Study on the secular variation of geomagnetic field in China based on CHAOS-5 model

Using CHAOS-5 model of geomagnetic field ,this paper has calculated and analyzed the geomagnetic secular variation in China since 1997.The temporal and spatial characteristics of the change of the geomagnetic field are discussed by the annual change rate and its contour map,the change of the special isochronous line with time and the long-term acceleration distribution,etc.The annual variation ratio curve of 12 stations in China has been calculated and the time variation of different stations has been analyzed.The result shows that the secular variation of geomagnetic non-dipole field in the mainland of China has a long-term slow change from 1997 to 2015.Secular variation at different stations are different,and the long-term changes of different factors at the same station are not synchronous.Secular acceleration distribution is not uniform,the amount of change is small,but can clearly show the increase or decrease of the area.