Particle Shape and Orientation Evaluation in Ice Clouds Using S-Band Doppler Polarimetric Radar

1. Evaluation of particle shape and orientation within ice clouds using the S-band Doppler Polarimetric radar Tara – supersite H. Y.Dufournet, H. Russchenberg COPS workshop – October 28th

2. Radar Tara : characteristics • FMCW S-band radar (3.3 GHz) • Doppler and Polarimetric capabilities : vertical and horizontal reception and transmission performed in sequences transmitter receiver Ice and mixed-phase cloud measurement + precipitation measurement V H V H • Wind mode • antennas: 75 degrees • Polarimetry: VV VH HH OB1 OB2 (3 beams) • time res.: ~ 3 s • min range res.: 15 m • max altitude: ~13 km • microphysical mode • antennas: 45 degrees • Polarimetry: VV VH HH (1 beam) • time res.: ~ 3 s • min range res.: 15 m • max altitude: ~ 7 km

3. Tara within COPS airport • Period: July and August • Placed in Hornisgrinde • 264 measurements (310 hours of raw data) • Orientation: 116° N (towards ARM site) • measurements mode : mainly wind mode + 8 days in microphysical mode Radar direction ( www.cops2007.de )

4. Microphysic and radar measurements ? Spectral polarimetric measurements Spectral reflectivity Microphysical characteristics of ice particles: velocity 0 • particle orientation • particle shape • PSD (obtain from a microphysical model, not discussed in this presentation)

5. 16 15 14 13 12 11 10        sZdr categorization  Built using large data set category num > 10 Horizontal alignment Mono-modal 0 Bi-modal 0 0 Category numb < 9 Vertical alignment 0 0 Mono-modal 0 0 0 0 Bi-modal Category numb = 0  Not classified Category numb = -2  Not good enough sLDR < - 15 dB sρ > 0.97 sZvv > -20 dBZ

6. sZdr simplified categorization Horizontal alignment Vertical alignment Not classified 1st case: 21/07/07 (SOP 2 – EUFAR related) Frontal activities and mesoscale convective system development Ice and mixed-phase cloud Melting layer Boundary layer echo drizzle rainfall

7. 21/07 – statistical interpretation (whole box) Category number Plates and dentrites formation region Not classified (aggregates) Mostly horizontally aligned particles Hypothesis: presence of aggregates and plates or dentrites with preferred horizontal alignment

8. sZdr monomodal plates bimodal plates aggregates alone velocity 21/07 : vertical cloud structure From 2D-C probe (ATR42) From the radar (sZdr) Riming and diffusional growth aggregation www.safire.fr and www.eufar.net

9. Mean particle velocity (m.s-1) Doppler width (m.s-1) 2nd case: 11/07/07  Showers events A lot of turbulence  processing not optimum yet

10. 11/07 – statistical interpretation (whole box) Category number Columns formation region Mostly vertically aligned particles Hypothesis: presence of aggregates and columns with preferred vertical alignment Not classified (aggregates)

11. Conclusion • This new retrieval of particle shape and orientation seems feasible within ice and mixed-phase clouds but more study has to be carry out • 8 days will be processed within COPS using such technique: • 27/06 - 11/07 • 21/07 - 09/08 • 17/08 - 21/08 & 22/08 • 28/08