GNSS Ionospheric Modeling And Its Application In Coupling Events In The Middle And Lower Atmosphere

The lower atmosphere(troposphere and stratosphere)and the ionosphere are a tightly coupled system.The energy interaction and coupling between the two systems has become an important topic that people are very interested in but do not fully understand in recent years.The anomalous changes in the ionosphere are not only affected by solar activities and geomagnetic changes,but also to some extent by meteorological activities happened in the lower atmospheric.The study of ionospheric anomalies is of great significance to human production and life.The research on the dynamic changes and the abnormal disturbance of the ionosphere during the disaster has become a hot topic in current study.Accurately monitoring,tracking anomalies and extracting anomalous features by using GNSS technology is an outstanding manifestation of the high-precision,widerange,and continuous real-time advantages of geodetic surveying,and the differential sequence of total electron content(TEC)of the ionosphere can be used to monitor ionospheric anomalies in a wide range and high precision.At the same time,by exploring the abnormal excitation mechanism,an accurate space weather warning model could be established to provide a better service for human life,which has important scientific significance and practical value.In this paper,based on the introduction of the basic characteristics of the ionosphere,the principle and data processing flow of acquiring TEC,the ionospheric anomaly extraction method based on GNSS TEC,the construction and monitoring of computerized ionospheric tomographic model,the ionospheric anomalies monitoring during a heavy rainfall event and preliminary discussion of the ionosphere-lower atmosphere coupling mechanism are introduced.The main contents of this paper are as follows:(1)Ionospheric physical properties,TEC acquisition and ionospheric anomaly extraction The ionosphere is an important part of the space environment.In this paper,the basic physical characteristics and detection methods of the ionosphere are systematically introduced.Then the process of acquiring TEC by using groundbased GNSS and several methods for detecting ionospheric anomalies are introduced.(2)Construction and monitoring of computerized ionospheric tomographic(CIT)model The ionospheric two-dimensional model is based on the single-layer hypothesis.The changes in the ionospheric electron content from the model can't reflect the vertical distribution structure of the ionosphere and its changes,while the threedimensional computerized ionospheric tomographic model can clearly reflect the changes of ionization in the vertical direction,which is a new way to fully understand the structure of the ionosphere.Firstly,a three-dimensional tomographic model using the mapping function is introduced and it is proved to have high precision.Then,a magnetic storm event is used to validate the algorithm.The three-dimensional reconstruction of the ionosphere is carried out,and the three-dimensional tomography changes of the ionospheric disturbance are obtained,which shows that anomalies have propagation characteristics.Finally,the results of the tomography results are verified by SWARM satellite data,which confirmed the reliability of the model.(3)Analysis of ionospheric anomalies during heavy rainfall and discussion on coupling mechanism On July 9,2013,Sichuan Province suffered a continuous heavy rainfall.In order to explore the ionospheric conditions in severe convective weather,in this paper,we select the GNSS data of Sichuan region during rainfall,and use the sliding average method to detect ionospheric TEC anomalies.It can be found that,before and after of rainfall,the ionosphere has obvious anomalies,and has obvious fluctuation and propagation characteristics.The three-dimensional CIT was used to reconstruct the ionosphere and the propagation characteristics of the ionospheric anomalies were also reflected.Based on the assumption of homosexuality,the horizontal velocity of the anomaly propagation in the ionosphere is about 271 m/s,which is estimated using GNSS multi-station observations.Then,the study area is divided into uniform grids,and the ground position of the anomalous excitation is determined by grid searching method.It is estimated to locate at the western boundary of Sichuan Province,where terrain fluctuations are large.Finally,the coupling mechanism between the ionosphere and the lower atmosphere is discussed.In this paper,the main mechanism for the anomaly is supposed that the convective motion during the rainfall process stimulates the atmospheric gravity wave,and it propagates upwards in the presence of terrain and wind.Then,it reaches the ionosphere and releases energy,causing an ionospheric anomaly.