M. Q. Chen

Ionospheric positive storm phases at the magnetic equator close to sunset

[1] During geomagnetic activities, perturbed electric fields at middle and low latitudes of the ionosphere may result from the effect of prompt penetration from high latitudes and the disturbance dynamo mechanism, respectively. The polarity of penetration electric fields depends on the orientation of the interplanetary magnetic field (IMF) Bz, and that of electric fields associated with the disturbance dynamo is almost opposite to that in the quiet time condition. Although a few hours are required to build up the perturbed electric fields through the disturbance dynamo mechanism, the dynamo electric fields can persist for several hours after geomagnetic activities cease. It turns out that the low‐latitude electric field disturbances associated with the disturbance dynamo mechanism should be more persistent than that associated with the direct penetration from the polar cap, especially for the period in the recovery phase. Model results show a significant, westward disturbance dynamo electric field at period close to sunset, but it seems not important in the empirical model. This perturbed electric field at sunset will weaken the intensity of the prereversal enhancement and of the following fountain effect in the storm time. Relative to the quiet time condition, it produces an enhancement in the total electron content. This phenomenon is seasonal. It only occurs at period close to equinox, when the hemispheric wind (summer to winter) is minimal. These theoretical results have been substantiated by model results of the National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model and by the global integration and modeling in this study. Both results show that the positive phase of the ionospheric storm at the magnetic equator close to sunset is produced by the westward disturbance dynamo electric field.

Ionospheric total electron content observed during the 24 October 1995 solar eclipse

Abstract During the solar eclipse of October 24, 1995, the effect of an eclipse on the total electron content (TEC) of the ionosphere can be investigated by using measurement of the Global Positioning System (GPS). The TEC derived from five GPS ground-based receivers have been used to observe ionospheric variations over the geomagnetic equatorial, equatorial anomaly, and mid-latitude regions. The deviations in the TECs on the eclipse day from those on reference days show that during the eclipse days the ionosphere experienced some changes. Four features of the TEC deviations, pre-ascension (PA), major depression (MD), sunset ascension (SA), and secondary depression (SD) have been observed. Possible mechanisms explaining in the four features are investigated and discussed.

Ray tracing simulation for GPS radio occultation in non-spherically symmetric atmosphere with ECMWF analysis

In this research, a ray tracing model is built up to simulate the propagation of signal in global positioning system (GPS) radio occultation (RO) mission. When GPS signal propagate through the Earths atmosphere, it will be bent and delayed due to the gradient atmosphere refractive index and received by low Earth orbit (LEO) satellite. Then the parameter profiles of atmosphere can be retrieved by using the received signal. In the previous research, in order to simplify the simulation, the Earths atmosphere is assumed as spherical symmetry and the positions of GPS and LEO satellites are not considered in simulations. In the model, the shape of the Earth is assumed as an ellipse. The information of European Centre for Medium-Range Weather Forecasts (ECMWF) is used to construct the refractive index of Earths atmosphere. And two aiming algorithm are developed to control the initial propagating direction of GPS signal to begin from the prescribed GPS satellite position and end at the LEO satellite position. The model is tested and verified by comparing with analytical and observational data.