Computer Science – Sound
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sm22b11c&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SM22B-11
Computer Science
Sound
2752 Mhd Waves And Instabilities, 2794 Instruments And Techniques
Scientific paper
Remote sensing of the magnetospheric plasma density from the ground provides an important means to understand the global dynamics of the magnetosphere. In particular, the only way identified to sound the mass density of the plasma is to measure the characteristics of the geomagnetic field perturbations driven by the MHD waves in the magnetosphere. A well-tested technique, namely the gradient method, using the data from pairs of closely separated ground magnetometers has shown promise of being an effective way sounding the magnetosphere. Detecting the resonance of magnetospheric field lines, the gradient method is analogous to the normal mode method in terrestrial seismology and helioseismology. In this study, we present a new approach to sound the magnetosphere by using the travel time of the preliminary impulse in the sudden impulse events. The preliminary impulse is caused by the sharp transition when the discontinuity in solar wind dynamic pressure is hitting the magnetosphere. The impulse travels in the magnetosphere via the fast mode and the converted Alfven mode, and the consequential geomagnetic field perturbations mainly come from the Alfven wave whose energy is guided along the field. From the observations by GPS synchronized ground magnetometers, we found that the difference in the arrival time of the preliminary impulse can be distinguished. The travel time pattern is also consistent with the propagation of MHD waves. A parametric density model can therefore allow us to estimate the plasma density. This alternative approach of sounding the magnetosphere is more similar to the body wave travel times method in terrestrial seismology.
Chi Peter J.
Russell Christopher T.
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