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2014-03-02, 10-11 UTC PowerPoint PPT Presentation

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2014-03-02, 10-11 UTC. Supercooled liquid water. Moments only from „ principal peak “; can change between liquid and ice peak depending on which one is stronger !.

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2014-03-02, 10-11 UTC

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2014-03-02, 10-11 UTC

Supercooled liquid water

Moments onlyfrom „principalpeak“; canchangebetween liquid andicepeakdepending on whichoneisstronger!

Characteristicsofcloudwaterpeak: Ifturbulenceislow, peakisverynarrow (narrow PSD), closeto 0 m/s, oftenseparatedfromfasterfallingsmalliceandaggregates. Can beusedastracerforestimatingverticalairvelocity.

Thicknessofsupercooledlayer at cloud top (usethe MDV switchingartefact!) seemstobewellcorrelatedwith LWP curve.

The RS-RH profilesuggests a secondpossiblelayerofsupercooledwater at around 500m. Sinceturbulenceincreasesdrastically in thelowest 500m itis not easy to find a clear liquid peakhere. Maybethesizeandconcentrationofdropletsis just tosmall/lowtobedetected…


Starting at the liquid layerwealready find a peakbetween 0.5 and 1 m/s. This couldbe due tosmalliceandfirstaggregatesoralreadyrimedsinglecrystals (hardtosaywithoutotherparameters)

Just a fewhundredmetersbelow, the dominant peakisalreadybetween 1 and 1.7 m/s whilewe find a large areaof different icevelocities. Those large Doppler velocitiesindicate additional riminghashappenedduringthe last fewhundredmeters

Finally, at 500m, themainpeakspeedsupto 1.5 to 2 m/s, a clearrimingfeaturebecausevertical wind speedseemstobeingenerallow in thiscloud. Youcan also nicelyseethespeedingupofthespectra in therangespectrogram! Watch also thenicecorrelationbetween LWP maximaand MDV maxima!


At 400m thespectralpeaksare still clearlyseparatedandrelativelynarrow. Also the temporal variabilityofthe MDV isrelativelysmall.

A fewrangegatesbelow, theseparatedspectramoreandmoremergetoonepeak due toturbulencebroadening. The variations in MDV (see Time Spectrogram) are also muchstrongerandof larger „frequency“.

At 275m aboveground, wecanonlyidentifyonebroadpeakandthevariations in MDV stronglyincreased.

2014-02-01, 11-12 UTC

Cloud Structure– Fallstreaks – Size SortingEffects

Unlikethecasebeforewe find forthiscloudtiltedfallstreaks. At cloud top the wind speedis larger than at e.g. 1km. Can thisexplainthetiltedfallstreaks?

Formoredetails, seemy ERAD talk on Tuesday…


Snowflake,vdop= 1 m/s

Rimedsnow, vdop = 2 m/s

Verticalprofileof horizontal wind u (unidirectional)

Note: The time fortheparticleto fall 600m (600s) is not neccesarilyequaltothe time onewouldderivefromthefallstreakstructure (300s) !

„Background“ ice/snowspectruminbetweenthefallstreaks

Movingtotheleft, weentertheleftsideofthestreakwhereweexpectthe fastest particlestoappear (notetherightpeak in thespectrum!)

Movingfurthertotheleft, the fastest particlesdisappear, andthe fast peakseemstomergewiththebackgroundspectrum

Super-cooled liquid water

RS indicatesthicklayer at cloud top with 100% RH. Withinthislayerwecanoftenseethenarrow liquid peak. LWP andplumestructureseemtobecorrelated.

The HSRL lidardatashowthat liquid wateralreadyexistswhenthe RS firstreaches 100% (2km). However, thedropletsizesand/orconcentrationsseemtobelowandthusthe liquid peakisveryweak.


At the top ofthefallstreaks/plumestheparticlesarealready (at least partly) rimed

But also outside thefallstreaks, thespectrarevealrimedparticlesbelowthethick liquid layer.

Multi-peak Spectra

Itis not trivial tosaywherethe multiple peakscomefromsincetheyareinfluencedbydynamicaleffects (e.g. mergingoftwofallstreaks) aswellasbymicrophysicaleffects (e.g. riming).

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