Fronts And Frontogenesis As Revealed
PNASARI?1005e,lNASAReference Publication1005Fronts and Frontogenesis as Revealedby High Time Resolution DataAlbertAUGUSTE. Frankand DavidA. Barber1977,.,’ ,, ‘:-. ,-*-.,i 1’ \ yIUASA,‘.”.:’‘.
NASAReference Publication1005Fronts and Frontogenesis as Revealedby High Time Resolution DataAlbertGeorgeMarshallE. FrankC. MarshallSpace FlightNational Aeronauticsand Space AdministrationScientific and TechnicallpformationOffice1977and DavidA. BarberSpace FlightCenter,CenterAlabama
TABLE OF CONTENTSPagePURPOSE OF THE STUDY . . . . . . . . . . . . . . . . . .1HISTORICAL3REVIEW OF FRONTAL CONCEPTS. . . . . . . . . ., .ConceptsPriorto 1948. .More Recent Studies.Summary.2Upper Level THE SYNOPTIC SITUATION.361212324. . . . . . . . . . . . . . . . . 29DESCRIPTION OF THE DATA. . . . . . . . . . . . . . . . 36METHODOLOGY OF THE ANALYSES. . . . . . . . . . . . . . 39DISCUSSION OF THE CROSS SECTIONS . . . . . . . . . . . . 43PRESENTATION OF THE HIGH RESOLUTION CROSS SECTIONS . . . 72DISTRIBUTIONOF POTENTIAL VORTICITY. . . . . . . . . . 84COMPUTATION OF FRONTOGENESIS . . . . . . . . . . . . . . 89VERIFICATIONOF THE COMPUTATION. . . o . . . . . . . .107COMPUTATION OF VERTICAL VELOCITY. . . . . . . . . . . .114.118SUMMARY AND CONCLUSIONS.SUGGESTIONS FOR FURTHER RESEARCH .121BIBLIOGRAPHY. . . . . . . . . . . . . . . . . . . . .123DERIVATION OF THE FRONTOGENESIS EQUATIONIN ISENTROPIC COORDINATES . . . . . . . . .127APPENDIX:.111
LISTOF Frontal3Compositefrontsof Reed and Danielsen(1959).temperatureand isotachsofOn the left:the geostrophicflow normal to the section;isentropesand potentialvoron the right:ticity.18low levelfrontfrom Sanders(1955).Top:Isentropesand isotachsof flow normal toIsentropesevery 2.4 K andthe section.isotachsof long frontvelocityevery 4 mset-1from model frontof Hoskins(1971). . .20Isentropes(1971).of long frontvelo. . . . . . . . . . .22Isentropiccross sectionfrom Staley(1960)showing an example of a troposphere-spanningfront.D . . . . . . . . . . . . . . . . . . .257Cross sectionsfrom Petterssen268a-eStipplingindicatesareasWeather depiction.of steady precipitation;. . . . . . . o . . . 30-349Stationsparticipatingment and locations456of termsequationanalysisfromofBerggrenModel frontfrom Hoskinsevery 7.8 K and isotachscityevery 10.5 m set-1.through(1956)ofMiller's(1948). . . . . . . . . . . .(1952). . . .a zone of frontogenesis. . . . . . . . . . . .in AVE II pilotexpericross sections. . . . .81637lOa-iCross sectionsalong lineI from figure9.isotachsof flow normal toIsentropes,sectionsand stableregions. . . . . . . . . 44-52lla-iCross sectionsalong line II from figure9.Notationas for figure10. . . . . . . . . . . . 53-6112a-dHighfromflowresolutionfigure9.normal tocross sectionsalong lineIIsentropesand isotachsofsection. . . . . . . . . . . . 73-76iv
a-cPageHigh resolutioncross sectionsalong lineII in figure9.Notationas per figure12with additionsof valuesof potentialvorticityplottedon selectedisentropicsurfaces. . . . . . . . . . . . . . . . . .Illustratingshear inservative78-the effectof horizontalconcentratingisoplethsof conpropertyS. . . . e . . . . . . . .Isobarson isentropicsurfacesand locationsof frontogenesiscomputationsfor 0600 UT,12 May, 1974. . . . . . . . . . . . . . . . .Streamlinesand isotachson isentropicsurfacesfor 0600 UT, 12 May, 1974. . . . . .819194-969917a-cFrontalboundaries,dp/dt,and computedfrontogenesison isentropicsurfacesfor0600 UT, 12 May, 1974 . . . . . . . . . . . . 100-10218a-cValues of terms of equation[21 at pointsindicatedon figure15 for 0600 UT,12 May, 1974. . . . . . . . . . . . . . . . . 103-10519Six hour verticaldisplacementfollowinga parceland verticaldisplacementcomputedby integratingdp/dtover the lengthofthe trajectory. . . . . . . . . . . . . . .115IsotachsandTop:312 K,east side ofUT, 12 May,11720dp/dtabout jet streaks.2100 UT, 11 May, 1974 ontrough.Bottom:312 K, 09001974, on west side of trough. .
FRONTS AND FRONTOGENESIS AS REVEALED BYHIGH TIME RESOLUTION DATAPURPOSE OF THE STUDYFronts,by largewindthewhichvaluesshear,typicalthatand mainsInthisofclarifyingthefronts2.showsand structurefrontsreport,ofofsetthesethisstudyTo use hightimeses whichwillscaleusuallynotTo urinimportancea ro-known as-streams,and detailssome oftheIndeed,,FallerThe wellresponsibleHowever,a uniqueatmosphere.(19521,jetresultedand es,studycharacterizedand verticalnecessarilywithand dissolution.aboutofOfFultzheatedfrontslayersand ysuggestsociationingslopingpan experimentsand otherstating,ofarerotatingareforbasictheirmuch uncertaintyoffrontsdatawillre-and frontogenesis.be utiondatashow frontalto produceevolutionanaly-on a timeobtainable.analysestheto determineobservedchangestheinprocessesthefronts
3.To compareobtainedand contrastby othertheseinvestigators.resultswiththose
HISTORICALREVIEW OF FRONTAL CONCEPTSConceptsPriorgiststothehad littlestructurestormswe todaythewas clearlyothersnizeddue toisobars1820,fromtheairwouldofcloudswhichlifttems northeofaresurfacewithprovidedgradientofan integralofhe asexisted.to weathersys-frontstoform.reasonablyUsinga denseconfluenceand notedtheThe now wellwas describedfronts.asno modelfirstofsea levelmass ofand ofzonesunrecog-exceptwave cycloneregions.by theand severalcausingfrontsit.regardedEven as earlymass,offronts,and precipitationof(1850)implicitThe coldhow an advancingthepartwarm and )wereair,masses.warm ta,theofan opposingBjerkneswhichexclusionexplaincentury,(The warm frontand precipitation.couldpictureoflater.(1820)theby me 20 years1948a front.modelsoftoofofcallcycloneto be regionsfrontdecadeconceptionthatin many iatedtemperatureknown patternand relatedalsotoexplainedof
4how thetemperatureutilizedtheby as a sourceofaboutthetransportedair.Thatwiththem odelcyclone,fromoccludedand notedofcoldfrontsinthewas definedwererolethatto re-cyclonesas-part(1928)how heactingtothisfieldsand n occurindescribed,anda lineartransporttheproblema station-fieldofisentropesalongwas an important(1936)case.second-analy-thatthetwoitsHe showedofoccur,itstudiedwas anonlinearconservativea nonstationaryaThe m.alsocouldidealizedcycletheand heatfirstandwave tothehow ascentcirculationwillInand methodsfamiliesdeformationdilatation.ofbehindor dissipate.temperatureofairwas theorder.They describedand described,in the general.at ontsshortprocess.typesaryheatand theinvortex.ofbeand showedshown to be an integraland ldatmosof
isdilatation.studythethea certainangletion.A furthercontributionchangeofperty.arethetionA rontsfromWorldWar convergencebecauseitofofiswas thetheofthantherequiredkinematicswereofAs latecan be littlephenomenon".the(andofend ofcharacteristicallytheflowas 1940,doubtfirstdevelopmentUntilof view.studiesfronts.a kinematicdefinetimefriction,thetreatmenta ingforhorizontaloftotalAn importantpresencenecessaryfieldtheof viewofwas toand Austinvorticity.inpaperworkorientedaxisare broughtby Petterssennamely,some years,iswinds.thatthethisa conservativeofcyclonicfront;to thethewiththethey45O) oftwo airpaperfrontogenesisifand Bergeron'sactionofterms,namelygradientwhereby theonlyofto dfoundcontractionwithininof maximum gradientno ssenfrontogene-The majoradvancesofi
lowingderivedoftheseofstudieswas theand itsoflaterthejetinvestiga-by Millertheaffectingdefinitionequationin meteorologicalpaperbetweenprocessesPetterssen'sa kinematiccom-Studieschangesimportantas a bridgeconceptscon-fronts.theand philosophy,allon aand theThe discoveryimplicationscouldareasof Meteorologydynamics.upperto be revealed.on frontalSchooltheno rticlessurfacestructuresThe need forledofthemeteorologistsoversubsequentinand thenetworktime,More Recentinterpretedto occhangesdata.radiosondefirstexamininghad profoundInimportantwar yearsatmosphereHence,on atmosphericoftheexpandedtheatmosphericThe secondtionsofbasis.ofina vastlythemselvesplexitytwobeganwas an improvementand ons.studyfromthatof meteorologicala practicalestablishmentair1940'sand quantityimprovedmentand frontogenesisof meteorology.The thodsand subseintensity.frontogenesis,frontogenesiscan beMillerinthree
7dimensions.Miller'swherethetiveofAa ax sincc &IE w,Sz)sincD( 8,y-axisispropertytangentialS, and c1 isS and theisaF3 (cos-equationgtotheB(uxSx-theangleC wxsz)cossurfacesbetweenc%of- conservathegradientsx-axis.The processesareAt aboutNewton(1948)thisThe d ofhorizontallayerin(1948)was shown to be a slopinga allysame time,and largethroughon theirofdescribedshown by analysesface.shearthe400 mb).figure1.and Palm&andpolarthe500 mb (thoughThe warm and coldas
fequation.of frontogeneticterm B of Miller'sof frontogeneticterm C of strationeffectofequation.of frontogeneticterm D of Miller'sIllustrationofgenesisequation.xtermsof Miller'sof frontogeneticterm E .of Yiller's(1948)fronto-
9airmassestialon eitherstream)ofhighthecurrentwas foundabovethethenearlocation500-600themb stan-isas a ptedwas foundto be lowwarm air,and gnificant,neartheand thehorizontalnearwindtheforlevelfrontisas Berggrenof refore,aone thatmustshear.The firstpapertoby Reed and henearlylevelwesterlyfront.toshowed,windspeedThe tropopausehighuppermost(1952)thewhereThe failureofofbaroc1inity.L'A narrowinsidea case(thiseffectstudy(1953).ofofupperthebe accountedtheeffectfrontwilland itsinfrontogenesisThey calofand400mb)by variationsmagnitudewasinthebe referredrepresentationina direc-verticalto as theas theL/Thispaper willfollowthe conventionsof Godson (1951)and callsuch broad regionsof baroclinitylackingsharp"frontalzones,"whilethe terms "front"orboundaries"hyperbarocliniczone" willbe reservedfor the well definedlayersof more intensebaroclinity.
10"tiltingofsinkingmotionwarm edge icityReedlevelmentionedthethefrontneed on thevorticitythatthe"withtropopausedown intotheoutfronta thinintensemeantformeddue foldingstratosphericcase,300velocitya bodythethe(betweenas thecan arisebasisgainsstratosphereintensifiedinbe considereda pre-itlowerthecasefrontHe pointedfront.thata frontaltheand 500 mb) due to variationsacrosstheofanotheri.e.,warmingby tiltingwithand verifiedpaper:temperatureReed and nesisshear)axis.and appearance(1955)neartheinvorticitywas a "portioncharacterto be a regionsubsidenceintensifies(windofstrongwas founddifferencesa nsversehorizontalcomponentthefront.due toand increasesingThe upperterm.").ofairdown totheslicing700 or800 mb.Palm&extrusionlimitedand mtheagainstand insteadstratospheresuchconsidera deepato be "a
11necessaryaccompanimentnectingthemum windfrontogeneticand drynesspretedas being(Sanders,regionsideofa trough.forfrontsisstronglyofsup-vorticityand ozonethehighvicinityofaltitudetheofexamineda frontthesefronts.frontscan alsoofwithinairThe exbe sedand thisstudyand estabi-followingtheprocessesres-at differentto be importantA differenceisthough,inbetweenisthattheone of many processesfront.thefrontand d,dominantatReed and Reed and500 lusiontheacrosswas wrappedfrontogenesis-.---. - quationsequationsponsibleSanders,theMiller'sAn importantvectionThe presenceand potentialmotion.flowlevelof maxi-and 1954)exitlity,thetroposphere."due to by turesignificancethead-
vorticity,arefoundto be ithan lywarm airofa facedue alisthemotionfrontogeneticwith-ofthesurfaceandThe neteffectfront.respectineffectatthethis(1955).and frontolyticfront(withcan bethestrongwhichtheto be entrainedtheredemonstratesThe frontogeneticwithinmaximum windtherewarm ingstabi-shown by tself.strongfrontThe strongjustfrontdecreasesforlowfrontwarm airfluenceisan intenseofmotiona fieldisshown to acrosstheofiniswindisdivergencedamped tedsufficientlysurfacetoverticalno tilting.isratea The sobutgencelitythefronttocon-and tothe
Not onlydifferentoflevelisand ceedatIfa eflowmotionrequiresinkinginwas stspeedwillbe diver-air.by Sawyertowardand itswarm air.coldthepressureThe resultintempera-may be unablechangingacrossjet.tropo-magnitudeof maximum wind,thethehorizontaladvectionstoflowand risingsuch a circulationsmallesta deep layerpace,thegencestructuresThe lowzone shouldtemperatureaway fromfrontsThe asewithlayer-averagedThe .and thelow ft,surface.and thereforethermaladjusttwoactingincreasegradienton lowfurthersame generalConfluenceand movesactingeven when theyspace,thethedecreasewhy ds.be no heairprocessesforofand absoluteindividualthethosetwo typesfrontslopearefromtheAs thislevels.itgradientContinuityThe role(1956).He
14constructedtrajectoriesfoundmany e ntforthisalsolackeda tthethefront,.butmiddleBothupperthatinthewarm tionon bothwarm air,was d smallstudiedtheinmotionstroposphereofaHe ob-stability(1962)compensateconfluencea strophicofdirectionreleasea zone ofand neutraland confirmedthe(19709inby thesystem.verticaland lowertheheighttheEliassenlevels.withofandno confluenceand sinkingThe intensityallowingnotedupper-airthewarm airthehypothesisshowedcloudespeciallywarm air.incirculationto varytheThe strengthwas greatestininwhen pleparti-be yto be regionsdescribedthecontinuinginfrontogenesisAVE I Experiment.usingthree-hourlyThe resultsofhis
15studyareilluminatingcontradictionsinbetweendil ,?tcirculationsdirectcirculations.helpingto resolvefrontogenesisand thatdue toassociatedHe foundtheapparentthermallywiththermallyin-thatin the currentcase the initialfrontogeneticmechanism arisesfrom the cross-streamgradientof verticalvelocitywith thestrongestsubsidenceon the warm side ofthe barocliniczone.Horizontalconfluencebecame a frontogeneticfactorin the laterstages.The change from a thermallyindirectto a thermallydirectcirculationiscontrolledby the passage of a short wavecontainingthe barocliniczone around thebottom of the long wave datwindshearinthethisextendup onictothatHe inter-and thean grensimilarofwarm airthenearandsid
types of occluded fronts and noted the existence of second- ary cold fronts in the cold air behind the storm. The polar front was defined and described, and methods for its analy- sis were given. Cyclone families were also described, and t
o Air masses of North America Fronts o Stationary fronts o Cold fronts o Warm fronts o Fronts and the jet stream o Frontogenesis o Drylines o Occluded fronts . - transient weather systems (Rossby waves) - small scale f
Ted Funk WFO Louisville, KY January 2004 with contributing graphics from Peter Banacos Storm Prediction Center Ron Przybylinski WFO St. Louis, MO General Outline ¾Frontogenesis defined ¾Components of frontogenesis ¾What causes frontogenesis?: ¾Horizontal divergence/difluence ¾Horizon
Structure of fronts We observe that fronts slope with height, and that they almost always slope toward the cold air. We can derive a simple formula that does a reasonable job of representing this slope First, we note that pressure must be continuous across the front. For the typical case of cold air to the north, and
fronts o fronts: a boundary between air masses there are three types of fronts o cold fronts: move quickly. cold air pushes against warm air, causing the warm air to rise. cumulus clouds heavy storms a
Fronts are the boundaries between two air masses. Fronts are the basic building blocks of weather systems. Fronts occur where two large air masses collide at the earth's surface. Each air mass has a different temperature associated with it. Fronts are caused by winds moving one air mass
Stationary fronts behave like warm fronts, but are more quiescent. Many times the winds on both sides of a stationary front are parallel to the front and have opposite direction. Typically stationary fronts form when polar air masses are modified significantly so as
between two air masses stalls, the front is called a stationary front. Cloudy skies and light rain are common along stationary fronts. Occluded Front Cold fronts move faster than warm fronts. When a fast-moving cold front catches up with a slow-moving warm front, an occluded, or blocked, front forms. Occluded fronts usually bring precipitation.
List of Plates Plate 1 Tea break! 4 Plate 2 Outline of robbed out wall visible in Trench 2c. Taken from the N. 8 Plate 3 W facing fireplace [2055], during excavation. Taken from the SW. 9 Plate 4 General view of fire place and rake out area following excavation, Trench 2c. Taken from the SW. 9 Plate 5 Stake [2091], set into natural sand (2072). Taken from the N 10
