New global electron density observations from GPS-RO in the D- and E-Region ionosphere

摘要

A novel retrieval technique is developed for electron density (N-e) in the D- and E-region (80-120 km) using the high-quality 50-Hz GPS radio occultation (GPS-RO) phase measurements. The new algorithm assumes a slow, linear variation in the F-region background when the GPS-RO passes through the D-and E-region, and extracts the N-e profiles at 80-130 km from the phase advance signal caused by N-e. Unlike the conventional Abel function, the new approach produces a sharp N-e weighting function in the lower ionosphere, and the N-e retrievals are in good agreement with the IRI (International Reference Ionosphere) model in terms of monthly maps, zonal means and diurnal variations. The daytime GPS-RO N-e profiles can be well characterized by the alpha-Chapman function of three parameters (N-mE, h(mE) and H), showing that the bottom of E-region is deepening and sharpening towards the summer pole. At high latitudes the monthly GPS-RO N-e maps at 80-120 km reveal clear enhancement in the auroral zones, more prominent at night, as a result of energetic electron precipitation (EEP) from the outer radiation belt. The D-/E-region auroral N-e is strongly correlated with K-p on a daily basis. The new N-e data allow further comprehensive analyses of the sporadic E (E-s) phenomena in connection with the background N-e in the E-region. The layered (2-10 km) and fluctuated (2 km) E-s components, namely N-e_Layer than N-e_perb, are extracted with respect to the background Ne-Region on a profile-by-profile basis. The N-e_layer component has a strong but highly-refined peak at similar to 105 km, with an amplitude smaller than N-e_Region approximately by an order of magnitude. The N-e_pert component, which was studied extensively in the past, is similar to 2 orders of magnitude weaker than N-e_Layer, Both N-e_Layer and N-e_pert are subject to significant diurnal and semidiumal variations, showing downward progression with local time in amplitude. The 11-year solar cycle dominates the N