Analysis Of Weather Radar Clear-air Echo Character And Its Elementary Application

Now the construction of the new generation Doppler weather radar (NEXTRAD) network which is composed of 158 S-band and C-band coherent Doppler weather radar has been nearly completed. Up to date in the weather sites where the NEXRAD have been operated, the meteorological workers and researchers have studied on the intensity and Doppler velocity information which relate to severe weather, while there are few research on spectrum width information, the unique character, obtained from Doppler radar. In this paper, one method is induced to extract a useful factor forecasting and warning severe weather from the spectrum information which is attained in clear-air echo before severe convection occur, excepting it will improve the short-term forecast to some extent.In chapter one, the development of weather radar at home and abroad, the purposes of this research and structures of this research are given.Clear-air echo concept is induced and the cause of its formulation is analyzed in chapter two. It is believed that the clear-air echo which is non-birds, non-insects, non-airplane echo in boundary layer detected by high sensitive pulse Doppler weather radar are formulated by the scattering when the electromagnetic wave irradiate on the turbulent mass and its refraction index is non-homogeneous random distributed. And then turbulence and its character are concerned. According to the turbulent spectrum theory, the Kolmogorov's similarity hypothesis is induced to analyze the turbulent inertial range, and it is concluded that as the Reynolds number increases the turbulent energy cascade transportation will be strengthened and the rate of turbulent energy dissipation will be larger.Then in chapter three, it is described that the method to extract the CINRAD's information (Doppler velocity and spectrum width data). And then by deducing the formula to show the -1/3 exponent rule of the refract index varying according towavelength, this paper verifies the ability of detecting the clear-air echo using weather radar.Subsequently, the factors affecting the spectrum width are discussed in chapter four. Then the relation in the form of theory formula between the spectral data and the turbulent energy dissipation rate e is provided.In chapter five, we use the clear-air echo spectrum width data acquired by CINRAD/S A in Guangzhou during the severe weather procedure occurred on August 11, 2004 to do some study work. The quality control of data is pre-processed and the turbulence energy dissipation rates of different lower angle are calculated according to the formula as foregoing. It can be found that the rate of turbulent energy dissipation in lower layer is reinforced before the rough weather system came. It distinctly exposes the noticeable character before this severe weather event.Finally, in chapter six the conclusions in this paper are showed and the future refinement is suggested.