NUMERICAL SIMULATIONS ON IONOSPHERIC CONTROL OF POLARIZATION OF LOW-LATITUDE GEOMAGNETIC-PULSATIONS

By using a realistic east-west distribution of the height-integrated i onospheric Pedersen and Hall conductivities, numerical simulations on the ionospheric control of polarization of low-latitude Pc3-4-band geo magnetic pulsations have been made. It has been confirmed that the til ting of the major axis of the H-D plane polarization ellipse observed on the morning side is due to the ionospheric conductivity enhancement associated with sunrise. It has also been found that the magnetic fie ld having a standing oscillation structure in the north-south directio n and an amplitude peak in the neighborhood of the magnetic equator is valid as a source held of the low-latitude pulsations transmitted fro m the magnetosphere in the fast mode (or the poloidal mode). Further, it has been found that the sense of rotation of the magnetic perturbat ion vector in the H-D plane is controlled by the sense of east-west pr opagation. The sense of rotation-is clockwise for eastward propagation and counterclockwise for westward propagation in the northern hemisph ere, and vice versa in the southern hemisphere.