jasmine r émillard and pavlos kollias mcgill university

Cloud Climatology and Microphysics at Eureka Using Synergetic

Measurements from a Cloud Radar and a Cloud-Aerosol Lidar

Jasmine Rémillard and Pavlos Kollias

McGill University

Scale 1:5 000 000courtesy of the Atlas of Canada

~2km

~1.5

km

~1.5km

~600m

~1.5

km

Locating Eureka

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courtesy of CANDAC

79.9903°N 85.9389°W

InstrumentationMillimeter wave cloud

radar (MMCR)• active and vertically pointing

• 8.66mm or 34.86GHz (Ka)

• 10s and 45m resolutions (interpolated to the lidar’s for the synergistic)

• provided by M. Shupe

Rawinsondes• launched at Eureka’s weather station (~1 km South)• interpolated to the lidar’s resolutions• mainly for the temperature profiles in the phase classification

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High spectral resolution lidar (HSRL)

• active and vertically pointing

• 532nm (green)

• 0.5s and 7.5m resolutions (used with 180s and 30m)

• provided by E. Eloranta

Example of measurements

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radar’s(sensitive to crystals)

lidar’s(sensitive to droplets)

temperatures

Objectives

• characterize the clouds and precipitation at Eureka– occurrence, overlap, type, phase…

– 2-year period (September 2005-2007)

• present some results and their analysis– BL clouds

– supercooled liquid hydrometeors

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Methodology – Phases

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Populous particles dominate the lidar backscatter signal

Thus, in mixed-phase conditions, spherical liquid droplets keep the lidar depolarization low

Above 0°C, everything should meltBelow -40°C, every nucleus is assumed

to form ice on it

2-year results – hydrometeor phases

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fraction of hydrometeors, at a given height (lines are isotherms: -40, -20, 0°C)

fraction of time that liquid was observed at any height

2-year observation of liquid

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Height of the liquid

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Winter Summer

Consistency

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supercooled liquid (12.3%)solid above -40°C (87.7%)

2-year results – number of layers

• In a profile, an hydrometeor layer is defined as a group of consecutive gates that all have a radar reflectivity greater than -60 dBZ.

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Methodology – Types

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and everything below the lidar liquid base is assumed to be precipitating

definition of the cloud types based on the cloud base and top heightsbase = lowest height without precip within the layertop = highest radar echo within the layer

2-year results – type of clouds

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BL clouds occurrence

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BL clouds persistence

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Different daily thresholds

A persistent mixed BL cloud

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Radar echo top

Lidar liquid base

Radar echo base

Analysis of the liquid base

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snow

more turbulent near top…

…and at night!

Summary• Clouds are a predominant feature at Eureka

– more than 60% of most months– usually in single-layer systems

• Hydrometeors are usually in their solid phase, but supercooled liquid is also found– ice clouds are less turbulent, but have greater

velocities– normally at temperature greater than -20°C and high

relative humidity• Types of clouds are seasonal-dependant (higher in

summer…)– Mixed-phase BL clouds seem to be driven by the

turbulence at their top

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Future work

• Add more persistent BL cases in their analysis

• Use CloudSat and CALIPSO data to see if those results stand for a larger area than just Eureka

• Compare with the results obtained during other campaigns (SHEBA, NSA site…)

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