Download - tides - Earth Science · Tides are not explicitly included in the NGSS Performance Expectations. From the NGSS Framework (M.S. Space Science): “There is a strong emphasis on a systems

I.WhatareTides?II. CausesofTidesIII.TidalVariationsIV. LunarDayandFrequencyofTidesV. MonitoringTides

Tides

WikimediaFoxyOrange[CCBY-SA3.0

https://commons.wikimedia.org/wiki/File:Gorey_Harbour_at_low_tide.JPG



TidesarenotexplicitlyincludedintheNGSSPerformanceExpectations.

FromtheNGSSFramework(M.S.SpaceScience):“Thereisastrongemphasisonasystemsapproach,usingmodelsofthesolarsystemtoexplainastronomicalandotherobservationsofthecyclicpatternsofeclipses,tides,andseasons.”

FromtheNGSSCrosscuttingConcepts:Observedpatternsinnatureguideorganizationandclassificationandpromptquestionsaboutrelationshipsandcausesunderlyingthem.ForElementarySchool:• Similaritiesanddifferencesinpatternscanbeusedtosort,classify,communicate

andanalyzesimpleratesofchangefornaturalphenomenaanddesignedproducts.• Patternsofchangecanbeusedtomakepredictions• Patternscanbeusedasevidencetosupportanexplanation.ForMiddleSchool:• Graphs,charts,andimagescanbeusedtoidentifypatternsindata.• Patternscanbeusedtoidentifycause-and-effectrelationships.

Thetopicoftideshaveanimportantconnectiontoglobalchangesincespringtidesandkingtidesarecausingcoastalfloodingassealevelhasbeenrising.

TidesareoneofthemostreliablephenomenaonEarth-theyoccuronaregularandpredictablecycle.Alongwithdeathandtaxes,tidesareacertaintyoflife.

SamuelWantman/WikimediaCommons.LicensedunderCCBY-SA3.0viaCommons

I.WhatareTides?

Tidesareapparentchangesinlocalsealevelthataretheresultoflong-periodwavesthatmovethroughtheoceans.PhotosoflowandhightideonthecoastoftheBayofFundyinCanada.

https://en.wikipedia.org/wiki/Tide#/media/File:Bay_of_Fundy_High_Tide.jpg




Thedifferenceinheightbetweenthehightideandthelowtideiscalledthetidalrange.

Whenthehighestpartofthetide(crest)reachesthecoast,hightideoccurs.Lowtideoccurswhenthelowestpartofthewave,oritstroughreachesthecoast.

TidalcurrentsareparticularlyimportantinregionsliketheS.F.Bay.

Atidalcurrentisthehorizontalmovementofwaterthataccompaniestherisingandfallingofthetide.Theincomingtidealongthecoastandintothebaysandestuariesiscalledafloodcurrent.Theoutgoingtidalcurrentiscalledanebbcurrent.

TwobulgesofwateroccuronoppositesidesoftheEarthduetothegravitationalinfluenceoftheMoon-onethatroughlyfacestheMoonandanotherontheoppositesideoftheEarth.

II.CausesofTides

SincetheMoonorbitstheEarthslowerthantheEarthrotatesonitsaxis,theEarthrotatesinandoutofthetidalbulges.

Mostcoastlinesexperiencetwohightidesandtwolowtidesabouteachday.

HightidesarecommonlyunequalinheightduetotheaxialangleoftheEarth’srotation.Forexample,thelocationontheEarthatAhasafairlylargehightide.Butwhenthispositionhasrotatedin12hourstotheothersideatA’,notethatthehightideisnotashigh.

NOTTOSCALE!

A

A’

NOAANOTTOSCALE!

ThemostcommonmodelforwhytheEarthhastwotidalbulgesisbecausegravityandinertiaareopposingforcesactingontheEarth’soceans,creatingtidalbulgesonoppositesitesoftheplanet.

http://oceanservice.noaa.gov/education/kits/tides/media/supp_tide03.html

NOTTOSCALE!

OntheoppositesideoftheEarth,inertialforcesdominate,creatingasecondbulge.OnesimplewayofthinkingaboutitisthattheEarth(B)ispulledawayfromthewateronthatfarsidebecausethegravitationalforceexertedbytheMoonatpointBislargerthanthatexertedatpointC.Inthismodel,gravityandinertiacreatetwobulgesofwater.OneformswheretheEarthandmoonareclosesttogether,andtheotherformswheretheyarefurthestapart.Thisisgreatlyoversimplifiedbutmayserveasagoodmentalmodelfortidalbulges.

OnthesideoftheEarthfacingtheMoon,thegravitationalinteractionoftheMoonresultsinabulge(A).

ABCMoon

WikimediaUserKrishnavedalaCCBY-SA3.0

Thepreviousmodelfortheformationoftwotidalbulgesisnottechnicallycorrect.ItisanoversimplificationtostatethatthetidalbulgesareduetothesimplegravitationalattractionoftheMoon.However,anaccurategravitationmodeltodescribethetide-generatingforceisbeyondthescopeofmostK-12classrooms.

LunargravitycreatesadifferentialfieldontheEarth’ssurfaceknownasthetide-generatingforce(asindicatedbythevectorsinthefigure).Themajordifferencebetweenthetwomodelsfortheformationofthetwotidalbulgesiswhetherthetidalbulgesarepulledbysimplegravitationalattraction(leastaccurate)orsqueezedbythedifferentialgravitationalfield(moreaccurate).

https://en.wikipedia.org/wiki/Tide#/media/File:Field_tidal.svg





Tidalforcesarebasedonthegravitationalinteractionbetweentwoormorebodies.Withtidalforces,thedistancebetweentwoobjectsusuallyismorecriticalthantheirmasses.Thus,theMoon,beingcloserhasamuchstrongereffectontidesontheEarththandoestheSun.

The“back-of-the-envelope”calculationsshowthatthetide-generatingforceoftheMoonismorethantwicethatoftheSun.

NOAA

http://oceanservice.noaa.gov/education/tutorial_tides/media/supp_tide02.html

III.TidalVariations

Thevariationoftidesandtidalrangesisduetoavarietyoffactorsincluding:

1. AlignmentoftheMoonandSun2. DeclinationofMoon3. EccentricityoftheEarth’sorbit4. EccentricityofMoon’sorbit5. Regionalfactorssuchastheshapeofthecoastline

1.AlignmentoftheMoonandSun

RememberthatboththeSunandtheMoonaffecttidesonEarth.

WhentheEarth,SunandMoonarealigned,theaffectoftheSunandtheMoonareadditiveandthetidesareattheirhighestandlowest-theseareknownasspringtides.

Springtidesoccurduringfullandnewmoons.

NOAANottoscale.

http://oceanservice.noaa.gov/education/kits/tides/media/supp_tide06a.html

WhentheSunandMoonareatrightanglestooneanother-thecontributionfromtheSunpartiallycancelsouttheeffectoftheMoonandresultsinlowerhightidesandhigherlowtides-knowasneaptides.

NeaptidesoccurduringthefirstandthirdquartersoftheMoon.

Nottoscale.

NOAA


NOAA

2.DeclinationofMoonTheMoon’sdeclination(angleoftheMoon’sorbitwithrespecttotheEarth’sequator)variesovera18.6yearcyclefromamaximumof~28°toaminimumof~18°.TheanimationshowsthechangeintheangleoftheMoon’sorbitalplane.TheEarth’stidalbulgestrackthepositionoftheMoonandhaveaeffectontheheightoftides.

Nottoscale.

NavalPostgraduateSchool

http://oceanservice.noaa.gov/education/tutorial_tides/media/supp_tide04.html

http://www.oc.nps.edu/nom/day1/partc.html

WikimediaUserChris55

3.EccentricityoftheEarth’sorbitTheorbitoftheEartharoundtheSunisslightlyeccentric.PerihelionistheEarth’sclosestapproachtotheSunandis147.1millionkm.AphelionistheEarth’sfarthestdistancefromtheSunandis152.1millionkm.Thedifferencebetweenperihelionandaphelionis~5millionkm.

SincethetidalinfluenceoftheSunisafunctionofthedistance,thesmallchangethedistancebetweentheEarthandSunresultsinasmallchangeinthesolartidalcomponent(heightoftide).

Nottoscaleandorbitaleccentricityisexaggerated.

https://en.wikipedia.org/wiki/Perihelion_and_aphelion#/media/File:Perihelion-Aphelion.svg

NASA

4.EccentricityofMoon’sorbit TheorbitoftheMoonaroundtheEarthisslightlyeccentric.PerigeeistheMoon’sclosestapproachtotheEarthandis363,396km.ApogeeistheMoon’sfarthestdistancefromtheEarthandis405,504km.Thedifferencebetweenperigeeandapogeeis~42,000km.

SincethetidalinfluenceoftheMoonislargelyafunctionofthedistance,thetidegeneratinginfluenceoftheMoonincreasesduringperigee.WhentheMoonisatperigee,itappears~14%largerwhenviewedfromEarthandiscommonlyknownasasupermoon.

Nottoscaleandorbitaleccentricityisexaggerated.

NASA

http://science.nasa.gov/science-news/science-at-nasa/2011/16mar_supermoon/

NOAA

TheeffectoftheeccentricorbitsoftheEarthandMoonhaveaverysmallinfluenceontides.Atmost,theeffectmaybeonlyafewinches.Althoughthiseffectmaybesmall,itcanbeadditivewithotherfactorsthataffecttides.

SincethetidalrangeisdrivenbytherelativepositionsoftheEarth,Moon,andSunandtheirellipticalorbits,kingtidesoccurwhentheEarth,MoonandSunarealignedatperigeeandperihelion.

Nottoscaleandorbitaleccentricitiesareexaggerated.

KGOTV

Theterm“kingtide”isnotascientificterm;itiscommonlyusedtodescribeextralargehightides.

http://oceanservice.noaa.gov/education/kits/tides/media/supp_tide06b.html

http://abc7news.com/weather/king-tides-to-flow-into-san-francisco-bay-through-christmas/1134558/

Thisimageshowsamodeloftheseasurfaceheightamplitudeinmetersduetoatides.

NASA/TOPEX

5.Regionalfactors

Wefindthatthetidalrangemayvaryconsiderablealongdifferentcoastlines.Underwaterbathymetry(shapeofseafloor)andtheshapeofthecoastlinecandramaticallyaffectthelocaltidalrange.AstheEarthrotateswithinthetidalbulges,thecontinentsdisruptthemigrationofthebulgeintheoceans.

https://www.esr.org/polar_tide_models/Model_TPXO62.html

https://www.esr.org/polar_tide_models/Model_TPXO62.html

IV.LunarDayandFrequencyofTidesMostcoastalareasexperiencetwohightidesandtwolowtidesinacyclethattakes24hoursand50minutes-alunarday.AlunardayistheamountoftimetakesforaspecificpointontheEarthtorotatefromanexactpointundertheMoontothesamepointundertheMoon-24hoursfortherotationoftheEarthandanadditional50minutesbecausetheMoonhasmovedinitsorbitaroundtheEarth.BecausetheEarthrotatesthroughtwotidal“bulges”everylunarday,coastalareasexperiencetwohighandtwolowtidesevery24hoursand50minutes.

NavalPostgraduateSchool

http://www.oc.nps.edu/nom/day1/partc.html

Anareahasasemidiurnaltidalcycleifitexperiencestwohighandtwolowtidesofapproximatelyequalsizeeverylunarday.Anareahasamixedsemidiurnaltidalcycleifitexperiencestwohighandtwolowtidesofdifferentsizeeverylunarday.

Anareahasadiurnaltidalcycleifitexperiencesonehighandonelowtideeverylunarday.

NOAA


NOAA

IftheEarthhadnocontinentsandwasuniformlycoveredbyocean,theentireplanetwouldexperiencetwoequallyproportionedhighandlowtideseverylunarday.OnEarth,thecontinentsblockthemigrationofthetidalbulgesastheEarthrotates.Theinterferenceofthecontinentsresultincomplextidalpatternsindifferentregionsdependingupontheshapeofthecoastlineandseafloorbathymetry(shapeoftheseafloor).

http://oceanservice.noaa.gov/education/tutorial_tides/media/supp_tide07b.html

V.MonitoringTides

NOAA

Predictingtideshasalwaysbeenimportantforshipping,marineindustriesandcommercialfishing.Forexample,navigatingshipsthroughshallowwaterportsrequiresknowledgeofthetimeandheightofthetidesaswellasthespeedanddirectionofthetidalcurrents.In2002,fourlargeindustrialcraneswereshippedtoOaklandfromChina.TheshipcarryingthecranesneededtogoundertheBayBridgeandclearedthebottomofthebridgebyonly6feetduringlowtide.

http://oceanservice.noaa.gov/education/tutorial_tides/tides09_monitor.html

Atidegaugeisadeviceformeasuringthechangeinsealevelrelativetoabaselinesuchasmeansealevel.Sensorscontinuouslyrecordtheheightofthewaterlevel.Waterentersthebottomofapipeandsensorsmeasureitsheightinside.Inrecentyears,tidegaugesareautomatedwithelectronicsensorsandreal-timetidedataareavailableonline.

Dataareavailablefrommorethan1,750tidegaugesworldwide.Sometidegaugeshavebeenincontinuousoperationforcenturies.ThemapshowsthedistributionoftidegaugesfortheGlobalSeaLevelObservingSystem(GLOSS)network.

NOAA

ThetidegaugeatCrissyFieldhasbeenincontinuousoperationsince1845.

http://www.oco.noaa.gov/tideGauges.html

Tidegaugeshavebeenanimportantsourceofdatafordocumentingtheincreaseinmeansealevelduetoclimatechange.ThedatashowmonthlymeanwaterlevelsfromtheSanFranciscoCrissyFieldtidegaugethathasbeenoperatingsince1854.Globalsealevelrise~2.0mm/year.

NOAA

https://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?stnid=9414290

Download - tides - Earth Science · Tides are not explicitly included in the NGSS Performance Expectations. From the NGSS Framework (M.S. Space Science): “There is a strong emphasis on a systems

Top Related