Explorations in Meteorology 43 Lab 10 Answer Key

ANSWER KEYPart I: 500–mb Analysis

1. Usinganerasablepencil,plotthefollowing500–mbobservationsonFigure3,accordingtotheplottingmodelinFigure2.UseFigure1fortheradiosondelocations.(Note:Table3containsmeasurementsexpressedtotenthsofdegreesandtenthsofknots.Youmayneedtoroundthedatatoplotaccordingtothestandardconventions.)

Table 3 – Selected 500–mb Observations from 0000 UTC on 17 October 1996

Station ID

Station Name Latitude LongitudeHeight (in m)

Temp(in °C)

Dewpoint(in °C)

Wind Speed (in kts)

Wind Direction(in deg)

ABR Aberdeen,SD 45.45°N 98.43°W 5590 –16.3 –19.2 48.6 235

AMA Amarillo,TX 35.23°N 101.70°W 5740 –11.1 –36.1 44.7 285

BNA Nashville,TN 36.13°N 86.68°W 5770 –12.5 –22.5 15.5 260

EYW KeyWest,FL 24.55°N 81.75°W 5880 –4.9 –13.9 7.8 95

GGW Glasgow,MT 48.22°N 106.62°W 5470 –30.5 –45.5 9.7 260

GJT GrandJunction,CO 39.12°N 108.53°W 5620 –23.1 –24.6 48.6 255

OTX Spokane,WA 47.68°N 117.63°W 5500 –31.7 –38.7 25.3 305

OUN Norman,OK 35.22°N 97.45°W 5750 –10.9 –31.9 29.1 245

TFX GreatFalls,MT 47.45°N 111.38°W 5460 –30.9 –43.9 19.4 230

TUS Tucson,AZ 32.12°N 110.93°W 5800 –9.9 –45.9 17.5 325

2. Analyzethe500-mbheightfieldonFigure3bydrawingheightcontoursatintervalsof60m(6decameters,or6dam).Useanerasablepencil,andusetheacceptedcontourvaluesof5340,5400,5460…meters(534,540,546dam).Youmayfinditusefultostartwiththeheightcontourof552dam(inCentralWY).Whenyouaresatisfiedwiththeplacementofyourheightlines,traceoverthemwithablackcoloredpenciltosolidifyyouranalysis. [Note:Because theobservationsare roundedto thenearest10m,aplottedvalueof564damcouldrepresenta500-mbheightfrom5635mto5644m.Thisdegreeofuncertaintyintheplottedmeasurementsallowssomefreedomindrawingandsmoothingtheheightcontours.Theoverallsmoothnessofthecontourismoreimportantthan“forcingafit”ofagivencontourlinetoanyoneobservation.]

Explorations in Meteorology 44 Lab 10 Answer Key

Figure 3 – Completed 500–mb Chart for 0000 UTC on 17 October 1996

3. Usingasolid,redzigzagline,marktheheightridge(s)onthe500-mbmapinFigure3.Similarly,useadashed,redstraightlinetoindicateanyheighttrough(s).

4. Onyour500-mbanalysis (Figure3), (a)whereare thestrongestgeostrophicwindsand (b)whereare theweakest geostrophic winds? (c) Discuss what you see as the relationship between the strength of thegeostrophicwindsandthespacing(distance)betweentheheightcontours.

Location(s)ofstrongestgeostrophicwinds–ThestrongestgeostrophicwindsareinthefourcornersregionoftheSouthwesternUnitedStates.Speedsreach50ktsinnorthernAZandinwesternCO.

Location(s)ofweakestgeostrophicwinds–TheweakestwindsareinnorthernMT,southernFL,andtheMid-Atlanticregion(TNthroughVA).Windsintheseareasare10-15kts.

Whenthedistancebetweenheightcontoursisrelativelysmall,thegeostrophicwindsarequitelarge.Whenthedistancebetweenheightcontoursisrelativelylarge,thegeostrophicwindsaremuchweaker.

Explorations in Meteorology 45 Lab 10 Answer Key

5. Ingeneral,(a)dothe500-mbheightsincreaseordecreasefromnorthtosouthovertheUnitedStates(e.g.,fromMinnesotatoTexas)?(b)Explainwhytheyincreaseordecrease.

The500-mbheightsincreaseasyoumovesouthovertheUnitedStates.Ingeneral,theatmospherewarmsconsiderablyasonegoesfarthersouthintheUnitedStates.Thus,acolumnofairoverMNwouldbemorecompactthanwouldacolumnofairoverTX(i.e.,thedensityofairdecreasesastheairtemperatureincreases).Weexpectthe500-mbsurfacetobeclosertothegroundwheretheaircolumnismorecompact(higherdensityair)andfartherfromthegroundwheretheairiscolumnexpanded(lowerdensityair).

6. Comment on the temperature pattern as it relates to the orientation and alignment of the troughs andridges.

Thetroughsarerelativelycoldandtheridgesarerelativelywarm.InNorthernCalifornia,the500-mbtemperaturesare~-15°C(intheridge).Atapproximatelythesamelatitiudeinthetrough(saySaltLakeCity)the500-mbtemperatureis–29°Canditwarmsto–15°CovertheMidwestU.S.

7. (Advanced Students/Meteorology Majors) Explainwhy500mbwaschosenasamandatorylevelandisroutinelyanalyzed.[Hint:Thinkabouttheresultingmotionofa30-mtallpolefromhorizontalforcesappliedequallyatheightsof5m,15m,and25m.]

Thesurfacepressureisapproximately1000mb.Sincepressureistheweightoftheatmosphere,the500mbleveliswherehalfofthemassoftheatmosphereisaboveandhalfisbelow.Forcesactingatthemidpointofanobjecthavegreatinfluenceonhowtheobjectmoves(i.e.,steeringcurrentsintheatmosphere).

Part II: 850–mb, 700–mb, and 300–mb Analyses

In addition to the 500-mb map, meteorologists examine surface, 850-mb, 700-mb, and 300-mb (or 250-mb)chartstounderstandthecurrentstateoftheatmosphereinthreedimensions.Inthissection,youwillworktounderstandthethree-dimensionalpicturefor17October1996.Figures4,5,and6displaytheisobaricmapsfor850mb,700mb,and300mb,respectively.Figure7displaysthesurfacemap.Usethesefigurestoanswerthefollowingquestions.

Explorations in Meteorology 46 Lab 10 Answer Key

Figure 4 – 850–mb Chart for 0000 UTC on 17 October 1996 with Height Contours (thick, gray lines) and Isotherms (thin, red lines)

8. Calculatethedewpointtemperatureat850mb(Figure4)forthefollowingstations:Boise,ID;Bismarck,ND;Buffalo,NY;KeyWest,FL;Nashville,TN;MooreheadCity,NC;Norman,OK;Oakland,CA;Omaha,NE;andTopeka,KS.WritethedewpointvalueingreenonFigure4abovethecorrespondingstationtemperature.

9. The850-mbchartisusedfrequentlytoanalyzetheamountofmoistureavailableforcloudsandprecipitation.

UsingFigure4,whereisthedriestairintheUnitedStatesat850mb?Whereisthemaximummoistureat850mb?

Locationofdriestairat850mb–Thedriestairat850mbisoverthePacificCoast,specificallynorthernCA.Fairlydryairat850mbalsoexistsoverthenorthernplains.

Locationofmaximummoistureat850mb–Themoistairat850mbcanbefoundacrossthecentralandsouthcentralGreatPlains(seeKOUN)andacrosssouthernFlorida.

Explorations in Meteorology 47 Lab 10 Answer Key

Figure 5 – 700–mb Chart for 0000 UTC on 17 October 1996 with Height Contours (thick, gray lines) and Isotherms (thin, red lines)

10.Use the700-mbchart (Figure5) andagreenpencil tooutlineandshade theareaswhere thedewpointdepression(T-D)islessthanorequalto3°C.Theseshadedareaslocateregionswherethereissubstantialmoistureandperhapsextensivecloudcover.Inadditiontothe850-mbchart,the700-mbchartisusedtoanalyzetheamountofmoistureavailableforcloudsandprecipitation.

11. Ifyouwereapilotandyourlicenselimitedyouto“visualflightrule”conditions(i.e.,clearskies),whatarea(s)ofthecountrywouldyoumostlikelyremaingrounded?

Asapilot limited toVFRconditions,youwould remaingrounded in thenorthernGreatPlainsandpartsof theGulfcoast.

12.UsingFigure5,whatisthedirectionofthegeostrophicwindat700mboverthenorthwestU.S.?Basedonlyonthisgeostrophicwindandtheconfigurationoftheisotherms(Figure5),wouldyouexpectthe700-mbtemperatureoverColoradotoincrease,decrease,orstaythesameduringthenext12hours?

Directionofgeostrophicwindat700mboverNWU.S.Thegeostrophicwindblowsparalleltotheheightcontours,soitisfromtheNorthwest.

Temperature over CO will decrease during next 12 hours (because much colder temperatures (–8°C to –12°C) areupstream(northwest)ofColorado)

Explorations in Meteorology 48 Lab 10 Answer Key

13. The300-mbchartisusedfrequentlytoanalyzethelocationandstrengthofthejet stream(i.e.,arelativelynarrowcurrentofstrongwinds)anditsinfluenceonweathersystems.Thejetstreamoccursnearthislevelbecause thegeostrophicwindsare fasterhere thanat theothermandatory levels.On the300-mbchart(Figure6),drawathick,bluecurvedlinewhereyouthinkthejetstreamislocated.Thejetstreamshouldbeparalleltotheflowandextendfromonesideofthemaptotheother.[Hint:Startbyfindingthefastestwindspeeds.]

14.Comparetheisobaricchartsfor700mb(Figure5),500mb(Figure3),and300mb(Figure6).Discusshowthetroughoverthewest-centralU.S.changesitslocationwithheight.

Thetroughaxistiltswestwardbetweenthe700-mbsurfaceandthe500-mbsurface.Thelocationofthetroughbetweenthe500-mband300-mblevelsshiftsonlyslightlywestwardwithheight.Evenso,theaxisofthetroughtiltswestwardwithheightfromthesurfaceto300mb.

15.Comparethe500-mbchart(Figure3)withitscorrespondingsurfacemap(Figure7).Geographically,wherearethe500-mbtroughs/ridgeslocatedascomparedtothesurfacehighsandlows?

ThereisanareaofsurfacehighpressureacrossthePacificNorthwest,andanotherintheSoutheast.AnareaofsurfacelowpressureandasurfacetroughexistsintheCentralPlains.The500-mbtroughexistswestofthesurfacetroughandsurfacelow-pressuresystem.Ridgesaloftarelocatedoverthetwoareasofsurfacehighpressure.Thus,alow-pressurecenteratthesurfaceisassociatedwithatroughintheupperlevelsoftheatmosphere,andanareaofhighpressureatthesurfaceisassociatedwitharidgeintheupperlevels.

Figure 6 – 300–mb Chart for 0000 UTC on 17 October 1996 with Height Contours (thick, gray lines)