On the Regulation of the Geospace System by Solar-Wind/IMF Discontinuities and Ionospheric Outflow.

[摘要] The terrestrial environment is controlled by many external factors, some of whichcan potentially drive strong geomagnetic storms. In this dissertation, how the terrestrialmagnetosphere-ionosphere (MI) system responds to solar wind variations andthe subsequent self-modulation within the MI system are investigated by utilizing theSpace Weather Modeling Framework (SWMF).Studies of an interplanetary magnetic field (IMF) southward turning demonstratethat the arrival of the IMF discontinuity at the bow shock does not immediatelydisturb the ionosphere. With a solar wind speed of 400 km/s, the delay is about 10minutes later. In addition, we find that a sudden increase in the solar wind densityproduces a two-phase response observed in ground-based magnetic perturbations andionospheric potentials. The two phases are ascribed to the emergence of two successivepairs of field-aligned currents (FACs), which are caused respectively by dusk-to-dawninductive electric fields due to a sudden compression of the magnetosphere and bymagnetospheric vortices associated with the high-pressure gradient under northwardIMF conditions or associated with large shear flows under southward IMF conditions.Although actual observations suggest that not all the solar wind density increaseevents are associated with a two-phase pattern, numerical simulations confirm theexistence of the two-phase response. In addition to the two-phase response, thesudden compression launches Earthward-propagating waves that are further reflectedmultiple times between the Earth and magnetopause boundaries, resulting in multiplesets of the two-phase response.Although the solar wind variations create disturbances in the MI system, one of theself-modulation processes within the MI system, the ionospheric heavy ion outflowinto the magnetosphere, is equally important. The dayside cusp-origin heavy ionoutflow significantly disturbs the magnetotail and provides significant energy to thering current; while direct leakage of the heavy ions into the inner magnetosphere fromthe nightside aurora provides little geomagnetic feedback. Sufficient mass loadinginto the magnetosphere can lower the threshold of the Kelvin-Helmholtz instability,triggering surface waves more easily near the equatorial magnetopause boundary,changing the efficiency of the solar wind-magnetosphere coupling.

[发布机构] University of Michigan

[效力级别] Atmospheric

[关键词] Regulation of the Terrestrial System by External/Internal Variations;Atmospheric;Oceanic and Space Sciences;Science;Space and Planetary Physics