We describe here for the first time the morphology of the equatorial electrojet (EEJ) in the Central American Sector based on an analysis of the geomagnetic field components from six stations distributed on both sides of the dip equator along the 60• W geographic longitude sector. Diurnal and latitudinal variations in the horizontal and vertical components are shown to follow the Chapman model of EEJ. The horizontal component vector due to the ionospheric current aligned itself close to magnetic north, with a mean Declination of 10• W (ranging from 9• W to 14 • W). There was a significant counter-electrojet effect before sunrise at stations close to the dip equator, suggesting late reversal of solar-quiet (S q ) electric field in the morning hours. The observed variations in the magnetic meridional current did not seem to be associated with EEJ currents. The centre of the electrojet was around 0.25• S of the dip equator in the morning hours and shifted gradually to 1.5• S by the evening hours. Magnetic storms occurring during the midday hours produced an exceptionally large decrease in the H (horizontal component) field at stations close to the dip equator. Key words: Equatorial electrojet, magnetic storm effects, abnormal large Declination region, dip equator in Central American Sector, sunrise counter-electrojet. Theme of the PaperIt would be useful to define the various mean magnetic field components used in the paper. These are (1) H (in nT), the scalar value of the horizontal component, (2) Z (nT), the vertical component pointing downward, (3) D• , the Declination, which is the deviation of the magnetic meridian from the geographic meridian; it is a positive value if the shift is east of geographic north, (4) X (nT), which is the horizontal component pointing to the geographic north and equal to H cos D, (5) Y (nT), which is the eastward component pointing to geographic east and equal to H sin D, (6) I• , which is the inclination of the magnetic field lines from the horizontal (positive, pointing downwards); it is equal to tan −1 (Z /H ). These magnetic field components are the result of sources inside the solid Earth in the region. There are also currents outside the solid Earth causing regular solar daily variations in the magnetic field components; these are designated as H , Y and Z and are computed as the deviation of the component at any time t of the day with respect to the corresponding value at the preceding midnight. These components define the electric currents in the ionosphere and magnetosphere together with their induced parts in the conducting regions inside the solid Earth.The main theme of the paper is to identify if the ionospheric currents that affect the diurnal variations of the Copyright c The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB. mean magnetic field in this 60• W geographic region. H is the pe...

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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 (

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