DSpace collection: 期刊論文

Vertical and longitudinal electron density structures of equatorial E- and F-regions

title: Vertical and longitudinal electron density structures of equatorial E- and F-regions abstract: From global soundings of ionospheric electron density made with FORMOSAT 3/COSMIC satellites for September 2006-August 2009, day-night variations in vertical and longitudinal structures of the electron densities in equatorial E-and F-regions for different seasons are investigated for the first time. The results reveal that the wavenumber-3 and wavenumber-4 patterns dominated the nighttime (22:00-04:00 LT) F-region longitudinal structures in solstice and in equinox seasons, respectively. In daytime (08:00-18:00 LT) F-region, the wavenumber-4 patterns governed the longitudinal structures in the September equinox and December solstice, and wavenumber-3 in March equinox and June solstice respectively. A comparison of the daytime and nighttime longitudinal electron density structures indicates that they are approximately 180 degrees out of phase with each other. It is believed that this out of phase relation is very likely the result of the opposite phase relation between daytime and nighttime nonmigrating diurnal tidal winds that modulate background E-region dynamo electric field at different places, leading to the day-night change in the locations of the equatorial plasma fountains that are responsible for the formation of the F-region longitudinal structures. Further, a good consistency between the locations of the density structures in the same seasons of the different years for both day-time and nighttime epochs has been noticed indicating that the source mechanism for these structures could be the same.

Validation of Earthquake Precursors-VESTO Preface

title: Validation of Earthquake Precursors-VESTO Preface

Uneven compression levels of Earth's magnetic fields by shocked solar wind

title: Uneven compression levels of Earth's magnetic fields by shocked solar wind abstract: The magnetopause is the boundary where the reduced solar wind dynamic pressure is equal to the magnetic pressure of the Earth's outer magnetosphere. With hundreds of magnetopause crossings identified from the THEMIS data, we estimate a ratio (f) of the compressed magnetic field just inside the subsolar magnetopause to the purely dipolar magnetic field. Previous theoretical studies reported that the ratio f was nearly independent of the subsolar standoff distance (r(0)). Here we report that the ratio f is linearly proportional to r(0) for both northward and southward interplanetary magnetic field (IMF). The proportionality constant for southward IMF is larger than that for northward IMF, implying that the compression level of the magnetic field by inward magnetopause for southward IMF is smaller than that for northward IMF.

Tracking the epicenter and the tsunami origin with GPS ionosphere observation

title: Tracking the epicenter and the tsunami origin with GPS ionosphere observation abstract: The global positioning system (GPS) can be used to monitor the seismic perturbation induced by the 2011 off the Pacific coast of Tohoku Earthquake (magnitude 9.0), Japan, on March 11, 2011, and to trace the tsunami across the Pacific Ocean by measuring the changes in the ionospheric total electron content (TEC). We estimate the vertical and horizontal mean speeds of the seismic and tsunami waves using the time and distance of the TEC perturbation, and then, taking into account those determined speeds, trace back to the epicenter and the tsunami origin by applying a 3-dimensional spherical model. The results show that both the tracked epicenter and the tsunami origin are quite close to the epicenter reported by the USGS, with a mean horizontal propagation speed of 2.3 km/s after the earthquake and about 210 m/s after the tsunami. This consistency confirms that the perturbation sources in the ionosphere are due to the earthquake. This implies that the GPS-TEC measurements have the potential to be part of a lower cost, ground-based, tsunami monitoring system.