Analysis Of The Prediction Ability Of IRI2016 Model For TEC Anomalies And The Refinement Of Model Parameters

Due to the comprehensive influence of various factors,the ionosphere shows a variety of irregular anomalies.Whether these anomalies can be correctly predicted is an important indicator to evaluate an ionospheric model.The International Reference Ionosphere 2016（IRI2016）model is the latest release model,and there are few verification studies on the prediction ability of this model in abnormal regions.Based on the GPS-TEC data and IGS-TEC data provided by the International GNSS Service（IGS）,this paper analyzes the characteristics of total electron content（TEC）anomalies in the ionosphere from the time and space perspectives and compares the results with the IRI2016 model.The ability of the IRI2016 model to predict ionospheric TEC anomalies is analyzed to further improve the model in predicting TEC in ionospheric anomaly areas.The main contents of the thesis are as follows:（1）Using the Center for Orbit Determination in Europe Global Ionospheric Maps（CODE GIMs）and GPS-TEC data,aiming at the three time scale anomalies of the ionosphere:winter anomaly,annual anomaly and semi-annual anomaly,combined with solar activity and geomagnetic activity,the prediction ability of IRI2016 model for these three anomalies is analyzed.The results show that in the northern hemisphere,the IRI2016model can better show the winter anomaly,and there is no winter anomaly in the southern hemisphere.The IRI2016 model can show obvious annual and semi-annual ionospheric TEC anomalies,but the IRI2016 model fails to show the details of ionospheric TEC temporal variation.（2）Using CODE GIMs data and GPS-TEC as the comparison data,the performance of IRI2016 model in Mid-latitude Summer Night Anomaly（MSNA）and Equatorial Ionization Anomaly（EIA）regions was analyzed.The results show that in the MSNA region,the IRI2016 model only describes the MSNA phenomenon in some regions.In most test days,the model underestimated the TEC value in the region and failed to clearly reflect the diurnal variation characteristics of TEC in the region.In the EIA region,the EIA bimodal described by the IRI2016 model is too narrow and long,and the error of the model in most test time is large.（3）The improvement of the old version of IRI2016 was studied,and the consistency between the calculated TEC values and the measured values of the bottom thickness parameter model of IRI2016 and the corresponding height of the peak electron density of F₂ layer（Height of F₂ peak,Hmf₂）model was analyzed.Then using the difference between GPS-TEC and TEC calculated by IRI2016 model,two input values of IRI2016 model are updated by iterative method:Rz₁₂（12-month running mean of sunspot number）and IG₁₂（Ionospheric Index）.After comparison,it is found that the updated IRI model value is closer to the GPS-TEC value than the non-updated IRI2016 model,and the improved IRI model value can obtain better TEC value on quiet days and magnetic storm days,and the improvement of TEC in daytime is better than that in nighttime.