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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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Supercooled liquid water
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.

Cloud structure fallstreaks size sorting effects
Cloud Structure– Fallstreaks – Size SortingEffects

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

For more details see my erad talk on tuesday
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 snow spectrum inbetween the fallstreaks
„Background“ ice/snowspectruminbetweenthefallstreaks

Movingtotheleft, weentertheleftsideofthestreakwhereweexpectthe fastest particlestoappear (notetherightpeak in thespectrum!)

Movingfurthertotheleft, the fastest particlesdisappear, andthe fast peakseemstomergewiththebackgroundspectrum

Super cooled liquid water
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 of the fallstreaks plumes the particles are already at least partly rimed
At the top ofthefallstreaks/plumestheparticlesarealready (at least partly) rimed

But also outside the fallstreaks the spectra reveal rimed particles below the thick liquid layer
But also outside thefallstreaks, thespectrarevealrimedparticlesbelowthethick liquid layer.

Multi peak spectra
Multi-peak Spectra

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