Analysis of the Geomagnetic Component Z Daily Variation Amplitude Based on the China Geomagnetic Network

Abstract. The daily variation amplitude of geomagnetic component Z is one of the important data products in Geomagnetic Network of China (GNC). It comes from the difference between maximum and minimum of the component Z recorded by the geomagnetic instrument in a day. Based on this data product, the daily variation amplitude of Z is analyzed in the past twelve years (2008–2019), including variation for each month in high and low solar activity years, seasonal variations and comparisons between the stations in Yunnan Province and in southeast China. The study indicates that the ionospheric conductivity mainly contributes to the Z daily variations amplitude in the same month or season changing along with solar activity. But the neutral wind in ionosphere could make the Z daily variations amplitude in equinox months equal to or greater than it in summer solstice months during some solar high activity years. Due to the complicated underground electrical structures in Yunnan province, the conductivity underground acts as an amplifier to make the Z daily variations amplitude increase by about 12 % ~ 41 % in Yunnan Province during equinox and summer solstice months.