Microstructure of Israeli Clouds and their Suitability for Seeding Eyal Freud and Daniel Rosenfeld יום עיון מחקרי רשות המים, 21 ביוני 2011.

Microstructure of Israeli Microstructure of Israeli Clouds and their Suitability Clouds and their Suitability

for Seedingfor Seeding

Eyal Freud and Daniel Rosenfeld

.2011 ביוני 21יום עיון מחקרי רשות המים,

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Mediterranean climate in northern and central Israel

50-70 days with precipitation annually 400-1200mm (comparable with Europe) but

higher evaporation Mostly convective precipitation

But significant orographic contribution

Mainly by a “Cyprus low” Most prec. is post-frontal

Introduction: PrecipitationIntroduction: Precipitation

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Background: Cloud MicrophysicsBackground: Cloud Microphysics

0°C

-40°C

An example of the relation between re and temperature in a hypothetical cloud. The different microphysical phases in the cloud are marked as well.

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Background: Cloud Seeding in Background: Cloud Seeding in IsraelIsrael

Seeding with AgI for precipitation enhancement started in 1961

Aims at accelerating cold processes in the cloud and convert super-cooled cloud water into precipitation

Inexpensive water Seeding effect is decreasing with time (15%

0%) “Hot” scientific debate “Israel 4” experiment

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Main ObjectiveMain Objective

Characterize the microphysical properties of the clouds in northern Israel and assess their suitability for seeding

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ApproachesApproaches

Aerosol measurements below cloud base over sea and inland

Cloud vertical profiling from base to top (discrete levels or spiral) to document: Droplet growth Precipitation formation Total (supercooled) LWC

Satellite analysis

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Ambient: Temperature; Pressure (static, dynamic); GPS

Aerosols: CN CCN PCASP-X2

Clouds/Precipitation: CAS CIP CDP Hot Wire LWC Acquisition software:

PACS, PADS (DMT), Hyper Terminal

InstrumentationInstrumentation

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Execution: 2008-2011Execution: 2008-2011

22 Sorties in the last three seasons in various conditions (thermodynamic and aerosol)

Total ~60hrs Plenty of data A few challenges Constant

improvement

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A rainy day in Northern IsraelA rainy day in Northern Israel

Galilee Golan

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ResultsResultsIs there any seeding potential in the Israeli clouds?

~10,000 data points

No separation between seeded/unseeded, and different cloud types

Abundant super-cooled LWC at around -10ºC

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ResultsResults

20100228: Windy Close to the sea Pollution

20100412: Haze / Dust No gradient except in

pollution (R&B) 20100326: Calm and

Clear No giant CCN even

near shore (G)

Giant CCN – Where and when?

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ResultsResults

Tail over Sea 20100228 Tail over sea 20091213

(CAS) No tail mid level cloud

20100120 Tail over Galilee 2010228 Tail over Galilee (dust)

20100412 Small Tail over Golan

20100318 No tail over shore 20100326

Giant CCN effect on DSD?

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105018.1370

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104843.1598

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104608.2258

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[g m

-3 µ

m-1

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Droplet Diameter [µm]

20100412 Descent - Over Galil

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4 6 8 10 12 14 16 180

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CN

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ResultsResults

How do we define the onset of precipitation?

A decent proxy is the cloud droplet effective radius. Around 11μm probability increases the most.

Clouds had to acquire a minimum depth of 1 to 3km for the cases with higher droplet Concentration

When did clouds precipitate?

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IsraelCaliforniaIndia

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cipi

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Droplet Effective Radius [µm]

QP(100-250m)>0.01 g/kg

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0.01 g/kg

0.03 g/kg

Dp = 976 + 1.89 N

a R= 0.92

Dp = 1489 + 2.49 N

a R= 0.91

Clo

ud

Dep

th f

or

qP =

qP ,

DP [

m]

Activated CCN [mg-1]

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c

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Summary and Conclusions Summary and Conclusions (1)(1)

Coastal range orographic clouds are often naturally seeded by ice hydrometeors falling from mature convective clouds

On windy days sea spray seeds the clouds hygroscopically, with greatest effect near the coast

Desert dust can also act as a natural seeder

Quite effective natural seeding

but…

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Summary and Conclusions Summary and Conclusions (2)(2)

There are still decent amounts of super-cooled cloud liquid water in certain clouds = Potential for seeding

Seeding efforts should be shifted to the eastern range and focused on orographic clouds where less natural seeding occur

Real time satellite imagery should be used to identify the target clouds with super-cooled LWC.

Pursuing radar echoes, i.e. already precipitating clouds, is redundant

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Thanks for your attention!Thanks for your attention!Questions???