Monitoring The Effect Of Solar Flares On Ionosphere By Means Of GPS And Analysis Of Some Results

The theory and method of monitoring the solar flare using dual-frequency GPS receiver observation data are discussed in details. The main work contains:The factors influencing the vertical total electron contents (VTEC) of the ionosphere are summarized,and some knowledge about the solar flare is introduced. Besides these,the effects of the solar flare on the ionosphere and of the flare burst on the GPS measurements are clarified.The present methods of studying ionosphere and their characters are analyzed. Meanwhile,the feasibility and advantage of studying the solar flare using GPS are expounded. According to the present status of studying the solar flare using GPS,a new algorithm of processing GPS data studying the solar flare is brought forward:After the instrumental bias has been determined,with the data of dual-frequency GPS code and phase and navigation message,the VTEC at the satellite's EPP can be worked out. In addition,the importance of eliminating the instrumental bias during calculating the VTEC is pointed out.The advantages of the new method of calculating the VTEC including:(1) Because the instrumental bias is considered,the VTEC's change going with time is closer to their real change. (2) With the precision of calculated the VTEC improved,the VTEC can reflect the increase of the VTEC resulted from the solar flare.The GPS data from Crustal Movement Observation Network of China (CMONOC) in a week time before and after the flare burst on July 14,2000 are analyzed. The characters of VTEC's change are analyzed from spatio-temporal domain during the flare burst:(1) The VTEC calculated using the data of all the GPS observation stations exposed to the sun have an evident "tremble" phenomenon. That is,the VTEC at the satellite's IPP increases quickly after the flare burst,and then reduces gradually. The course of the increasing and reducing of the VTEC calculated by all the stations is identical to a large extent. (2) The VTEC's increasing resulted from the solar flare is different not only with the local time of the stations,but also with the longitude and the latitude of the satellite's IPPs. And the change of VTEC in the high latitude is larger than that in the low. (3) The "abnormal" increasing of the VTEC of some stations in the latitude between 20 and 35 before a day of the flare burst has been founded. This kind of "abnormal" phenomenon in the result of the GPS data during the flare burst on November 22,1998 can also be found.The method of calculating the change rate of the VTEC using phase data is introduced. With the help of this efficient method,the solar flare is analyzed in this thesis. The advantages and disadvantages of this method with calculating VTEC are compared. The results show that the effects of even smaller class solar flare can be reflected using this method.