ANALYSIS ON STRUCTURE OF THE VARIABLE GEOMAGNETIC FIELDS AT MIDDLE AND LOW LATITUDES

The data of the variable geomagnetic fields observed at some observatories in China have been analyzed by using the method of Natural Orthogonal Components (MNOC). The separated components of the variable magnetic fields at the middle and low latitudes are:(1) Sq produced by the ionospheric dynamo currents,(2) Sd produced by the disturbance currents, and (3) Dut regulated by the universal time UT.The relative magnitudes of these components change with season and their amplitudes have definite latitudinal distributions.