2004 Fiscal Year Final Research Report Summary
Studies on generation and propagation processes associated with magnetospheric substorms
| Project/Area Number |
14540415
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (C)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Space and upper atmospheric physics
|
|---|
| Research Institution | Yamaguchi University |
|---|
Principal Investigator |
ITONAGA Masahiro Yamaguchi University, Faculty of Education, Professor, 教育学部, 教授 (60213104)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
FUJITA Shigeru Meteorological College, Associate Professor, 助教授
|
|---|
| Project Period (FY) |
2002 – 2004
|
| Keywords | Alfven wave / field-aligned current / ionosphere / magnetosphere / MHD simulation / Pi2 pulsation / quasi-oscillatory current wedge / substorm |
|---|
| Research Abstract |
At the initial stage of a substorm expansion phase, the perturbations of field-aligned current (FAC) are generated efficiently around the dawn- and dusk-side edges of auroral breakup region centered at L = 9 and LT = 22.5 hour by an increase of the plasma pressure therein. These perturbation FACs propagate along magnetic field lines and reflect at the polar ionospheres. As a result, quasi-periodic field line oscillations of shear Alfven waves occur at auroral latitudes. The sense in flow direction of the perturbation FAC associated with the field line oscillation at the dawn-side edge of the breakup region is opposite to that at the dusk-side edge. These perturbation FACs with opposite senses are closed via the ionospheric and cross-tail perturbation currents. Thus, a quasi-oscillatory current wedge with a time scale of 1 to 2 min is formed and it is a main source of Pi 2 pulsations. The cross-tail portion of the quasi-oscillatory current wedge generates a fast magnetosonic wave. During its passage within the magnetosphere, the magnetosonic wave excites shear Alfven waves owing to the effects of inhomogeneous medium and curvilinear magnetic field line. These waves are secondary sources of Pi2 pulsations. On the basis of such a scenario a propagation model of Pi2 pulsations in the magnetosphere is constructed and its validity has been confirmed observationally. Three-dimensional MHD simulations also suggest the validity of the above scenario and propagation model.
|
