The Study On The Characteristics Of Superdarn Backscatter Echoes

The Super Dual Auroral Radar Network （SuperDARN） can be used to detect themotion of ionospheric irregularities, which have been contributed to analyze manyphenomenon in space weather and to solve many related problems. The analysis ofcharacteristics of backscatter echoes of High Frequency radar as SuperDARN and thedetermination of the location of SuperDARN ionospheric echoes is always achallenging problem. Based on the building up and operation of Chinese first PhasedArray HF Radar in Zhongshan Station in Antarctica, this dissertation focuses on theecho characteristics of SuperDARN HF radars. Using the HF radio ray tracingtechnique, the deviation of SuperDARN standard location model is calculated and anew location model is proposed. The new model is determined by two parameters,which is the radar slant range and the elevation angle, instead of the standard locationmodel determined by radar slant range only. Simultaneously, we put forward a methodto estimate the ionosphere parameters using the ground scatter echoes in frequencysweep mode of SuperDARN. Finally, the characteristics of Polar Mesosphere SummerEchoes （PMSE） observed by Zhongshan radar are analyzed.Using the observation data in channel A by the new built Zhongshan radar inAntarctica in2010, the distribution of ionospheric echoes counts with the echo power,Doppler velocity, spectral widths and gate are studied and the characteristics aresummarized. The result shows that, most ionospheric echoes detected by Zhongshanradar are in near gates, and obvious difference appears in the echo counts for differentbeams, the beam with smaller numbers can detect less echoes with lower average echopower, Doppler velocity and spectral widths. The data observed in different frequencybands in channel B of Zhongshan radar are used to analyze the variation of echo counts,power and occurrence with frequency, which shows great difference. Of the operatingfrequency bands in2010,9~10MHz is the best operating frequency band. Thedifference of echo occurrence between beams is related to the beam pointing direction,and the different regions that the radar can observe for different frequency radio wavesarise from the area in which the orthogonality condition between the wave vector andthe Earth’s magnetic field is achieved.The diurnal and seasonal variations of Zhongshan radar echoes and the influence ofgeomagnetic activity on it have been analyzed statistically. The result shows that thediurnal and seasonal variation is very obvious and the influence of geomagnetic activity is significant. The peak echo occurrence occurs at dayside during geomagnetic quiettimes, and shifts toward nightside and exhibits an obvious decrease with the increasinggeomagnetic level. The result also indicates that the average line-of-sight velocity hasobvious diurnal variation. At nightside, the velocity is mainly positive and toward theradar, but negative and away from the radar at dayside, which is related to the anti-sunconvection at higher latitude. The average power and the line-of-sight velocity areapparently higher in geomagnetic active times than that during quiet times, which is inconsist with the enhancement of ionosphere convection with the more activegeomagnetic activity. In contrast, the echo occurrence and Doppler spectral width arelower. Generally, the echo occurrenc and average echo power are higher in winter thanin summer. In different months, the line-of-sight velocity is different in MLT and gate.The spectral widths are larger in winter than in summer.Using the ionospheric echo data of CUTLASS Finland radar （Hankasalmi） in2008and2009, the echo location characteristics are analyzed. The IRI-2007model isinserted into the ray tracing simulation technique, combined with the ionosonde datacollected at Sodankyla, which is in the field-of-view of CUTLASS Finland radar, thelocation of backscatter echoes is estimated. The results show that the echoes can bedetected in the ionosphere over a very large area and the location is various in differentionosphere environment. The deviation of standard location model of SuperDARN iscalculated and the results show that greater error is introduced for larger gates for thissingle-parameter location model, leading to the mixture of ionospheic echoes location,which has the influence on the ionosphere convection and the determination ofconvection map. We firstly proposed a new location model determined by radar slantrange and elevation angle, and the new model can improve the location accuracyobviously. The ionosphere parameters （electron density profile, critical frequency） inthe field of view is critically important for the determination of the new model and inthe absence of the ionosphere parameters, we put forward a method to estimate theionosphere parameters using the ground scatter echoes in frequency sweep mode ofSuperDARN and the evaluation of the method shows that the variation trend ofionosphere parameters can be estimated in a reasonable area.SuperDARN has been successful in addressing a wide range of scientific questionsconcerning processes in the magnetosphere, ionosphere and thermosphere, themesosphere studied by SuperDARN is in the initial stage. In the last chapter in thisdissertation, the Polar Mesosphere Summer Echoes observed by ZhongshanSuperDARN radar and the characteristics of PMSE are analyzed. Considering the special location of Zhongshan Station, we investigate the effect of auroral particleprecipataton on the PMSE, establishing the foundation of the study on mesospherestructure by Zhongshan HF radar.