Absorption index of super cooled liquid water in the microwave range 0 300 ghz
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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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Absorption index of super cooled liquid water in the microwave range 0 300 ghz

Absorption indexof super-cooled liquid water in themicrowaverange 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 ‚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.


The opt depth ratio idea m tzler et al 2010

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).


How to come from the ratios to the absorption coefficient itself

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!


Absorption index of super cooled liquid water in the microwave range 0 300 ghz

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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