IdentificationoftheITCZUsingOceanVectorWindFieldsDuringSPURS-2

AaronC.Paget&JamesB.EdsonDepartmentofMarineSciences,UniversityofConnecticut

InternationalOceanVectorWindsScienceTeamMeeting2-4May2017,LaJolla,California

ImageSource:ShadesofBlue,SPURS-2NotesfromtheField

Episode:SPURS-IITHEFATEOFFRESHWATER

NASASPURS-2(SalinityProcessesintheUpperOceanRegionalStudy-2)Tostudythefateoffreshwater(Precipitation)• IntheIntertropicalConvergenceZone(ITCZ)• Cruisedates:August– September2016• WHOIBuoyMooringat10°N,125°W• Atmosphereandoceanobservation• Otherresourcesdeployedaswell

AtmosphericSoundings

DivergenceTerm(negativeconvergence)

𝜕𝑊𝜕𝑡 +

𝜕(𝑢𝑊)𝜕𝑥 +

𝜕(𝑣𝑊)𝜕𝑦 = 𝐸 − 𝑃

Dominguezetal.2006

Small

Wistheprecipitable watervaporintheatmospherePisprecipitationEisEvaporationu,v arethemoisture-weightedvelocitiesthatcontainboththemean

andeddycomponentsforzonalandmeridionalwindspeeds

Basicwatervaporconservationrecyclingmodel

Convergenceisrelatedtoprecipitation

MoistAir

NorthSouth TheoreticalITCZintheSPURS-2Region

Evaporation Evaporation

Condensation

PacificOcean

NearSurfaceWindNearSurfaceWindConvergence

Divergence

Can10-mwindsbeusedtoapproximatesurfaceconvergence?

GPCPPrecipitationandCCMPWind(V1)Convergence(Daily,1°)

ForSPURS-2analysisregion(30°N– 10°S,145°W– 100°W)(1996-2011)• 60%ofthePrecipitationrateis0mm/day

65

4

32

10

x105 x105

-10-4 010-4 s-1

2.5

2

1.5

1

0.5

0-10-4 010-4 s-1

ConvergentDivergent ConvergentDivergent

Coun

t

Coun

t

CCMP(Precip =0)* CCMP(Precip >0)

0 20 40 60 80mmday-1

106

104

102

100

GPCPPrecipitation

Coun

t *Duringsubsidence,weexpectsurfacedivergenceandnorain

AnalysisDomain

CorrelationCoefficients*Daily– -0.477day– -0.6414day– -0.70Monthly– -0.743Month– -0.78

*allsignificantcorrelations

MedianMonthlyPrecipitationRateforGPCP(1996-2016)15

10

5

0

mm/day

GaussianCurveFittoPrecipitationalong125WforSeptember

2σ

1σ

GaussianCurveGPCPdata

Latitude

PDF

𝑦 =1

𝜎 2𝜋� 𝑒5(657)89:8

MedianMonthlyProbabilityDistributionFunction(PDF)ofPrecipitation(GPCP1996-2016) MaximumNorthwardVelocity

0.42Degrees/Month

MaximumSouthwardVelocity0.62Degrees/Month

ITCZWidth(2σ)Δ6° – Δ8° Latitude

20

15

10

5

0

-5

Latitud

e

JanFebMarAprMayJunJulAugSepOctNovDec

Max +/- σ +/- 2σ

ITCZGuidance:• Centeredabout8°N

+/- 1° – 2° Latitude• Widthof6° – 8°

Along125°W

WindSat ASCAT

Convergenceof10-mWindsfromWindSat andASCAT23August2016– Swaths

GPCPTotalPrecipitationPeakat11.5°N

σ=2.85Range:8.6°N– 14.4°N(1σ)

5.8°N– 17.2°N(2σ)

QuikSCAT Convergent9°N– 16°N

During14dayperiod,ITCZshiftingNorth

QuikSCAT L3– 14Day(0.25x0.25)duringAugust200825

20

15

10

5

0

-5

25

20

15

10

5

0

-5

-145-135-125-115-105

-145-135-125-115-105

-50 510152025

-50 510152025

10-4 s-1

0

-10-4

mm25

20

15

10

5

0

4

2

0

-2

-4

-6

-8

x10-5 s-1

0.12

0.08

0.04

0

Median

Total

Divergence

Convergence

PDF

GPCPTotalPrecipitationPeakat10.4°N

σ=3.2Range:7.2°N– 13.6°N(1σ)

4.0°N– 16.8°N(2σ)

QuikSCAT Convergent8°N– 15°N

During28dayperiod,ITCZshiftingNorth

QuikSCAT L3– 28Day(0.5°x0.5°)duringAugust200825

20

15

10

5

0

-5

25

20

15

10

5

0

-5

-145-135-125-115-105

-145-135-125-115-105

-50 510152025

-50 510152025

10-4 s-1

0

-10-4

mm500

400

300

200

100

0

2

1

0

-1

-2

x10-5 s-1

0.15

0.1

0.05

0

Divergence

Convergence

PDF

PreliminaryConclusions• PrecipitationandConvergencearesignificantly

correlatedondaily– seasonaltimescales

• Onamonthlytimescale,theprecipitationhasanormaldistributionNorthtoSouthintheSPURS-2region

• PrecipitationmaximummeandersNorthandSouthatarateofupto+/- 0.5° month-1

• 10-mwindconvergencedoesnotperfectlymatchtheprecipitationpattern

• Weneedtoconsiderevaporationandatmosphericmoistureinourbalance

• Themoisturebudgetrequiresverticallyintegratedwinds– frommodels?- MERRA-2,ERA-Interim,NCEP-NCAR

• SPURS-2soundingsaretoocoarseforthebudget,butcanbeusedtovalidatemodels

• MoreinformationwillbesharedattheSalinityWorkshopatWHOI(22-26May)

FuturePlans

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