GPS Ionospheric mapping and disturbances during geomagnetic storms and earthquakes
【摘要】：The total electron content (TEC) and electron density profiles are two key parameters in the ionosphere. Therefore, imaging the TEC and electron density profile is very crucial to determine the status of the ionospheric activities. In the past decades, different observing instruments have been developed and used to gather information on the ionosphere, such as ionosonde, scatter radars, topside sounders onboard satellites, in situ rocket and satellite observations and LEO (Low Earth Orbit) GPS occultation measurements. However, most instruments are expensive and also restricted to either the bottomside ionosphere or the lower part of the topside ionosphere (usually lower than 800 km), such as ground based radar measurements. Nowadays, GPS satellites in high altitude orbits (~20,200 km) are capable of providing details on the structure of the entire ionosphere, even the plasmasphere. In this paper, a Regional Ionospheric Mapping and Tomography (RIMT) tool was developed, which can be used to retrieve 2-D TEC and 3-D ionospheric electron density profiles using ground-based or space-borne GPS measurements. Some results are presented from the RIMT tool using regional GPS networks in South Korea and validated using the independent ionosonde. GPS can provide time-varying ionospheric profiles and information at any specified grid related to ionospheric activities and states. For example, the responses of GPS-derived parameters at the ionospheric F2-layer to the 20 November 2003 geomagnetic storm are investigated over South Korea. It has found that a fairly large increase in the electron density at the F2-layer peak (the NmF2) (positive storm) is observed during this storm, which is accompanied by a significant uplift in the height of the F2 layer peak (the hmF2). The F2-layer peak height uplift and NmF2 increase are mainly associated with a strong eastward electric field, and are not associated with the increase of the O/N2 ratio obtained from the GUVI instruments aboard the TIMED satellite. In addition, the coseismic ionospheric disturbances on this event are investigated from national GPS network observations. It has found an intensive N-shape shock-acoustic wave propagating south-eastward at about 600 m/s. The wave front of the N-shape is parallel with the earthquake rupture direction (from NE to SW). It is almost consistent with seismometer, indicating the co-seismic ionospheric TEC disturbances were mainly derived from the main shock.