Asymmetry of TEC Between the Southern and Northern Hemispheres Based on IGS Data

Using ionosphere TEC data provided by IGS for the years 2000 to 2012, we studied ionosphere TEC asymmetry between the southern and northern hemispheres. By analyzing the Asymmetry Index (AI) of the TEC daily mean between the southern and northern hemispheres, we found that the absolute value of the maximum concentration of AI was about 0.4, the absolute value of the minimum concentration was about 0.3,demonstrating that there is a numerical asymmetry in the ionosphere TEC between the southern and northern hemispheres. With the Fourier analysis method, we found that there is an annual cycle and a 1/3 annual cycle existing in Asymmetry Index; more than 50% when the northern hemisphere ionospheric TEC exceeds the southern hemisphere ionospheric TEC in a year. The mean value was 58%, suggesting a temporal asymmetry of the ionosphere TEC between the southern and northern hemispheres. We analyzed the annua difference of the mean TEC between the southern and northern hemispheres, finding that the annual mean TEC of the northern hemisphere is higher than that of the southern hemisphere, and the Asymmetry Index of the annual mean TEC between the southern and northern hemispheres during 2000-2012 was about 0.036. Taking the asymmetry in the atmospheric distribution and the movement rule and thermosphere into consideration, we discuss the reasons for the asymmetry of the ionosphere TEC between the southern and northern hemispheres.