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UID:2502@i2m.univ-amu.fr
DTSTART;TZID=Europe/Paris:20181012T110000
DTEND;TZID=Europe/Paris:20181012T120000
DTSTAMP:20180927T090000Z
URL:https://www.i2m.univ-amu.fr/evenements/cloud-radar-reflectivity-factor
 -enhancement-due-to-turbulent-droplet-clustering/
SUMMARY: (...): Cloud radar reflectivity factor enhancement due to turbulen
 t droplet clustering
DESCRIPTION:: Radar observation is a powerful tool to obtain a two- or thre
 e-dimensional distribution data of cloud and precipitation particles. The 
 cloud radar reflectivity factor can be enhanced by the spatial correlation
  of scattering particles\, which is referred to as particulate Bragg scatt
 ering. It is well known that inertial particles such as cloud droplets for
 m a nonuniform distribution in air turbulence: That is\, inertial particle
 s concentrate in low-vorticity and high-strain-rate regions due to the cen
 trifugal effect. We thus investigate the quantitative influence of turbule
 nt droplet clustering on radar reflectivity factor by using the direct num
 erical simulation (DNS) of particle-laden isotropic turbulence. In the mec
 hanism of particulate Bragg scattering\, the increase of the factor is pro
 portional to the power spectrum of droplet number density fluctuations. Fi
 rstly\, we investigate the power spectrum for monodisperse droplets. The r
 esults show that the shape of obtained power spectrum is strongly dependen
 t on the Stokes number.Quantitative estimate of the radar reflectivity fac
 tor for an idealized cloud scenario reveals that turbulent clustering can 
 cause significant increase of the factor up to 14 dB for typical cloud dro
 plet sizes. Secondly\, we investigate the influence for the case of polydi
 sperse droplets. The results show that the coherence of cross spectrum for
  bidisperse droplets can be parametrized by using the Stokes number differ
 ence. By using the parametrization\, we propose a model for estimating the
  radar reflectivity factor enhancement for arbitrary droplet size distribu
 tion. Finally\, possible errors of radar observation due to turbulent clus
 tering is estimated by using the proposed model.http://www.jamstec.go.jp/s
 ouran/html/Keigo_Matsuda003286-e.html
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