n)? refrac/vity map to study land-surface …...refrac/vity map to study land-surface atmospheric...
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![Page 1: N)? Refrac/vity map to study land-surface …...Refrac/vity map to study land-surface atmospheric interac/on • Even though the target heights can be esFmated from terrain, there](https://reader036.vdocuments.us/reader036/viewer/2022081521/5e8502a64dc97422642de0de/html5/thumbnails/1.jpg)
Stepstowardsinges/ngradarretrievedrefrac/vityintonumericalmodelsYa-ChienFeng*andFrédéricFabry
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Acknowledgement:TheauthorsthankProf.DanielKirshbaumforprovidinglanduseandsoilmoisturefilesproducedbytheWRFiniFalizaFonandDr.DominikJacquesforpreparingtheensembleforecasFngdataanddiscussion.ThisprojectwasundertakenwiththefinancialsupportoftheGovernmentofCanadaprovidedthroughtheDepartmentoftheEnvironment.TheviewsexpressedhereinaresolelythoseofMcGillUniversity.
Whatisradarretrievedrefrac/vity(N)?φi (r) = 2π f
2ri nc
f:radartransmiQerfrequencyc:speedoflightinvacuumnair_near_sfc~1.0003
Radar Fixedgroundtarget
N = (n −1)×106 = 77.6 PT+ 3.73×105 e
T 2
r:rangeofradarbeampathP:pressure(mb)T:temperature(K)e:watervaporpressure(mb)
TheFmeforwavestotravelbackandforthbetweentheradarandafixedtarget.
• Thephaseϕofafixedgroundtargetchangeswith therefracFvityNofair,aproxyoflow-levelmoisture(Fabryetal.,1997).Seeimageatright.
• Radarrefrac/vityissensi/vetothemoisturevaria/on:T=18°C,ΔT=1°CàΔN=1
Δq=0.2g/kgàΔN=1
• Thecharacteris/csoferrorsarecri/calfordataassimila/on,orradarrefrac/vitynetworksimplementa/on.• Radar N fields have been assimilated to improve the iniFal condiFon of low-level moisture for a beQerquanFtaFveprecipitaFonforecasFngresult,butwithassumedobservaFonalerrorsandrepresentaFveheight.
Quan/fyingtheobserva/onerrorsforvaria/onalmethods
• Radar refracFvity provides valuable high-resoluFon low-level thermodynamic fields to study the land-surfaceatmospheric interacFon, and help model evaluaFon and data assimilaFon in mesoscale and regional numericalweatherpredicFonmodels.
• AbeQerunderstandingof thebiasesandquanFficaFonoferrorsprovidessoliddatacharacterisFcs forvariaFonalmethod,suchasdataassimilaFonandsynergizingwithotherboundarylayerinstruments.
• RadarsandgroundtargetsarethereinthenaFonalradarnetwork.Whynotmakerefrac4vityopera4onal?
Groundtargetreliability Good
Bad
Refrac/vitymaptostudyland-surfaceatmosphericinterac/on
• EventhoughthetargetheightscanbeesFmatedfromterrain,therearesFllsomeuncertainFes.
• Theσ(N)islargerforsteeperterrainslopesunderthemostextremedN/dzcondiFons;inMontreal,suchcondiFonsarerare.
• TheradarrefracFvityretrievalprovidesinsightsonhigh-resolu/onnear-surfacemoisture,whichisimportanttounderstandingconvecFoniniFaFonandevoluFonaswellasboundarylayerprocesses.
• The radar retrieved N showsconsistent trends with the N ofthesurfacesta/ons.-RadarNat~20maboveterrain,closethelowestlevelofmodel.-ThedifferenceinNislargelydueto the refracFvity profiles (dN/dz)andheightdifference.
Terrain(m)
• σ2(ϕ) can be esFmated by groundtargetreliability.
• σ(N)isNOTrandomlydistributed.N is reliable in thedensegoodtargetsarea.σ(N)iswithin±1N-unit.
• Larger observaFonal errors in the lessdensetargetareaisquanFfied.
σ(N)
- Theerrorvariance(σ2)ofNisaffectedbythemeasuredphase(ϕ)ofasingletargetandretrievalmethod:σ2(N)=σ2[retrievalmethod(σ2(ϕ))]σ2(ϕ)=σ2(RadartransmiQerfrequency,hardware)
+σ2(AntennaphasepaQern,refracFvityprofiledN/dz) +σ2(RefracFvityprofiledN/dz,targetheights)+σ2(AtmosphericscinFllaFon) +σ2(Targetmovement)+σ2(complexityoftargets:point/extended) Error:Uncertainty.
Cannotbecorrected,butcanbesimulated
Bias:SystemaFc.Canbecorrected.(Fengetal.2016)
σ(N):uncertainheight
• The N map shows the near-surfaceairthermodynamicspa/alcontrast between urban andsuburban areas in Montreal(Canada).-Nurban<Nruralorsuburban-ThelocalvariaFonofwatervaporis affected both by horizontalmoisture advecFon and byevaporaFonfromthelandsurface.
Refrac/vityintheopera/onalradarnetworkforaregionalmodel• CanradarrefracFvity fromthenaFonal radarnetworkprovidea low-
levelthermodynamicconstraintforthemodelatregionalscales?-Horizontalauto-correlaFonofrefracFvityfieldat thecenterofeachsquare grid at the lowestmodel level suggestsN informaFonwouldpropagate. (Environment Canada regionalmodel, 15 km resoluFon,forecasFng12hr,20ensemblesthoughmoreareneeded)
• WebelievetheaveragerefracFvityoverasmallregion(~30kmradius)can be very precise and would be more representaFve than pointobservaFons.
Dry,warm
Moist,coolNaverageinthreecleardays
urban
Summervolumetricsoilmoisture NdiurnalvariaFoninurban/suburban
• The N map shows consistencywith the climatology of summervolumetric soil moisture (m3m-3)from U.S. Geological Survey land-usedatabase.- High spaFal-temporal resoluFonofNmighthelpstudyland-surfaceatmospheric interacFon over aheterogeneouslandsurface.
Summary:Whatcanradarrefrac/vitydoforyou?
Horizontalauto-correlaFonofN