SM43D-1621
Effects of Dipole Tilt Angle on Geomagnetic Activities
Relationships between the clock angle of the interplanetary magnetic field (IMF) and each of the AL and AU indices are examined under various Earth's dipole tilt angles using the observational data for a period of 1978 to 1988. This study is performed by correlating the interplanetary magnetic field data obtained from the IMP 8 satellite, the AL and AU indices with the corrected seasonal variations, and the dipole tilt angle. It is found that for any value of the IMF clock angle, the values of AL and AU decrease when the dipole tilt angle becomes larger. It suggests that the geomagnetic activities strongly depend on the dipole tilt angle. Furthermore, our results are consistent with the semiannual variation of the geomagnetic activity and the predicted relationships between the geomagnetic activity, the IMF clock angle, and the dipole tilt angle, derived from the MHD simulation.
SM43D-1622
Geomagnetic Activity and Eclipse Coronae
Geomagnetic proxies (presented by various geomagnetic indices) are analyzed during the periods close to the total solar eclipses in the past. Geomagnetic variations are traces of the solar wind and interplanetary magnetic field, and of the topological evolution of large-scale magnetic fields on the Sun. We have considered historical coronal drawings in the relation to the phase of geomagnetic and sunspot cycles. It is established a coronal shape of "maximum" and "minimum" geomagnetic types. Any significant long-term trends are not detected in the changing of coronal structures. We suggest that secular increasing of AA geomagnetic indices is mainly due to the internal geomagnetic variability but it is not a response to external solar forcing.
SM43D-1624
On the difference between active and steady magnetospheric response to moderate solar wind IMF driving
Recently we have examined the differences between steady magnetospheric convection (SMC) and sawtooth behavior through global MHD simulations of 2 specific events; the SMC event of February 3, 1998 and the Sawtooth event of April 18, 2002. Since then we have explored whether the qualitative difference in magnetospheric activity, clear in both the observations and simulations, is due to quantitative differences in solar wind conditions. To this end, we have rerun the Feb 98 event with several modifications of the observed solar wind; 1) increased the IMF Bz to raise the level of IMF Ey to about the April 2002 level, 2) increased Vx to get the same increase in Ey, and 3) increased solar wind density to match the higher kinetic pressure in (2) with no Ey change. Preliminary results indicate that case (1) shows significantly less activity while case (2) exhibits significantly more. With our latest run (3), we will discuss in this presentation the changes due to variations in the 2D parameter space of IMF Ey and Alfven Mach Number/kinetic pressure.
SM43D-1625 [WITHDRAWN]
A Numerical Study of the Ionospheric Environment for Different Strengths of the Geomagnetic Main Field
Effects of the strength of the geomagnetic main field on the ionosphere are very complex because almost all the physical parameters in the ionosphere depend more or less on the geomagnetic field either directly or indirectly. The ionospheric conductivities depend on the geomagnetic main field, and therefore, electric currents in the ionosphere change with the strength of the magnetic field. Since auroral precipitation and high-latitude ionospheric convection are associated with magnetospheric processes, change in the strength of the main magnetic field would alter high-latitude ionospheric processes. The thermospheric structure and dynamics are also altered by changes in Joule heating and ion convection, indicating that ionospheric dynamo and magnetosphere-ionosphere interaction are affected by the magnitude of the main magnetic field. Numerical modeling of the magnetosphere-ionosphere-thermosphere system could be a useful tool for understanding such complicated processes, although current models have some assumptions and approximations based on present conditions of geospace environment. We will focus on changes in the ionospheric environment including electrodynamic processes. We will present some results of our study of ionospheric environment for different strengths of the geomagnetic main field using our magnetosphere-ionosphere-thermosphere model.