Distribution Of Ionospheric Currents Research Articles

Day‐to‐day and average magnetic variations along the IMS Alaska Meridian Chain of observatories and modeling of a three‐dimensional current system

The daily magnetic variations above 60° in magnetic latitude are studied by using records from the International Magnetospheric Study Alaska meridian chain of observatories. Several days with activity varying from moderate to disturbed are chosen to study day‐to‐day variations, namely, the daily variability of polar magnetic variations. The average daily magnetic field variations and the equivalent current pattern are also obtained by using the successive records between March 9 and April 27, 1978. They represent the disturbance condition on a moderately disturbed day (the average ΣKp value during this period was 23o). The equivalent current pattern reveals clearly the large‐scale features, in particular the so‐called ‘two‐cell’ pattern. Then, the distribution of the ionospheric currents and the field‐aligned current are computed on the basis of the average daily magnetic field variations. It is shown that the computed ionospheric current distribution has little resemblance to the two‐cell pattern. It is concluded that the main part of the ionospheric currents must be fed by field‐aligned currents with a distribution similar to that inferred from Triad satellite data.

The SQP magnetic variation, equivalent current, and field‐aligned current distribution obtained from the IMS Alaska Meridian Chain of magnetometers

The solar quiet day daily variation (Sqp) in the polar region is studied by using magnetic records on March 12, 1978 (ΣKp = 6−), and on March 25, 1978 (ΣKp = 6−), from the International Magnetospheric Study Alaska meridian chain. The results are somewhat different from those obtained by earlier studies which dealt with an exceptionally quiet day (ΣKp = ∼1+). The results are discussed in terms of the ionospheric current distribution and field‐aligned current distribution, computed on the basis of the Sqp magnetic field vector distribution. On a quiet day the type I and type II field‐aligned currents and the connected ionospheric currents are mostly confined in the dayside half of the polar region. Comparing these current distributions with those on a moderately disturbed day, one can see that both current systems extend along the auroral oval to the nightside half of the polar cap on a disturbed day. It is also shown that it is not justifiable to infer the convection pattern by using the distribution of magnetic vectors (thus by assuming that Sqp variations are caused mainly by the Hall current).

Distribution of ionospheric currents induced by the solar wind interaction with Venus

The electric currents induced in the atmosphere of a non-magnetic planet such as Venus by the interaction of the solar wind satisfy a generalized Ohm's Law relationship with tensor conductivity. The distribution of these currents within the planetary ionosphere may be calculated by a variational technique which minimizes the Joule heating over the ionospheric volume. In this paper, we present the development of the variational technique, and apply it to a model of the solar wind interaction with Venus. Potential and current distributions are shown, and the use of these distributions in determining convective transport patterns of planetary ions is discussed.

Rocket measurements of current distribution in a normal and an intense equatorial electrojet

Two Petrel rockets, each carrying a rubidium magnetometer, were launched from Thumba, at times close to the diurnal electrojet peaks, on different days. The peak electrojet intensity during one of the days was unusually large, approaching twice that of the other day. A comparison is made of the ionospheric current distribution during these two events.

Field-aligned and ionospheric currents

Zmuda and Armstrong (1974) showed that the field-aligned currents consist of two pairs; one is located in the morning sector and the other in the evening sector. Our analysis of magnetic records from the TRIAD satellite suggests that in each pair the poleward field-aligned current is more intense than the equatorward current, a typical ratio being 2:1. This difference has a fundamental importance in understanding the coupling between the magnetosphere and the ionosphere. We demonstrate this importance by computing the ionospheric current distribution by solving the continuity equation ▽ . I = j ∥ using the “observed” distribution of j ∥ for several models of the ionosphere with a high conductive annular ring (simulating the auroral oval). It is shown that the actual field-aligned and ionospheric current system is neither a simple Birkeland type, Boström type nor Zmuda-Armstrong type, but is a complicated combination of them. The relative importance among them varies considerably, depending on the conductivity distribution, the location of the peak of the field-aligned currents, etc. Further, it is found that the north-south segment of ionospheric current which connects the pair of the field-aligned currents in the morning sector does not close in the same meridian and has a large westward deflection. Thus, it has an appreciable contribution to the westward electrojet. One of the model calculations shows that the entire north-south closure current contributes to the westward electrojet.