Space Weather Phenomena in the Equatorial Ionosphere

Our increasing dependence on space-based technological systems requires that we understand the factors that determine "space weather," which affects the operation of satellites as well as space-based communication and navigation systems. The latter are particularly vulnerable to conditions in the dip equatorial ionosphere where geometry of the geomagnetic field creates conditions for the growth of certain plasma instabilities, which produce sub-kilometer scale structure in the ionospheric plasma that are capable of scattering VHF and higher frequency radio waves. The phenomenon of the equatorial plasma bubble (EPB) that occurs in the postsunset equatorial and low latitude ionosphere is therefore an important component of space weather in this region. Forecasting of this space weather phenomenon involves not only the identification of ambient conditions responsible for the day-to-day variation in its occurrence and spatial structure during magnetically quiet periods but also understanding the influence of solar variability on these conditions. This paper discusses briefly our present understanding of the role played by certain parameters of the equatorial ionosphere in the development of EPBs and the influence of solar activity on the equatorial ionosphere, in the context of its role in the generation of ionospheric irregularities that may be detrimental to the operation of space-based communication and navigation systems.