Longitudinal effects in geomagnetic disturbances at mid-latitudes

The paper describes the differences in the magnetic disturbance effect on horizontal geomagnetic field (H) and declination (D) at Alibag (India), Lunping (Taiwan), Chichijima (Japan) and Kakioka (Japan). It is suggested that the trapped particles in the earth’s magnetic field lines are guided by the dipole declination and not by the ground declination and follow the direction towards the geomagnetic pole. The disturbance vector is given by sin (ψ - D) where ψ and D are dipole and ground declinations of the station respectively. The mean disturbance daily variation (SD) of H field is similar at all stations but SD of eastward field (Y) is negative at Alibag but positive at Lunping, Chichijima and Kakioka. Similarly, the daily mean values of H field systematically decrease with increasing ring current index (decreasing value of Dst index) for all stations. But declination values are positively related with Dst index at Alibag and negatively related at Lumping, Chichijima and Kakioka. The SSC amplitude in Y field shows negative values at Alibag but positive values at Kakioka. The storm-time variations Dst(H) show negative excursion during the main phase of the storm at Alibag, Lunping, Chichijima and Kakioka. On the other hand, the Dst variations in declination during the main phase show negative excursions at Alibag but positive excursions at Lumping and Chichijima. This shows a very significant longitudinal inequality in storm-time behavior of eastward geomagnetic field at any place on the earth.