Electric Current Approach Research Articles

A new understanding of why the aurora has explosive characteristics

ABSTRACT This article describes a new understanding of the explosive nature of auroras, called auroral substorms, on the basis of a series of processes, from power supply (dynamo), circuit/current, and dissipation (auroral substorms) – the electric current approach, in which the magnetosphere or more specifically the primary magnetosphere-ionosphere coupling system (the primary M-I system) plays a crucial role. The primary M-I system has an anomaly; it cannot dissipate the dynamo power much for about 1 h after the dynamo power becomes above 1011 w. This anomaly is due to a low conductivity of the quiet-time ionosphere to dissipate increasing power. Thus, the power is accumulated in the inner magnetosphere (at about 6 Re; Re = earth’s radius) as magnetic energy, inflating the inner magnetosphere. When the accumulated energy reaches to about 1016 J, the primary M-I system seems to become unstable and unload impulsively the accumulated magnetic energy, deflating the magnetosphere. This deflating process generates the secondly M-I system, which is associated with an electric field 5–50 mV/m and field-aligned currents, ionizing the ionosphere and increasing the conductivity. Therefore, the primary M-I system can perform like an ordinary electrical system. It is this particular nature that exhibits explosive auroral displays. This paper describes systematically and semiquantitatively key points of this series of processes based on a few decades of work. The electric current approach is rather ‘new’ in substorm research and thus is rudimental at its development stage, so that n crucial issues are mentioned for future studies at the end.

A Review of Studies of Geomagnetic Storms and Auroral/Magnetospheric Substorms Based on the Electric Current Approach

The progress of space physics is reviewed from my personal point of view, particularly how I have reached my present understanding of auroral substorms and geomagnetic storms from the time of the earliest days of space physics. This review is somewhat unique in two ways. First of all, instead of taking the magnetic field line approach (including magnetic reconnection), I have taken the electric current approach; it consists of power supply (dynamo), transmission (currents/circuits), and dissipation (auroral/magnetospheric substorms). This is the basic way to study electromagnetic phenomena and it is much more instructive in understanding the physics involved in the chain processes. Secondly, this is not a textbook-like review, but it is hoped that my humble experience may be useful to see how a new science of space physics has evolved with a number of controversies. On the other hand, it can be seen that the electric current approach is still in a very rudiment stage. Thus, new generations of researchers are most welcome in taking this new way of studying auroral/magnetospheric substorms and geomagnetic storms.

Four Subjects in Solar Physics from the Point of View of the Electric Current Approach

Four major subjects in solar physics, the heating of the corona, the cause of the solar wind, the formation of sunspots and the cause of solar flares, are discussed on the basis of the electric current approach, a sequence of processes consisting of power supply(dynamo), transmission (currents/circuits) and dissipation(high coronal temperature, solar wind, sunspots and solar flares).This is because the four subjects have hardly been considered in terms of the electric current approach in the past, in spite of the fact that these subjects are various manifestations of electromagnetic processes. It is shown that this approach provides a new systematic way of considering each subject; (1) the long-standing issue of the coronal temperature, (2)the long-standing problem on the cause of the solar wind, (3)the presence of single spots(forgotten or dismissed in the past) and its relation to unipolar magnetic regions and (4) the crucial power/energy source and subsequent explosive processes of solar flares. The four subjects are obviously extremely complicated and difficult subjects, but it is hoped that the electric current approach might provide a new insight in considering the four subjects.

Electric Current Approach Studying Both Auroral Substorms and Solar Flares Together

Auroral substorms and solar flares are basically various manifestations of electromagnetic energy dissipation, so that it is useful to consider both phenomena in terms of a chain of processes, consisting of power supply (dynamo), transmission (currents/circuits) and dissipation (auroral substorms, solar flares), the electric current approach. In this short review, we briefly describe both phenomena together on the basis of the chain process. It is shown that the introduction of a dynamo process in this consideration provides a step-by-step way of studying both phenomena. It is shown: (a) Both the solar wind-magnetosphere dynamo and a photospheric dynamo proposed by Lee et al. (1995) have enough power to accumulate enough energy for the explosive features of both phenomena, respectively. (b) For substorms, the power is accumulated in the inner magnetosphere and inflates it, and for flares the power is likely to be accumulated in a loop current along and above two-ribbon flares. (c) For substorms, the energy release (unloading) process deflates the inner magnetosphere, resulting in an earthward electric field, and for flares the disruption of the loop current suggested by Alfven (1950) may be responsible for the energy release. (d) The processes in (c) are responsible for the explosive features of both phenomena.

On the explosive nature of auroral substorms and solar flares: The electric current approach

Both auroral substorms and solar flares have explosive nature. Since both are mostly various manifestations of electromagnetic energy dissipation processes, it is basic to consider both phenomena as a chain of electromagnetic processes, which consists of a dynamo process as the power supply, power transmission and manifestations of dissipative processes (auroral substorms and solar flares)--the electric current approach. Based on this view, since both phenomena are powered by a dynamo and have an explosive component, they are likely to have the component directly driven (DD) by the dynamo and the component which results from the unloading (UL) process of accumulated energy (generated also by the dynamo). Thus, it is crucial to identify and distinguish the dynamo-produced power/energy/dissipation into two components in both morphology and theory. In this paper, since we have taken this approach for auroral substorms, we attempt to apply it for solar flares by adopting a photospheric dynamo theory by Lee et al. (1995) and Choe and Lee (1996a, 1996b); their dynamo process takes place on the photosphere under a magnetic arcade. It is shown that their dynamo can supply both the power and energy needed for flares, providing the arcade field-aligned currents for the two-ribbon Hα emission (DD) and the current loop along the dark filament above the arcade for the explosive process (UL).

The Explosive Characteristics of the Aurora: The Electric Current Line Approach

The aurora shows explosive activities a few times in 24 hours on a moderately active day. This specific phenomenon is called the auroral substorm, which consists of the growth, expansion and recovery phases; the explosive activities occur during the expansion phase. As an introduction, the explosive activities of the aurora are morphologically described first on the basis of ground-based all-sky and satellite images. In terms of theoretical understanding, the processes for the explosive activities have been considered almost exclusively in terms of “the magnetic field line approach” in the past, including the process of magnetic reconnection. Instead, in this paper, we consider the processes in terms of “the electric current line approach”. This approach requires that the whole process of auroral substorms should be considered as a chain of processes, which consists of power supply (dynamo), transmission (currents/circuits) and dissipation (auroral substorms). An increased power of the solar wind-magnetosphere dynamo (≈ 5x1018 erg/s or 1011w) intensifies the electric currents mainly in the main body (just outside of the ring current) of the magnetosphere, resulting in accumulating energy in its inductive circuit and inflation of the magnetosphere. When the accumulated energy reaches about 5x1022 ergs (5x1015 J), the magnetosphere tends to become unstable (because of current instabilities). As the current intensity is reduced as a result, the magnetosphere is deflated. It is suggested that it is in this deflation process, during which the accumulated energy is unloaded, and an earthward electric field (5-50 mV/m) is produced on the equatorial plane, establishing the current system (the UL current system), which is responsible for the expansion phase, including the most characteristic features of the expansion phase, such as the poleward advance of the aurora and the development of the auroral electrojet. The electric current approach is rather new and needs much more effort to develop.

Photospheric dynamo as the power supply process for solar flares: Electric current approach

Photospheric dynamo as the power supply process for solar flares: Electric current approach

The electric current approach in the solar–terrestrial relationship

Abstract. The sequence of phenomena consisting of solar flares, coronal mass ejections (CMEs), auroral substorms, and geomagnetic storms is mostly a manifestation of electromagnetic energy dissipation. Thus, first of all, it is natural to consider each of them in terms of a sequence of power supply (dynamo), power transmission (electric currents/circuits), and dissipation (mostly observed phenomena), i.e., as an input–output process and the electric current line approach. Secondly, extending this concept, it is attempted in this paper to consider the whole solar–terrestrial relationship in terms of electric currents. This approach enables us to follow through not only the sequence in solar flares, auroral substorms, and geomagnetic storms but also to connect all phenomena naturally as a continuous flow of magnetic energy (V[B2∕8π]) from the sun across the magnetopause. This consideration gives some insight into all the processes involved equally well compared with the magnetic field line approach, which has been adopted almost exclusively in the past.

A Measurement System for the Complex Far-Field of Physically Large Antenna Arrays Under Noisy Conditions Utilizing the Equivalent Electric Current Method

Precipitation in the form of snow or rain could severely degrade the performance of large antenna arrays, in particular if knowledge about the beam shape and pointing direction in absolute numbers is necessary. In this paper, a method of estimating the far-field of each individual antenna element using the equivalent electric current approach is presented. Both a least squares estimator and a Kalman filter was used to solve the resulting system of equation and their performance was compared. Simulation results shows that the estimated far-field for one antenna element is very accurate if there is no noise on the signal. During noisier conditions the Kalman filter gives less noisy results while the systematic errors are slightly larger compared to the least squares estimator.