Source, Evolution, and Properties of Non-Parker-spiral IMF and Its Role on Geomagnetic Activity.

[摘要] The most important driver of geomagnetic activity has been shown to be out of ecliptic or non-Parker-spiral interplanetary magnetic field (IMF), especially large-amplitude and long-duration (LALD) southward IMF. However, neither current solar/heliospheric models provide accurate forecasts of IMF Bz component, nor they provide them at all. This thesis combines in situ observations of magnetic field,plasma, and ion composition with remote sensing measurements of solar features as well as predictive modeling of the solar wind and IMF to understand the source, evolution and properties of IMF Bz. We find that the integrated duration and number of Bs-events follow the sunspot number when Bz < -5 nT. We suggest that the emergence of the non-Parker-spiral is not the result of random fluctuations of the solar wind or IMF. We also find the major contribution to the LALD IMF Bs events is from solar wind transients (ICME, SIR, Alfvenic fluctuations), and that the low-latitude coronal hole (LLCH) with nearby solar activity in the closed magnetic field configuration is the solar source of CIR with LALD IMF Bs intervals. We analyze the correlation between the LALD IMF Bs-events and geomagnetic activity indices and find that the strongest storms and substorms are not associated with the same type of event, and noted that great Bs events (Bz < -10 nT, t > 3 hrs) do not always induce large storms. We also point out that MC, ejecta, and SIR drive storms in different ways, and that while Alfvenic Bs-events are relatively weak in triggering geomagnetic storms, they are possible drivers for large-scale ULF wave oscillations in the Earth;;s magnetosphere. We also show that the probabilistic forecasting technique provides a tool for predicting the occurrence rate of geomagnetic activity based on a combination of solar wind quantities, obtainable from either measurements or models. We finally propose that the evolution of the active region adjacent to the LLCH, and the geometric parameters of the LLCH are important to determine the intensity of the IMF Bs intervals observed at 1 AU, which could be used to improve the current spaceweather forecasting.

[发布机构] University of Michigan

[效力级别] Predictive Model

[关键词] Space Weather;Predictive Model;Solar Wind/Interplanetary Magnetic Field;Atmospheric;Oceanic and Space Sciences;Science;Atmospheric, Oceanic and Space Sciences