poleis in complete darkness. Note carefully the shadedand unshaded area of Earth in figure 1-2-4 forall four positions.

At t he time of the equinox in March a nd a gainin September, t he tilt of Eart hs axis is neithertoward nor away from th e Sun. For these rea sonsEar th receives an equal amount of th e Sunsenergy in both the Northern Hemisphere and theSouth ern Hem isphere. During th is time the Sun srays shine most perpendicularly at the equator.

In December, the situ at ion is exactly reversedfrom tha t in Ju ne. The South ern Hemisphere nowreceives more of the Suns direct rays. The mostperpendicular rays of the Sun are received at23 1/2S lat i tude (the TROPIC OF CAPRI-CORN) . The sou the rn po l a r r eg ion i s nowcompletely in sunsh ine; the north ern polar regionis completely in darkness.

Since the revolution of Earth around the Sunis a gradual process, the changes in the areareceiving th e Sun s ra ys an d th e changes in sea sonsare gradual. However, i t is customary andconvenient to mark these changes by specific datesand to identify them by specific names. Thesedates are as follows:

1 . March 21 . The VERNAL EQUINOX,when E art hs axis is perpendicular t o the Su nsrays. Spring begins in the Northern Hemisphereand fall begins in the Southern Hemisphere.

2. June 21. The SUMMER SOLSTICE, whenEa rt hs axis is inclined 23 1/2 towar d th e Sunand t he Sun has r eached i ts northernmost zenitha t the Tropic of Cancer. Summer off ic ia l lycommences in the Northern Hemisphere; winterbegins in the Southern Hemisphere.

3. September 22. The AUTUMNAL EQUI-NOX, when Ea rt hs axis is again per pendicularto the Sun s ra ys. This date m ark s th e beginning

of fall in th e Northern Hemisphere a nd spring inthe Southern Hemisphere. It is also the date, alongwith March 21, when t he Sun reaches its highestposition (zenith) directly over the equator.

4. December 22. The WINTER SOLSTICE,when the Sun has reached its southernmost zenithposition at th e Tropic of Capricorn. It m ark s th ebeginning of winter in the Northern Hemisphereand the beginning of summer in the SouthernHemisphere.

In some years, the actual dates of the solsticesand the equinoxes vary by a day from the datesgiven here. This is because the period of revolutionis 365 1/4 days an d th e calendar year is 365 daysexcept for leap year when it is 366 days.

Because of its 23 1/2 tilt and its revolutionaround the Sun, Ear th is mar ked by five natu rallight (or hea t) zones a ccordin g to the zonesrelat ive position to th e Sun s ra ys. Since the Su nis ALWAYS at its zenith between the Tropic of Cancer and the Tropic of Capricorn, this is thehottest zone. It is called the Equ atorial Zone, theTorrid Zone, the Tropical Zone, or simply theTropics.

The zones between the Tropic of Cancer andthe Arctic Circle and between the Tropic of Capr icorn and the Antarc t ic Ci rc le a re theTemperate Zones. These zones receive sunshineall year, but less of it in th eir respective wintersand more of it in their respective summers.

The zones between the Arctic Circle and theNorth Pole an d between th e Antar ctic Circle andth e South Pole receive th e Sun s ra ys only forparts of the year. (Directly at the poles there are6 months of dark ness an d 6 months of sunsh ine.)This, naturally, makes them the coldest zones.They are therefore known as the Frigid or PolarZones.

RADIATION

The term RADIATION refers to the processby which electromagnetic energy is propagatedthrough space. Radiation moves at the speed of light, which is 186,000 miles per second (297,600km per second) and travels in straight lines in avacuum. All of the heat received by Earth isthrough this process. It is the most importantmeans of heat transfer.

SOLAR RADIATION is defined as the totalelectromagnetic energy emitted by the Sun.The Sun s sur face emits gamm a ra ys, x-ra ys,ultraviolet , visible l ight , infrared, heat , andelectromagnetic waves. Although the Sun radiates

1-2-6


23/479

in all wavelengths, about half of the radiation isvisible light with most of the remainder beinginfrared. (See fig. 1-2-5. )

Energy radiates from a body by wavelengthswhich vary inversely with the temperature of thatbody. Therefore, the Sun, with an extremely hotsurface temperat ure, emits short wave radiation.

Ear th has a much cooler tempera ture (15Caverage) and th erefore rer adiat es the Sun s energyor heat with long wave radiation.

INSOLATION

Insolation (an acronym for INcoming SOLarradiATION) is the rate at which solar radiationis received by a unit horizontal surface at anypoint on or above the surface of Earth. In thismanual, insolation is used when speaking aboutincoming solar radiation.

There is a wide variety of differences in theamounts of radiation received over the variousport ions of Ea rt hs sur face. Thes e differences inheating are important and must be measured orotherwise calculated to determine their effect onthe weather.

The insolation received at the surface of Earthdepends upon the solar constant ( the rate atwhich solar r adiat ion is r eceived outside Ea rt hsatmosphere), the distance from the Sun, inclina-t i on o f t h e S u n s r a y s , a n d t h e a m o u n t o f insolation depleted while passing through theatmosphere . The las t two are the impor tantvariable factors.

D e p l e t i o n o f S o l a r R a d i a t i o n

If the Su ns ra diation was n ot filtered ordepleted in some manner, our planet would soonbe too hot for life to exist. We must now considerhow the Sun s heat energy is both disper sed an ddepleted. This is accomplished through dispersion,scattering, reflection, and absorption.

DISPERSION. Earlier i t was learned thatEarths axis is inclined at an angle of 23 1/2. Thisinclinat ion cau ses th e Sun s r ays t o be receivedon the surface of Earth at varying angles of incidence, depending on the position of Earth.When the Suns ra ys are n ot perpendicular to thesurface of Ear th , the energy becomes DIS-PERSED or sp read ou t ove r a g rea t e r a r ea

Figure 1-2-5.Elec t romagne t i c spec t rum.

1-2-7


24/479

Figure 1-2-6.-Dispers ion of insola t ion .

(fig. 1-2-6) . If the available energy reaching theatmosphere is constant and is dispersed over agreater area, the amount of energy at any givenpoint with in the ar ea decreases, and th erefore thetemperature is lower. Dispersion of insolation inthe atmosphere is caused by the rotation of Earth.Dispersion of insolat ion also tak es place with t heseasons in all latitudes, but especially in thelatitudes of the polar areas.

SCATTERING. About 25 percent of theincoming solar radiation is scattered or diffusedby the atmosphere. Scattering is a phenomenonthat occurs when solar radiation passes throughth e air a nd some of th e wavelength s ar e deflectedin all directions by molecules of gases, suspended

par t ic les , and water vapor. These suspendedparticles then act like a prism and produce avariety of colors. Various wavelengths and particlesizes result in complex scattering affects thatproduce the blue sky. Scattering is also responsiblefor the red Sun at sunset, varying cloud colorsat sunrise and sunset, and a variety of opticalphenomena (discussed in Unit 5, Lesson 3).

Scattering always occurs in the atmosphere,but does not always produce dramatic settings.Under certain radiation wavelength and particlesize conditions, all that can be seen are whiteclouds and a whitish haze. This occurs when there

is a high moisture content (large particle size) inthe air and is called diffuse reflection. Abouttwo-thirds of the normally scattered radiationreaches Earth as diffuse sky radiation. Diffuse skyradiation may account for almost 100 percent of the radiation received by polar stations duringwinter.

REFLECTION. Reflection is the processwhereby a sur face tur ns a port ion of the incident

radiation back into the medium through whichthe radiation came.

Some insolation is reflected by a substance.This means that the electromagnetic waves simplybounce back into space. Ear th reflects a n a verageof 36 percent of the insolation. The percent of reflectivity of all wavelengths on a surface isknown as its ALBEDO. Ear ths avera ge albedois from 36 to 43 percent. That is, Earth reflects36 to 43 percent of insolation back into space. Incalculating the albedo of Earth, the assumptionis made tha t th e average cloudiness over Ea rth is52 percent.

All surfaces do not have the same degree of reflectivity; consequently, they do not have thesame albedo. Some examples are as follows:

1. Upper surfaces of clouds reflect from 40to 80 percent, with an average of about 55 percent.

2. Snow surfaces reflect over 80 percent of incomin g sun light for cold, fresh sn ow and a s lowas 50 percent for old, dirty snow.

3. Land surfaces reflect from 5 percent of incoming sunlight for dark forests to 30 percentfor dry land.

4. Water surfaces (smooth) reflect from 2percent, when the Sun is directly overhead, to 100percent when, t he Su n is very low on the horizon.This increase is not linear. When t he Sun is morethan 25 above the horizon, the albedo is less than10 percent. In general, the albedo of water is quitelow.

When Earth as a whole is considered, cloudsurfaces are most impor tant in de terminingEa rt hs albedo.

ABSORPTION. Earth and i ts atmosphereabsorb about 64 percent of the insolation. Landand water surfaces of Earth absorb 51 percent of this insolation. The remaining 13 percent isdirectly absorbed by ozone, carbon dioxide, andwater vapor. These gases absorb the ins olation atcertain wavelengths. For example, ozone absorbsonly a small percentage of the insolation. Theportion or type the ozone does absorb is criticalsince it reduces ultraviolet radiation to a levelwhere animal life can safely exist. The mostimportant absorption occurs with carbon dioxideand water vapor which absorb strongly over abroader wavelength band. Clouds are by farthe most important absorbers of radiation atessentially all wavelengths. In sunlight, cloudsreflect a high percentage of the incident solarradiation and account for most of the brightnessof Earth as seen from space.

1-2-8


25/479

There are regions, such as areas of clear skies,where carbon dioxide and water vapor are at aminimum and so is absorption. These areas arecalled a tm ospheric windows an d a llow insolationto pass through the atmosphere relatively un-impeded.

G r e e n h o u s e E f fe c t

The atmosphere conserves the heat energy of Earth because it absorbs radiation selectively.Most of the solar radiation in clear skies istra nsmitted to Ear ths surface, but a lar ge partof the outgoing terrestrial radiation is absorbedand reradiated back to the surface. This is calledthe GREENHOUSE effect. A greenhouse permitsmost of the short-wave solar radiation to passthrough the g lass roof and s ides , and to beabsorbed by the floor, ground or plants inside.These objects r eradiate en ergy at t heir tempera -tures of about 300K, which is a higher

temperature than the energy that was init ial ly

received. The glass absorbs the energy at thesewavelengths and sends part of i t back into thegreenhouse, causing the inside of the structure tobecome warmer than the outside. The atmosphereacts similarly, transmitting and absorbing insomewhat the same way as the glass. If thegreenh ouse effect did not exist, Ea rt hs temp era-

tu re would be 35C cooler th an th e 15C avera getemperature we now enjoy, because the insolationwould be reradiated back to space.

Of course, the atmosphere is not a containedspace l ike a greenhouse because there are heattransport mechanisms such as winds, vert icalcurrents , and mixing wi th surrounding andadjacent cooler air.

RADIATION (HEAT) BALANCEIN THE ATMOSPHERE

The Sun radiates energy to Earth, Earthradiates energy back to space, and the atmosphere

ra diates energy also. As is shown in figur e 1-2-7,

Figure 1-2-7.Radia t ion ba lance in the a tmosphere .

1-2-9


26/479

a balance is maintained between incoming andoutgoing radiation. This section of the lessonexplains th e var ious ra diation processes involvedin maintaining this critical balance and the effectsproduced in the atmosphere.

We have learned that an object reradiatesenergy at a higher temperature. Therefore, the

more the Sun heats Earth, the greater the amountof heat energy Earth reradiates. If this rate of heatloss/gain did not balance, Earth would becomecontinuously colder or warmer.

Te r r e s t r i a l (E a r t h ) R a d i a t i o n

Radiation emitted by Earth is almost entirelylong-wave radia t ion. Most of the ter res t r ia lradiation is absorbed by the water vapor in theatmosphere and some by other gases (about 8percent is radiated directly to outer space). This

radiant energy is reradiated in the atmospherehorizontally and vertically. Horizontal flux (flowor transport) of energy need not be considered dueto a lack of horizontal temperature differences.The vertical, upward or downward, flux is of extreme significance.

Some of this radiation is carried aloft byconvection and turbulence. Water vapor, under.going the condensation-precipitation-evaporationcycle (hydrological cycle), carries the remainderinto the atmosphere.

A t m o s p h e r i c R a d i a t i o n

The atmosphere reradiates to outer space mostof th e terrest rial ra diation (about 43 percent) andinsolation (about 13 percent) that it has absorbed.Some of this reradiation is emitted earthward andi s k n o w n a s C O U N T E R R A D I AT I O N . T h i sradiation is of great importance in the greenhouseeffect.

H e a t B a l a n c e a n d Tr a n s f e ri n t h e At m o s p h e r e

Earth does not receive equal radiation at allpoints as was shown in figure 1-2-4. The east-westrotation of Earth provides equal exposure tosunlight but latitude and dispersion do affect theamount of incident radiation received. The polesreceive far less incident radia t ion than theequator. This uneven heating is called differentialinsolation.

Due t o this different ial insolat ion t he t ropicalatmosphere is constantly being supplied heat and

the temperature of the air is thus higher than inareas poleward. Because of the expansion of warmair, th is column of air is much th icker a nd lighterthan over the poles. At the poles Earth receiveslitt le insolation and th e column or air is less th ick and heavier. This differential in insolation sets upa circulation that transports warm air from the

Tropics poleward aloft and cold air from the polesequatorward on the surface . (See fig. 1-2-8. )Modifications to this general circulation arediscussed in detail in Unit 3.

S u m m a r y

This is the account of the TOTAL radiation.Some of the radiation makes several trips, beingabsorbed, reflected, or reradiated by Earth or theatmosphere. Insolation comes into the atmosphereand all of it is reradiated. How many trips itmakes while in our atmosphere does not matter.The direct absorption of radiation by Earth andthe atmosphere and the reradiations into spacebalance. If the BALANCE did not exist, Earthand its atmosphere, over a period of time, wouldsteadily gain or lose heat.

Although radiation is considered the mostimportant means of heat transfer, it is not the onlymethod. There are others such as conduction,convection, and advection that also play animportant part in meteorological processes.

These will be discussed in more detail later-inthis unit .

Figu re 1-2-8.Beginn ing o f a c i r cu la t ion .

1-2-10


27/479

UNIT 1LESSON 3

P R E S S U R E

OVERVIEW OUTLINE

Describe how pressure is measured and determine Definitionhow the atmosphere is affected by pressure.

Standards of Measurement

Standard Atmosphere

Vertical Distribution

Pa scals Law

P R E S S U R E

P r e s s u r e i s o n e o f t h e m o s t i m p o r t a n tparameters in meteorology. A knowledge of thedistribution of air a nd th e resultan t variat ions inair pressur e over the eart h is vital in un derstan ding

Ear ths fascinat ing weather patt erns.

Learn ing Objec t ive : Descr ibe how pr essur ei s m e a su r e d a n d d e t e r m i n e h o w t h e a t m o s -p h e r e i s a ffe c t e d b y p r e s s u r e .

D E F I N I T I O N

Pressure is the force per unit area. Atmos-pheric pressure is the force per u nit ar ea exertedby the atmosphere in any par t of the at mosphericenvelope. Therefore, the grea ter th e force exertedby the air for any given area, the greater thepressure . Al though the pressure var ies on ahorizontal plane from day to day, the greatestpressure variations are with changes in alt i tude.Nevertheless, horizontal variations of pressure areult imately importan t in m eteorology because thevariations affect weather conditions.

Pressure i s force , and force i s re la ted toaccelerat ion a nd ma ss by Newtons second law.This law states that acceleration of a body isdirectly proportional to the force exerted on thebody and inversely proportional to the mass of that body. I t may be expressed as

where a is the acceleration, F is the forceexerted, and m is the mass of the body. Thisis probably the most important equation in themechanics of physics dealing with force andmotion.

NOTE: Be sure to use units of mass and notunits of weight when applying this equation.

STANDARDS OF MEASUREMENT

Atmospheric pressure is normally measuredin meteorology by the use of a mercurial oraneroid barometer. Pressure is measured in manydifferent units . One atmosphere of pressure is29.92 inches of mercury or 1,013.25 millibars.These measurement s are made under establishedstandard conditions.

1-3-1


28/479

STANDARD ATMOSPHERE

The establishment of a standard atmospherewas necessary to give scientists a yardstick tomeasure or compare actual pressure with a knownstandard. In the International Civil AeronauticalOrganization (ICAO), the standard atmosphere

assu mes a m ean sea level temperat ure of 59F or15C and a standard sea level pressure of 1,013.25millibars or 29.92 inches of mercury. It also hasa temperature lapse rate (decrease) of 3.6F per1000 feet or 0.65C per 100 meters up to 11kilometers and a tropopause and stratospheretemperature of 56.5C or 69.7F.

VERTICAL DISTRIBUTION

Pressure at any point in a column of water,mercury, or any fluid, depends upon the weightof the column above that point.

Air pressure at any given alt i tude within theatmosphere is determined by the weight of theatmosphere pressing down from above. There-fore, the pr essure decreases with altit ude becau sethe weight of the atmosphere decreases.

I t ha s been found t hat the pressure decreasesby half for each 18,000-foot (5,400-meter) increasein altitude. Thus, at 5,400 meters one can expectan average pressure of about 500 millibars and

at 36,000 feet (10,800 meters) a pressure of only250 millibars, etc. Therefore, it maybe concludedtha t a tmospheric pressures a re greatest a t lowerelevations because the total weight of the atmos-phere is greatest at these points.

There is a change of pressur e whenever eitherthe mass of the atmosphere or the accelerations

of the molecules wi th in the a tmosphere arechanged. Although altitude exerts the dominantcontrol , temperat ure a nd m oisture al ter pressureat an y given altitu deespecially near E ar thssurface where hea t and humidi ty, a re mostabundant. The pressure variations produced byheat a nd hu midity with h eat being the dominantforce, are resp onsible for Ear th s winds th roughthe flow of atmospheric mass from an area of higher pressure to an area of lower pressure.

P ASCALS LAW

Pascals Law is an important law in atmos-pheric physics. The law sta tes t hat fluids (includ-ing gases such as Ear th s atm osphere) tran smitpressur e in all directions. Therefore, the pressur eof the atmosphere is exerted not only downwardon the surface of an object , but also in al ldirections a gainst a sur face tha t is exposed to theatmosphere.

1-3-2


29/479

UNIT 1LESSON 4

T E M P E R AT U R E

OVERVIEW OUTLINE

Desc r ibe how t empera tu re i s measu red and Definitiondetermine how the atmosphere is affected bytempera ture . Temperature Scales

Vertical Distribution

Heat Transfer

T E M P E R AT U R E

One of the most important properties of theatm osphere is i ts abil ity to absorb an d lose heat .The heating and cooling of the atmosphere exertsa tremendous influence on the processes thatdetermine the weather. Consequently, tempera-ture i s one of your pr inc ipal concerns . I t i s

necessary to know the meaning of temperature,the scales and instruments used in i ts measure-ment , and the impor tant tempera ture values .Procedures for observing temperature were dis-cussed in the AG3 rate training manual.

Learning Objec t ive : Descr ibe how temper-a t u r e i s m e a su r e d a n d d e t e r m i n e h o w t h ea t m o s p h e r e i s a f fe c t e d b y t e m p e r a t u r e .

D E F I N I T I O N

Temperature may be regarded as a measureof molecular motion. Its intensity is determinedfrom absolute zero (Kelvin scale), the point atwhich all molecular motion stops. Temperatureis the degree of hotness or coldness, or it may beconsidered as a measure of heat intensity.

TEMPERATURE SCALES

Long ago it was recognized that uniformityin the measurement of temperature was essential.It would be unwise to rely on such subjective

judgments of temperature as cool, cooler, andcoolest; therefore, arbitrary scales were devised.Some of them are described in this section. They

are Fahrenheit , Celsius, and absolute (Kelvin)scales. These are the scales used by the meteoro-logical services of all the countries in the world.Table 1-4-1 shows a temperature conversion scalefor Celsius, Fahrenheit, and Kelvin.

Fah renhe i t Sca l e

The Fa hren heit scale was invented by GabrielDaniel Fahrenheit about 1710. He was the firstto use mercury in a th ermometer. The Fah renheitscale has 180 divisions or degrees between thefreezing (32F) and boil ing (212F) points of

water.

Celsius Scale

The Celsius scale was devised by AndersCelsius also during the 18th century. This scalehas reference points with respect to water of 0Cfor freezing and 100C for boiling.

It should be noted that many publicationssti l l refer to the centigrade temperature scale.

1-4-1


30/479

Table 1-4-1 .Temperature Convers ion Scale

1-4-2


31/479

Cen t ig rade s imp ly means g radua ted in 100increments , and has recent ly and off ic ia l lyadopted the name of its discoverer, Celsius.

Absolute Scale (Kelvin)

Another scale in wide use by scientists in manyfields is th e absolute s cale or Kelvin scale. It wasdeveloped by Lord Kelvin of England. On thisscale the freezing point of wat er is 273K an d th eboiling point of wat er is 373K. The a bsolut e zerovalue i s cons idered to be a point a t whichtheoretically no molecular activity exists. Thisplaces the absolute zero at a minus 273 on theCelsius s cale, since the degree divisions a re equ alin size on both scales. The a bsolut e zero value onthe Fahrenheit scale falls at minus 459.6F.

Sca l e Conve r s ions

Two scales , Fahrenhei t and Cels ius , a recommonly used. With the Celsius an d F ahr enheits c a l e s , i t i s o f t e n n e c e s s a r y t o c h a n g e t h etemperature value of one scale to that of the other.Generally a temperature conversion table, liketable 1-4-1, is used or a temperature computer.If these are n ot available, you must then use oneof th e following ma th emat ical met hods to convertone scale to another.

M a t h e m a t i c a l M e t h o d s

It is important to note that there are 100divisions between the freezing and boiling pointsof water on the Celsius scale. There are 180divisions between the same references on theFahrenheit scale. Therefore, one degree on theCelsius scale equals nine-fifths degree on theFahrenheit scale. In converting Fahrenheit valuesto Celsius values the formula is:

In converting Celsius values to Fah renheit valuesthe formula is:

One way to remember when to use 9/5 andwhen to use 5/9 is to keep in mind that the

Fahrenheit scale has more divisions than theCelsius scale. In going from Celsius to Fahrenheit,multiply by the ratio that is larger; in goingfrom Fahrenhei t to Cels ius , use the smal lerratio.

Another method of converting temperaturesfrom one scale to another is the decimal method.This method uses the ratio 1C equals 1.8F. Tofind Fahrenheit from Celsius, multiply the Celsiusvalue by 1.8 and add 32. To find Celsius fromFahrenheit , subtract 32 from the Fahrenheit anddivide the remainder by 1.8.

Examples:

To change a Celsius reading to an absolutev a l u e , a d d t h e C e ls i u s r e a d i n g t o 2 7 3 algebraically. For example, to find the absolutevalue of 35C, you would add minus 35 to273K algebraically. That is, you take 273 andcombine 35 so you u se th e minu s ( ) functionto arrive at 238K.

To change a Fahrenheit reading to an absolutevalue, first convert t he F ahr enheit rea ding to itsequivalent Celsius value, which is then added

algebraically to 273. Consequently, 50F ise q u i v a l e n t t o 2 8 3 a b s o l u t e , a r r i v e d a t b yconverting 50F to 10C and then adding theCelsius value algebraically to 273.

VERTICAL DISTRIBUTION

Ea rt hs at mospher e is divided into layers orzones according to various distinguishing features.

1-4-3


32/479

(See fig. 1-4-1. ) The temperatures shown here are o n e a t m o s p h e r e , n o t b y a n u m b e r o f s u b -generally based on the latest U.S. Extension to atmospheres.the ICAO Standard Atmosphere and are repre-senta t ive of mid- la t i tude condi t ions . The ex- L a y e r s o f t h e A t m o s p h e r etension shown in the insert is speculative. Thesedivisions are for reference of thermal structure The layers and zones ar e discussed un der two(lapse rat es) or other significan t featur es and are separate classifications. One is the METEORO-

not intended to imply that these layers or zones LOGICAL c l a s s i f i ca t ion tha t de f ines zonesar e independent domains. Eart h is surrounded by according to their significance for the weather.

Figure 1-4-1.Ear th s a tmosphere .

1-4-4


33/479

The other is the ELECTRICAL classification thatdefines zones according to electrical characteristicsof gases of the atmosphere.

M E T E O R O L O G I C A L C L A S S I F I C A -TION. In the meteorological classification (com-

mencing with E ar th s sur face and pr oceedingupward) we have the troposphere, tropopause,stratosphere, stratopause, mesosphere, meso-pause, thermosphere, and the exosphere. Theseclassifications ar e based on temperat ure char ac-teristics. (See fig. 1-4-1 for some examples.)

Tr o p o s p h e r e . The tr oposphere is t he layerof air enveloping Earth immediately above Earthssurface. It is approximately 5 1/2 miles (29,000ft or 9 km) th ick over th e poles, about 7 1/2 miles(40,000 ft or 12.5 km) thick in the mid-latitudes,an d about 11 1/2 miles (61,000 ft or 19 km ) thick over the Equator. The figures for thickness areaverage figures; they change somewhat fromday to day and f rom season to season. Thetroposphere is thicker in summer than in winterand i s t h i cke r du r ing the day than du r ingthe n ight . Almost a l l weather occurs in thetroposphere. However, some phenomena such asturbulence, cloudiness (caused by ice crystals), andthe occasional severe thunderstorm top occurwithin the tropopause or stratosphere.

The troposphere is composed of a mixture of several different gases. By volume, the com-

position of dry air in the troposphere is as follows:78 percent nitrogen, 21 percent oxygen, nearly 1percent argon, and about 0.03 percent carbondioxide. In addition, it contains minute traces of other gases, such as helium, hydrogen, neon,krypton, and others.

The air in the troposphere also contains avariable amount of water vapor. The maximumamount of water vapor that the air can holddepends on the temperature of the air and thepressure. The higher the temperature, the morewater vapor i t can hold at a given pressure.

The air also contains variable amounts of impurities, such as dust, salt particles, soot, andc h e m i c a l s . T h e s e i m p u r i t i e s i n t h e a i r a r eimporta nt becau se of th eir effect on visibility a ndthe part they play in the condensation of watervapor. If the air were absolutely pure, there wouldbelittle condensation. These minute particles actas nuclei for the condensation of water vapor.Nuclei which ha ve an a ffinity for wat er vapor a recalled HYDROSCOPIC NUCLEI.

The temperature in the troposphere usuallydecreases with height, but there may be inversionsfor relatively thin layers at any level.

Tr o p o p a u s e . The tropopause is a transi-t i on l aye r be tween the t roposphe re and thestratosphere. It is not uniformly thick, and it isnot continuous from the equator to the poles. Ineach hemisphere the existence of three distincttropopauses is generally agreed uponone in thesubtropical latitudes, one in middle latitudes, andone in subpolar latitudes. They overlap each otherwhere they meet.

The tr opopau se is cha ra cterized by little or noincrease or decrease in t emperatur e with increasingaltitude. The composition of gases is about thesame a s th at for t he tr oposphere. However, watervapor is found only in very minute quantities atthe tropopause and above i t .

S t r a t o s p h e r e . The stratosphere directlyoverlies the tropopause and extends to about 30miles (160,000 ft or 48 kilometers). Temperaturevaries little with height in the stratosphere throughthe first 30,000 feet (9,000 meters); however, inthe uppe r po r t i on the t empera tu re i nc reasesapproximately l inearly to values nearly equal tosurface temperatures. This increase in temperaturethr ough t his zone is at t r ibuted to the pr esence of ozone that absorbs incoming ultraviolet radiation.

S t r a t o p a u s e . The stra topause is the top of

the stratosphere. I t is the zone marking anotherreversal with increasing alt i tude (temperaturebegins to decrease with height).

M e s o s p h e r e . The mesosphere is a layerapproximately 20 miles (100,000 ft or 32 kilo-meters) thick directly overlaying the stratopause.The temperature decreases with height.

M e s o p a u s e . The mesopause is the thinboundary zone between the mesosphere and thethe rmosphe re . I t i s marked by a r eve r sa l o f temperatures; i .e . , temperature again increases

with alt i tude.

T h e r m o s p h e r e . The thermosphere, a secondregion in which the temperature increases withheight , extends f rom the mesospause to theexosphere.

E x o s p h e r e . The very outer limit of Ea rt hsatmosphere is regarded as the exosphere. It is thezone in which gas atoms are so widely spaced they

1-4-5


34/479

rarely collide with one another and have individualorbits around Earth.

ELECTRICAL CLASSIFICATION. Th eprimary concern with the electrical classificationis the effect on communications and radar. Theelectrical classification outlines three zonesthetroposphere, the ozonosphere, and the iono-sphere .

Tr o p o s p h e r e . The troposphere is importantto electrical transmissions because of the immensechanges in the density of the atmosphere thatoccur in th is layer. These density changes, causedby differences in heat and moisture, affect theelectronic emissions t hat tra vel th rough or in thetroposphere. Electrical waves can be bent orrefracted when they pass through these differentlayers and the range and area of communicationsmay be seriously affected.

O z o n o s p h e r e . This layer is nearly coincidentwith th e stra tosphere. As was discussed ear lier inthis section, the ozone found in this zone isresponsible for the increase in temperature withheight in the stratosphere.

I o n o s p h e r e . The ionosphere extends fromabout 40 miles (200,000 ft or 64 kilometers) toan indefinite height. Ionization of air moleculesin this zone provides conditions that are favorablefor radio propagation. This is because radio wavesare sent outward to the ionosphere and the ionizedparticles reflect the radio waves back to Earth.

HEAT TRANSFER

The atmosphere is constantly gaining andlosing heat. Heat is constantly being transportedfrom one part of the world to another by windmovements. It is due to the inequalities in gainand loss of heat that the air is almost constantlyin motion. The motions and heat transformationsare directly expressed by wind and weather.

Me thods

In meteorology, one is concerned with fourmethods of heat transfer. These methods areconduction, convection, advection, and radiation.H e a t i s t r a n s f e r r e d f r o m E a r t h d i r e c t l y t othe atmosphere by radiation, conduction, andadvection. Heat is transferred within the atmos-phere by radiation, conduction, and convection.Advection, a form of convection, is used in a

special ma nner in m eteorology. It is discussed asa separate method of heat transfer. As radiationwas discussed earlier in the unit, this section coversconduction, convection, and advection.

CONDUCTION. Condu ction is the tr an sferof heat from wa rmer to colder ma tt er by cont act.Although of secondary importance in heating theatmosphere, it is a means by which air close tothe surface of Earth heats during the day andcools during the night.

CONVECTION. Convection is t he m ethodof heat transfer in a fluid resulting in the transportand mixing of the propert ies of that f luid.Visua lize a pot of boiling wat er. The wat er a t t hebottom of the pot is heated by conduction. Itbecomes less dense and rises. Cooler and denserwater from th e sides and th e top of th e pot ru shesin and replaces the rising water. In time, the wateris thoroughly mixed. As long as heat is appliedto the pot, the water continues to transfer heatby convection. The transfer of heat by convectionin this case applies only to what is happening tothe wa te r i n t he po t . I n me teo ro logy, t heterm convection is normally applied to verticaltransport .

Convection occurs regularly in the atmosphereand is responsible for the development of airturbulence. Cumuliform clouds, showers andthunderstorms occur when sufficient moisture ispresent and strong vertical convection occurs.Ver t ica l t ransfer of hea t in the a tmosphere(convection) works in a similar man ner. War mer,less dense air rises an d is replaced by descendingcooler, denser air, which in turn, acquires heat.

Speci f ic Heat

The specific heat of a substance shows howmany ca lor ies of hea t i t t akes to ra ise thetemperature of 1 gram of that substance 1C.Since it takes 1 calorie to raise the temperatureof 1 gram of water 1C, the specific heat of wateris 1. The specific heat of a substance plays atr emendous r ole in m eteorology becau se it is tieddirectly to temper atu re changes. For inst ance, thespecific heat of earth in general is 0.33. Thismeans it takes only 0.33 calorie to raise thetempera ture of 1 gram of ear th 1C. S ta tedanother way, earth heats and cools three timesas fast as water. Therefore, assuming the sameamount of energy (calories) is available, waterheat s (and cools) at a slower r at e tha n lan d does.The slower rate of heating and cooling of water

1-4-6


35/479

is the reason temperature extremes occur over landareas while temperatures over water areas aremore consistent.

The specific heat of various land surfaces isalso different, though the difference between oneland surface and another is not as great as betweenland and water. Dry sand or bare rock has the

lowest specific heat. Forest areas have the highestspecific heat. This difference in specific heat isanother cause for differences in temperature forareas with different types of surfaces even whenthey are only a few miles apart; this differenceis important in understanding the horizontaltransport of heat (advection) on a smaller scale.

ADVECTION. Advection is really afo rm o f convec t ion , bu t i n me teo ro logy i tmeans the transfer of heat or other properties

HORIZONTALLY. Convec t ion i s t he t e rmreserved for the VERTICAL transport of heat.In this manual the words convection and advec-tion ar e used to mean t he vertical and horizontaltransfer of atmospheric properties, respectively.

Horizontal transfer of heat is achieved bymot ion of the a i r f rom one la t i tude and/or

longitude to another. It is of major importancei n t h e e x c h a n g e o f a i r b e t w e e n p o l a r a n dequatorial regions. Since large masses of air areconst an tly on t he move somewher e on Ea rt hssurface and aloft, advection is responsible fortransporting more heat from place to place thanany other physical motion. Transfer of heat byadvection is achieved not only by the transportof warm air, but also by the transport of watervapor t ha t r e l ea ses hea t when condensa t ionoccurs.

1-4-7


36/479


37/479

U N I T 1 L E S S O N 5

M O I S T U R E

OVERVIEW OUTLINE

Recognize how moisture affects the atmosphere. Atmosphere Moisture

Water Vapor Characterist ics

Terms

MOISTURE

More t ha n t wo-thirds of Ea rt hs sur face iscovered with water. Water from this extensivesource is continually evaporating into the atmos-phere, cooling by various processes, condensing,and then fall ing to the ground again as variousforms of precipitation.

The rem aind er of Ea rt hs sur face is composedof solid land of various and vastly different terrainfeatu res. Knowledge of terr ain differen ces is veryimportant in analyzing and forecasting weather.The wor lds t e r r a in var ies f rom lar ge-scalemountain ranges and deserts to minor rolling hillsand valleys. Each type of terrain significantlyinfluences local wind flow, moisture availability,and t he resul t ing weather.

L e a r n i n g O b j e c t i v e : D e s c r i b e h o wm o i s t u r e a f fe c t s t h e a t m o s p h e r e .

ATMOSPHERIC MOISTURE

Moisture in the atmosphere is found in threestatessolid, liquid, and gaseous. As a solid, ittakes the form of snow, hail, ice pellets, frost,ice-crystal clouds, and ice-crystal fog. As a liquid,it is found as rain, drizzle, dew, and as the minutewater droplets composing clouds of the middle

and low stages as well as fog. In the gaseous state,water forms as invisible vapor. Vapor is the mostimportant single element in the production of clouds and other visible weath er ph enomena. Theavailability of water vapor for the production of precipitation largely determines the ability of aregion to support life.

The oceans are the primar y source of moistur efor the atmosphere, but i t is also furnished bylakes, rivers, swamps, moist soil, snow, ice fields,and vegetation. Moisture is introduced into theatm osphere in i ts gaseous sta te, and may th en becarried great distances by the wind before it isdischarged as liquid or solid precipitation.

WATER VAPOR CHARACTERISTICS

There is a l imit to the a mount of water vaporthat air, at a given temperature, can hold. Whenthis limit is reached, the air is said to be saturated.The higher the air temperature, the more watervapor the air can hold before saturation is reached

and condensation occurs. (See fig. 1-5-1. ) Forapproximately every 20F (11C) increase intemperature between 0F and 100F (18C and38C), the capacity of a volume of air to holdwater vapor is about doubled. Unsaturated air,conta in ing a g iven amount of water vapor,becomes saturated if i ts temperature decreasessufficiently; further cooling forces some of thewater vapor to condense as fog, clouds, orprecipitation.

1-5-1


38/479

Figu re 1-5-1.Satu ra t ion o f a i r depends on i t s t empera tu re .

T h e q u a n t i t y o f w a t e r v a p o r n e e d e d t oproduce sa tura t ion does not depend on thepressure of other atmospheric gases. At a giventemperature, the same amount of water vaporsaturates a given volume of air. This is truewhether it be on the ground at a pressure of 1000mb or at an altitude of 17,000 ft (5,100 meters)with only 500 mb pressure, if the temperature isthe same. Since density decreases with altitude,a given volume of air cont ains less mass (gra ms)at 5,100 meters than at the surface. In a saturatedvolume, there would be more water vapor pergram of air at this al t i tude than at the surface.

Te m p e r a t u r e

Although the quantity of water vapor in asaturated volume of atmosphere is independentof the air pressure, IT DOES DEPEND ON THETEMPERATURE. The higher the temperature,the greater the tendency for liquid water to turninto vapor. At a higher temperature, therefore,more vapor must be injected into a given volumebefore th e satu rat ed state is reached and dew orfog forms. On th e oth er h an d, cooling a sat ura tedvolume of a i r forces some of the vapor tocondense a nd th e quan tity of vapor in the volumeto diminish.

Condensa t i on

Condensation occurs if moisture is added tothe air after saturation has been reached, or if cooling of the air reduces the temperature belowthe saturation point. As shown in figure 1-5-2,th e most frequent cause of condensat ion is coolingof the air and often results when; (a) air movesover a colder surface, (b) air is lifted (cooled byexpansion), or when (c) air near the ground is

coo l ed a t n igh t a s a r e su l t o f r ad i a t i ona lcooling.

P r e s su r e (Da lton s Law)

The laws relative to the pressu re of a mixtu reof gases were formulated by the English physicist,John Dalton. One of the laws states that thepartial pressures of two or more mixed gases (orvapors) are the same as if each filled the spacealone. The other law states that the total pressureis the sum of all the partial pressures of gases andvapors present in an enclosure.

For instance, water vapor in the atmosphereis independent of th e presence of other gas es. Thevapor pressure is independent of the pressure of the dry gases in the atmosphere and vice versa.However, the t otal atm ospheric pressur e is foundby adding all the pressuresthose of the dry airand the water vapor.

TERMS

The actual amount of water vapor containedin the air is usually less than the saturationamount. The amount of water vapor in the airis expressed in several different methods. Someof these principal methods are described in thefollowing portion of this section.

Re la t i ve Humid i ty

Alth ough the m ajor port ion of th e atm osphereis not saturated, for weather analysis it is desirableto be able to say how near it is to being sat ur at ed.This relationship is expressed as relative humidity.The relative humidity of a volume of air is theratio (in percent) between the water vapor actuallyp r e s e n t a n d t h e w a t e r v a p o r n e c e s s a r y f o r

1-5-2


39/479

Figure 1-5-2.Causes o f condensa t ion .

saturation at a given temperature. When the aircontains all of the water vapor possible for it tohold at i ts temperature, the relative humidity is

100 percent. (See fig. 1-5-3. ) A relative humidityof 50 percent indicates t hat the air conta ins ha lf of the water vapor that it is capable of holdingat i t s tempera ture .

Relative humidity is also defined as the ratio(expressed in percent) of the observed vaporpressure to that required for saturation at the sametemperatur e and pressure .

Relative humidity shows the degree of sat ur a-tion, but it gives no clue to the actual amount of water vapor in the air. Thus, other expressionsof humidity are useful.

Ab s o l u t e H u m i d i t y

The mass of water vapor present per unitvolume of space, usually expressed in grams per

cubic meter, is known as absolute humidity. Itmay be thought of as the density of the watervapor.

Spec i fi c Hum id i ty

Humidity may be expressed as the mass of water vapor conta ined in a u nit ma ss of air (dryair plus t he wat er vapor). It can also be expressedas the ratio of the density of the water vapor tothe density of the air (MIXTURE OF DRY AIRAND WATER VAPOR). This i s ca l led thespecific humidity and is expressed in grams pergram or in grams per k i logram. This va luedepends upon the measurement of mass, and massdoes not change with temperature and pressure.

The specific humidity of a parcel of air remainsconsta nt unless water vapor is a dded to or t akenfrom the parcel. For this reason, air that is

Figure 1-5-3.Rela t ive humid i ty and dewpoin t .

1-5-3


40/479

unsaturated may move from place to place orfrom level to level, and its specific humidityremains the same as long as no water vapor isadded or removed. However, if the air is saturatedand coo led , some o f t he wa te r vapo r mus tcondense; consequently, the specific humidity(which reflects only the water vapor) decreases.If saturated air is heated, its specific humidity

remains unchanged unless water vapor is addedto it. In this case t he specific humidity increases.The ma ximum specific humidity th at a pa rcel canhave occurs at saturation and depends upon boththe temperature and the pressure. Since warm aircan hold more water vapor than cold air at con-stant pressure, the saturation specific humidity athigh temperatures is greater than at low tempera-tu res. Also, since moist air is less dense t han dryair at constant temperature, a parcel of air hasa greater specific humidity at saturation if thepressure is low than when the pressure is high.

Mixing Rat io

The mixing rat io is defined as t he ra tio of themass of water vapor to the m ass of DRY AIR an dis expressed in grams per gram or in grams perkilogram. It differs from specific humidity onlyin tha t i t is related to the mass of dry air insteadof to the total dry air plus wat er vapor. It is verynearly equal numerically to specific humidity, butit is always slight ly great er. The mixing rat io hasthe same characteristic properties as the specifichumidity. It is conservative (values do not change)for atmospheric processes involving a change intemperature. It is nonconservative for changesinvolving a gain or loss of water vapor.

Previously it was learned that air at any giventemperature can hold only a certain amount of water vapor before it is saturated. The totalamount of vapor that air can hold at any giventemperature, by weight relationship, is referredto as the saturation mixing ratio. It is useful tonote that the following relationship exists betweenmixing rat io and relat ive humidity. Relativehumidity is equal to the mixing ratio divided bythe saturation mixing ratio, multiplied by 100. If an y two of the th ree components in th is relation-ship are known, the third may be determined bysimple mathematics.

D e w p o i n t

The dewpoint is the temperature that air mustbe cooled, at constant pressure and constant watervapor content, in order for saturation to occur.The dewpoint is a conservative and very usefulelement. When atmospheric pressure stays con-stant, the dewpoint reflects increases and de-creases in moisture in the air. It also shows at aglance, under the same conditions, how muchcooling of th e air is r equir ed to condens e moistur efrom the air.

UNIT 1REFERENCES

Aerographer s Mate 3 and 2, N AV E D T R A10363-E1, Naval Educat ion and Tra in ingProgram Development Center, P ensacola, FL,1976.

Byers, Horace Robert , General Meteorology,F o u r t h E d i t i o n , N AVA I R 5 0 - 1 B - 5 1 5 ,McGraw-Hill Book Company, NY, 1974.

Glossary Of Meteorology, American Meteoro-logical Society, Boston, MA, 1959.

S ource Book of the S olar-Geophysical E nviron-ment, AFGWC/TN-82/002, Depar tment of the Air Force, 1982.

H a l t i n e r , G e o rg e J . a n d M a r t i n , F r a n k L . , Dynam ical and Physical Meteorology, NAV-AIR 50-1B-533, McGraw-Hill Book Com-pany, NY, 1957.

Meteorology For Army Aviators, United StatesArmy Aviation Center, Fort Rucker, AL,1981.

Riley, Denis and Spolton, Lewis, World Weather and Climate, Cambridge University Press,London, 1974.

Trewartha, Glenn T. and Horn, Lyle H., A n In t roduct ion To Cl imate , Fi f th Ed i t i on ,McGraw-Hill Book Company, NY, 1980.

1-5-4


41/479

U N I T 2

AT M O S P H E R I C P H YS I CS

FOREWORD

The science of physics is devoted to finding, defining, and reaching solu-tions to problems. It is the basic science that deals with motion, force, andener gy. Ph ysics, th erefore, not only breed s curiosity of ones environm ent ,but it provides a means of acquiring answers to questions that continue toar ise. Atmospher ic physics is a bran ch of physical meteorology th at deals witha combination of dynamic and thermodynamic processes that account for theexistence of numerous atmospheric conditions.

To understan d t he weath er elements a nd t o analyze meteorological si tua -tions you must know how to apply the fundamental principles of physics andatmospheric physics. This does not mean that you must be able to under-stand all of the complicated theories of meteorology. It does mean, however,that you should have a fair working knowledge of elementary physics. Yous h o u l d l e a r n h o w t o a p p l y t h e r u l e s of p h y s i cs t o u n d e r -stand the atmosphere. This is necessary to perform your duties as anAerographer s Mate in a credita ble mann er.

A forecast er s un derst an ding of mat hema tics becomes importa nt to anever-increasing degree. Your progression must include a basic mathematicalknowledge of ratio, proportion, interpolation, percentage, and trigonometricfunctions of a right triangle. As you move further into the field of meteorology,you will find it helpful to increase your ma th emat ical kn owledge by referringto the fo l lowing t ra in ing manuals : Mathematics, VOL 1, N AV E D T R A10069-D, Mathematics, Vol. 2, NAVEDTRA 10071-B, or Mathematics, Vol.3, NAVEDTRA 10073-A. Additional sources of information include the manymathematical courses offered by colleges. Information on these courses andmanuals may be obtained from your Educational Service Office (ESO).

Unit 2 covers the following lessons: Lesson 1, Motion; Lesson 2, Matter;Lesson 3, Gas Laws; and Lesson 4, Atmospheric Energy.

2-0-1


42/479


43/479

U N I T 2 L E S S O N 1

MOTION

OVERVIEW OUTLINE

Descr ibe the laws of mot ion and de termine Termshow motion is affected by external forces.

Laws of Motion

Work

Energy

Force

MOTION

Any general discussion of the principles of physics must contain some consideration of theway in which ma ss, force, and m otion a re r elated.In physics, the laws of motion state that anobject at rest never starts to move by itself; a push

or a pull must be exerted on it by some otherobject. This applies to weath er a lso. Weat her ha smany complex motions, both in the vertical andhorizontal planes. To fully understand how andwhy weather moves , you must have a bas icknowledge of motion and those external forcesthat affect motion.

Lea r n ing Ob jec t i ve : Desc r ibe t h e l aws o f m o t i on a n d d e t e r m i n e h o w m o t io n i s a f-f ect ed by ex t e r na l fo r ce s .

T E R M S

In dealing with motion several terms shouldbe defined before you venture into the study of motion. These ter ms a re inert ia, speed, direction,velocity, and acceleration.

I n e r t i a

An object at rest never moves unless some-thing or someone moves it. This is a propertyof all forms of matter (solid, liquid, or gas).Inertia, therefore, is the property of matter toresist any change in its state of rest or motion.

S p e e d

Speed is th e rate at which something movesin a given a mount of time. In meteorology, speedis the term that is used when only the rate of movement is meant. If the rate of movement of a h urr icane is 15 knots, we say its speed is 15 knotsper hour.

Direction

Direction is the line along which somethingmoves or lies. In meteorology, we speak of direc-tion as toward or the direction from which anobject is moving. For example, northerly windsare winds COMING FROM the north.

Velocity

Velocity describes both the rate at which abody moves and the direction in which it istraveling. If the hurricane, with its speed of 15

2-1-1


44/479

knots per hour, is described as m oving westward,it now has velocityboth a rate and direction of movement.

Accelera t ion

This term applies to a rate of change of thespeed and/or the velocity of matter with time. If

our hurricane, which is presently moving at 15knots, is moving at 18 knots 1 h our from n ow an d21 knots 2 hours from now, it is said to be ac-celerating at a rate of 3 knots per hour.

LAWS OF MOTION

Everything around us is in motion. Even abody supposedly at rest on the surface of Earthis in m otion becaus e th e body is a ctually movingwith the rotat ion of Earth; Earth, in turn, isturning in its orbit around the Sun. Therefore,the te rms rest and motion are r elat ive terms. Thechange in position of any portion of matter is

motion. The atmosphere is a gas and is subjectto much motion. Temperature, pressure, and den-sity act to produce the motions of the atmosphere.These motions are subject to well-defined physicallaws. An explanation of Newtons laws of mo-tion can help you to understand some of thereasons why the atmosphere moves as it does.

N e w t o n s F i r s t L a w

S i r I s a a c N e w t o n , a f o r e m o s t E n g l i s hphysicist, formulated three important laws relativeto motion. His first law, th e law of inert ia, stat es,every body continues in its state of rest or

un iform motion in a st ra ight line unless it is com-pelled to change by applied forces. Although theatmosphere is a mixture of gases and has physicalproperties peculiar to gases, it still behaves inmany respects as a body when considered in theter ms of Newtons law. Th ere would be n o move-ment of great quantities of air unless there wereforces to cause that movement. For instance, airmoves from one area t o another because th ere is aforce (or forces) great enough to change its direc-tion or t o overcome its tenden cy to rema in at rest .

N e w t o n s S e c o n d L a w

Newtons second law of motion, force, andacceleration states, the change of motion of abody is proportional to the applied force and takesplace in t he direction of the str aight line in whichtha t force i s appl ied . In respect to the a t -mosphere, this means that a change of motion inthe atmosphere is determined by the force actingupon it, and that change takes place in the direc-tion of that applied force.

From Newtons second law of motion thefollowing conclusions can be determined:

1. If different forces are acting upon t he sa memass, different accelerations are produced thatare proportional to the forces.

2 . For d i fferent masses to acqui re equal

acceleration by different forces, the forces mustbe proportional to the masses.3. Equal forces acting upon different masses

produce different accelerations that are propor-tional to the masses.

N e w t o n s T h i r d L a w

Newt ons th ird la w of motion st at es, to everyaction t here is a lways opposed an equa l reaction;or, the mutual actions of two bodies upon eachother are always equal, and directed to contraryparts. In other words forces acting on a body

originat e in oth er bodies that ma keup its environ-ment. Any single force is only one aspect of amutual interaction between two bodies.

W O R K

Work is done when a force succeeds in over-comin g a bodys

Aerographer’s Mate Second Class, Volume 1

Documents

Transcript of Aerographer’s Mate Second Class, Volume 1