Research On The Applied Technology Of MST Radar

The MST radar observes the Mesosphere, Stratosphere and Troposphere and obtains the atmospheric wind profile and turbulence parameter based on clear air scattering principal. Wuhan MST radar is the first MST radar, located at Chongyang, Hubei (geographical location:114°8?8?E,29°31?58?N, dip latitude 19.56°). MST radar is important for monitoring the temporal and spatial changes of the atmospheric wind profile, investigating the atmospheric dynamic process, clarifying the upper atmospheric and ionospheric coupling mechanism, establishing the atmospheric model and providing the space weather service. The main work of this thesis includes as follows:1. B-V (Brunt-Vaisala) frequency is obtained from vertical wind profile of MST radar products. The inversed atmospheric temperature profile is obtained from B-V frequency, which is compared with the rawinsonde wind measurement. The results indicate that the two temperature profiles are consistent. The results also reveal that the average tropospheric B-V frequency is different from the stratospheric B-V frequency. The change point indicates the location of the tropopause.2. In order to estimate the height of tropopause and analyze the structure of tropopause, by statistic analyzing the observations from Wuhan and Beijing MST radars, this paper built a more general model to estimate the tropopause in consideration of that the tropopause may incline. Comparing the results from the radiosondes, the heights of meteorological tropopause are higher than that of radar tropopause about 2 km. The relative echo intensity of tropopause reflects the aspect sensitivity, which is helpful to understand the formation, expiration, and structure of tropopause. The statistical results from Wuhan and Beijing MST radars in 2012 show:1) the heights of tropopause in Chongyang county is higher than that in Xianghe county about 1 km, because the heights of tropopause will decrease with latitude increase; 2) the relative echo intensity of tropopause in Chongyang county is stronger than that in Xianghe county about 4 dB, which illustrate the tropopause at higher latitude may be more sparse; 3) the standard deviation of heights and relative echo intensity of tropopause in two county are very close, which declare the change of tropopause at different region almost is the basic consistent. The relative echo intensity of tropopause can be modulated by the tidal waves and planetary waves, so the tidal waves and planetary waves can affect the formation, expiration, and structure of tropopause.3. The simulation experiment of refractive index has indicated the reflectivity of rain particles and atmospheric turbulences are the same level for the wavelength of 6 m electromagnetic wave (the wave length of Wuhan MST radar is 5.58 m), so Wuhan MST radar can simultaneously obviously observe the radar echoes from the rain particles and atmospheric turbulences. Base on the spectrum of radar echoes between the rain particles and atmospheric turbulences, the separation model of frequency spectrum is built and used to calculate the motion parameters of raindrops and motion state of background atmosphere in the rain environment. Wuhan MST radar is used to observe the atmospheric stratiform rainfall and convective rainfall and study the echo characteristics, motion state, background atmosphere of different rain environment. The results indicate:1) the echo spectrum from rain particles are wider than that from atmospheric turbulences, which can distinguish the melting layer and below it; 2) the radar echoes of stratiform rainfall appear below the zero isotherm, but the radar echoes of convective rainfall may appear up the zero isotherm; 3) the background winds are very disorder in the convective rainfall environment with a shorter time of duration; 4) the radar echoes of stratiform rainfall can be used to analyze the character of bright band and melting layer and calculate the raindrop size distribution at different heights. Furthermore, the local strong convection make different direction radar beams to observe different atmospheric motion state, so it is hard to form average atmospheric wind field in the scanning space of radar beams which make a great challenge for getting atmospheric three-dimensional (3D) wind field by beam scanning. This paper uses the observations from Wuhan MST radar in the convective rainfall environment to comprehensively analyze the dilemma for measurement of 3D wind by radar beam scanning and gives some advice of detection.4. This paper utilizes the observation data of Wuhan MST radar to discuss and analyze the inertia gravity waves (IGWs) in the troposphere and the lower stratosphere (TLS) and also analyze the propagation characteristic of the gravity wave excited by the severe convection and tropopause jet stream based on the quasi monochromatic gravity wave model. More than two-year observation data are used to make statistic analysis about the atmospheric IGWs in the troposphere, including intrinsic frequencies, vertical wavelengths, horizontal wavelengths, vertical wavenumber spectra, energy density spectra of upward and downward IGWs. Moreover, the Lomb-Scargle analytical method are utilized to seasonally detect and analyze the tidal waves and planetary waves in the TLS from the meridional wind and zonal wind observations of the Wuhan MST radar in 2012. The results show:1) the diurnal tide is relatively stronger in each season and the tides with small periods are weaker and the amplitude of tidal waves have obvious cyclical changes; 2) the amplitude of tidal waves will be modulated by tidal waves and planetary waves with the larger period, but the smaller period waves have none effect on them; 3) the shorter period planetary waves mainly exist in the lower troposphere and the larger period planetary waves mainly exist in the upper troposphere and lower stratosphere.5. Using digital beam forming technique, this paper analyze the echo characteristics from different beams, different tilted angle and different heights, also calculates the aspect sensitivity (atmosphere angular spectrum) of radar echo and respectively discuss the physical mechanism of radar echo at different heights. The results manifest:1) in the troposphere with small tilted angle, the partial reflection and anisotropy turbulent scattering mainly contribute to the radar echo, but when the tilted angle become larger, the radar echo comes from the common scattering of isotropy and anisotropy turbulent; 2) the higher heights and the larger tilted angle, the isotropy turbulent scattering make more contribution to the radar echo, and the radar echo in the mesosphere and lower thermosphere mainly comes from the isotropy scattering; 3) the radar echo aspect sensitivity from the atmospheric stable layer is quite small because atmospheric structure of the stable layer is relative denseness which make well partial reflection for the radio wave, but by changing the tilted angle, we find the atmospheric stable layer has a horizontal scale.6. This paper utilizes the echo difference from the symmetric radar beams to research the inclining condition of the atmosphere. When the echo from one of the symmetric beams is apparently higher than the other one, the atmosphere incline to the direction of echo higher. As to the angle of inclination, continuous sweeping would be took by using different tilted angle and the tilted angle of the echo highest is the angle of inclination. In order to study what factors will influence the inclining condition of the atmosphere, this paper makes period detection for the echo difference from the symmetric beams at different heights. The results indicate:1) in the troposphere, the waves with all kinds of scale (such as gravity wave, tidal wave and planetary wave) almost would make some effects on the structure of atmospheric stratification; 2) in the lower stratosphere, the effects from the planetary wave and small scale gravity wave on the structure of atmospheric stratification become very weak, but the tidal waves with the period of 8h,12h, and 24h are relatively stronger; 3) in the mesosphere and lower thermosphere, the tidal waves almost become the only one effect on the structure of atmospheric stratification, and the 24h tidal wave has the widest spectrum showing the pulsation of the 24h tidal wave is the strongest.