How the shape of sand dune indicate the wind direction延伸文章資訊，搜尋引擎最佳文章推薦

1. Sand dune

Lighter winds blow from several different directions, and the dunes, being of ... repetition of dune shapes and spacings when they are close together indicate that ...SandduneSectionsArticleIntroductionGeomorphiccharacteristicsSandsWindsFormationandgrowthofdunesDuneandsheetpatternsFixeddunesinsemiaridregionsShowmoreMediaVideosImagesAdditionalInfoAdditionalReadingMoreArticlesOnThisTopicContributorsArticleHistoryLoadPreviousPageWindsWindshavethreesourcesofvariationthatareimportant—namely,direction,velocity,andturbulence.Mostofthegreatdesertsarefoundinthesubtropicalareasofhighatmosphericpressure,wherethewindscirculateinaclockwisedirectionintheNorthernHemisphereandacounterclockwisedirectionintheSouthernHemisphere.Thehigh-pressuresystemstendtodipdowntotheeastsothatwindsarestrongerthere,apatternmirroredbythedunes.PolewardofthesecirculationsystemsarethezonesofeastwardmovingdepressionsinwhichtherearegenerallywesterlywindsthatmoldthedunesoftheNorthAmericanandCentralAsiandesertsandofthenorthernSahara.Theboundariesbetweenthesetwocirculationsystemsmigratebackandforthseasonally,sothatcomplicateddunepatternsarefoundinthezonesofoverlap.Onlyafewdeserts,notablytheTharDesertofIndiaandtheSonoranDesertoftheAmericanSouthwest,areaffectedbymonsoonalwindsystems.Somedunesarebuiltbyseabreezesandlocalwinds,asincoastalPeru.Thedirectionofthewindatanyoneplaceinthedesertisaffectedbyanumberoflocalfactors.Windsareparticularlychanneledaroundtopographicalfeatures,suchastheTibestiMassifintheSahara,sothatdunesareaffectedbydifferentwindsondifferentsidesoftheobstruction.Windsalsocanbechanneledaroundthedunesthemselves,therebydevelopingpatternsofsecondaryflowthatmodifytheshapesofthedunes.Thepatternofwindvelocityalsoisimportant.Likemanynaturalphenomena,windvelocitieshavealog-normaldistribution:therearealargenumberofmoderatebreezesandadiminishingnumberofincreasinglymoreviolentwinds.Thegreatestvolumesofsandareprobablymovedbyunusuallystrongwinds,becausetheamountofsandmovedbywindisapowerfunction(exponentialfact

2. Types of Dunes

These dunes form under winds that blow from one direction, and they also are ... The largest crescentic dunes on Earth, with mean crest-to-crest widths ... Straight or slightly sinuous sand ridges typically much longer than they ...RipplesonaduneinEurekaValley,California(photographbyTerrenceMoore).AworldwideinventoryofdesertshasbeendevelopedusingimagesfromtheLandsatsatellitesandfromspaceandaerialphotography.Itdefinesfivebasictypesofdunes:crescentic,linear,star,dome,andparabolic.ThemostcommonduneformonEarthandonMarsisthecrescentic.Crescent-shapedmoundsgenerallyarewiderthanlong.Theslipfaceisonthedune'sconcaveside.Thesedunesformunderwindsthatblowfromonedirection,andtheyalsoareknownasbarchans,ortransversedunes.Sometypesofcrescenticdunesmovefasteroverdesertsurfacesthananyothertypeofdune.Agroupofdunesmovedmorethan100metersperyearbetween1954and1959inChina'sNingxiaProvince;similarrateshavebeenrecordedintheWesternDesertofEgypt.ThelargestcrescenticdunesonEarth,withmeancrest-to-crestwidthsofmorethan3kilometers,areinChina'sTaklimakanDesert.ThesecrescenticdunesofcoastalPeruaremigratingtowardtheleft(photographbyJohnMcCauley).Straightorslightlysinuoussandridgestypicallymuchlongerthantheyarewideareknownaslineardunes.Theymaybemorethan160kilometerslong.Lineardunesmayoccurasisolatedridges,buttheygenerallyformsetsofparallelridgesseparatedbymilesofsand,gravel,orrockyinterdunecorridors.SomelineardunesmergetoformY-shapedcompounddunes.Manyforminbidirectionalwindregimes.Thelongaxesofthesedunesextendintheresultantdirectionofsandmovement.LineardunesadvanceonsmallplayaseastofLakeEyreintheSimpsonDesertofcentralAustralia(photographbyC.Twidale).LineardunesinthewesterndesertsofEgypt(photographbyCarolBreed).Radiallysymmetrical,stardunesarepyramidalsandmoundswithslipfacesonthreeormorearmsthatradiatefromthehighcenterofthemound.Theytendtoaccumulateinareaswithmultidirectionalwindregimes.Stardunesgrowupwardratherthanlaterally.TheydominatetheGrandErgOrientaloftheSahara.Inotherdeserts,theyoccuraroundthema

3. Dunes

Dunes. In physical geography, a dune is a hill of sand built by either wind or ... superposed or coalesced forms, usually of barchanoid or linear shapes. ... Simple dunes represent a wind regime that has not changed in intensity or direction ...SkiptomaincontentEarthScienceDesertsSearchfor:DunesInphysicalgeography,a dune isahillofsandbuiltbyeitherwindorwaterflow.Dunesoccurindifferentformsandsizes,formedbyinteractionwiththeflowofairorwater.Mostkindsofdunesarelongeronthewindwardsidewherethesandispusheduptheduneandhaveashorter“slipface”intheleeofthewind.Thevalleyortroughbetweendunesiscalleda slack. A“dunefield”isanareacoveredbyextensivesanddunes.Largedunefieldsareknownasergs.Somecoastalareashaveoneormoresetsofdunesrunningparalleltotheshorelinedirectlyinlandfromthebeach.Inmostcasesthedunesareimportantinprotectingthelandagainstpotentialravagesbystormwavesfromthesea.Althoughthemostwidelydistributeddunesarethoseassociatedwithcoastalregions,thelargestcomplexesofdunesarefoundinlandindryregionsandassociatedwithancientlakeorseabeds.Dunesalsoformundertheactionofwaterflow(fluvialprocesses),andonsandorgravelbedsofrivers,estuariesandthesea-bed.Themodernword“dune”cameintoEnglishfromFrenchcirca1790.Inancienttimes,wordscognateto“dune”probablyhadthemeaningofabuilt-uphillorcitadelfortification.[1]ErgChebbi,Morocco ConservationDunehabitatsprovidenichesforhighlyspecialisedplantsandanimals,includingnumerousrarespeciesandsomeendangeredspecies.Duetowidespreadhumanpopulationexpansion,dunesfacedestructionthroughlanddevelopmentandrecreationalusages,aswellasalterationtopreventtheencroachmentofsandontoinhabitedareas.Somecountries,notablytheUnitedStates,Australia,Canada,NewZealand,theUnitedKingdom,andNetherlands,havedevelopedsignificantprogramsofduneprotectionthroughtheuseofsanddunestabilization.IntheU.K.,aBiodiversityActionPlanhasbeendevelopedtoassessduneslossandtopreventfuturedunesdestruction.SandblowingoffacrestintheKelsoDunesoftheMojaveDesert,California.AeolianduneshapesCrescentic“Crescent-sh

4. Phase diagrams of dune shape and orientation depending on ...

New evidence indicates that sand availability does not only control ... wind conditions, transverse linear dunes form where sand availability ...SkiptomaincontentThankyouforvisitingnature.com.YouareusingabrowserversionwithlimitedsupportforCSS.Toobtainthebestexperience,werecommendyouuseamoreuptodatebrowser(orturnoffcompatibilitymodeinInternetExplorer).Inthemeantime,toensurecontinuedsupport,wearedisplayingthesitewithoutstylesandJavaScript.AdvertisementnaturescientificreportsarticlesarticlePhasediagramsofduneshapeandorientationdependingonsandavailabilityDownloadPDFSubjectsGeodynamicsGeomorphologyAbstractNewevidenceindicatesthatsandavailabilitydoesnotonlycontroldunetypebutalsotheunderlyingdunegrowthmechanismandthesubsequentduneorientation.Herewenumericallyinvestigatethedevelopmentofbedformsinbidirectionalwindregimesfortwodifferentconditionsofsandavailability:anerodiblesandbedoralocalizedsandsourceonanon-erodibleground.Thesetwoconditionsofsandavailabilityareassociatedwithtwoindependentdunegrowthmechanismsand,forbothofthem,wepresentthecompletephasediagramsofduneshapeandorientation.Onanerodiblesandbed,lineardunesareobservedovertheentireparameterspace.Then,thedivergenceangleandthetransportratiobetweenthetwowindscontrolduneorientationanddynamics.Foralocalizedsandsource,differentdunemorphologiesareobserveddependingonthewindregime.Therearesystematictransitionsinduneshapefrombarchanstolineardunesextendingawayfromthelocalizedsandsourceandvice-versa.Thesetransitionsarecapturedfairlybyanewdimensionlessparameter,whichcomparestheabilityofwindstobuildthedunetopographyinthetwomodesofduneorientation.DownloadPDFIntroductionDuneshavebeenprimarilyclassifiedaccordingtotheirshapeconsideringbothsandavailabilityandwinddirectionalvariability1.ThewinddirectionalvariabilityisusuallymeasuredbytheRDP/DPdimensionlessparameter.Itistheratiobetweentheresultantdriftpotential(RDP,thenormofthemeansandfluxvector)andthedriftpotential(DP,themeanofthenormsoftheindividualsandfluxvectors).Inzonesoflowsandavail

5. (PDF) Analysis of sand dunes to determine wind direction and ...

The studies have shown that wind prevailing direction is eastern-north to western-south, the strong wind being in north-south direction. It can also ...ArticlePDFAvailableAnalysisofsanddunestodeterminewinddirectionanddetectsandsourcesites(casestudy:KhartooranErg,Iran)January2007Project:Thestudyofremoval(detachment)andtransitionalregionsofwinderosionupongroundindicator(Casestudy:KhartouranErg)Authors:NaserMashhadiUniversityofTehranHadiAhmadiUniversityofTehranMREkhtesasiMREkhtesasiThispersonisnotonResearchGate,orhasn'tclaimedthisresearchyet.SadatFeizniaUniversityofTehranShowall5authorsHideDownloadfull-textPDFReadfull-textDownloadfull-textPDFReadfull-textDownloadcitationCopylinkLinkcopiedReadfull-textDownloadcitationCopylinkLinkcopiedCitations(15)References(7)Figures(1)AbstractandFiguresWindregimeandsandgrainsizearetwoofthefactorsthatdeterminethemorphologyanddynamicsofsanddunesindesertareas.RegardingtheimportanceofwindeffectsonsanddunesespeciallyinIran,inthisstudy,KhartooranErgwasanalyzedtodeterminewinddirectionandtodetectsandsourcesites.KhartooranErgislocatedoneasternnorthofIranandliesinKhorasanRazaviandSemnanprovinces.TheareaofErgwasdeterminedbasedongeologicalandtopographicalmapsandsatelliteimages.Then,sanddunesofergwereclassified,basedonaerialphotographandsatelliteimageinterpretation.SandduneformsintheKhartooranErgareoftenbarchansandcombinationofbarchanicridges,buttherearealsocomplextypesoflinearsanddunes.Basedonfieldsurveyfindings,thestabilizedinthesouthernpartoftheErgwereseparated,becauseofthesesandduneshavingbeendeformed.Accordingtothepresentedmodelsrelationshipbetweenmorphologyandwinddirection,thesandduneswereanalyzed.Thestudieshaveshownthatwindprevailingdirectioniseastern-northtowestern-south,thestrongwindbeinginnorth-southdirection.ItcanalsobesaidthatsandduneswhicharelocatedintheadjacentofErgandaresimpleandseparatecanbeusedasthemostsuitablecriteriatodeterminepredominantwind.Also,regardingtheErglocationwithrespecttoupperplainsanddeterminedwinddirection,itcanben

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Dune sand transport as influenced by wind directions, speed ... | How the shape of sand dune indicate the wind direction
quantity of aeolian sand transported was calculated for various wind speed levels and directions, and ... patchy sand sheets, and protruding tongue-shape sand ... image of the main body of Mu Us Sandy Land, the arrow indicates a sand sheet ...
Fact Sheet #2: How Do Sand Dunes Move | How the shape of sand dune indicate the wind direction
These winds are called unidirectional winds because they always move in the same direction, from the southwest to the northeast. As the wind blows, it pushes the ...
Types of Dunes | How the shape of sand dune indicate the wind direction
These dunes form under winds that blow from one direction, and they also are ... The largest crescentic dunes on Earth, with mean crest-to-crest widths ... Straight or slightly sinuous sand ridges typically much longer than they ...
Phase diagrams of dune shape and orientation depending on ... | How the shape of sand dune indicate the wind direction
New evidence indicates that sand availability does not only control ... wind conditions, transverse linear dunes form where sand availability ...
dune | How the shape of sand dune indicate the wind direction
A dune is a mound of sand this is formed by the wind, usually along the beach or in a desert. Dunes form ... The man's turban helps keep him cool in extreme desert conditions. ... Their shapes are roughly the same, but the slipface of a parabolic dune is on its inward side. ... to endure, allow, or put up with.
Analysis of sand dunes to determine wind direction and detect ... | How the shape of sand dune indicate the wind direction
Regarding the importance of wind effects on sand dunes especially in Iran, in this study, ... Keywords: Khartooran Erg; Sand dune; Wind direction; Barchan; Geomorphology; Prevailing wind. 1. ... The shield type edifice remains in its shape.
Dune | How the shape of sand dune indicate the wind direction
A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a ... Dunes occur in different shapes and sizes, but most kinds of dunes are longer ... These dunes form under winds that blow consistently from one direction ... The largest crescentic dunes on Earth, with mean crest-to-crest widths of ...
(PDF) Analysis of sand dunes to determine wind direction and ... | How the shape of sand dune indicate the wind direction
The studies have shown that wind prevailing direction is eastern-north to western-south, the strong wind being in north-south direction. It can also ...
Dunes | How the shape of sand dune indicate the wind direction
Dunes. In physical geography, a dune is a hill of sand built by either wind or ... superposed or coalesced forms, usually of barchanoid or linear shapes. ... Simple dunes represent a wind regime that has not changed in intensity or direction ...
Sand dune | How the shape of sand dune indicate the wind direction
Lighter winds blow from several different directions, and the dunes, being of ... repetition of dune shapes and spacings when they are close together indicate that ...