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Absorption index of super- cooled liquid water in the microwave range 0 – 300 GHz

Absorption index of super- cooled liquid water in the microwave range 0 – 300 GHz. Absorption coefficient in Np /km for different models. The ‚ straight way ‘:. The total optical thickness can be derived via the well- known T_mr approach : while

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Absorption index of super- cooled liquid water in the microwave range 0 – 300 GHz

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  1. Absorption indexof super-cooled liquid water in themicrowaverange 0 – 300 GHz

  2. Absorption coefficient in Np/km for different models

  3. The ‚straightway‘: The total opticalthicknesscanbederived via the well-knownT_mrapproach: while Whenthewatervaporand dry componentcanbeestimatedwith a RT model, andif an INDEPENT informationabout LWP andcloudtemperatureisavailable, the liquid opticaldepthcanbeusedtoderivetheapsorptioncoefficient via: PROBLEM: Difficulttodisentanglethe different errorsources, atmosphericconditionsneedtobeknownveryprecisely.

  4. The opt.depthratioidea (Mätzler et al. 2010): Idea: Fast opacitychangesaremainly due to liquid waterfluctuations. Ifonetakessmall time (e.g. 10 min) periodsthevariationsΔτareonly due to The ratiosof such changesat different frequenciesareindependentofΔLWP andthusidenticaltotheratioofabsorptioncoefficients: Ratioscanbederivedbyplottingopticalthicknessesat f1 against f2 (linear in contrastto TBs!). Ratiosare also very robust (e.g. offsetsdon‘tchangetheratio a lot).

  5. Howtocomefromtheratiostotheabsorptioncoefficientitself? Idea: Find a frequencywhereyou ‚trust‘ a model (e.g. Stogrynat 90 GHz). Havingthisspecificandratioscontainingthisspecificfrequencyyoucandirectlyderivetheabsorptioncoefficientattheotherfrequencyby: In thefollowingslidesthishasbeendone, assumingthatStogryniscorrectat 90 GHz so that e.g. αat 150 GHz canbedirectlyderived (orateveryother 90/f combination!

  6. Alternative: Use fast LWP changesfromHatproand fast opacitychangesfrom DPR toderiveabsorptioncoeff. At 90 or 150 directly: Idea: Again, theassumptionis, thatthe fast changes in opt. thicknessareonly due to liquid water. Thus, wecanwrite: Iftherearecorrelated IWV variationsonehastoestimatetheirinfluence but thatispossiblewithourdata, I think. The benefithereisagain, thatthediefferencesarelesspronetoretrieval/calibrationoffsets. On the Zugspitze therearesometimes strong and fast LWP changes due toturbulenceoverthemountaincrestwhichcanbenicelyusedtogothisway… I triedtheapproachwiththe AMF/UFS data…

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