Global characteristics of occurrence of an additional layer in the ionosphere observed by COSMIC/FORMOSAT-3

Global observations of electron density profile (EDP) from the COSMIC/FORMOSAT-3 satellites were used to investigate, for the first time, the additional stratification of the F2 layer over the equatorial ionosphere on a global scale, which is called F3 layer. The F3 layer in EDP was recognized through the altitude differential profile featured by two maxima existing from 220 km to the peak height of the electron density. There were ~9,400 cases of F3 layer selected out of ~448, 000 occultation events at low and equatorial areas during the period of April 2006 - September 2010. Statistical results show that the highest occurrence of F3 layer appears at dip latitude 7~8°/−7~−8° for Northern/Southern Hemisphere and is more pronounced during summer months at 10:00 - 14:00 LT. The occurrence also has a clear longitude dependence during boreal summer, with relatively higher occurrence at −80~−100°, −20~20°, 80~120° and −160~−170° longitudes, that is possibly associated with the wavenumber-3 diurnal tide (DE3). The results support the principle of the F3 layer proposed by Balan et al. (1998), which in turn validate the accuracy of the retrieval of the COSMIC EDP data.