Sensitivity Of The W Band Airborne Cloud Radar Reflectivity Factor Z To Cloud Parameters

The detection of cloud particles has the vital significance to radiation balance of the earth-atmosphere system and the development process of cloud and precipitation in weather forecast. Because of millimeter wavelengths close to the scale of cloud particles, more and more millimeter radar systems are being used to detect cloud (watercloud and icecloud) and small precipitation particles. In order to make research on the effect of various atmospheric factors on radar reflectivity ,the software named as "SimRAD" (Simulating airborne Radar detection and Data processing) was used to simulate cloud and precipitation radar reflectivity factor Z profiles of the W band airborne cloud radar under different cloud parameters, and discuss the Sensitivity of the reflectivity factor to cloud parameters. To study the attenuation for the millimeter wavelength radar detecting non-precipitation cloud, the relationship between attenuation coefficient k and radar reflectivity factor Z were calculated at mm wavelengths for cloud and precipitation particles.Main conclusion:1. when the 3.2 mm wavelengths radar was used to detect watercloud, the radar reflectivity factor Z made a great difference with different particle size distribution and liquid water content, different cloud drop size spectra exerted an influence on radar reflectivity factor Z, which has a great difference between modified gamma distribution and exponential distribution, while the exponent number of modified gamma distribution had little influence on Z. when the radar was used for icecloud, particle size distribution and ice water content had a great impact on radar reflectivity factor; While the contrary to ice density and the exponent number of modified gamma distribution. Study of cloud parameters impact on the radar reflectivity factor Z was conductive to analysis microphysical processes of cloud and precipitation, and had great significance in data processing and analysis of the millimeter wavelength airborne cloud radar.2. What's more the attenuation caused by cloud and precipitation particles' scattering and absorption together with the water vapor and oxygen absorption at millimeter wavelength must be take into account. In order for the actual need of mm wavelengths cloud radar data processing, presuming that the cloud particles were sphere particles, the relationship between attenuation coefficient k and radar reflectivity factor Z were calculated at 3.2 and 8.6 mm wavelengths for spherical cloud (include watercloud and icecloud) and precipitation particles. It shows the attenuation at 3.2mm was 5-10times larger than that at 8.6mm under the same conditions of the drop size spectra. The attenuation coefficient k for ice particles was less than that for cloud particles by 2-3 exponent number. The parameters of cloud drop size spectra were defined under the non-precipitation cloud field observational data in our country, the k-Z relationship calculated in this paper were more applicable in the data processing and analysis for millimeter wavelength airborne cloud radar in our country and it was available for attenuation correction of mm radar. Using SimRAD to study the attenuation for the millimeter wavelength airborne cloud radar under the formulas ,the attenuation caused by cloud particles and gases were serious,while the attenuation caused by ice particles was infinitesimal.