The growth of snow The growth of snow as seen by profiling as seen by profiling

radarsradars

P. Kollias and I. ZawadzkiMcGill University

1where we show a sample of

situations of snow growth.

The growth of snow as seen by VertX

Reflectivit

Dopplervelocity

Dopplerspectra

The growth of snow as seen by VertX

The growth of snow as seen by VertiX

The growth of snow as seen by VertX

The growth of snow as seen by VertX

The growth of snow as seen by VertX

The growth of snow as seen by VertX

y y yVertX

convergencedivergenceconvergencedivergenceconvergence

The growth of snow as seen by VertX

The growth of snow as seen by VertX

Combining VertX data with divergencefrom scanning radar

2Arctic Cloud Systems

Arctic Cloud StationsBarrow

SHEBA

Eureka

Alert

Ny’Alesund

Tiksi

Radar Lidar

An Example Station

Slide provided by M. Shupe, NOAA

Radar

Lidar

• Very cloudy in general at all stations (~75% total)• Lots of low-level clouds• Liquid is present throughout the year more than half of the time!• Mixed-phase clouds: Maxima in transition seasons

Slide provided by M. Shupe, NOAA

High Spectral Resolution Lidarbackscatter

High Spectral Resolution Lidadepol

Millimeter-Wavelength Radar,backscatter

Millimeter-Wavelength Radarvelocity

Thin Liquid Layer ~ high

lidar

backscatter

Thin Liquid Layer ~ no

lidar depol

Thin Liquid Layer ~ Most of the time not detected

by MMCR’s

Thin Liquid Layerdetection required lidar

in space

Lessons LearnLessons Learned:ed:

1. Profiling radars give information on 1. Profiling radars give information on microphysics and dynamics of snow systemsmicrophysics and dynamics of snow systems

2. Snow exhibits great variability in 2. Snow exhibits great variability in typestypes and fromand from one location to anotherone location to another

3. Lowest km critical for determination 3. Lowest km critical for determination of snow amountof snow amount

4. 4. Low cost, low maintenance ground base Low cost, low maintenance ground base XX--band profiling radars could be deployed band profiling radars could be deployed in some high latitude locations which in some high latitude locations which would nicely complement spacewould nicely complement space--borne borne

systemssystems

3Some theoretical computations

and spaceborne radar measurements

Radar Requirements for Radar Requirements for spaceborne spaceborne polar polar hydrology missionhydrology mission

Sensitivity of Sensitivity of --15 dBZ is required to 15 dBZ is required to detect ice cloudsdetect ice clouds

Vertical Resolution of 100m is desirable Vertical Resolution of 100m is desirable to infer surfaceto infer surface snow amount and detect snow amount and detect

sublimationsublimation

Snow fall Doppler velocity range is 0.5Snow fall Doppler velocity range is 0.5--1.5 1.5 m/sm/s. . AnAn accuracy of 0.1 accuracy of 0.1 m/s m/s is is

required to infer snow microphysics and required to infer snow microphysics and system dynamicssystem dynamics

CloudSat

Radar frequency for detection

The sensitivity requirements -15 dBZ for ice cloud detection and -5 dBZ for snow detection (Joe, 2003) and the need to provide high vertical resolution and near the surface

observations can be achieved only with a 94-GHz radarCloudSat Snow Profiles CloudSat Rain Profiles

rimed

Non rimed

Interpretation of snow reflectivity depends on snow density:dual frequency gives information on density

Attenuation is negligible in snow; no

information from single frequency

Dreaming in two colors (13.4 and 94GHz band)

Thanks