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Alessandro Battaglia , Simone Tanelli , Gerry Heymsfield and Lin Tian

The Dual Wavelength Ratio knee: a signature of multiple scattering in airborne K u - K a observations. Alessandro Battaglia , Simone Tanelli , Gerry Heymsfield and Lin Tian. Paper now out in J. Appl. Meteorol . Climatol ., early on line release. Focus and motivation.

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Alessandro Battaglia , Simone Tanelli , Gerry Heymsfield and Lin Tian

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  1. The Dual Wavelength Ratio knee: a signature of multiple scattering in airborne Ku-Ka observations Alessandro Battaglia, Simone Tanelli, Gerry Heymsfield and Lin Tian Paper now out in J. Appl. Meteorol. Climatol., early on line release

  2. Focus and motivation • Convective towers  heavy precipitation events • CloudSat and TRMM providing single frequency observations of convective towers. GPM-DPR: first dual wavelength observations from space. • CloudSat observations certainly affected by multiple scattering. For TRMM hints that rain rates were underestimated in deep convection (maximum not occurring under the convective core, Liu Chuntao) TRMM Ku-band CloudSat W-band

  3. GPM proxy: NASA-HIWRAP Ku-Ka MC3E observations Region of strong attenuation Very likely presence of hail (ground reports+ Ground-based S-pol radars) Heymsfield et al., 2013: Airborne Radar Observations of Severe Hail Storms: Implications for Future SpaceborneRadar, J. Appl. Meteorol. Climatol.

  4. Vertical reflectivity profiles in sector II S-band Z above 60 dBZ only in the last 4 km High-density ice layer 3dB/km Ku Ka i Inflexion point Anomalous sloping  DWR knee 0.5dB/km 1.6dB/km one way Absence of surface return peak

  5. The Dual Wavelength Ratio knee This feature was observed during MC3E in several convective cells >10 dB >12 dB In a single scattering world …..

  6. Single scattering explanation?DWR sources from hail/graupel/rain Differential attenuation Mie effects ways how to decrease DWR Only hail particles in this range of size But almost monodisperse can produce a decrease in DWR. Rain and wet hail cannot!! However quite hard to produce a 12 dB effect! Vertical microphysical processes not supported by S-band observations. Even if DWR can be explained there is no explanation of the disappearance of the surface with realistic s0 values

  7. The multiple scattering explanation Dense ice layer high SS albedo Anomalous sloping and surface peak disappearing have been already documented for CloudSat, but quite astonishing to see this features in Ku-Ka airborne observations. Ka is expected to be more heavily affected by multiple scattering than Ku.

  8. Simulation framework: single ice layer Two features must be carefully treated: Antenna pattern Size of the convective cell

  9. Pulse stretching effect generated by an hail layer DWR profile Pulse stretching Ku profile The MS strength is a strong function of the horizontal extent of the system  lateral diffusion allows radiation to re-enter the small footprint (whose 3 dB radius is of the order of 500 and 200 m for HIWRAP at 10 km distance for Kuand Ka, respectively) after being scattered away from it.

  10. Profile with hail explaining sector II HIWRAP+S-band observations Ku profile Heuristic top-bottom approach Ka profile Grey-shaded envelopes=observed HIWRAP profiles within 1, 3, 5 km from the cluster center The radar Is loosing its ranging capabilities DWR profile Radiation height

  11. GPM configuration SS attenuated SS effective 3km 10km • Maximum in DWR strongly suppressed • Appearance of a knee • Even negative DWR possible! 5km MDT MDT

  12. Conclusions AKa-KuDualWavelengthRatio knee was frequently observed during MC3E. This signature is straightforwardly explained with the help of multiple scattering theory in presence of hail-bearing highly-diffusive convective cores with large horizontal extents  Ka pulse stretching typically exceeding that occurring in the Kuchannel  anomalous sloping knee, visible thanks to the profile large attenuation and to the good HIWRAP sensitivity (10 and 0 dBZ at 20 km for Kuand Ka, respectively). Multiple scattering effects are likely to be more pronounced in the upcoming space-borne GPM-DPR observations. Our forecast: DWR knees will be observed by the GPM radar when overflying high-density ice shafts embedded in large convective systems  their explanation must not be sought in differential attenuation or differential Mie but via multiple scattering but interplay witn non uniform beam filling still under study. With real GPM-DPR data, we will be able to confirm or refute our conjecture.

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