An improved model equatorial electrojet with a meridional current system

Abstract

The σyy model for the equatorial electrojet presented earlier is revised by including a meridional current system, thus making the current density divergence‐free. Using a spherical harmonic expansion for the geomagnetic field, a model electrojet is constructed for each of the longitudes of 0°, 40°, 80°, 180°, and 280°E. It is shown that the essential feature of the meridional current system is the existence of two current loops, one on each side of the dip equator and with an equatorward current in the lower E region, an upward current over the dip equator, and a return current flowing in the upper E region. The intensities of the electrojet and the associated meridional current are significantly dependent on longitude, being strongest over Peru and weakest over India. The new model predicts a reversed (westward) current in a thin, narrow layer located at several degrees off the dip equator, which is due to a reversal of the vertical polarization field. The meridional current loop creates a toroidal magnetic field of an intensity comparable with that of the main electrojet.

POGO Observations Of The Equatorial Electrojet

“…We can see from Figure 19 which is reproduced from Sugiura and Poros (1969), that the computed current pattern at 80°west longitude is displaced about 0.5°south of the dip equator. This displacement is due to the fact that the field is weaker to the south at these-longitudes.…”

“…It is interesting to note that the dip equator computed from the satellite derived model has too low a dip at Huancayo and thus places the dip equator just north of the average electrojet minima. A similar tendency is seen over India where the current model by Sugiura and Poros (1969) predicts very little displacement.…”

“…No one has yet attempted to use such theoretical models as that of Sugiura and Poros (1969), to see whether there is agreement in the shape of the curves, and if so, 3 what might be the parameters. This model does contain a very weak westward current.…”

“…The most recent development of a model electrojet is that of Sugiura and Poros (1969) who showed that for a reasonable model of ionospheric parameters and magnetic field, and some assumptions on the behavior of the eastward current and boundary conditions, the electrojet width is of the order of 400 km flowing over an altitude range from 100 to 120 km. Other facets of their results include the presence of an equally strong meridional component of flow in two cells which center 2-3°on each side of the dip equator in a direction so that the horizontal flux is eastward inside the south cell and westward within the north.…”

“…More theoretical work on the possible current structures by Untiedt (1967) and by Sugiura and Poros (1969) established that the east-west current flow is accompanied by two cells of toroidal flow in the meridian plane near the equator, Radar measurements near Peru (Cohen and Bowles, 1963) have established that an instability occurs in the electrojet and is detectable after the current rises past a threshold value. The effect of this phenomena on electrojet theory appears to have not yet been developed.…”