Simultaneous observations of a pulsation event from the ground, with balloons and with a geostationary satellite on August 12, 1978

Extensive three-dimensional computer simulations of the magnetosphere-ionosphere (M-I) coupling are performed to study self-excitation of an auroral arclike structure with special emphasis on (1) nonlinear evolution of the feedback instability in the M-I coupling system, (2) controlling mechanisms of the arc structure, (3) formation of a field-aligned electric potential structure in association with the development of the feedback instability, and (4) effects of the parallel potential generation on the development of the arclike structure. The present study takes the first step toward the theoretical understanding of the M-I coupling system with parallel potentials. As was already shown by Sate [1978] and Watanabe and Sate [1988], it is reconfirmed that the feedback instability produces a longitudinally elongated, latitudinally striated structure where the upward field-aligned current and the ionospheric density are locally enhanced. On top of this the present extended study reveals the following important new features: The global distribution of the striation structure is primarily governed by the magnetospheric convection pattern and the ionospheric density distribution. There appears a significant dawn-dusk asymmetry in the arc formation, even though the apparent geometrical relationship is symmetric. This dawn-dusk asymmetry reflects the geometrical fact that the ionospheric Pedersen current closing the magnetospheric current is antisymmetric with respect to the noon-midnight plane, while the self-closed Hall current is symmetric. The recombination effect plays a significant role in the global, as well as local, development of the arc structure. The nonlinearity of recombination, in conjunction with the closure of an arc-associated local field-aligned current system, acts to destroy an old arc and creates a new arc in a different but adjacent position. This results in a peculiar dynamic evolution of the arclike structure. A V-shaped field-aligned potential structure is created in association with an arc structure, when we introduce the parallel anomalous resistivity. The nonlinear phase mismatching due to the parallel resistivity reduces the growth rate of the feedback instability, and suppresses the growth of the arc structure. When the effect of precipitating hot electrons is taken into account, the ionospheric density is considerably enhanced locally at the foot of the field lines where the field-aligned potential is generated. An oscillatory behavior is observed in the development of the ionospheric density, field-aligned current and potential. The period seems to be governed by the Alfv•n bounce time and the ionospheric density. INTRODUCTIONAuroral phenomena in the Earth's polar region are considered to occur in the final stage of the energy transport processes from the solar wind into the ionosphere through the energy conversion processes in the magnetospheric boundary region, the magnetotail, and the acceleration region of auroral electrons. Auroras are, as a whole, classified, according to their acti...

Section: In Our Simulation Modelmentioning

confidence: 99%

Comprehensive simulation study on local and global development of auroral arcs and field‐aligned potentials

Watanabe¹,

Oya²,

Watanabe³

et al. 1993

“…It is interesting to find Pi 2 pulsations in several parameters observed both on the ground, on balloons and on GEOS-2. These data should be analyzed in as much detail as was done by Iversen et al [1984] for Pc 5 pulsations. They may then be suitable for comparison with the new theory for Pi 2 pulsations by Rothwell et al [1986].…”

Section: The Ion Phase Space Density Near Midnight At Geosynchronous mentioning

confidence: 99%

Different phases of a magnetospheric substorm on June 23, 1979

Tanskanen¹,

Kangas²,

Block³

et al. 1987

Self Cite

A detailed case study was carried out of a magnetospheric substorm on June 23, 1979. Satellite, balloon and ground based particle and field data were used to correlate observations covering an extended area both in longitude and in latitude. The loading phase of the substorm was characterized by an equatorward convex, southward moving precipitation boundary. During the equatorward motion a hardening of the electron spectrum is seen. We show that betatron acceleration is stronger than Fermi acceleration for earthward converting particles in a dipolelike field, and that the reverse is true for a taillike field. It is argued that the observed precipitation front represents an ionospheric mapping of an injection boundary. Energy dependent increases of the ion phase space density during the loading phase can be explained in terms of an earthward displacement of the inner edge of the neutral sheet current. Pi 2 pulsations on the satellite and on the ground are present both at substorm onset and at subsequent intensifications. Evidence is given for plausible correlation between changes in the IMF and variations in ionospheric electric fields as observed on balloons. It is suggested that changes of the IMF from south to north may have triggered the substorm and expansion phase intensifications.

“…The amplitude of the electric field is higher in the ionosphere than at geostationary orbit. A reasonable mapping factor is 6 [Walker, 1980;Iversen et al, 1984]. For the height-integrated Pedersen conductivity a typical value of 4 S is taken [Greenwald and Walker, 1980].…”

Section: P = « • Y•pei 2 Da Where Y• Is the Height-integrated Pedersmentioning

confidence: 99%

A statistical study of dayside magnetospheric electric field fluctuations with periods between 150 and 600 s

Junginger¹,

Geiger²,

Haerendel³

et al. 1984

Self Cite

One hundred eighty‐six days of electric field data from the GEOS 2 electron beam experiment have been used to study magnetospheric fluctuations at geostationary orbit with periods between 150 and 600 s. While fluctuations are nearly always present in the electric field data from the dayside magnetosphere with typical amplitudes between 0.2 and 0.5 mV/m, it is often hard to find well‐defined concurrent pulsations in the GEOS 2 magnetic field data. Most events occur near noon and have the same characteristics: They are toroidal and nearly linearly polarized, the sense of polarization and the orientation angles of the polarization ellipses change sign near noon, the instantaneous frequency of the fluctuations is correlated with the instantaneous electron density, and in a given sector of the magnetosphere the sense of polarization depends on the frequency. There is strong evidence that these fluctuations are fundamental mode eigenoscillations of field lines in the vicinity of the spacecraft which are generated in the inhomogeneous plasma of the magnetosphere by some kind of solar wind‐driven surface waves at the magnetopause or at the low‐latitude boundary layer.