成大物理系徽
高能組博士班專題討論 (Seminar)
演講題目: Probing The Space Weather Effects To The Earth's Space Environment By The Global Positioning System (GPS)
演講人: 林建宏 教授
Prof. Charles Lin
成大太空天文與電漿科學研究所
演講時間: 2008 年 12 月 4 日
星期四  下午 4 : 10
演講地點: 國家理論科學研究中心二樓演講廳(R203)
內容摘要:  
Abstract

The space weather effects originated from the Sun have great impacts to the Earth’s space environment from the magnetosphere to the upper atmosphere. These magnetic disturbances affect the satellites, satellite communications, positioning precision, electrical power grids, oil drills, and aviation safety. Among these space weather impacts, the positioning precision is one of the most important effects, since the applications of global positioning system (GPS) have grown up rapidly in widely aspects of everyday life. One of the major error sources of the GPS signals comes from the ionosphere which is a layer of charged ionized particles located at approximately 80 - 1000 km above the Earth's surface and has been defined as "the part of the Earth's upper atmosphere where ions and electrons are present in quantities sufficient to affect the propagation of radio waves." The ionosphere is formed by the absorption of the solar EUV/UV radiations in the Earth’s upper atmosphere, which produces appreciable photoionization leading to a partially atmospheric region.
On the other hand, with increasing availability of global observations from mass ground-based stations and innovative satellite missions carrying the space-borne receivers of the GPS, studies of the Earth’s ionosphere have entered a new era. Through the techniques built for retrieving ionospheric information from received signals, receiver networks of the GPS provide continuous observations of the ionosphere electron density structure globally. These widely available and continuous observations provide unprecedented details of the ionosphere and, therefore, new plasma structures are found, such as the ionospheric drainage plume as the signature of the plasmaspheric tail often seen in the North America, the large-scale and meso-scale travel ionospheric disturbances (LSTIDs and MSTIDs) seen over Japan, the longitudinal wavenumber four structure of the equatorial ionosphere produced by the atmospheric waves originated from terrestrial weather system, and the anomalous nighttime enhancement of the electron density at mid- and high-latitudes. These new ionospheric structures result from either the magnetosphere-ionosphere or the ionosphere-atmosphere coupling processes and greatly improve our understanding of the ionosphere dynamics. In this presentation, examples of these new ionospheric plasma structures and the corresponding physical mechanisms are presented and discussed. Additionally, perspective studies that can be further reached by GPS observations will also be addressed.