| The millimeter-wave cloud radars in resently years have proven to be an invaluable tool for observing the non-precipitating and weak precipitating clouds. Comparing centimeter-wave weather radars, they have the characteristics of detecting small particles, high speed measuring precision and high spatial resolution. The94GHz radars can detect the smaller cloud droplets and can be used on plane or satalite easily because of short wavelength. At present, the domestic35GHz cloud radar has been developed successfully, the domestic94GHz millimeter-wave cloud radars are developing. The cloud characteristics and microphysical parameters are analysed by using Britain’s94GHz radar and the94GHz SKY cloud radar developed by China’s Anhui Sun-create electronic company in the work. Additionally, the detection ability of the SKY cloud radar is discussed. The concrete research contents are as follows:(1) The study on cloud scattering and attenuation characteristics. DDA algorithm is mainly used to calculate. Because scattering and attenuation characteristics of the particles at random orientations are isotropic on macro performance, they have nothing to do with the incident wave polarization state. The scattering and attenuation characteristics of the particles at horizontal orientations are related to incident wave polarization and incident angle, and the particles with different shapes have different scattering characteristics. Backscattering of ice crystals or water droplets with diameter less than1mm basicly meets Rayleighscattering, and that with diameter greater than1mm oscillates. The sensitivity of the backscattering properties of hexagonal ice crystals to ratio aspects, orientations, and shapes is higher, and to temperatures is lower. In the actual ice clouds, for vertically horizontal polarization wave, treated the hexagonal ice crystals as same volume spherical particles will underestimate attenuation and backward scattering, and backward scattering are more undervalued. Treated aggregations as same spherical volume will overestimate the scattering and attenuation. The backscattering of bullet flower compared with the spherical volume someines decreases and someines increases, but the attenuation is smaller. According to the types of several liquid clouds with non-precipitation, the relationships between their radar reflectivity factor and liquid content are derived. By using specific ice cloud model, the relationships between the echo intensity and attenuation coefficient and water content of ice cloud are also obtained. Due to the influence of the Rayleigh scattering, the rainfall rate and the intensity relation is no longer the form of index, so we get the new the form of non-index at last.(2) The analysis of echoes and capability of94GHz cloud radars. The echo characteristics and capability of94GHz cloud radars are introduced by using94GHz Galileo radar,35GHz radar, raindrop disdrometer, rain gauge and sounding data in England. The significant echo characteristics that distinguish94GHz cloud radars from centimeter wave radars are that decreased the radar reflectivity factor at the bottom of bright bands is slightly or not and the dim bands which are caused by non-Rayleigh scattering of bigger rainfall or ice crystal respectively. The suddenly increased radar reflectivity factor, Doppler velocity, and spectral width indicate the top of melting layer.94GHz and35GHz radars detect the dim bands at the same time show that ice particles at least are more than6.8mm. Compared with35GHz radars,94GHz cloud radars may underestimate the top height of high clouds and the reflectivity factor of94GHz cloud radars is weaker than that of35GHz radars due to the signals attenuation and non-Rayleigh scattering of94GHz cloud radars. Additionally,94GHz radars are fairly immune to ground clutter that is detected through antenna side lobes in a vertically pointing beam mode because of their short wavelength.94GHz radars can observe the fog, and the Doppler speed of the fog is cluttered. The research results would provide a reference for reliability analysis of94GHz cloud radar echoes in China.(3) Using the millimeter-wave cloud radars (35GHz,94GHz) in England combined with lidar and sounding data, the supercooled water of non-precipitating clouds and precipitating clouds are identified. The liquid water path obtained by microwave radiometers or Doppler spectrum density obtained by millimeter wave radars are used to verify the results. Finally, the bimodal spectrums of Doppler velocity are used to inverse the supercooled water content. The millimeter-wave cloud radars combined with lidar can identify the supercooled water using the method of threshold value, and the mixed-phase clouds with larger spectrums width have bimodal spectrums. The inversion according to the radar reflectivity factor of mixed-phase clouds which mainly depends on ice crystals will underestimate the cloud liquid water content. Some non-precipitating clouds has supercooled water layer.(4) The echoes observed and the retrieval of microphysical parameters of the clouds by Chinese94GHz SKY cloud radar. Using the successfully observed cloud echoes by Chinese indigenous94GHz SKY cloud radar, the macrostructure and the microphysical parameters of stratocumulus with drizzle in Anhui province on8June2013and the cloud system of a hundershower are analyzed, and the detection ability of SKY cloud radar is also discussed. Using the formulas deduced in this paper and the experience formulas of the abroad, the cloud liquid water content, ice water content and cloud particle effective radius are studied using SKY radar for the first time. SKY radar can observe the time-varying macroscopic and microphysical parameters, and indicate microscopic structure and small scale changes of the clouds. The radar’s sensitivity is comparatively higher because the minimum radar reflectivity factor is about-35dBZ in this experiment, and the threshold of radar reflectivity factor to measure LDR of stratocumulus is commonly-11-14dBZ and should decrease with the increase of turbulence. The velocity spectrum width of cloud droplets only is smaller, but the spectrum width of the cloud containing cloud droplets and drizzles is bigger. It is needed to distinguish the cloud droplets from the drizzle for the inversion of cloud liquid water content and particle effective radius, and the liquid water content of drizzle is lower than cloud droplets at the same radar reflectivity factor. The airborne exploration shows the echo intensity of the non-precipitating ice clouds or mixed phase clouds is between-30-5dBZ, and linear depolarization ratio is related to the particle shapes and the radar scanning mode. LDR by94GHz SKY radar can identify the height and thicknessof melting zone. |
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