Longitudinal effects in geomagnetic disturbances at mid-latitudes

The paper describes the differences in the magnetic disturbance effect on h orizontal geomagnetic field (H) and declination (D) at Alibag (India), Lunp ing (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 direct ion towards the geomagnetic pole. The disturbance vector is given by sin ( psi - D) where psi and D are dipole and ground declinations of the station respectively. The mean disturbance daily variation (SD) of H field is simil ar at all stations but SD of eastward field (Y) is negative at Alibag but p ositive at Lunping, Chichijima and Kakioka. Similarly, the daily mean value s of H field systematically decrease with increasing ring current index (de creasing value of Dst index) for all stations. But declination values are p ositively related with Dst index at Alibag and negatively related at Lumpin g, Chichijima and Kakioka. The SSC amplitude in Y field shows negative valu es 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, Lu nping, Chichijima and Kakioka. On the other hand, the Dst variations in dec lination during the main phase show negative excursions at Alibag but posit ive excursions at Lumping and Chichijima. This shows a very significant lon gitudinal inequality in storm-time behavior of eastward geomagnetic field a t any place on the earth.