Explorations in Meteorology 34 Lab 8 Answer Key

ANSWER KEYPart I: Introduction to the Skew-T

1. UsetheSkew-TinFigure4tocalculatetherelativehumidityvaluesforthefourlevelsabove999mb.

Table 3 – Calculations of Relative Humidity from a Greensboro, NC Soundingat 1200 UTC on 4 December 2002

LevelMixing Ratio

(w)Saturation Mixing

Ratio (wS)Relative

Humidity (RH)

925mb 0.2gkg–1 2.5gkg–1 8%

850mb 3.3gkg–1 4.1gkg–1 80%

700mb 3.6gkg–1 3.9gkg–1 92%

500mb 2.3gkg–1 2.6gkg–1 88%

2. UsingFigure5,plotthefollowingselectedobservations(Table4)fromGreensboro,NCthatwereobservedonthemorningof5December2002.Plotthetemperatureinredandthedewpointingreen.

Figure 5 – Blank Skew–T Log–P Diagram for Question #2

Explorations in Meteorology 35 Lab 8 Answer Key

3. WhatistheelevationofthesoundingsiteatGreensboro,NC?

Elevation=270m

4. UsingtheSkew-TdiagramyouplottedonFigure5,calculatetherelativehumidity(RH)at850mb,700mb,and500mb.Showyourwork.

RHat850mb=83%(w=5.7gkg–1;ws=6.9gkg–1)

RHat700mb=100%(w=5.5gkg–1;ws=5.5gkg–1)

RHat500mb=89%(w=2.5gkg–1;ws=2.8gkg–1)

5. Using the Skew-T diagram you plotted on Figure 5, describe the changes that occurred at the surfacebetweenDecember4thandDecember5th.

Thesurfacepressuredecreased,thetemperatureincreased,andthehumidityincreasedtosaturation.

6. InFigure5,whichlevelsorlayersaresaturated,asdepictedontheGreensborosounding?Whichlayershaveinversions?

Levelsorlayersthataresaturated985mb,925mb,and700mb

Layerswithinversions925to850mb

7. WhattypeofweatherlikelywasoccurringatthesurfaceinGreensboroat1200UTCon5December2002?

Freezingrain,lowclouds,andfog.

8. HowcriticalwasthesurfacetemperatureforecasttothecitizensofGreensboro,NCon5December2002?Wouldaforecasterrorof3°C,eithercoolerorwarmer,leadtodifferentactionsordecisionsbyGreensborocitizens?

Asurface temperature thatwas3degreeswarmerwould result inaharmlesscold rain rather thanadangerous icestorm.

9. (Advanced Students/Meteorology Majors) Examine the differences between the soundings plotted inFigures4and5.WhatprocessoccurredbetweenDecember4thandDecember5thtochangethesounding?

Evaporationalcooling(i.e.,thewet-bulbeffect)

Explorations in Meteorology 36 Lab 8 Answer Key

Part II: Sounding Interpretation

Forthispartofthelabexercise,studentsshouldworkinpairs.Onestudentshouldplotthe16April2002soundingfromAberdeen,SD(ABR)whiletheotherstudentplotsthe27January2000soundingfromFortWorth,TX(FWD).Usebothsoundingstoanswerthequestionsinthissection.Listyourpartner’snamebelow.

Nameoflabpartner______________________________

10. UsingdatafromeitherAberdeen,SD(Table5)orfromFortWorth,TX(Table6)andtheblankSkew-TLog–Pdiagram (Figure6), plot temperature anddewpointdata versuspressureat only the mandatory levels(notedinboldontable).Usearedpencilforthetemperaturedataandagreenpencilforthedewpointdata.Lightlycircleeachmandatoryleveldotwithablackpencil.Donotconnectthedotsatthistime.

11. UsingtheSkew–TLog–Pdiagramfromquestion10(Figure6),plottheentiredataset(i.e.,bothmandatoryandsignificantlevels)forABR(Table2)orFWD(Table3).Usearedpencilforthetemperaturedataandagreenpencilforthedewpointdata.Usearulertoconnecteachsetofsuccessiveobservations(redforthetemperaturetrace,greenforthedewpointtrace).

Explorations in Meteorology 37 Lab 8 Answer Key

12. Withyourpartner,examineyourcompletedthermodynamicdiagrams(Figure6).Arethemandatory level datasufficienttodeterminetheverticalstructureoftemperatureanddewpointintheatmosphereovereitherlocation?Whyorwhynot?

Themandatoryleveldataarenotsufficient.Keystructuralcharacteristicsoftheenvironment(moistlayers,drylayers,thecappinginversion,etc.)arenotcapturedwhenonlythemandatoryleveldataareused.

13. Withyourpartner,examineyourcompletedthermodynamicdiagrams(Figure6).Arethesignificant leveldatasufficienttodeterminetheverticalstructureoftemperatureanddewpointintheatmosphereovereitherlocation?Whyorwhynot?

Yes.Bydefinition,significantlevelsarecodedonlywhensignificantchangestothetemperatureandmoisturestructureoccur.Therefore,theessenceofthelayeredstructureoftheatmosphereiscapturedbyusingsignificantlevels.(Note:sometimesmandatorylevelsalsoaresignificant.)

Explorations in Meteorology 38 Lab 8 Answer Key

14. With your partner, label the following levels or layers on both plotted soundings (from ABR and FWD):(a) the lowest freezing level, (b) all inversions (i.e., layers where temperature increases with height), and(c)thetropopause.Useablackpenciltolabelyourfigures.

Explorations in Meteorology 39 Lab 8 Answer Key

15. Withyourpartner,examinebothsoundings.Waseitherlocationexperiencingprecipitationatthetimeoftheradiosondelaunch?

AberdeenSounding–Althoughtheboundarylayerisclosetosaturation,moisturewithinthelowerhalfofthetroposphereisnotsufficient to indicate thatprecipitation is falling.There isvery littlemoisturebetween850and500mb.A fewmeasurementsindicatethattheairisnearsaturationjustabove500mb.Atthemost,somemid-levelclouds,suchasaltocumulus,maybeseenatthistime.

FortWorthSounding–Theatmospherewassaturatedfromnearthesurfacetoalmost700mb(~3kmdepth).Itislikelythatatleastlightprecipitationoccurredatthistime.Basedonthesounding(warm,above-freezingairoverthetopofcold,sub-freezingair),theprecipitationlikelywasfallingintheformoflightfreezingrain.Observationsverifiedthatlightfreezingrainwasoccurringatthetimeofthelaunch.

16. (Advanced Students/Meteorology Majors) Both sets of sounding data in this lab contain height dataalongwiththepressure,temperature,moisture,andwindinformation.Theradiosondeinstrumentpackage,however,doesnotmeasureheight.Describehowtheheightdataareobtained.

Usethetemperature(actuallycalculatethevirtualtemperature)andpressurevaluestosolvethehypsometric(thickness)equation(ahydrostaticassumption)forheight.

17. (Advanced Students/Meteorology Majors)Atmospheric thickness isdefinedas thedifference inheightbetweentwopressurelevels.UsingTables2and3,calculatethe1000–500mbthicknessvaluesforbothsoundings.Howdothethicknessvaluesdifferbetween16April2002and27January2000?Usingconceptsdiscussed in lecture or your textbook, what is the physical reason as to why the two thickness valuesdiffer?

1000–500mb thickness forABRon16April 2002at1200UTC5630m–20m=5610meters

1000–500mbthicknessforFWDon27January2000at1200UTC5660m–166m=5494meters

Warmairislessdensethancoldair.Pressurechangesmuchmorerapidlywithheightincoldairthanitdoesinwarmair.ThesmallerJanuaryvaluemeansthatthe1000–500mblayeroccupieslessspacethandoesthesamelayerinAprilbecauseJanuaryairiscolderandmoredense,henceless“thick”thantheAprilair.

18. (Advanced Students/Meteorology Majors)What is thephysical reason for thedifference in tropopauseheightsbetweenthetwosoundings?

ThetropopauseheightintheAprilsoundingwasnear200mb,whileintheJanuarysoundingthetropopauseheightwasnear260mb.BecausethemeanvirtualtemperatureofthetroposphereintheJanuarysoundingiscolderthanintheAprilsounding,thetropopauseshouldbelowerintheJanuarycase.Remember,coldairtakesuplessspacethandoesthesameamountofwarmair.