# FUNDAMENTALS OF METEOROLOGY

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CHAPTER 1FUNDAMENTALS OF METEOROLOGYMeteorology is the study of atmosphericphenomena. This study consists of physics, chemistry,and dynamics of the atmosphere. It also includes manyof the direct effects the atmosphere has upon Earth’ssurface, the oceans, and life in general. In this manualwe will study the overall fundamentals of meteorology,a thorough description of atmospheric physics andcirculation, air masses, fronts, and meteorologicalelements. This information supplies the necessarybackground for you to understand chart analysis,tropical analysis, satellite analysis, and chartinterpretation.Table 1-1.—Common Prefixes in the Metric System1PrefixSYSTEM OF MEASUREMENTLEARNING OBJECTIVE: Recognize theunits of measure used in the Metric System andthe English System and how these systems ofmeasurement are used in Meteorology.DecimalValueScientific 0-1Centic.0110-2Millim.00110-31To work in the field of meteorology, you must havea basic understanding of the science of measurement(metrology). When you can measure what you aretalking about and express it in numerical values, youthen have knowledge of your subject. To measure howfar something is moved, or how heavy it is, or how fastit travels; you may use a specific measurement system.There are many such systems throughout the ond) has been recognized for usein science and research. Therefore, that system isdiscussed in the paragraphs that follow, with briefpoints of comparison to the English System (FPS,foot-pound-second). The metric units measure length,weight, and time, respectively. The derivation of thoseunits is described briefly.SymbolThese prefixes are used with all metric units such asmeters, grams, liters, and seconds (eg., kilometers,hectometers, centiliters, milliseconds).Since the C in CGS represents centimeters (cm)you should see from table 1-1 that the centimeter isone-hundredth of a meter, .O1M, or 10-2 M.Conversely, 1 M equals 100 cm. To describe a gram,the G in the CGS system, you must first have afamiliarization with area and volume.AREA AND VOLUMEA square has four equal sides and it is a one-planefigure—like a sheet of paper. To determine how muchsurface area is enclosed within the square you multiplythe length of one side by the length of the other equalside. If the sides were 1 centimeter (cm) in length thearea of the square would be 1 cm 1 cm 1 square cm,or 1 cm2. If squares having an area of 1 cm2 werestacked on top of each other until the stack was 1 cmtall, you would end up with a cube whose sides wereeach 1-cm in length. To determine the volume of thecube you simply multiply the length by the width andheight. Because each side is 1 cm you end up with avolume of 1 cubic centimeter (cm3) (1 cm 1 cm 1cm 1 cm3). More simply stated, multiply the area ofone side of the cube by the height of the cube. Once youunderstand how the volume of a cube is determined,you are now ready to review the G in the CGS system.LENGTHTo familiarize you with the conventional units ofmetric length, start with the meter. The meter is slightlylarger than the English yard (39.36 inches vs. 36inches). Prefixes are used in conjunction with the meterto denote smaller or larger units of the meter. Eachlarger unit is ten times larger than the next smaller unit.(See table 1-1.).1-1

WEIGHTREVIEW QUESTIONSQ1-1. What units does the metric (CGS) systemmeasure?The conventional unit of weight in the metricsystem is the gram (gm). You could use table 1-1 andsubstitute the word gram for meter and the symbol (gm)for the symbol (M). You would then have a table formetric weight. The gram is the weight of 1 cm3 of purewater at 4 C. At this point it may be useful to comparethe weight of an object to its mass. The weight of the 1cm3 of water is 1 gin. Weight and mass are proportionalto each other. However, the weight of the 1 cm3 of waterchanges as you move away from the gravitationalcenter of Earth. In space the 1 cm3 of water isweightless, but it is still a mass. Mass is expressed as afunction of inertia/acceleration, while weight is afunction of gravitational force. When we express themovement of an object we use the terms mass andacceleration.Q1-2. What is the difference between weight andmass?Q1-3. What does a dyne measure?EARTH-SUN RELATIONSHIPLEARNING OBJECTIVE: Describe howradiation and insolation are affected by theEarth-Sun relationship.The Sun is a great thermonuclear reactor about 93million miles from Earth. It is the original source ofenergy for the atmosphere and life itself. The Sun’senergy is efficiently stored on Earth in such things asoil, coal, and wood. Each of these was produced bysome biological means when the Sun acted upon livingorganisms. Our existence depends on the Sun becausewithout the Sun there would be no warmth on Earth, noplants to feed animal life, and no animal life to feedman.TIMETime is measured in hours, minutes, and seconds inboth systems. Hence, the second need not be explainedin the CGS system. With knowledge of how the CGSsystem can be used to express physical entities, younow have all the background to express such things asdensity and force.The Sun is important in meteorology because allnatural phenomena can be traced, directly or indirectly,to the energy received from the Sun. Although the Sunradiates its energy in all directions, only a small portionreaches our atmosphere. This relatively small portion ofthe Sun’s total energy represents a large portion of theheat energy for our Earth. It is of such importance inmeteorology that every Aerographer’s Mate shouldhave at least a basic knowledge about the Sun and theeffects it has on Earth’s weather.DENSITYWith the previous explanation of grams andcentimeters, you should be able to understand howphysical factors can be measured and described. Forexample, density is the weight something has per unitof volume. The density of water is given as 1 gram percubic centimeter or 1 gm/cm. By comparison, thedensity of water in the English system is 62.4 poundsper cubic foot or 62.4 lb/ft3.SUNThe Sun may be regarded as the only source of heatenergy that is supplied to earth’s surface and theatmosphere. All weather and motions in the atmosphereare due to the energy radiated from the Sun.FORCEForce is measured in dynes. A dyne is the force thatmoves a mass of 1 gram, 1 centimeter per squaresecond. This is commonly written as gin cm per sec2,gin cm/sec/sec or gm/cm/sec2. The force necessary fora gram to be accelerated at 980.665 cm/sec2 at 45 latitude is 980.665 dynes. For more detailed conversionfactors commonly used in meteorology andoceanography, refer to Smithsonian MeteorologyTables.The Sun’s core has a temperature of 15,000,000 Kand a surface temperature of about 6,000 K (10,300 F).The Sun radiates electromagnetic energy in alldirections. However, Earth intercepts only a smallfraction of this energy. Most of the electromagneticenergy radiated by the Sun is in the form of light waves.Only a tiny fraction is in the form of heat waves. Evenso, better than 99.9 percent of Earth’s heat is derivedfrom the Sun in the form of radiant energy.1-2

the Sun is radiated from the photosphere. Above thephotosphere is a more transparent gaseous layerreferred to as the chromosphere with a thickness ofabout 1,800 miles (3,000 km). It is hotter than thephotosphere. Above the chromosphere is the corona, alow-density high temperature region. It is extended farout into interplanetary space by the solar wind—asteady outward streaming of the coronal material.Much of the electromagnetic radiation emissionsconsisting of gamma rays through x-rays, ultraviolet,visible and radio waves, originate in the corona.Solar CompositionThe Sun may be described as a globe of gas heatedto incandescence by thermonuclear reactions fromwithin the central core.The main body of the Sun, although composed ofgases, is opaque and has several distinct layers. (See fig.1-1.) The first of these layers beyond the radiative zoneis the convective zone. This zone extends very nearly tothe Sun’s surface. Here, heated gases are raisedbuoyantly upwards with some cooling occurring andsubsequent convective action similar to that, whichoccurs within Earth’s atmosphere. The next layer is awell-defined visible surface layer referred to as thephotosphere. The bottom of the photosphere is the solarsurface. In this layer the temperature has cooled to asurface temperature of 6,000 K at the bottom to4,300 K at the top of the layer. All the light and heat ofWithin the solar atmosphere we see the occurrenceof transient phenomena (referred to as solar activity),just as cyclones, frontal systems, and thunderstormsoccur within the atmosphere of Earth. This solaractivity may consist of the phenomena discussed in thefollowing paragraphs that collectively describe thefeatures of the solar disk (the visual image of the outerCORONASOLARATMOSPHERERESEVSOL ERALDIAMARIN D ETERSEPTHSOLAR SURFACETEMPERATUREOAPPROX. 6,000 KSOMOHREPHCEIVTEC ENV ONCO Z3,000KmRADIATIVE ZONEPHOTOSPHERECENTRAL CORE(THERMONUCLEARREACTIONS) APPROX.15,000,000O KAGf0101Figure 1-1.—One-quarter cross-section depicting the solar structure.1-3

They have a fibrous structure and appear to resist solargravity. They may extend 18,500 to 125,000 miles(30,000 to 200,000 km) above the chromosphere. Themore active types have temperatures of 10,000 K ormore and appear hotter than the surroundingatmosphere.surface of the sun as observed from outside regions).(See fig. 1-2).Solar Prominences/FilamentsSolar prominences/filaments are injections of gasesfrom the chromosphere into the corona. They appear asgreat clouds of gas, sometimes resting on the Sun’ssurface and at other times floating free with no visibleconnection. When viewed against the solar disk, theyappear as long dark ribbons and are called filaments.When viewed against the solar limb (the dark outeredge of the solar disk), they appear bright and are calledprominences. (See fig. 1-2.) They display a variety ofshapes, sizes, and activity that defy general description.SunspotsSunspots are regions of strong localized magneticfields and indicate relatively cool areas in thephotosphere. They appear darker than theirsurroundings and may appear singly or in morecomplicated groups dominated by larger spots near thecenter. (See fig. 1-2).PLAGESOLAR PROMINENCES(FILAMENTS)SUNSPOTSFLAREAGf0102Figure 1-2.—Features of the solar disk.1-4

Flares are classified according to size andbrightness. In general, the higher the importanceclassification, the stronger the geophysical effects.Some phenomena associated with solar flares haveimmediate effects; others have delayed effects (15minutes to 72 hours after flare).Sunspots begin as small dark areas known as pores.These pores develop into full-fledged spots in a fewdays, with maximum development occurring in about 1to 2 weeks. When sunspots decay the spot shrinks insize and its magnetic field also decreases in size. Thislife cycle may consist of a few days for small spots tonear 100 days for larger groups. The larger spotsnormally measure about 94,500 miles (120,000 kin)across. Sunspots appear to have cyclic variations inintensity, varying through a period of about 8 to 17years. Variation in number and size occurs throughoutthe sunspot cycle. As a cycle commences, a few spotsare observed at high latitudes of both solarhemispheres, and the spots increase in size and number.They gradually drift equatorward as the cycleprogresses, and the intensity of the spots reach amaximum in about 4 years. After this period, decay setsin and near the end of the cycle only a few spots are leftin the lower latitudes (5 to 10 ).Solar flare activity produces significant disruptionsand phenomena within Earth’s atmosphere. Duringsolar flare activity, solar particle streams (solar winds)are emitted and often intercept Earth. These solarparticles are composed of electromagnetic radiation,which interacts with Earth’s ionosphere. This results inseveral reactions such as: increased ionization(electrically charging neutral particles), photo chemicalchanges (absorption of radiation), atmospheric heating,electrically charged particle motions, and an influx ofradiation in a variety of wavelengths and frequencieswhich include radio and radar frequencies.Plages are large irregular bright patches thatsurround sunspot groups. (See fig. 1-2). They normallyappear in conjunction with solar prominences orfilaments and may be systematically arranged in radialor spiral patterns. Plages are features of the lowerchromosphere and often completely or partiallyobscure an underlying sunspot.Some of the resulting phenomena include thedisruption of radio communications and radardetection. This is due to ionization, incoming radiowaves, and the motion of charged particles. Satelliteorbits can be affected by the atmospheric heating andsatellite transmissions may be affected by all of thereactions previously mentioned. Geomagneticdisturbances like the aurora borealis and auroraAustralia result primarily from the motion ofelectrically charged particles within the ionosphere.FlaresEARTHSolar flares are perhaps the most spectacular of theeruptive features associated with solar activity. (See fig.1-2). They look like flecks of light that suddenly appearnear activity centers and come on instantaneously asthough a switch were thrown. They rise sharply to peakbrightness in a few minutes, then decline moregradually. The number of flares may increase rapidlyover an area of activity. Small flare-like brighteningsare always in progress during the more active phase ofactivity centers. In some instances flares may take theform of prominences, violently ejecting material intothe solar atmosphere and breaking into smallerhigh-speed blobs or clots. Flare activity appears to varywidely between solar activity centers. The greatest flareproductivity seems to be during the week or 10 dayswhen sunspot activity is at its maximum.Of the nine planets in our solar system, Earth is thethird nearest to (or from) the Sun. Earth varies indistance from the Sun during the year. The Sun is 94million miles (150,400,000 km) in summer and 91million miles (145,600,000 km) in winter.PlagesMotionsEarth is subject to four motions in its movementthrough space: rotation about its axis, revolution aroundthe Sun, processional motion (a slow conical movementor wobble) of the axis, and the solar motion (themovement of the whole solar system with space). Ofthe four motions affecting Earth, only two are of anyimportance to meteorology.1-5

direct sunlight covers the area from the North Poledown to latitude 66 1/2 N (the Arctic Circle). The areabetween the Arctic Circle and the North Pole isreceiving the Sun’s rays for 24 hours each day. Duringthis time the most perpendicular rays of the Sun arereceived at 23 l/2 N latitude (the Tropic Of Cancer).Because the Southern Hemisphere is tilted away fromthe Sun at this time, the indirect rays of the Sun reachonly to 66 1/2 S latitude (the Antarctic Circle).Therefore, the area between the Antarctic Circle andthe South Pole is in complete darkness. Note carefullythe shaded and the not shaded area of Earth in figure 1-4for all four positions.The first motion is rotation. Earth rotates on its axisonce every 24 hours. One-half of the Earth’s surface istherefore facing the Sun at all times. Rotation aboutEarth’s axis takes place in an eastward direction. Thus,the Sun appears to rise in the east and set in the west.(See fig. 1-3.)The second motion of Earth is its revolution aroundthe Sun. The revolution around the Sun and the tilt ofEarth on its axis are responsible for our seasons. Earthmakes one complete revolution around the Sun inapproximately 365 1/4 days. Earth’s axis is at an angleof 23 1/2 to its plane of rotation and points in a nearlyfixed direction in space toward the North Star (Polaris).At the time of the equinox in March and again inSeptember, the tilt of Earth’s axis is neither toward noraway from the Sun. For these reasons Earth receives anequal amount of the Sun’s energy in both the NorthernHemisphere and the Southern Hemisphere. During thistime the Sun’s rays shine most perpendicularly at theequator.Solstices and EquinoxesWhen Earth is in its summer solstice, as shown forJune in figure 1-4, the Northern Hemisphere is inclined23 1/2 toward the Sun. This inclination results in moreof the Sun’s rays reaching the Northern Hemispherethan the Southern Hemisphere. On or about June 21,SUNRISENOONSUNSETMIDNIGHTAgf0103Figure 1-3.—Rotation of the Earth about its axis (during equinoxes).1-6

N/PMARCH 21S/PN/PDECEMBER22JUNE 21S/PN/PS/PSUNN/PSEPTEMBER22S/PAGF0104Figure 1-4.—Revolution of Earth around the sun.In December, the situation is exactly reversed fromthat in June. The Southern Hemisphere now receivesmore of the Sun’s direct rays. The most perpendicularrays of the Sun are received at 23 1/2 S latitude (theTropic Of Capricorn). The southern polar region is nowcompletely in sunshine and the northern polar region iscompletely in darkness.3. September 22. The autumnal equinox, whenEarth’s axis is again perpendicular to the Sun’s rays.This date marks the beginning of fall in the NorthernHemisphere and spring in the Southern Hemisphere. Itis also the date, along with March 21, when the Sunreaches its highest position (zenith) directly over theequator.Since the revolution of Earth around the Sun is agradual process, the changes in the area receiving theSun’s rays and the changes in seasons are gradual.However, it is customary and convenient to mark thesechanges by specific dates and to identify them byspecific names. These dates are as follows:4. December 22. The winter solstice, when theSun has reached its southernmost zenith position at theTropic of Capricorn. It marks the beginning of winter inthe Northern Hemisphere and the beginning of summerin the Southern Hemisphere.In some years, the actual dates of the solstices andthe equinoxes vary by a day from the dates given here.This is because the period of revolution is 365 1/4 daysand the calendar year is 365 days except for leap yearwhen it is 366 days.1. March 21. The vernal equinox, when Earth’saxis is perpendicular to the Sun’s rays. Spring begins inthe Northern Hemisphere and fall begins in theSouthern Hemisphere.Because of its 23 1/2 tilt and its revolution aroundthe Sun, five natural light (or heat) zones according tothe zone's relative position to the Sun's rays mark Earth.Since the Sun is ALWAYS at its zenith between theTropic of Cancer and the Tropic of Capricorn, this is thehottest zone. It is called the Equatorial Zone, the TorridZone, the Tropical Zone, or simply the Tropics.2. June 21. The summer solstice, when Earth’saxis is inclined 23 1/2 toward the Sun and the Sun hasreached its northernmost zenith at the Tropic of Cancer.Summer officially commences in the NorthernHemisphere; winter begins in the SouthernHemisphere.1-7

surface emits gamma rays, x-rays, ultraviolet, visiblelight, infrared, heat, and electromagnetic waves.Although the Sun radiates in all wavelengths, abouthalf of the radiation is visible light with most of theremainder being infrared. (See figure 1-5.)The zones between the Tropic of Cancer and theArctic Circle and between the Tropic of Capricorn andthe Antarctic Circle are the Temperate Zones. Thesezones receive sunshine all year, but less of it in theirrespective winters and more of it in their respectivesummers.Energy radiates from a body by wavelengths,which vary inversely with the temperature of that body.Therefore, the Sun, with an extremely hot surfacetemperature, emits short wave radiation. Earth has amuch cooler temperature (15 C average) and thereforereradiates the Sun’s energy or heat with long waveradiation.The zones between the Arctic Circle and the NorthPole and between the Antarctic Circle and the SouthPole receive the Sun’s rays only for parts of the year.(Dir

CHAPTER 1 FUNDAMENTALS OF METEOROLOGY Meteorology is the study of atmospheric phenomena. This study consis